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L E N A
Linear Electronic Network Analysis
program manual
Release of 31 January 1994
==============================================
Programs, Documentation and Instructions
by
Leonard H. Anderson
Copyright (c) 1994, all rights reserved
==============================================
Linear frequency analysis of electronic circuits having up to
56 nodes and 204 branches, solving single node voltage or
impedance at DC or swept-frequency. Branch types include
single components, series and parallel passive components in
one branch, macromodels of transmission line, two-winding
variable coupling transformer, bipolar hybrid-pi transistors,
operational amplifier with one internal breakpoint. Requires
8086 or later CPU, 142 KB free RAM, any ASCII-character-set
display and printer. Numeric co-processor version included.
LENA is a smaller version of LINEA (released August 1993) and
compatible in every way except repetitive waveform analysis.
TABLE OF CONTENTS
GENERAL............................................................1
Consent and Disclaimer.......................................1
Conventions in this Document.................................2
DESCRIPTION/OPERATION OF LENA......................................4
Introduction.................................................4
Program Command Organization.................................4
INPUT...........................................................6
General Keyboard Input in LENA...............................6
Numeric Value Entry..........................................6
Y/N Queries..................................................7
Main Commands (Listing)......................................7
Output Command Combinations.................................10
Printer Margins and Pagination..............................10
ASCII-Character Plot Equivalents............................11
Output Plot Scale Choices...................................11
Rotating Twiddle Characters.................................12
Off-Line Use of Solution Files..............................12
GENERAL INPUT-OUTPUT SOLUTION COMMANDS.........................13
Setting Frequency Limits....................................13
Node of Solution............................................13
Zero-Decibel Reference Voltage..............................14
Opening or Closing a Branch.................................14
CIRCUIT LIST COMMANDS..........................................15
Starting or Continuing a Circuit List.......................15
Branch Description and Designation..........................15
Modifying a Branch Value....................................15
Deleting a Branch...........................................16
Inserting a New Branch......................................16
General Branch-Node Circuit Building in LENA................16
CIRCUIT COMPONENTS AVAILABLE IN LENA...........................18
Type Descriptions...........................................18
Passive Single Branches.....................................18
Independent Current Sources.................................19
Current Direction in Sources................................19
Dependent Current Sources...................................19
Macromodels.................................................21
Transformer Macromodel Details..............................22
Unbalanced Transmission Line Macromodel Details.............22
Bipolar Transistor Macromodel Details.......................23
Operational Amplifier Macromodel Details....................24
ENTERING CIRCUIT COMPONENTS....................................25
Branch Entry, Single-Value Branches.........................25
Branch Entry, Double-Value Branches.........................26
Quicker Entry, Single-Value and Double-Value Branches.......26
Dependent Current Source Value Entry........................27
Signal (Generator) Value Entry..............................27
Macromodel Entries..........................................28
Required-Listed Macromodel Values...........................28
Seeing the Full Circuit List................................29
Circuit List Hardcopy.......................................30
CIRCUIT LIST EDITING...........................................30
Special Note on Insert Command..............................30
Special Notes on All Macromodels............................31
LENA - Contents Page i
DISK DATA FILES................................................31
Setting the Data Storage Drive:\Directory Path..............31
Reading/Writing Circuit Files...............................32
Circuit Creation Dates and Remarks..........................32
Solution Storage and Retrieval..............................33
Compatibility with LINEA Data Files.........................33
SOLUTIONS AND OUTPUT...........................................34
General Solution Organization of LENA.......................34
Scale Limit Selection on Plot...............................34
Two Forms of Impedance Plot.................................34
Syntax on Solution Type and Form............................35
Generating Plot Artwork.....................................35
Single DC Output............................................35
CONVERTING FROM SCHEMATIC TO LISTING...........................36
In the Beginning............................................36
Node Numbers Must be Contiguous.............................36
Commons, "Ground" and Supply Lines..........................36
Parasitic Reactance, Resistance.............................37
Current Through Dependent Branches..........................37
Voltage Across Dependent Branches...........................38
Creating "Stiff" Voltage Sources............................38
Negative Resistance or Reactance............................38
Operational Amplifier Circuits..............................38
Field-Effect Transistor Models..............................39
Bandwidth-Alterable Networks with Transformer Macromodel....39
Creating "Black Box" Sub-Circuits...........................39
INSTALLING LENA...................................................40
LENA Program Set Files......................................40
Appendices..................................................40
Registry....................................................41
CPU Versions and Copies.....................................41
FIRST-USE LENA PRIMER/TUTORIAL....................................42
On-Line Help................................................42
Getting Acquainted With Circuit Listings....................42
Trying Out a Macromodel.....................................43
Trying Out Circuit Edit Functions...........................44
Saving a Circuit File, Trying out DOS Functions.............45
APPENDICES are contained in text files LE_APX_*.TXT; titles and file
names are given here for reference.
Appendix A, LENA Data file structures....................LE_APX_A.TXT
Appendix B, Example circuit PHASER.......................LE_APX_B.TXT
Appendix C, LENA Configuration...........................LE_APX_C.TXT
Appendix D, General history of CAE, LINEA, LENA..........LE_APX_D.TXT
Appendix E, Comparison of current "BBS" programs.........LE_APX_E.TXT
=============================================
Important: See page 40 (Installing LENA) for
files and necessary procedures to make your
personal working copy of LENA.
=============================================
LENA - Contents Page ii
.
GENERAL
=======
LENA is a Linear Electronic Network Analysis program set for determining
the frequency response of an electronic circuit having a maximum of 204
component (branches) and 56 connection points (nodes). Components may be
resistors, capacitors, inductors, series and parallel resistor-reactances,
reactances with specified Q, stimuli, and dependent current sources.
Macromodels of transformers, transmission lines, transistors and
operational amplifiers are included. Frequency range may be anything from
DC to Terahertz in linear or logarithmic increments. Numerical input is
free-form, scaling letter suffixes from femto to Tera at user's option.
Analysis solutions may be printed or plotted on any ASCII character-set
printer. Circuit lists and solutions may be stored on or retrieved from
disk.
LENA works in any MS-DOS computer, 80x86 CPU or later, having a minimum of
142 kilobyte contiguous free RAM. There is no restriction or requirement
on special display devices, but ANSI.SYS should be present as a DEVICE
stated in DOS CONFIG.SYS file to see color. Any ASCII character printer
may be used for hard copy output. The Standard version is for any 8086,
80186, 80286, 80386, or 80486 CPU computer, with or without a numerical
coprocessor. The Numerical coprocessor version is for any 80386DX or
80486DX CPU or those with 80x87 numeric coprocessors. A Numeric co-
processor version can decrease analysis-solution times by a factor of
three to seven.
LENA is an analysis _tool_, useful to engineers, technicians, educators,
and advanced electronics hobbyists alike. It is not intended as a
teaching aid but it is very useful in lending insight into frequency-
domain properties of complex circuits.
The LENA program set is Shareware. Anyone may try out the LENA set on
one computer for a period of 21 days; beyond that time every user is
obligated to obtain a registration for continued use, including
commercial, educational, or governmental associations.
CONSENT AND DISCLAIMER
LENA, associated LENA files and documentation are the exclusive property
of Leonard H. Anderson and are copyrighted 1994. No part of the LENA
program set (programs plus documentation) may be reproduced, transmitted,
transcribed, stored in a retrieval system, or translated into any other
language or computer language in whole or in part, in any form or by any
means, except for distribution without fee as a program collection or for
individual single-user archive purposes, without prior written consent of
the author.
The author disclaims all warranties as to this software, whether express
or implied, including, without limitation, any implied warranties of
merchantability, fitness for a particular purpose, functionality,
accuracy, data integrity or protection.
The included CPUID.EXE file was written and assembled by Intel Corporation
and was declared public domain by Intel Corporation.
LENA - Page 1 of 46
Distribution of the LENA program collection by Bulletin Board Systems is
encouraged. Companies and organizations engaged in the collection and
sale of shareware shall require permission from the author before
distributing all or part of the LENA program set.
CONVENTIONS IN THIS DOCUMENT
This Manual is an explanation of the LENA program operation and
application. Users are expected to know the basics of electronics and be
familiar with electronic terms. There is very little of esoteric material
found in comprehensive textbooks for college courses, yet the program
operates with such esoterica and solves node-branch circuit arrangements
accurately and quickly for frequency-domain analysis. The LENA program
set is useful to working electronics engineers, electronic technicians,
hobbyists, students and educators alike. The author is an electronics
engineer who is also an electronics hobbyist and a writer published in
BYTE, Ham Radio, ELECTRONICS, and Popular Electronics magazines.
LENA and its documentation files were written with a prime rule that the
American Standard Code for Information Interchange (ASCII) characters are
to be used for ALL input-output. This makes it possible to display
everything, regardless of display type, and to be printed on nearly
every page-size printer used in North America.
As a result of restrictions to ASCII characters, the few "schematics" in
here are somewhat lacking in quality and appearance. Given those
limitations, diagrams are as simple and understandable as possible. Also,
many of the terms common to electronics notations use subscripts and
superscripts and italics, features missing in ASCII. To bridge the gap
between common use and LENA, the following is a short list of not-quite-
standard notation:
Hfe = Hybrid forward current gain, common-emitter transistor;
common term is all-lower-case italics.
Hoe = Hybrid output conductance, common-emitter transistor;
common term is all-lower-case italics.
Ic = Transistor DC collector current, commonly written
"I-sub-c."
Ft = Transistor cut-off frequency; commonly written
"f-sub-t."
Zo = Characteristic impedance, as applied to transmission
lines; commonly written all-caps as "Z-sub-O."
Fc = "Corner frequency" in operational amplifiers, point of
frequency intersection between open-loop gain and
slope of gain falling at a rate of 20 db per decade.
Av = Voltage gain, commonly written "A-sub-V", used in here
denoting open-loop gain of operational amplifiers.
gm = transconductance, values in mhos.
<units> = Any number not having a specific value name, as
opposed to Ohms, Farads, Henries, Hertz, etc.
<xyz> = General designation for entry, "<xyz>" explained in
text.
Main Commands and Branch Type Designations have no rule regarding case.
They can be entered as capitals, 'small' letters, or mixed-case...the only
requirement is that the letters be correct and contiguous as shown. All-
capitals notation in text here is an emphasis device.
LENA - Page 2 of 46
Where keyboard inputs are described within text, they are shown
capitalized within single- or double-quotes. Single- or double-quotes
themselves are NOT keyboard entries.
All documents in the LENA program set are formatted for 8.5 x 11 inch page
sizes, 85 characters maximum line width, 66 lines maximum per page.
Printer Form-Feed control characters are not used. Documents are limited
to 75 characters per line and include a 5-character left margin; printing
is continuous and automatically paginated.
For better illustration of single-branch components and their formulae,
the user is directed to Byte Books' publication "Simulation; Programming
Techniques Volume 2," edited by Blaise W. Liffick, pp 87-97, article
entitled "Linear Circuit Analysis" by Leonard H. Anderson. Byte
Publications is now owned by McGraw-Hill and the "Simulation" book,
copyrighted 1979, was out of print a few years ago. Among several texts
on computer-aided design/engineering, the author has found the following
to be useful:
"IBM Electronic Circuit Analysis Program," by Randall W. Jensen and Mark
D. Lieberman (Prentice-Hall, 1968). ECAP is the grand-daddy of all CAE
programs and the frequency-domain modelling techniques are applicable to
LENA.
"Computer Methods for Circuit Analysis and Design," by Jiri Vlach and
Kishore Singhal (Van Nostrand Reinhold, 1983). A very detailed overview
and theory of all CAE programs, although a bit "academic" for working
circuit designers.
"Basic Circuit Theory with Digital Computations," by Lawrence P.
Huelsman (Prentice-Hall, 1972). Gets down to basics on individual
components and presents many FORTRAN routines to analyze components and
networks.
LENA - Page 3 of 46
.
DESCRIPTION/OPERATION OF LENA
=============================
INTRODUCTION
LENA analyzes the response of an electronic circuit modelled from passive
and active component branches connected to contiguous nodes. Complex
voltage (from specified stimuli) or complex impedance may be measured at
any node at any frequency for up to 200 frequencies in a sweep, linear or
logarithmic-increment. Each circuit may have a maximum of 204 branches
and 56 nodes. Branches may be single R, C, or L; series or parallel R-C,
R-L combinations; L or C with frequency-independent Q; dependent current
sources specified by transconductance or current gain; independent current
sources. Macromodels of an isolated two-winding transformer, unbalanced
transmission line, bipolar transistor, and operational amplifier are
included. Circuit models and analysis-solutions may be stored on disk.
All values are named and have scaling letters.
All non-integer numeric entries may use mantissa/decimal-point/fraction
format, 'E format' common to BASIC or FORTRAN languages, or Scaling Letter
suffixes ranging from femto to Tera, or any mixture thereof. Except for
Scaling Letters and circuit list Remarks, there is NO distinction on entry
case. No PC function keys, Control or Alternate key combinations are used
at any time. All LENA program commands are done at a Main Command level
using clear English words or accepted abbreviations. Circuit model lists
are just lists of components; all frequency limit settings and output type
selection is done at the Main Command level. Circuit lists and solution
outputs may be directed to a printer port or screen; printer may be any
ASCII character set type and pagination is automatic for a 66-line
standard print page. "Line-printer" style graph equivalents, using ASCII
characters, may be selected in lieu of tabulated values. Scale range of
every graph plot output is selectable to default minimum-maximum or to
user-specified limits.
Each circuit model list is editable from Main Command level. Branches and
macromodels may be added, inserted, deleted, have values modified, or
switched open or closed. Open branches remain in a circuit list but are
not analyzed. Circuit lists may be named and have remarks; all are time-
date-stamped for later reference. Branch type descriptions may include
reference designations. Output is selectable to any circuit node. Each
circuit list is checked for errors after entry with extensive description
to permit easy correction.
On computer systems with color displays, functions are color-coded. If
data entry is required but not entered as part of a Main Command, LENA
will prompt for the data. Extensive checking is done to guard against
impossible solution conditions, error messages explaining the nature of
error for correction. LENA should not crash under any condition.
PROGRAM COMMAND ORGANIZATION
All LENA program commands are done at a 'Main Command' level, using clear
English words or accepted abbreviations. Most commands are one word.
Command words may be abbreviated to the first 3 letters, first 2 letters,
or, sometimes, as a single letter or symbol. A few commands use two words
separated by a space. Where some numeric value should be entered
following the first command word, a "data word," that numeric value may be
LENA - Page 4 of 46
entered following a space separator as a 'second word.' If a first
command word requiring data input is given, but data inadvertently
omitted, LENA displays a prompt for the type and kind of data. If that
data should consist of two or three numerics and only one is entered, LENA
will re-prompt for all of them.
Command word entry may be the following, depending on command:
<WORD>
<WORD> <DATAWord> <-- space separator
<1stWORD> <2ndWORD> <-- space separator
Data words have contiguous characters, individual data items separated by
a comma, semicolon, or forward-slant delimiter.
Data words may be entered as:
<DATAWord> (single item)
<ITEM1>,<ITEM2> or <ITEM1>;<ITEM2> or <ITEM1>/<ITEM2>
^ ^ ^
(any of the three delimiter characters accepted)
<ITEM1>,<ITEM2>,<ITEM3>
Circuit entry is handled much the same as Main Commands. Component type
descriptions recognize, in order, first letter, first two letters, or
first three letters of a component name. All other letters or numbers,
including a few symbols, may be added for reference designation. The Node
number entries (integer) describe the location of the branch in the
circuit. Entering type but no node numbers results in a prompt for node
numbers. Numeric value entry for a branch is prompted next, some branches
requiring two values; omitting one value of a two-value entry will result
in a "re-entry" prompt. It is possible to enter everything for a single
branch on one line.
Throughout LENA, the organization is aimed at being interactive, clear-
language, communicating with the user. There is a minimum of 'programese'
spoken, no "command line shorthand," no screen cluttering with pull-down
menus or small screen displays. The only jargon is that of electronics.
LENA - Page 5 of 46
.
INPUT
-----
GENERAL KEYBOARD INPUT IN LENA
All keyboard input is free-form in nature. No PC Function keys or Ctrl-
<key> or Alt-<key> combinations are used for any purpose. The program is
controlled from a 'Main Command' level having the following screen prompt:
MAIN*> (printer port inactive) (yellow, black background)
-or-
Main-> (printer port active) (white on blue background)
Main Command expects an all-alphabetic 'command word' to be entered. The
'word' itself may be an abbreviation of, in order, the first three
letters, the first two letters, or the first letter or a symbol. Some
commands may require two words; two words must be separated by at least
one space.
Command words may be entered in all-capitals, all-lower-case, or even
mixed-case; only the letters themselves matter. Exception to this overall
rule occurs only with Scaling Letters or textual input for Circuit List
Remarks.
NUMERIC VALUE ENTRY
Some commands require data as the second word. A 'data word' in LENA
consists of alphanumeric data of one to five items. Each data item is
separated (delimited) from the following data item by a comma, semicolon,
or forward-slant ('/'). No entry for an item is considered a space for
alphabetic data or zero for numeric data.
ALL numeric data items in LENA have flexible input format. Each data item
may have any one or a mixture of any of the following formats:
* Mantissa-decimal-point-fraction.
* 'E-format' style common to BASIC and FORTRAN
* Scaling letter suffixes from femto to Tera.
Scaling letter multipliers are as follows:
T = Tera = 1E+12 f = femto = 1E-15
G = Giga = 1E+9 p = pico = 1E-12
M = Mega = 1E+6 n = nano = 1E-9
K = Kilo = 1E+3 u = micro = 1E-6
<none> = 1 m = milli = 1E-3
Scaling letter case MUST be observed. All below unity require lower-case,
all above unity require upper-case. The lower-case 'u' has been
substituted for the Greek 'mu' to permit direct compatibility with ASCII-
character printers.
LENA - Page 6 of 46
The following keyboard-entry combinations all denote the same numerical
quantity:
12345.67 12.34567E+3 12.34567K
0.01234567E+6 .01234567e+6 1234567m
12.34567KE-6 .01234567M
Scaling letter suffixes take precedence over any 'E-format' power of ten;
in the 7th example (12.34567KE-6), the "E-6" would be ignored. E-format
allows either case for the "E."
The maximum number of digits in the mantissa is limited to 7. The
exponent ranges are limited to E+29 and E-28. Polarity is considered
positive by default (plus signs are ignored) and a minus sign must precede
a number to indicate it is negative. Except for Scaling Letters and the
"E", all other characters are ignored. Where data required is expected to
be integer-only, any fractional part of an entry is ignored.
Data item delimiters within a numeric data word are a comma, semicolon, or
forward-slant. Two contiguous separators indicate a zero value between
the delimiters. In the case of a delimiter character being the first
character in a data word, the first data item would be zero (null entry).
Depressing an <Enter> key without entering anything else in response to a
prompt will make ALL requested data items zero.
Y/N QUERIES
In several LENA functions there are Yes-No queries having "[Y/n]" or
"[y/N]" entry prompts, each having only one letter capitalized. Pressing
<Enter> key without entering anything else is the same as entering the
capitalized key.
MAIN COMMANDS
All of LENA's Main Command words are listed following. All-capitals form
is used here to emphasize required _letters_; user may enter either case
or even mixed-case. These are all "first words"; if a second word is
required, LENA will prompt for it if not entered. This list, in
abbreviated form, is duplicated in the HELP display on-line and in text
file MAINCMND.LST.
QUIt QUI QU Q
-or- Quit LENA and return to DOS level.
EXIt EXI EX X
HELp HEL HE ? Display 1 to 6 screens of on-line Help
information.
DOS DO \ Temporary drop to DOS level. One DOS
request will return to LENA afterwards
unless word 'COMMAND' is entered...will not
leave DOS level until 'EXIT' is entered.
LENA - Page 7 of 46
NEW NE Begin entry of a new circuit list. Old
circuit data is discarded.
ADD AD A Add to an existing circuit list.
LISt LIS LI L List entire circuit to screen or printer.
ON ( Enable printer port to accept outputs or circuit
listing. Main Command prompt changes to "Main->"
when printer port is on/enabled. All PRInts, PLOts,
or LISts are directed to the printer when ON. Active
printer port is that set by Operating System.
Printer port remains on until turned off.
OFF OF ) Disable printer port. All outputs are directed back
to screen and Main Command prompt returns to "MAIN*>"
to show printer port is off. Default state when LENA
is first run.
DRIve DRI DR & Select another Drive:\Directory path for reading or
-or- writing Circuit, Solution, or Waveform data files.
DIRectory DIR DI Default on LENA start is same Drive:\Directory as
LENA program drive and directory.
REAd REA RE R Read a Circuit file from disk. Requires only the
8-character-maximum filename. File extension of .LIN
is automatically appended. 'LIN' file extension is
LENA's identification for Circuit list files.
WRIte WRI WR W Write an existing Ciruit file to disk. Same
filename and extension conditions as REAd.
SAVe SAV SA / Save a solution to disk, including frequency limits
and circuit filename (but not circuit itself).
Requires only the 8-character-maximum filename. File
extension of .LNA is automatically appended. 'LNA'
is LENA's identification for Solution data files.
BRIng BRI BR B Bring (back) a previously-SAVed solution. Same file-
name and extension conditions as SAVe. Displays
filename of circuit that was solved but does not read
it in. Used for viewing previous solutions.
OPEn OPE OP O Open the connection of a designated circuit branch.
Branch remains in circuit list but is not part of
circuit solution. Opening a previously-opened branch
has no effect. If an OPEn designates any branch in a
macromodel, the entire macromodel is Opened.
CLOse CLO CL C Close, or reconnect a designated circuit branch.
Opposite of OPEn. Closing an already-closed branch
has no effect. If a CLOse command designates any
branch in an opened macromodel, the entire macromodel
is closed.
MODify MOD MO M Modify only the values of a designated circuit
branch. Type and nodes remain intact. Inoperative
with macromodels.
LENA - Page 8 of 46
.
DELete DEL DE | Delete a designated circuit branch from a circuit
list. All higher-listed branches move down to fill in
list. If a DELete command designates one branch of a
macromodel, the entire macromodel is Deleted.
INSert INS IN ^ Insert a new branch at the designated branch position
in a list. Branch type, nodes, value prompts and
entries are the same as for one component under NEW or
ADD. Designated branch and all higher branches move
move up to make room for INSertion.
NAMe NAM NA $ Change existing circuit list filename. Circuit file
REAds and WRItes assume the existing filename or allow
choice of another filename; this command is primarily
for hardcopy outputs so as to show the new filename
prior to any WRIte to disk.
REMark REM RE * Change 47-character Remark line accompanying each
circuit list or output title. Remark line is written
to or read from disk with other circuit list data.
NODe NOD NO N Select NODe of solution. Every NEW circuit or
ADDition to a circuit, MODification of branch value,
INSert of a new branch, DELetion of an old branch,
REAd-in of a circuit from disk will always make the
highest node in a circuit as the node of solution.
DBRef DBR DB D Change reference voltage for 0 db on all outputs.
Default at LENA start is 1 Volt. Does not affect
solution voltage, only decibel value equivalent to
solution voltage.
FREquency -or- First Command Word to select frequency limits, first
FRE FR F or second word to select frequency-voltage output
type. At LENA start there are no frequency limits.
IMPedance -or- First or second word to select frequency-impedance
IMP IM Z output.
PRInt PRI PR P First or second word of an output to select printed,
tabulated solution values.
PLOt PLO PL = First or second word of an output to select ASCII-
character plot equivalents.
MARgin MAR Select margins for hardcopy; 1 to 7 characters left
margin (5 is default), 1 to 6 lines top and bottom
equally (3 is default). Margins do not appear on
screen displays.
SETtings SET SE Convenience screen display to show user the current
circuit filename, circuit creation time/date,
circuit Remarks, current time, node of solution,
open circuit branches (if any), frequency limits, 0 db
reference voltage, and Data file directory path.
DATe DAT Current computer time and date. Convenience only;
computer time and date are resettable only from DOS
level.
LENA - Page 9 of 46
OUTPUT COMMAND COMBINATIONS
A solution output is obtained by a two-word combination of <type> <format>
or <format> <type>. FREquency and IMPedance are <type> words, PRInt and
PLOt are <format> words. Either order is fine but each word must be
separated by at least one space, no other character. To obtain an
IMPedance PLOt, any of the following two-word combinations can be used:
PLOT IMPEDANCE IMPEDANCE PLOT
PLO IMP IMP PLO
PL Z Z =
For user convenience, the following single-word, three-letter acronyms may
be used as an alternate for output:
PRF - Print tabulation of complex node voltage over frequency.
PRZ - Print tabulation of complex node impedance over frequency.
PLF - Plot node voltage over frequency, ASCII-character plot.
PLZ - Plot node impedance over frequency, ASCII-character plot.
PRINTER MARGINS AND PAGINATION
Printer-directed output is formatted for the 8.5 x 11 inch North American
standard page size, expecting 85 columns per page horizontal ("10 Pitch" or
ten characters per inch) and 66 lines per page vertical (6 lines per inch).
Top and bottom page margins, left margin are selected via the "MAR" main
command. Top and bottom margins (equal) are selectable from 1 to 6 lines,
3 line margin (half inch) being default at LENA start. Left margin is
selectable 1 to 7 characters/columns, 5 characters (half inch) being
default at LENA start.
Pagination of "Page nn of mm" is done at the bottom right of each page and
"...continued from Page nn" at the top left of each page after the first
page. The first page always begins with a title bearing circuit filename,
when circuit was created (or last changed), remarks, current time and date,
any circuit branches which are set open.
Margins and the "...continued" identification are omitted from screen
displays and "Page nn of mm" only appears on screen if an output or circuit
list goes beyond a single page. Top and bottom margins (always equal)
allow the following number of solution data lines per page:
Margin Lines 1st Page Data Lines 2nd, subsequent Pages' Lines
1 52 55
2 50 53
3 48 51 <- default
4 46 49
5 44 47
6 42 45
LENA - Page 10 of 46
ASCII-CHARACTER PLOT EQUIVALENTS
The "character plot" technique is an old method of making a coarse graph
plot equivalent using only printer characters as data and graph marks. It
is also the fastest and most equipment-versatile, requiring only that a
printer support ASCII characters.
LENA outputs plot graphs having 6 major divisions, 60 minor divisions,
'rotated' a quarter turn so that the lowest frequency is at page top,
amplitude increasing from left to right. Every line is identified by
frequency.
Major graph divisions are identified by a plus sign. Any data plot
character will override a graph division character. The prime data
character is an asterisk, secondary a colon, tertiary an up-arrow.
If, for one plot point, characters are at the same plot location, the prime
character predominates. If the prime character location is calculated to
be beyond the scale extremes, a left or right arrow mark at appropriate
left or right limit lines indicates overscale.
Data location is very close to the physical center of a character. The
center of a colon character is mid-way between the two marks. Group Delay
is shown by an up-arrow and the _point_ of the up-arrow is significant.
Group Delay is the derivative of phase divided by derivative of radian
frequency; the point of the arrow is approximately mid-way between each
frequency, thus corresponding to approximate frequency of delay.
OUTPUT PLOT SCALE CHOICES
Every solution's plot output is scanned for minimum and maximum, those
minima and maxima shown as a screen prompt. Users have a choice to accept
those extremes as the scale limits or to enter desired limits. Pressing
_only_ the <Enter> key after the prompt accepts the solution's extremes as
scale limits. There is no auto-scaling by decades or octaves.
Phase-angle scale limits are fixed for frequency-voltage solutions, default
value at +/- 180 degrees. Phase-angle limits may be set to any other
values and will remain at those settings until changed.
Impedance plots are selectable polar (default) or rectangular. Polar form
impedance plot has the prime data mark signifying impedance magnitude,
secondary data mark signifying impedance phase-angle. Entered impedance
phase-angle plot limits remain only for that particular impedance plot.
Rectangular form impedance plot has prime mark indicating Real/Resistive
part, secondary mark indicating Imaginary/Reactive part.
All plot outputs have the scale limit values at the header of each page.
Limits can be reversed left-for-right by reversing the order of limit
entry.
If a re-plot of the same solution is desired with different scale limits of
some parameter, it may be done without delay. Solutions are stored
internally and re-plotting/re-printing may be done immediately without
waiting for a new solution.
LENA - Page 11 of 46
ROTATING TWIDDLE CHARACTERS
Every circuit solution requires all circuit branches to be mathematically
analyzed at each solution frequency. With large circuits, this may take
many seconds. To indicate this is in process, "Working!" is displayed on
the screen, preceded by a 'rotating twiddle character' that appears to turn
in 45-degree increments for every frequency. Every 8th frequency is marked
by the "equal symbol" composed of three stacked horizontal dashes. Both
indicators disappear after the last frequency's analysis is completed.
OFF-LINE USE OF SOLUTION FILES
All solutions may be stored on disk. All files generated by LENA are the
functional equivalent of ASCII files. Other programs may be used to parse
the characters for any other tabulation or plot format. A full description
of disk file data fields is given in Appendix file LE_APX_A.TXT.
LENA - Page 12 of 46
GENERAL INPUT-OUTPUT SOLUTION COMMANDS
--------------------------------------
SETTING FREQUENCY LIMITS
Entering F, FR, or FRE at the Main Command prompt without a second word
will invoke a prompt of:
Frequency Limits [Hz] (min,max,delta):
"min" and "max" are self-explanatory, but "delta" has two possibilities: A
positive delta entry is the linear frequency increment while a negative
delta entry refers to the _total_ number of logarithmic-increment
frequencies.
Entering "99K,101K,-17" would mean a log-sweep of 17 total frequencies
starting at 99 KHz and ending at 101 KHz.
An entry of "99K,101K,100" would mean a total of 21 linear-increment
frequencies starting at 99 KHz and ending at 101 KHz.
Maximum number of frequencies is 200, regardless of linear or logarithmic
increment. LENA checks for that and prompts if entry is incorrect. LENA
will accept a 0 minimum frequency (DC) if the delta is positive/linear, but
will not accept a 0 minimum frequency if the delta is negative/logarithmic.
If the delta entry is 0, regardless of whatever else is entered for minimum
and maximum, the "frequency" is DC. For all other conditions of delta,
minimum and maximum frequencies must be positive.
Frequency limits may be set at the Main Command level by entering "F
<limits>" where <limits> is the min-max-delta. This single-line short form
of command requires only that one or more spaces are between the "F" and
the first character of "<limits>;" also, the three data items of <limits>
are separated by commas, semicolons, or forward-slants, not spaces. It is
also possible to select a DC solution from the Main Command prompt by
entering "FREquency DC" or just "F DC".
NODE OF SOLUTION
Any node in a circuit may be selected as the "measuring point" for a
solution. Selection of a new node of solution will cause it to remain;
however, after every ADD or NEW circuit completion, INSert new branch,
DELete old branch, or REAd in of another circuit, the node of solution is
reset to the highest node in the circuit. If in doubt of the node of
solution, a user can use the SET command to see which node is the current
node of solution.
Node of solution may be set as a single-line command at Main Command level
by entering "N <node-number>".
LENA - Page 13 of 46
ZERO-DECIBEL REFERENCE VOLTAGE
Frequency-voltage outputs give both node voltage directly and in decibels
relative to a zero-db reference voltage. At LENA start, this reference
voltage is 1. It may be reset at any time and will remain at that voltage
reference until changed again. A zero or negative reference voltage is not
allowed.
Zero-db reference voltage may be given at Main Command by the single entry
of "D <voltage>".
OPENING OR CLOSING A BRANCH
Every single branch or an entire macromodel may be "switched" open or
closed, functionally the same as disconnecting and reconnecting a physical
component. An OPEned branch remains in the circuit list but is not solved.
CLOsing an open branch will restore it to solution with the rest of the
circuit.
As an example, consider a circuit having a load resistor. It may be
desireable to solve for the impedance looking into the load end, without
the load resistor. An easy way to do that is to OPEn the load resistor
branch, then request an impedance solution at that node. The load resistor
may be reconnected with a simple CLOse command for that branch. OPEns and
CLOses do not affect the circuit list order, type, nodes, or values.
Single-line Main Commands may be "O <branch>" for OPEn, or
"C <branch>" for CLOse. "<branch>" is either the branch order number or
the full type description (see circuit entry for differentiation,
explanation).
OPEning an open branch or CLOsing a closed branch has no effect.
A reminder: 'Open' and 'close' of a branch component refers to the
hardware connection; it has NO relation to computer _file_ terminology.
LENA - Page 14 of 46
CIRCUIT LIST COMMANDS
---------------------
STARTING OR CONTINUING A CIRCUIT LIST
The single command word, "NEW," at Main Command will begin a new circuit
list, starting at branch 1. All old circuit list data (if any) will be
lost.
The single command word, "ADD," or "AD," or just "A" at Main Command will
allow new branches to be added to an existing circuit list, beginning with
the next higher branch order following the last branch.
If there is no circuit data, the command ADD will also begin a new circuit
list, starting at branch 1.
Every branch entry begins with a type description. This is followed by
node connection data, finally by branch component values. Once branch data
has been fully entered, branch entry begins again with the next branch.
Branch entry continues until "END," "EN," "E," "ND," or "N" is entered for
a branch type, signifying completion of a circuit list.
BRANCH DESCRIPTION AND DESIGNATION
Branch type descriptions allow up to 8 characters per branch. The minimum
_first_ letters for electrical type identification are shown in the
comprehensive branch descriptions following. Those minimums are from 1 to
3 alphabetic characters. The remaining characters may be used for
reference designations or whatever the user wishes. As an example, a
single resistor branch will be identified as to type by just the single
first letter "R." Entering "RESISTOR," "R-123," "R_LOAD," or just "R"
would all signify a single resistor branch for the purposes of completing a
branch entry. The _entire_ type description may be used for designating a
branch for some action.
Main Commands OPEn, CLOse, MODify, DELete, and INSert require designation
of a particular branch. Designator <branch> for those commands may be
either the branch number or the full type description.
LENA parses the first character of a <branch> designator entry. If that
character is alphabetic, the entire circuit list is searched for a match
between <branch> and any type description; if there is a match, then the
circuit branch number has been reached. If that character is numeric, the
designator is assumed to call out the circuit branch number directly.
Since most circuit analyses concentrate on only a few components of a
circuit, it is probably easier to enter "OPEN R_LOAD" to open that branch
rather than entering "OPEN 109" (assuming R_LOAD was branch number 109).
MODIFY A BRANCH VALUE
A single-line Main Command "MOD <branch>" allows changing just the values
of that branch. Type description and nodes remain intact. MODify command
will not work with macromodels. The finish of a MODify will reset the
circuit creation time and date to that when the MODify took place.
LENA - Page 15 of 46
DELETING A BRANCH
A single-line Main Command "DEL <branch>" will remove the branch at
designator <branch>.
This may present some slight difficulty if the DELeted branch is the
dependent branch of a dependent current source. LENA does a circuit check
of each circuit after an Edit command. If LENA finds an improper
dependent branch relation, the dependent branch is automatically switched
open, and a warning message to that effect displayed on the screen. Such
an automatic Open cannot be CLOsed until the dependent branch exists in
proper form.
If a DELeted branch is the only link between two parts of circuit, one part
having a stimulus and the node of solution being in the other part,
solution analysis will stop and a warning message shown, citing that
probability.
DELeting any branch number within a macromodel will cause the _entire_
macromodel to be deleted.
After a DELetion, all higher-order branches will move down to fill in the
empty branch space. If any of the moved-down branches contain a dependent
branch, the dependent branch number of a dependent current source will be
automatically changed to the new number. The finish of a DELetion will
also reset the node of solution to the highest node in the remaining
circuit and reset the circuit creation time to the time of DELetion.
INSERTING A NEW BRANCH
The Main Command single-line command is "INS <branch>". The designated
branch and all higher branches will be moved up in the circuit list to make
room for the INSertion. LENA will issue a prompt for the inserted branch
type and nodes. Once the branch type is known (it may be a macromodel with
many branches), the list movement will take place.
If one of the moved branches is the dependent branch of a dependent current
source, the dependent branch number of that dependent source will be
automatically adjusted to be the new branch number. The finish of an
INSertion will reset the node of solution to the highest node in the new
circuit and reset the circuit creation time to the time of INSertion.
GENERAL BRANCH-NODE CIRCUIT BUILDING IN LENA
Every single component is called a "branch." Every connection point is
called a "node." Every branch is connected between two nodes. Node zero
is common-ground-earth to the entire circuit. Non-zero nodes must be
contiguous. A branch may not have each end connected to the same node.
There is no limit to the number of branches connected between the same two
nodes. There is no restriction to the ordering of branches in any circuit;
branches may be located anywhere in a listing.
Node location makes no difference to the final solution although it may
have some effect on speed of solution execution; more of that in
explanation of the sample circuits distributed with the LENA program set.
LENA - Page 16 of 46
As a practical matter, node ordering is best when following the general
flow of a schematic diagram; that makes for easier interpretation of a
circuit list at a later date.
Branch and node arrangement follows conventional theoretical analysis
techniques. LENA expands single component per branch theoretical concept
to include parallel R-L and parallel R-C, series R-L and series R-C
branches. While this is more for user convenience, in the physical world
every component contains combinations of resistance, capacitance, and
inductance. In LENA, each resistance is a pure resistance, each
capacitance is a pure capacitance, and each inductance is a pure
inductance.
Current flow in LENA is provided by current sources. Every current source
is assumed to be the theoretical type having an infinite source impedance.
There are no voltage sources in LENA. A theoretical voltage source has
zero source impedance. A voltage source may be approximated by a current
source in parallel with a very low resistance. This is no problem with the
large magnitude range of LENA's numeric calculation...a MegaAmpere current
source in parallel with a microOhm resistor would create a very 'stiff'
one-volt source...such would be numerically and theoretically correct
despite the impractical-seeming combination.
Current sources come in two varieties, "independent" and "dependent."
Independent current sources are the stimuli or the fixed sources. Note:
ALL stimuli are _always_ at phase-frequency coherence in LENA.
Dependent current sources are dependent on the voltage across a branch or
the current through a branch. More on those in the later section on
dependent current sources.
In this version of LENA, there are four macromodels. These are always
made up of contiguous branches, are always handled by commands as if they
were a single branch.
LENA - Page 17 of 46
CIRCUIT COMPONENTS AVAILABLE IN LENA
-------------------------------------
TYPE DESCRIPTIONS
All of the following branch type descriptions may be found in short form in
the Appendix and included in the HELP display within LENA. All TYPE
letter combinations are shown in all-capitals to emphasize the _letters_
required; users may enter letters of either case or even mixed case,
provided they are the correct letters. Circuit Lists will always show
branch types in all-capitals.
PASSIVE SINGLE BRANCHES
TYPE Description
---------- --------------------------------------------
R RE RES = Single pure resistance
C CA CAP = Single pure capacitance
L IN IND = Single pure inductance
LQ = Single inductance with specified Q; Q is constant over
frequency. Q is modelled as a loss resistance in series
with inductance. Loss resistance is magnitude of
inductive reactance divided by Q.
CQ = Single capacitance with specified Q; Q is constant over
frequency. Q is modelled as a loss resistance in
parallel with capacitance. Loss resistance is the
magnitude of capacitive reactance divided by Q.
SRL = Series R and L.
SRC = Series R and C.
PRC = Parallel R and C.
PRL = Parallel R and L.
E EN END = Non-branch. Entered by itself (no nodes), causes a
-or- termination of the circuit list entry and return to
N ND Main Command level.
B BA BAK = Non-branch. Entered by itself (no nodes), causes listing
to back up to the previous branch for re-entry. Used for
correcting errors made in previous branch entry.
? HE HEL = On-line Help screen listing circuit branch types.
At DC all inductors assume a resistance of 1 microOhm and all capacitors
assume an infinite resistance.
All passive branch values are normally entered as _positive_ quantities. A
negative value may be entered at the user's discretion. Negative entries
of inductance or capacitance will result in the same magnitude of reactance
LENA - Page 18 of 46
over frequency but the signs of those reactances are reversed. This is
useful in modelling certain theoretical circuit equivalents.
INDEPENDENT CURRENT SOURCES
TYPE Description
--------- -----------------------------------------------
S SI SIG = "Signal generator" stimulus, specified by current in
Amperes and phase-angle in degrees (optional) for
frequency solutions. For time solutions with repetitive
waveforms, phase-angle is ignored and the entered current
is the peak value of the described waveform.
D DC IDC = Direct current source. Active _only_ when the frequency
is zero (DC).
Independent current sources are automatically ignored during an impedance
solution.
All current sources have infinite source impedance. Voltage across the
nodes of any current source depends on the voltage drop through all other
branches connected across the current source nodes. A "stiff" voltage
source may be created by a high-current source in parallel with a low-value
resistance; source impedance of this "stiff" voltage source is that of the
low-value resistance.
CURRENT DIRECTION IN SOURCES
Current flow in LENA is assumed equal to _electron_flow_. Current flow
_within_ all current sources is from "plus node" to "minus node" if the
entered current value is positive. Entering a negative value of current or
current gain reverses the current flow.
Node entry order of all passive branches is irrelevant...except for those
which are dependent branches of a dependent current sources.
DEPENDENT CURRENT SOURCES
LENA has two types: GMS or transconductance-specified ('gm') dependent
current source, and HFS or current-gain-specified ('hfe') dependent current
source. Current is dependent on the voltage across a dependent branch
(type GMS) or the current through a dependent branch (type HFS). Dependent
branches may be any passive branch type located anywhere in the circuit;
dependent branches may not be another current source.
TYPE Description
---------- -----------------------------------------------
G GM GMS = Transconductance-specified current source. Current
depends on the specified transconductance ('gm') times
the voltage across the nodes of a specified dependent
branch. Transconductance is specified in mhos,
transconductance being the derivative of current divided
by derivative of voltage. Current is then proportional
to the voltage across a dependent branch.
LENA - Page 19 of 46
H HF HFS = Current-gain-specified ('hfe') current source. Current
depends on the specified current gain times the current
through the dependent branch.
Note: "hfe" is not conventional notation for
current gain, being the hybrid parameter of
collector current versus base current gain of a
common-emitter transistor; it is used due to
limitations of ASCII not allowing subscripts.
"hfe" to most circuit designers is fairly well
synonymous with current gain.
Current flow in circuits with dependent current sources is illustrated
following:
Plus node Plus nodes
o +e o ------------------o
| | | /|\
| | | Current | |
Rd -> GMS | Within Rm |
| | \|/ GMS | Current
| | | through
o -e o ------------------o Rm
Minus node Minus nodes
Dependent Type GMS Dependent Current Source
Branch with connected resistor Rm
Voltage drop across Rm is in-phase with voltage across Rd. Exchanging Plus
and Minus nodes of the GMS or dependent branch Rd will reverse current
through the GMS and through Rm. Exchanging Plus and Minus nodes of _both_
GMS and the dependent branch, Rd, will make current through the GMS and
through Rm as shown. Entering a negative transconductance value for the
GMS will also reverse current flow of the GMS.
If there are several branches connected to the same nodes as the dependent
branch, GMS current magnitude is dependent on the total impedance magnitude
across the dependent branch nodes...but GMS current direction is still
dependent on the Plus and Minus node entry of the dependent branch.
Plus node Plus nodes
o o-------------------o
| | | /|\
| /|\ | | Current | |
Rd | -> HFS | Within Rm |
| | | \|/ HFS | Current
| Current thru | | through
o dependent o-------------------o Rm
Minus branch Minus nodes
node
Dependent Type HFS Dependent Current Source
Branch with connected resistor Rm
LENA - Page 20 of 46
Current through Rm is in-phase with current through Rd. Exchanging Plus
and Minus nodes of the HFS or dependent branch Rd will reverse current
through the GMS and through Rm. Exchanging Plus and Minus nodes of _both_
HFS and the dependent branch, Rd, will make the current through HFS and Rm
as shown. Current flow in the HFS may also be reversed by entering a
negative value of current gain.
If several branches are connected to the same nodes of the dependent
branch, HFS current magnitude is dependent _only_ on the current through
the dependent branch...but HFS current direction is dependent on the node
entry order for the dependent branch.
MACROMODELS
Macromodels use 3 to 5 branches, branches _always_ being contiguous in any
list.
TYPE Description
---------- ---------------------------------------------
Z ZL ZLN = Unbalanced transmission line equivalent macromodel;
uses 3 branch spaces, requires 3 nodes (input, output,
common). Specified by characteristic impedance,
velocity of propagation, length in inches, and
decibels of loss per 100 feet.
T TR TRF = Two-winding ideal transformer having specified
coefficient of coupling between 0.01 and 0.99, DC
isolation between windings. Uses 4 branch spaces,
requires 4 nodes maximum (2 each for primary, secondary).
Specified by primary winding inductance, turns ratio of
primary winding to secondary winding, and coefficient of
coupling.
One node of primary, one node of secondary may be
common, if desired.
Q QT QTR = Bipolar transistor, hybrid-pi model. Creates 4
branches, requires 3 nodes (base, emitter, collector).
Specified by: Hfe or base-to-collector current gain;
Ft, cutoff frequency; Ic, average value of collector
current; Hoe, collector conductance in mhos.
Model does not include base spreading resistance, Rbb.
Model makes no distinction between PNP or NPN.
O OP OPA = Operational Amplifier. Creates 5 branches, requires
4 nodes (non-inverting input, inverting input, output,
common). Specified by: DC open-loop voltage gain in db;
Fc, or "corner frequency", the break-point of open-loop
gain where gain begins to decrease at a rate of 20 db per
decade; R-input, equivalent resistance of each input,
both assumed to have equal resistance; R-output, source
resistance of output.
Common node is common to both inputs as well as
output.
LENA - Page 21 of 46
TRANSFORMER MACROMODEL DETAILS
Two-winding isolated transformer macromodel is modelled as:
Primary o----o-----o o----o-----o Secondary
+ node | | | | - node
Lp HFSp < - - Ls HFSs
| | | |
Primary o----o-----o o----o-----o Seconday
- node \ + node
- - - - > - - - - - -^
where:
Lp' = Calculated primary inductance.
Ls' = Calculated secondary inductance.
HFSp = Current-gain dependent current source dependent on
current through Ls.
HFSs = Current-gain dependent current source dependent on
current through Lp.
with internal values:
Lp = Entered primary inductance.
N = Entered turns ratio, primary to secondary.
Ls = Secondary inductance calculated from primary inductance
divided by square of N.
K = Coefficient of coupling (entered)
Lp' = Lp x (1 - (K x K))
Ls' = Ls x (1 - (K x K))
Hfe of HFSp = -(K / N) <- [dependent branch is Ls]
Hfe of HFSs = -(K x N) <- [dependent branch is Lp]
DC isolation is a relative term here. Inductors have a 1 microOhm
resistance at DC to avoid an error-crash in the analysis-solution routine.
While that is a very low impedance, it will show up as a small, small
"leakage" of signal from primary to secondary and vice versa at DC.
One primary node may be common to one secondary node in the circuit list.
The orientation of secondary nodes is purposely chosen to yield a voltage
polarity of the same sign as voltage across the primary.
UNBALANCED TRANSMISSION LINE MACROMODEL DETAILS
Unbalanced transmission line macromodel is a pi-form having the same
attenuation at every frequency. Macromodel attenuation is internally
computed from the ratio of specified length to the loss per 100 feet. Loss
per 100 feet is a common specification for transmission lines and may be
taken directly from manufacturer's data. User must compensate for loss
varying over frequency. Lengths in meters must be converted to inches;
legal USA conversion is 2.54 centimeters = 1.0 inch.
LENA - Page 22 of 46
Open-line sections ('half-wave' resonant lines) may be created by having
the "output" node isolated from all other branches; in effect, that would
create the equivalent of an open end. 'Quarter-wave shorted stubs' are
simulated by connecting a very low resistance branch to the output node.
BIPOLAR TRANSISTOR MACROMODEL DETAILS
The created bipolar transistor hybrid-pi model is as follows:
Base node Collector node
o------*------- --------*------o
| | | |
| | | |
Cb'e Rb'e -> HFS (1/Hoe)
| | | |
| | | |
-------*-----*-----*--------
|
o Emitter node
where:
Hfe = base-to-collector current gain at Ic
Ft = cutoff frequency
Ic = average collector current
Hoe = collector-emitter output conductance
HFS is dependent on Rb'e branch current with current
gain equal to Hfe such that collector voltage is
at opposite phase relative to base voltage.
then:
Rb'e = (Hfe x 0.027) / Ic
Cb'e = 1 / (Ft x 2pi x Rb'e)
Hybrid-pi models have an additional resistance, Rbb, "base spreading
resistance," in series with the Rb'e-Cb'e junction and external base node.
Rbb is not readily calculated since it is subject to variations in design
and type of the base junction rather than operating parameters. If no Rbb
value is known, a suggestion is to use a value equal to or slightly larger
than Rb'e.
An added Rbb external to the macromodel can also include an independent DC
current source (IDC) to create the Vbe diode junction voltage. However,
the IDC current must be chosen to fit a PNP or NPN transistor; the bipolar
transistor macromodel is neither PNP nor NPN type. An IDC branch is active
_only_ at DC, ignored otherwise.
Important note: Those acquainted with SPICE programs may be used to SPICE
calculating the quiescent condition of transistors. LENA does not do that,
presuming the transistor model already represents that quiescent bias
condition.
LENA - Page 23 of 46
.
OPERATIONAL AMPLIFIER MACROMODEL DETAILS
The equivalent operational amplifier macromodel is as follows:
+Input node Output node
o--- ------*-----*----- -----*----o
| | | | | | |
| | | | | | |
Rin -> GMS+ GMS- Cfc Rfc -> GMSo Rout
| | | | | | |
| | | | | | |
*--------*-----*-----*----*--------*----*
| _ |
| /| |
Rin -> o
| Common node
|
o--- GMS+ dependent on Rin at +Input;
-Input node GMS- dependent on Rin at -Input with
gm negative;
GMSo dependent on Rfc
Where:
Av = open-loop voltage gain
Fc = 'corner frequency' or 'breakpoint' where Av
magnitude begins to decrease 20 db per decade.
Rfc = 1 Ohm
gm+ = transconductance of GMS+ = 1
gm- = transconductance of GMS- = -1
gmo = transconductance of GMSo = Av / Rout
Then:
Cfc = 1 / (Fc x 2pi)
The center of this op-amp macromodel is a summing point for the current
analogue to the non-inverting and inverting voltage inputs. It also
modifies the DC open-loop gain over frequency. Output is a current
analogue of the voltage at this center, summing 'node', multiplied by Av
and divided by output source resistance.
LENA simplifies this model by reducing 8 branches to only 5, using
mathematical equivalents to the center summing node and output GMS. Each
input node still 'sees' only R-input and the output node still has Rout.
The break-point frequency is found in manufacturer's data sheets. Most op-
amp ICs have more than one breakpoint frequency, the first somewhere around
or below 1 KHz, others about a decade or two higher. Any higher than the
first can be simulated by creating an external GMS-R-C cluster. Modelling
additional breakpoints are explained in Model Tips and Hints later in this
manual.
"Input resistances" are seldom specified for op-amp ICs. Their existance
in the macromodel is required for internal mathematical analysis-solution
of dependent current sources. An approximation can be done by entering a
very high resistance value. Since the exponent range of non-integer
numbers in LENA is very large, a high, seemingly-impractical value will
not disturb analysis-solution calculation.
LENA - Page 24 of 46
.
ENTERING CIRCUIT COMPONENTS
---------------------------
This is a step-by-step procedure on entering circuit components in LENA.
The process begins after entering "NEW" at the Main Command level. Note
that ALL input to any one prompt is considered a "data word;" that is, one
or more data items within the word must be separated by commas, semicolons,
or forward-slants, no spaces. There is no need to memorize any special
order of data entry; prompts for all items are self-explanatory.
BRANCH ENTRY, SINGLE-VALUE BRANCHES
The first prompt will be:
Branch 1, Type, Plus-node, Minus-node:
The user has a choice on input, Type description alone or Type description
with the Plus and Minus nodes. Assume that RESISTOR was entered by itself,
no node numbers. This results in another prompt:
Branch 1, Type "RESISTOR" Plus-node, Minus-node:
With the second prompt, the user gets verification that RESISTOR was indeed
the Type description (LENA supplies the double quotes around RESISTOR).
LENA requires _some_ kind of numerical data in response and will keep
requesting until it gets something. Let's say that the Plus node was 2 and
the Minus node was 3. Response to the prompt would be simply "2,3".
Supplying all three data items would have an entry to the first prompt of
"RESISTOR,2,3".
If a mistake was made in entry and it became "RESISTOR,2,2", then LENA
would recognize that both nodes were equal and the screen would show:
Nodes may not be equal, please re-enter.
Branch 1, Type, Plus-node, Minus-node:
Let's assume that entry was good, that the Type description is RESISTOR,
the Plus node is 2, and the Minus node is 3. The next prompt would be for
the Value:
Resistor value [Ohms]:
Let's say the value is 4700 Ohms. Scaling letters can be used and an entry
can be "4.7K". Or, E-format can be used for an entry of "47E2" or "4.7E3".
Or simply "4700". Whichever format is easiest for the user is fine with
LENA.
Completion of Value entry results in a prompt for the next branch:
Branch 2, Type, Plus-node, Minus-node:
Note that the branch number has been incremented in the prompt. This
incrementation will repeat until the list is terminated or after it has
LENA - Page 25 of 46
completed Branch 204, the maximum number of branches in LENA.
To end the circuit list entry at any time, just enter END or EN or E or ND
or N for the Type description, no node numbers. List entry will terminate
with a prompt showing the total number of branches and the node of solution
being the highest node in the circuit list...then return to Main Command
level.
Suppose that the resistor value should have been 47 KOhms instead of 4.7
KOhms and this mistake is seen. To correct it quickly, just enter "BAK" or
"BA" or "B" and the list entry 'backs up' to the previous branch's prompt
for Type and Nodes. Re-entering everything is required.
A mistake in Value entry could be corrected later by the MODify command...
but that requires a note to oneself to do so. Going back one branch is
easy enough to do now and corrects the entry immediately, allowing
concentration on entering all the other branches in the list.
BRANCH ENTRY, DOUBLE-VALUE BRANCHES
The same Type and Nodes prompt is issued for every branch; LENA doesn't
know what Values are required until the Type Description is entered. For
example, suppose the branch was type LQ, a single inductor with specified
Quality factor. After completion of Type and Nodes entry, the Value prompt
would be:
Inductance value [Henries], Q [Units]:
Suppose the inductance was 56 microhenries with a Q of 70. The data word
entry would be "56u,70".
Note the _lower_case_ "u" for 'micro'. Scaling Letters in entry must use
lower case for multipliers less than unity, upper case for greater than
unity. Letter "u" replaces Greek letter "mu" for ASCII compatibility.
If there was a mistake made and one Value was not entered, LENA would
detect that and issue the error message:
Caution: One or both values zero, please re-enter
...and then return to the Value entry prompt for that branch. That same
"zero" caution would appear with single-value branches if the single Value
entry was zero. LENA expects _something_ in the Value and keeps prompting
until it is entered.
QUICKER ENTRY, SINGLE-VALUE AND DOUBLE-VALUE BRANCHES
LENA has a built-in 'shortcut' to allow entry of everything about simple
branches on one line. Once the user becomes acquainted with Value entry
order, Values can be entered as part of the data word following the Type
and Nodes data items. For illustration, suppose the two previous examples
were connected to the same nodes; the screen display would look like:
Branch 1, Type, Plus-node, Minus-node: RESISTOR,2,3,4700
-and-
LENA - Page 26 of 46
Branch 2, Type, Plus-node, Minus-node: LQ,2,3,56u,70
It should be emphasized that users should not try this until they are
familiar with the Value entry order. It is easy to mix up two values...but
the Type description and Value entry order match...L is first, Q is second
in an LQ. In both kinds of R-L and R-C combinations, Resistance Value is
always first.
DEPENDENT CURRENT SOURCE VALUE ENTRY
Whether the Type description is GMS or HFS, the second Value data item is
_always_ the dependent branch identification. This identification can be
done either by dependent branch's Branch Number or by its entered Type
Description.
If the Type Description is used for identification, then it is required
that the dependent branch should have additional characters to make it
distinctive; the minimum Type Description entry might be repeated the same
way in several circuit list locations. For example, suppose an HFS has a
current gain of 2 and it is dependent on a resistor in Branch 6 which has
the Type Description of "R-78". The screen display of Value prompt and
subsequent keyboard entry would like:
Current Gain [Units], Dependent Branch No.: 2,R-78
-or-
Current Gain [Units], Dependent Branch No.: 2,6
Either form of entry is correct.
LENA checks the data of every branch after Circuit Entry termination.
Dependent branches must be passive types and they must exist in the circuit
list; if incorrect, an error message is made and the dependent current
source is switched open. Should that error happen, the MODify command can
be used to correct the dependent branch identification.
SIGNAL (GENERATOR) VALUE ENTRY
Value prompt for a SIG Branch Type is:
Signal-source cur.[Amps], phase-angle [Deg]:
Phase angle does not have to be entered. Omitting it will make the phase
angle zero. A circuit list may have more than one SIG and each one may
have a different current magnitude and phase angle; all stimuli are
"locked" frequency-phase, so phase angles are relative to one another.
Current magnitude _and_ phase angle applies only to frequency-voltage
solutions. For time solutions, current magnitude entry is equal to the
peak current of a waveform. Any phase angle entry is ignored for time
solutions.
On output of a circuit list, the display will be as if the circuit had a
frequency-voltage solution; i.e., magnitude and phase-angle. A zero phase-
angle will not be displayed, only assumed.
LENA - Page 27 of 46
.
MACROMODEL ENTRIES
Only the Type Description of a macromodel is required at the Type and Nodes
prompt. Once the Type Description is entered, a second prompt for specific
nodes for that macromodel is given. For illustration, let's assume a
Bipolar Transistor called "Q67" is to be entered beginning at Branch number
5 with Base node at 8, Emitter node at 9, and Collector node at 10. The
screen display of prompts and entries might look like:
Branch 5, Type, Plus-node, Minus-node: Q67
Base, Emitter, Collector nodes: 8,9,10
If the LENA user is familiar with node entry order, the one-line
'shortcut' method can be used. The screen display of prompt and entry
might look like:
Branch 5, Type, Plus-node, Minus-node: Q67,8,9,10
Either form is correct for LENA. Once all the nodes have been entered,
the first set of Values is prompted. There is no further 'shortcut' entry
method for Values of macromodels. Users have to follow the prompts.
Node entry order for other macromodels is as follows:
Transformer > Primary, Secondary, Primary Return, Sec. Return nodes
Transmission Line > Input, Output, Common nodes
Op-Amp > Non-inverting Input, Inverting Input, Output, Common nodes
Note that while the transformer macromodel is designed for DC isolation,
one node of the primary and one node of the secondary may be the same node.
The Transmission Line macromodel is entirely passive. "Input" and "Output"
labels only serve as identification.
REQUIRED-LISTED MACROMODEL VALUES
Individual macromodel branch data is not immediately available.
Macromodels are described and listed in parameters which apply to the
entire macromodel. These parameters are:
Transmission Line
* Characteristic Impedance in Ohms.
* Velocity of Propagation (if entered zero, defaults to
0.75)
* Length in inches (If length is Metric, users must convert
prior to entry, using legal conversion of one
inch equals 2.54 centimeters)
* Attenuation per 100 foot length (obtained from cable
tables or handbooks)
If the attenuation of the entered line length is known, user
should enter Attenuation-per-100-feet as known-attenuation
LENA - Page 28 of 46
multiplied by 1200. There is no compensation of attenuation
variation with frequency; users must limit frequency-sweep
range for accurate attenuation effects.
Ideal Transformer
* Primary Inductance
* Turns ratio, primary to secondary
* Coefficient of coupling
Coefficient of coupling is limited to a range of 0.001 to 0.999.
Bipolar Transistor
* Hfe, forward current gain, common-emitter (at Ic)
* Ft, cutoff frequency (at Ic)
* Ic, average DC collector current
* Hoe, collector conductance, mhos, common-emitter (at Ic)
Collector current DC value must be entered even if the Base
bias network is described in the circuit. LENA does not
"set" the DC collector current from any DC bias network.
Operational Amplifier
* Open-loop Voltage Gain in Decibels
* "Corner" frequency where 20 db slope per decade voltage
reduction intersects open-loop voltage gain.
* Input resistance, assumed identical for both inputs.
* Output source resistance.
SEEING THE FULL CIRCUIT LIST
Enter "LIS" or "LI" or "L" at the Main Command level. The Circuit List
will appear headed by a title display. For long lists, the Pause key may
have to be pressed to stop scrolling. Branch information is reasonably
easy to understand without further explanation.
Note: Although all non-integers are stored internally to the equivalent of
15 decimal digits, Value display is rounded-off to no more than 6 decimal
digits.
Any OPEned branches will be indicated by the * asterisks * in the spaces
between that branch's data. The last line of the title block also displays
branch numbers of opened branches; if none are switched open, the last line
indicates so.
Dependent branches in a dependent current source List-line are identified
by both list branch number and Type Description, in that order.
LENA - Page 29 of 46
CIRCUIT LIST HARDCOPY
Make sure the printer is powered on, then enter ON at the Main Command.
The Main prompt changes from "MAIN*>" to "Main->" indicating the output is
directed to the printer. If your display has color, the "Main->" will be
white letters on a screen-wide blue bar. When output is directed to the
printer, there is no screen display for that output but the word "Printing"
in flashing white letters on a blue background will indicate data going to
the printer. All prompts, messages, entries will still appear on the
screen but circuit lists, print tabulations and plot graphics are directed
to the printer port.
A reminder: LENA takes care of full printer page formatting. Before
sending anything to the printer, position the paper so that it begins on
the top edge of the paper. The end of a printout will stop at the bottom
of the last page, ready for the next page.
If a printout has been completed and output is to be directed back to the
screen, enter OFF at the "Main->" command prompt. The prompt changes back
to "MAIN*>" (yellow letters on black background) and the printer 'pops' one
line feed, positioning itself at the top of the next print page. That
'pop' is a peculiarity in I/O handling of the MS-FORTRAN runtime package;
the last character, usually a line-feed, is stored internally and will not
be sent out until another output is started, the printer port is closed
(OFF command), or exiting LENA.
CIRCUIT LIST EDITING
--------------------
The Edit commands are ADD, MODify, DELete, INSert, OPEn, and CLOse. They
are all done from Main Command level. Except for ADD, which re-starts
Circuit Entry immediately after the highest branch in the current list, all
will return to Main Command level when completed.
All Edit commands have been described prior to this section. Except for
ADD, they will require a branch identification. That identification may be
either Branch Number or full Type Description. If the identification is
incorrect, a warning message will be displayed and no further action taken
except a return to Main Command level.
A reminder: Except for OPEns and CLOsures, alterations in the Circuit List
are _final_. Old values and deleted branches cannot be restored. If
versions of a circuit are desired to be kept for comparison, they can be
sent to disk. See Disk Operations for storage and retrieval.
SPECIAL NOTE ON INSERT COMMAND
On the "INS <branch>", the <branch> refers to where the new, INSerted
branch will be located. The existing <branch> will be moved up in the
circuit list to INSert the new branch. From there, everything is as it was
with Circuit Entry, except that completion of a single branch or macromodel
INSert will return to Main Command level.
LENA - Page 30 of 46
.
SPECIAL NOTES ON ALL MACROMODELS
When an Edit command identifies a macromodel by Branch Number, it is
possible to call out _any_ of the 3 to 5 branch numbers of that macromodel
or just the Type Designation of the macromodel. LENA takes care of
identification/ordering of a macromodel.
A MODify will not operate with macromodels. INSert, DELete, OPEn, CLOse
will all operate on the _entire_ macromodel.
It may not be desireable to OPEn and CLOse an _entire_ macro-model; it may
be preferred to disconnect/connect just one node. In that case, sacrifice
a branch and node such that a single branch connects that macromodel node
to the rest of the circuit. The single branch could be switched OPEn or
CLOsed to achieve the disconnect/connect of one node.
DISK DATA FILES
---------------
LENA has two types of data files, identified by file extension:
.LIN = Circuit Lists
.LNA = Solutions
The file extensions are appended automatically for both reads and writes.
Users need only specify the filename. Filename follows DOS syntax: 8
characters maximum, first letter alphabetic, underline and dash allowed as
symbols, no spaces within filename. DOS itself does error-checking on
filenames; LENA interprets some DOS error codes to present clear-language
error messages.
All data files have values written in ASCII characters, and are otherwise
indistinguishable from text files. For data field specifications on all
data files, see the Appendix file LE_APX_A.TXT.
SETTING THE DATA STORAGE DRIVE:\DIRECTORY PATH
At LENA start, the Drive and Directory for all data files is, by default,
the same Drive and Directory where LENA itself is located. The user may
specify another location from the Main Command level by entering DRI or
DIR. LENA will display a prompt for the Drive:\Directory entry showing
the entry length for the Drive:\Directory string between vertical bars.
Use conventional DOS syntax with the Drive:\Directory string; i.e.,
alphanumeric characters, no punctuation, limiting symbols to dashes and
underlines, 8 characters per directory name. The following entry would be
acceptible:
C:\IN1492\COLUMBUS\SAILED\OCEAN\BLUE\
^
The trailing back-slant delimiter symbol need not be entered...LENA will
include it if missing. Drive C: and all five directories should already
exist. LENA will reject all read/write commands to non-existant drives or
directories.
Note: To check the disk(s) or to inspect the available directories,
enter "DOS" from Main Command level, then enter "COMMAND" (7 letters)
LENA - Page 31 of 46
to stay in the DOS shell. Conventional DOS commands can be used for
inspection or directory creation. When DOS operations are completed,
enter "EXIT" (4 letters) at DOS level to return to LENA. LENA has
remained in memory, all data intact.
For short Drive:\Directory strings, it is possible to enter everything in
one line at the Main Command level. The preceding example could have been
entered as:
DIR C:\IN1492\COLUMBUS\sailed\ocean\BLUE
Alphabetic character case is not important on entry. Each Drive:\Directory
entry completion has a confirmation prompt repeating the entry in all-
capitals.
READING/WRITING CIRCUIT FILES
To read in a Circuit file, enter "R <filename>" at Main Command. If no
filename is entered and no circuit list exists, LENA will prompt for the
filename, the prompt including an 8-character space for the filename.
If a circuit list exists, or did exist, the circuit _filename_ is in
storage and LENA will display the name, then query whether or not to use
it. The prompt ends with "[Y/n]" and the capitalized "Y" indicates that
depressing the <Enter> key alone will signify a Y for yes. Entering N (no)
to the query displays a prompt for a new filename entry.
When the <filename> entry is completed, the Circuit read is done and a
prompt is shown, indicating "New circuit read in, old circuit discarded."
This is followed by a display of the node of solution, the highest node
number in the circuit.
To write an existing Circuit to a disk file, enter "W <filename>" at the
Main Command level. If the filename is omitted, LENA will prompt for one
in the same manner as a Read.
Caution: Using the same filename as an existing file will cause the
existing file to be over-written. The only way to save an existing
file is to vary the filename of the Circuit to be written.
When a Circuit Write is completed, control returns to Main Command level
without further reminders or prompts.
CIRCUIT CREATION DATES AND REMARKS
Any time a Circuit Value is MODified, or any time a branch is DELeted or
INSerted, that time will be set into the "creation date" of the Circuit.
Creation Date is Read from, and Written to, disk. That is separate from
DOS' own file Write time-stamp; alteration may take place some time before
a new file is written. Creation Date is a convenience for keeping track of
several Circuit versions.
It is also useful to include short notes about a Circuit. The "REM" (also
"*") entry at Main Command level allows writing a 47-character Remarks
string for such notes. The Remarks string can be entered between vertical
bar symbols or directly, using "REM <remarkline>". Depressing the <Enter>
LENA - Page 32 of 46
key without entering anything will result in a blank Remarks string.
A Remarks string will remain as-is until changed manually or a new Circuit
is read in from disk. A Circuit Read will displace any old Remarks string
with that stored in the file, including any file-stored string which is
all-blanks.
SOLUTION STORAGE AND RETRIEVAL
Any completed Solution may be SAVed by entering "SAV <filename>" at the
Main Command level. If <filename> is omitted, its entry will be prompted.
Data stored consists of the magnitudes and phase angles over all
frequencies of solution, frequency limits, type of solution (frequency-
voltage, impedance, etc.), time-and-date of solution, and the filename of
the Circuit solved. Solution filenames may be the same as Circuit
filenames; file extensions identify which is which.
A Solution may be retrieved by entering "BRI <filename>" at the Main
Command level. ('BRI' for BRIng back) This restores the solution data and
displays the filename of the Circuit solved (stored by a SAVe). Solutions
may be viewed directly but _conditions_ of analysis-solution may not be
changed; i.e., if a frequency-amplitude solution is brought back, you
cannot request an impedance solution since the circuit itself may be
missing or the circuit does not have the same node maximum. Similarly, you
cannot change the Node of Solution other than what was originally SAVed.
Some care should be exercised with BRIng. You may BRIng back a PLOtted
solution, change scale limits to whatever you want, print out a new PLOt,
even do a PRInt-tabulation. This can be very useful in recording analysis
data or visually comparing solutions, but there is no greater capability of
that function.
Note: A great number of combinations of conditions were tried for
deliberately setting up a program crash situation. None were found but it
might happen if BRIng is used improperly.
The principal reason for Solution storage is to permit external program
data formatting/presentation. Viewing or hardcopying previous solutions is
only the secondary reason.
COMPATIBILITY WITH LINEA DATA FILES
LENA's circuit-list and solution files have an identical structure to
those of LINEA. LINEA-generated circuit and solution files are compatible
with LENA. LINEA has a third type of data file containing repetitive
waveform coefficients (.LWC). Since LENA has no waveform reconstruction
routines, that file type cannot be used with LENA.
LENA - Page 33 of 46
SOLUTIONS AND OUTPUT
--------------------
GENERAL SOLUTION ORGANIZATION OF LENA
LENA has two major solution forms: Frequency-voltage ('Frequency'), and
Impedance. Frequency-voltage solutions yield voltage magnitude and phase
angle at one selected Circuit node at each frequency of a specified
frequency sweep. Impedance solutions find the impedance at one selected
node at each frequency of a specified frequency sweep. Frequency sweep is
selectable up to a maximum of 200 discrete frequencies.
Two forms/format of output are selectable: Tabulation ('Print') of written
values or Graphical ('Plot') equivalent using characters in a simulated
plot. Either output form is available from one solution.
LENA compares all requested solution-output combinations requested with
previous solution-output combinations, calling the time-consuming
mathematical analysis-solution calculation routine only when required.
Users need only request output and form.
SCALE LIMIT SELECTION ON PLOT
Every parameter kind in a PLOt is scanned for minimum and maximum value,
then displayed with a query as to whether those extremes are to be used as
scale limits. Pressing the <Enter> key without entering anything else will
set solution extremes as scale limits. Entering specific numerical values
will make those values the scale limits.
If desired, all PLOt scales can be 'flopped' left-for-right by specifying
scale limits in reverse order.
Specific scale value entries follow the 'data word' rules of LENA.
Omitting a data item, entering only the separator character (comma,
semicolon, forward-slant), will make that data item zero.
Degree limits for phase angles in Voltage PLOts are fixed, _not_ set by the
solution. At LENA start, those degree limits are -180 and +180 degrees.
Degree limits may be set to anything else and will remain at those settings
until changed again.
TWO FORMS OF IMPEDANCE PLOT
Either Polar or Rectangular complex form may be selected for Impedance
PLOts (both forms are tabulated together in PRInts). At the query,
pressing <Enter> key without entering anything else will select Polar form;
an "N" for 'no' must be entered to select Rectangular form.
Polar form _phase_angle_ scale limits are default-set by solution values or
reset by user entry, unlike the Frequency-Voltage PLOt degree setting
rule.
LENA - Page 34 of 46
SYNTAX ON SOLUTION TYPE AND FORM
Only two Main Command words are required, one to select Type, the other to
select Format. They may be in either order. "PRInt FREquency" will yield
the same solution and tabulation as "FREquency PRInt." Or, to simplify
entry, "P F" or "F P." Or a three-letter acronym can substitute for either
double word. "PRF" would be equal to "P F" or "F P", itself
being an acronym for PRint Frequency.
GENERATING PLOT ARTWORK
ASCII-character "plotting" is rather coarse. Quick, yes, but still too
coarse for smooth graphic output. The character plot outputs can made in
sections so that a 2X to 10X larger master can be generated for tracing
finished art. The only requirement is that frequency spacing is continuous
and the scale extremes set to allow amplitude-phase-delay to be continuous.
All scale extremes may be set manually, including reverse, left-for-right
direction.
Solution files may be read by an auxilliary program (not included) which
can format data to whatever output device is available. Solution file data
is composed of ASCII characters in generally-decimal format. Records and
data fields are described in Appendix file LE_APX_A.TXT.
SINGLE DC OUTPUT
It is possible to PRInt and PLOt zero-frequency (DC) output but hardly
necessary to send such output to the printer. A DC-only PRInt or PLOt will
have only one line; manual notation at each node will be as easy as
printing one page for each node.
To set DC-only from Main Command, enter "F DC" or "F 0,0,0".
There are no provisions to analyze-solve all nodes at one output command.
It is possible to examine the DC stability of transistor bias networks and
the like, but somewhat cumbersome to perform with LENA. A branch(s) for
base-emitter diode voltage drop must be added and, possibly, an IDC branch
to simulate varying supply voltage to the bias network. MODify edit
functions can vary those values, plus the bias network values to see the
effect of change. It may be that conventional, manual techniques, using a
pocket calculator are quicker and easier.
LENA - Page 35 of 46
.
CONVERTING FROM SCHEMATIC TO LISTING
------------------------------------
LENA doesn't have any way to convert from a symbolic schematic drawing to
a Circuit List. To fully analyze and solve frequency response of a
circuit, you need to convert the components into the nodes and branches
which LENA will recognize. Most of those branches are simply duplicates
of schematic symbols.
IN THE BEGINNING...
...there was scratch paper. As a suggestion based on others' experiences,
enough paper should be available so that you can redraw schematics, make
notes, and tabulate all the branches before keying a circuit into LENA>
A few things will not appear the same as either schematic or actual
actual circuit or may require different components. Redrawing the
schematic saves the original diagram.
Node numbering can follow signal flow, low node numbers toward input, high
numbers toward output. That also results, generally, in quicker solution
execution times. LENA produces the same solution results regardless of
node ordering. One method is to mark redrawn schematics with node numbers
enclosed in a circle, a distinctive marking not usually used as a symbol
except in "Sams Photofact" (tm) schematics.
Passive components can convert readily to single branches. Since LENA
allows up to 8 characters for type descriptions, you can use conventional
reference designations such as "R-12," "C-5A," and so forth. Follow the
signal flow again, branches beginning at signal input, generally ending at
signal output.
NODE NUMBERS MUST BE CONTIGUOUS
LENA will check for missing node numbers and display a prompt indicating
each one. LENA won't "crash" but it will stop analysis of the circuit
(error message shown) or result in zero node voltage or impedance. It is
better to organize the node ordering in the beginning to avoid missing node
numbers.
During the course of analyzing-solving a circuit, a connecting branch may
be manually OPEned. If such an OPEn results in the equivalent of a missing
branch number, analysis may stop with an error message or produce a zero
solution. Again, non-fatal, but it can cause some confusion until the user
understands what was done. It is better to plan ahead and anticipate which
branch openings might result in breaking signal flow.
COMMONS, "GROUND" AND SUPPLY LINES
Overall circuit 'ground' (or 'earth' common) is ALWAYS node 0. Always.
Power supply lines can _also_ be node 0...provided they are well bypassed
to ground in the actual circuit. This is a startling departure from usual
circuit thinking but, considering LENA does the equivalent of "small-
signal" analysis-solution in frequency domain _only_, quite acceptible.
LENA - Page 36 of 46
LENA doesn't normally set bias, enabling DC control of collector current,
or the like. In "small-signal," frequency-domain analysis, all voltages
are presumed to be linear. There are no provisions for simulating
transistor or diode saturation or cut-off. As far as AC and RF are
concerned, power supply lines are just another common; if well bypassed to
ground, they can BE ground to LENA.
If there is some doubt as to a supply line's bypassing, use a separate node
or nodes for that line and simulate the bypassing, using series R-C
branches for electrolytics (resistance approximately calculated from an
electrolytic's ESR), possibly even small inductances in series with
capacitors.
It is possible to model a very-high-gain amplifier circuit in LENA. [over
200 db gain is possible] High-gain amplifiers might have destructive
feedback via inadequate supply line decoupling. LENA can show such
feedback without simulating the oscillation that would happen with a real-
world circuit.
PARASITIC REACTANCE, RESISTANCE
LENA branch types LQ and CQ are good for simulating lossy reactances at
RF. For practical programming and memory reasons, Q is the same at every
frequency except DC. A quick look at Q tables from manufacturer's data
sheets indicates Q does vary at least 2:1 over a wide frequency range.
Accurate simulation might require limiting analysis bandwidth, modifying Q
for the next limited analysis bandwidth, and so on.
LQ branches are simulated internally by a series R-L equivalent, resistive
part equal to inductive reactance magnitude divided by Q. CQ branches are
simulated internally by a parallel R-C equivalent, conductive part equal to
capacitive susceptance magnitude divided by Q. Together, an LQ branch and
a CQ branch can accurately portray a real L-C resonant circuit.
Resistors have some parasitic capacity in parallel with resistance, varying
from 100 femtofarads (SMTs) to 1 picofarad (axial-lead types). At
frequencies where that capacity becomes significant, a PRC branch should be
used. If a circuit has very long leads on a resistor, lead inductance can
have an effect on total component impedance but can be simulated with an
SRL branch. A capacitor with lead inductance or an inductor with lots of
winding capacity must each use two branches.
The most difficult part about modelling parasitics is _knowing_ what the
parasitics are. LENA can't help you there, but, once known, LENA can
simulate parasitics exactly.
CURRENT THROUGH DEPENDENT BRANCHES
Using a type HFS dependent current source to monitor current through a
branch is an excellent _non-intrusive_ technique of analysis. There is
absolutely no 'probe capacity' or change in any measured branch due to the
real-world measuring equipment. However, some of us 'schematic oriented'
analysts may fall into a trap with certain branches.
LENA - Page 37 of 46
LENA's double-component branches LQ, CQ, SRL, SRC, PRL, and PRC are
analyzed as complex quantities at each frequency. If you want to measure
the current through an LQ, you will get the current through the _entire_
series R-L equivalent branch, not just the inductor. With a type CQ,
current is the total to the parallel R-C, not just the capacitor.
Measuring separate resistive or reactive currents requires a circuit having
only resistance or reactance.
VOLTAGE ACROSS DEPENDENT BRANCHES
The voltage across a dependent branch for a type GMS dependent current
source is straightforward. It should be kept in mind that voltage polarity
depends on the ordering of Plus and Minus nodes for a dependent branch.
You can visualize a GMS's dependent branch as having a differential
voltmeter connection to the GMS...reversing the 'voltmeter' leads will
reverse the 'reading' polarity.
CREATING "STIFF" VOLTAGE SOURCES
Ideal current sources have infinite source resistance. Voltage across such
a source is the voltage drop across _everything_ connected to that source.
While that will correctly model a transistor collector or drain, or a
vacuum tube plate, you may want a very _low_ impedance voltage source or
one with a specified source impedance.
LENA allows real-world-impractical voltage sources. A 1000 Ampere current
source across a 1 milliohm resistance will produce a 1 Volt voltage source
having a source impedance of 1 milliohm. Add a series resistance of, say,
50 Ohms, and you have a voltage source with a 50 Ohm source resistance.
A Mega-Ampere current source across a micro-Ohm resistance makes an even
'stiffer' voltage source. Such is quite within the magnitude range of
LENA.
NEGATIVE RESISTANCE OR REACTANCE
There are a few _theoretical_ equivalents to real-world circuits that
require 'negative' value components. LENA allows this; just enter a
negative resistance, capacitance, or inductance.
Negative values do not change the magnitude of single-component branches,
only the phase-angle/polarity. A negative inductor has inductive reactance
magnitude proportional to frequency, a negative capacitor has capacitive
reactance magnitude inversely proportional to frequency.
OPERATIONAL AMPLIFIER CIRCUITS
All 'Op-Amp' Integrated Circuits have a built-in "breakpoint" frequency
where the open-loop gain begins to fall at a rate of 20 db per decade of
frequency...and also produces a definite phase-shift at higher frequencies.
This _will_ affect overall response of ideal voltage-frequency-selective
circuits which don't have compensation for that Op-Amp phase shift.
LENA - Page 38 of 46
If you are analyzing a circuit which is questionable as to such phase-shift
compensation, try setting all Op-Amp macromodels to high Megahertz
breakpoint frequencies at first. Get a hardcopy response printout, then
replace all the Op-Amp macromodels with those having a lower breakpoint
frequency, re-analyze, finally comparing the responses.
Note: At least two hardcover textbooks have circuit examples and tables
of values, all of which assume _ideal_, no-breakpoint Op-Amps. Such
circuits will only work as advertised over a frequency range _below_
real-world Op-Amp breakpoint frequencies.
FIELD-EFFECT TRANSISTOR MODELS
These were not included in LENA because they are simple enough to model
with four conventional branches: Three single capacitors representing the
three junction capacities and a GMS across the Source-Drain junction
dependent on Source-Gate capacitance voltage.
BANDWIDTH-ALTERABLE NETWORKS WITH THE TRANSFORMER MACROMODEL
Double-tuned transformers with specific coupling coefficients are a simple
way to set the passband of an amplifier. Coupling coefficient k is one of
the critical items. The transformer macromodel can be used quite
effectively in the analysis-solution of such circuits since coupling
coefficient is one of the parameters of the macromodel. There is one word
of caution on such use: The macromodel does not include quality factor Q
and Q is often the other critical parameter.
Q of a tuned transformer can be modelled with parallel resistances across
each winding. Resistance value is Q times the resonance-frequency
inductive reactance. An alternate can be a series resistance with each
winding, resistance equal to resonance-frequency inductive reactance
divided by Q. The alternate requires at least one extra circuit node,
which may not be practical in large circuits.
Another possibility is to not use the macromodel at all and to manually
calculate the four branch values illustrated under TRANSFORMER MACROMODEL
DETAILS. The difference here is that each winding can use an LQ branch
type instead of a pure inductance.
CREATING "BLACK BOX" SUB-CIRCUITS
If you have a component with _known_ characteristics over frequency, some
creativity will allow a combination of branches to simulate that component.
LENA will allow tailoring that "black box" simulation to fit the known
characteristics. That may take several nodes.
To apply such a simulation to the entire circuit, it can be re-created
there...but the nodes needed _within_ the simulation cannot be connected to
other parts of the entire circuit.
LENA - Page 39 of 46
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INSTALLING LENA
===============
LENA PROGRAM SET FILES
README.1ST - Short text description of LENA Program Set.
LENAMANL.TXT - Text file, description/instruction for LENA program.
LENACFG.EXE - Configuration program, LENA.CFG file generator.
LENAS.EXE - Standard/non-coprocessor version executable.
LENAN.EXE - Numeric coprocessor version executable.
LENAMAIN.HLP - On-line Help file for LENA Main commands.
LENACKT.HLP - On-line Help file for LENA circuit model types.
LENAREG.TXT - Text file for LENA Registry
SINGSHOW.LIN - Circuit file example, all single branches.
TRANSFRM.LIN - Circuit file for transformer macromodel circuit.
TLINE.LIN - Circuit file for transmission-line macromodel.
BIPOLAR.LIN - Circuit file for transistor macromodel circuit.
OPAMP.LIN - Circuit file for operational amplifier macromodel in a
Sallen-Key low-pass filter.
PHASER.LIN - Circuit file, audio phase-shift network for a
phasing-method SSB generator.
PHASER7.LNA - Solution file for PHASER circuit, node 7.
RES100K.LIN - Circuit file, simple 100 KHz resonant circuit.
FILE_ID.DIZ - Short text file description preferred in some BBSs.
LE_APX_A.TXT - Appendix text on LENA data file structure.
LE_APX_B.TXT - Appendix text on use of example circuit PHASER.
LE_APX_C.TXT - Appendix text on Configuring LENA, use of LENACFG file.
LE_APX_D.TXT - Appendix text, history of LINEA - LENA, other CAE.
LE_APX_E.TXT - Appendix text, comparison of LENA with other programs;
transferring circuits to/from SPICE net-lists.
LENACMND.LST - One-page list of main command words for optional user
reference.
CIRCTYPE.LST - One-page list of circuit model Type words for optional
user reference.
CPUID.EXE - CPU/numeric coprocessor identifying program; public
domain from Intel Corporation.
LENA.CFG is required to run either LENAS or LENAN (or their renamed equals)
and that file is generated by LENACFG.EXE. LENACFG must be run first.
Answering the few questions in that program will set up constants for
incorporation into the created LENA.CFG file. LENACFG does not alter any
other computer system data.
LENACFG will ask for your computer system's CPU (Central Processor Unit)
type and whether or not you have a numeric coprocessor. If you answer
"don't know" to that question, it will prompt you to run CPUID from within
LENACFG. CPUID will produce a one-line statement indicating the detected
CPU and coprocessor. All .EXE files are compiled to run with an 8086 or
higher CPU (every PC except the very first). If you have an 80386DX or
80486DX CPU, the numeric coprocessor is built in.
The last action of LENACFG is a request to rename/copy either LENAS or
LENAN to LENA. LENAS is compiled to include software mathematics routines
and will run whether or not a numeric coprocessor is present. LENAN is
compiled with in-line calls to a numeric coprocessor and is smaller in
code size and much faster in execution. Trying to run LENAN on a computer
without a numeric coprocessor will result in a system "hang."
LENA - Page 40 of 46
Once LENA.CFG is created and LENA.EXE copied/renamed, copy/move those two
files and the two .HLP files to a more-permanent directory. All four
should reside in the _same_ directory. Data files (.LIN and .LNA
extensions) may be in a different directory. Note: LENA allows for Data
files in other drives:\directories but, when first run, assumes the same
drive:\directory as LENA.EXE and LENA.CFG. The Help files (.HLP extension)
are optional. As an alternate to the Help files, the enclosed .LST files
are each one page, containing Main Command words and circuit model Type
words.
It is recommended that LENAMANL.TXT be printed out first. This text file
(the document now being read) is formatted for 8 1/2 by 11 paper size, 75
character maximum line width (5-character left margin provided), 66 lines
per page and is directly printable by DOS command "COPY LENAMANL.TXT PRN".
APPENDICES
All LE_APX_x.TXT files are appendices for this manual. Users can append
them to LENAMANL with any text editor, print them out separately, or leave
them as they are. Those references were split from the manual text so as
to make the manual more manageable.
CPUID.EXE is a public-domain executable file that may be used elsewhere or
on another computer to identify CPU type. It was written and assembled by
Intel Corporation. It is included as an aid to running LENACFG.
REGISTRY
The LENA Program Set is _not_ free. It is Shareware. You are free to use
it on a trial basis for 21 days. After the trial period, continued use
obligates the individual user to Register the LENA Program Set with the
author. Full details on Registry are found in text file LENAREG.TXT and
are briefly noted following:
Individual user Registry is $30 U.S., payable by check or money order.
This also applies to any business, organization, or educational institution
after the trial period. Upon registration, each registrant is sent a disk
containing the LENA Program Set without the registration message on-screen.
CPU VERSIONS AND PROGRAM SET COPIES
Installation of a numeric co-processor is highly recommended. LENA does
extensive floating-point numeric calculation; a numeric coprocessor can
greatly reduce execution times.
Additional copies of the LENA Program Set (with choice of disk size, on
high-density media) is available from the author for $10 U.S., postpaid,
surface mail only. Additional copies may be ordered only by registrants.
LENA - Page 41 of 46
FIRST-USE LENA PRIMER/TUTORIAL
-------------------------------
This assumes that the entire LENA program set is on disk and that LENACFG
has been run and completed. The following short primer assumes the user
has some knowledge of circuit theory but is unacquainted with computer-
aided design/engineering programs.
ON-LINE HELP
A short, 6-screen display of commands and circuit elements is available at
the Main Command by entering HELp, HEL, HE, or ?.
Help screens are always in the same order and all but the last have a
"More [Y/n] ?" prompt. To get the next screen, just depress the <Enter>
key or enter "Y". To exit the Help display, enter "N" and it will return
to Main Command level.
Help screens are stored on disk as a Text file, approximately 10K in size.
Users familiar with LENA may delete that .HLP file, if desired. If the
.HLP is deleted, a Help request will only result in an error message
indicating that the Help file cannot be read. Help file presence or
absence does not affect LENA operations.
GETTING ACQUAINTED WITH CIRCUIT LISTINGS
At the Main Command, enter "READ SINGSHOW". This reads example data file
SINGSHOW.LIN from disk into LENA, a non-working listing showing all
available single-branch circuit components. A prompt will appear
indicating a new circuit read in, old circuit (if any) discarded, and the
node of solution, then return to Main Command.
Enter "LIST" at Main Command. The circuit list will scroll up, headed by
the title display showing circuit filename, when it was created, remarks
for that circuit, node of solution, current time and date, and any branches
opened.
To get a printed copy, check that printer paper is positioned at the top of
a page, enter "ON" at Main Command, then enter "LIS" again. The screen
only shows the Main prompt which has changed from "MAIN*>" to "Main->"
indicating output is directed to printer. Enter "OFF" at Main; Command
prompt becomes "MAIN*>" again indicating output is to screen. [printer
will do one line-feed on the OFF command, quite normal]
List data is fairly self-explanatory. Branch type descriptions allow up to
8 characters maximum but only the first one, two, or three letters matter.
The first branch is designated RESISTOR but it could also have been "R-1"
or just "R" or even "R_FIRST."
Note: Branch type descriptions will always be displayed as all-capitals,
regardless of entry case.
'Plus' nodes and 'Minus' nodes have specific meanings only for current
_sources_ and for dependent branches of a dependent current source. If
this is confusing, please review the description of independent and
LENA - Page 42 of 46
dependent current sources given earlier. 'Plus' and 'Minus' nodes would be
arbitrary for a circuit composed entirely of passive branches.
In the value columns, two-value branches will always have the same ordering
as the minimum branch type description; i.e., an LQ branch would show
inductance first, Quality factor second. The number of significant digits
is rounded-off to five.
There is a bit of shorthand in the 3-letter type description of series and
parallel R-L and R-C branches. The first letter for a Series branch is
"S." The first letter of a Parallel branch is "P."
Dependent current sources GMS or HFS will always indicate their dependent
branches by both branch number and type description.
TRYING OUT A MACROMODEL
Read in circuit file TLINE ("R TLINE" at Main Command), then List it. Note
that SIG ('signal generator') and the two resistors (R-SOURCE, R-LOAD) are
in the same format as with SINGSHOW...all three are single branches. Type
"Z" is a minimum type description for a transmission line macromodel and
occupies three contiguous branch positions in a List, corresponding to the
three branches created and analyzed within LENA.
Where single branches had node numbers under both Plus and Minus columns, a
macromodel has only one node (under Plus column) with an identification of
that node of the model (under Minus column). [A transmission line doesn't
really have an "input" and "output" but that arbitrary identification is
better than saying "one end" and "other end."] Values are shown for the
entire model, not individual model branches.
Enter "F 1M,50M,-15" at Main Command. This tells LENA to set a frequency
sweep from 1 MHz to 50 MHz in 15 logarithmic steps. ["1M" and "50M" must
use upper-case M for Mega] You can confirm this by entering "SET" at
Main...resulting in a circuit title describing TLINE followed by frequency
range. A SETtings display is screen-only and useful for checking current
settings.
Enter "PRI FRE" at Main...requesting a Print (tabulation) of voltage
solutions over Frequency. Tabulation will scroll up on the screen. The
node of solution is 2 and the voltage across R-LOAD is 22.800 Volts. LENA
has a default zero-decibel reference of one volt so the DB column shows
27.15 decibels. TLINE has no reactive branches so the voltage remains
constant over frequency. Phase angle at node 2 varies over frequency
(expected) but Group Delay is constant at 13.556 nanoseconds.
Group Delay follows actual time delay from a signal source to node of
solution...provided that frequency increments are small enough and phase
angle changes are smooth enough...it is a calculated value of differential
phase angle divided by differential frequency. TLINE has a transmission
line length of 120 inches and a velocity of propagation of 0.75, equivalent
to a free-space path of 160 inches. Signal propagation at the speed of
light (299,792.5 KM/Sec) over a 160 inch distance is 13.556 nanoseconds.
Enter "DBR 25" at Main Command. This tells LENA to set the zero-db
reference at 25 Volts. Enter "P F" at Main to repeat the tabulation of
LENA - Page 43 of 46
voltage at node 2. Everything is the same as before except the decibels
column shows "-0.80 db" instead of the previous 27.15 db.
Enter "PLOT F" at Main. Three prompts will appear in sequence, each one
indicating minimum and maximum solution values of voltage, phase angle, and
group delay. To use solution extremes as scale limits, just use the
<Enter> key at each query. A simulation of a graph plot will appear
following a circuit title header. Scale limits are shown on the graph top.
Relative voltage in db [* mark] and Group Delay [^ mark] is fairly
constant; phase angle [: mark] changes over the entire scale range.
You can experiment with different scale limits by entering "PLF" (alternate
single-word command for "PLOt FREquency") and then entering your own values
at each limit prompt. Note: If there is no change in frequency limits, no
node of solution change, no circuit change, LENA retains the first
solution; repeated PLOts use the same solution data, changing only the
simulated plot mark positions.
Enter "NOD 1" at Main to tell LENA to solve for voltage at node one
(signal generator or transmission line 'input'). Enter "PRF" at Main
(shorthand for "PRInt FREquency"). Tabulation of voltage at node one shows
a constant 25 Volt, 0 db, 0 degree phase-angle over frequency. Considering
the 50 ohm characteristic impedance line is matched at both ends with
perfect 50 Ohm resistors, this is expected at the signal source end of the
line.
To check the "input" impedance of the line, enter the following at each
Main Command prompt: "O 2" (OPEn branch 2); "PR Z" (Print-tabulate
Impedance). R-SOURCE has been temporarily disconnected and LENA will
tabulate impedance "looking into" node 1. Impedance will be a constant,
resistive 50 Ohms. [All signal sources are automatically disconnected
during impedance solutions.]
Perfect transmission lines with perfect resistive terminations tend a bit
towards boredom. For variety, Open and Close the terminations and check
voltage at each end, or use the Modify command to change the termination
resistance values. This is quick way to see the effects of "open" and
"shorted" transmission line sections over frequency.
TRYING OUT CIRCUIT EDIT FUNCTIONS
Read in SINGSHOW and note branch number four's list line. Enter
"OPEN 4" at Main Command, then "LIST" again. Branch 4 will show asterisks
between the fourth branch's data, indicating that, while it is still in the
list, it is "struck out" of any analysis. Displays in color show an open
branch in grey rather than cyan. Branch 4 is now disconnected but it
remains in the listing. Note the bottom line in the circuit header display
indicating number 4 branch open.
At Main Command, enter "CLOSE 4," then "LIS." Branch 4 has no asterisks,
indicating its connections have been closed to the rest of the circuit.
The bottom line of the title display indicates that no branches are open.
Note branches 5 and 6, then enter "DELETE 5" at Main Command. Enter "LI"
to see the list again. Old branch 5 is gone and the former branch 6 now
occupies that list position. All higher branches have moved down one.
LENA - Page 44 of 46
Enter "INSERT 5" at Main Command. A new prompt for Type-Nodes will appear,
indicating that INSert has jumped into the Circuit Entry. Enter "CQ,1,5"
at the Type-Nodes prompt. Enter "5u,50" at the prompt for Branch 5 values.
The Main Command will return. Enter "L" to see the list again.
Branch 5 has been restored, and all higher branches have returned to their
original branch order numbers. However, a 5 microfarad capacitor with a Q
of 50 is unlikely while a 5 nanofarad capacitor is more realistic. Enter
"MODIFY CQ" at Main Command. This results in a request for values of
branch 5 (type "CQ"). Enter "5n,50" at the values prompt (being careful to
enter a lower-case 'n') then List the circuit. Branch 5 has been changed
to 5 nanofarads with a Q of 50. Note that the creation time and date is
now the same as the current time and date.
Enter "OPE 1" at Main Command. A prompt will appear indicating that branch
13 is dependent on an open branch and, as a result, branch 13 has been made
open also. List the circuit to show both branches indicated as open.
LENA has checked for this possibility after the OPEn command was
completed. Had this check not been done, LENA would not have crashed or
hung, merely stopped trying to analyze the circuit (and indicating it
stopped) and returned to Main Command. LENA lets you know what caused
most of the common errors.
Enter "CLO 1" at Main Command, then List the circuit. Branch 1 is back to
closed connection but branch 13 is still open. Notice also that 13 must
have a separate CLose command to restore it. The extra CLOse command is
necessary since one passive branch can be the dependent branch for several
dependent current sources.
Note the dependent branch description of branch 13. Enter "DE 1" at Main.
A notice will appear that branch 12 is now open and dependent on a "<none>"
branch. Branch 1, "RESISTOR," will be gone from a Listing, all higher
branches have moved down one list position, and the "HFS" branch is
dependent on branch "0, <none>." LENA automatically opened the HFS
dependent current source since it no longer has a dependent branch. The
HFS cannot be CLOsed...but you can MODify that branch to be dependent on
another branch that does exist in the circuit. Once the dependent branch
exists, a dependent current source can be CLOsed and OPEned at will.
You have the choice of entering a branch number or a branch's type
description for any edit function. This is also true for entry of
dependent branch of a dependent current source. LENA is quite flexible...
and forgiving.
An "ADD" at Main Command drops into Circuit Entry, beginning at the next
highest branch number...operation is otherwise identical to "NEW." This is
a good time to try out adding in your own circuit components, to get the
"feel" of building a circuit.
SAVING A CIRCUIT FILE, TRYING OUT DOS FUNCTIONS
With SINGSHOW circuit edited to something else, enter "WRITE" at Main
Command. A prompt will tell you that "SINGSHOW" filename exists and
queries if you want to use that name. Enter "N" for no. Another prompt
requests the new filename, cursor stopping at left-most position within two
vertical bars. Enter something like "TEST1." The edited file will be
LENA - Page 45 of 46
written to disk in the same directory containing LENA.
Enter "L" at Main Command. The List header now shows "TEST1" as the
filename, not "SINGSHOW." LENA always uses the last circuit filename
entered as the filename of the circuit title. Using the "NAMe" command,
just the circuit filename can be changed. Circuit title Remarks will
remain the same as for SINGSHOW and that can be changed any time with the
"REMarks" Main Command.
Enter "DOS" at Main Command. This goes into a 'DOS Shell' with LENA held
in memory. A prompt reminds you to enter "COMMAND" if you want to stay in
DOS; the Shell is good for only one DOS command unless that "COMMAND" word
is entered. Request DOS to show the directory. TEST1.LIN will appear in
the directory list, indicating you really did write the circuit file.
If you entered "COMMAND" once in DOS, you can stay in that environment
until you enter "EXIT." You can change directories, delete or rename old
files, do any DOS command. LENA remains patiently in the background, all
data intact. [Note: This assumes your computer has a minimum of 142K free
RAM] Entering "EXIT" takes you out of the DOS Shell and returns to
LENA...the Main Command prompt will appear, indicating you returned
safely. Enter an "L" for List and the TEST1 circuit will scroll up.
Except for the DRIve and DIRectory commands, LENA has no other DOS
functions within program. The "DATe" command at Main is a user-
convenience, display-only function; resetting the computer time and date
must be done at DOS level.
To change the DRIve:\DIRectory for LENA data files, drive and directory
must _already_ exist; LENA doesn't create them. If a non-existant drive
or directory is specified, a prompt is issued to that effect, no read or
write is done, and there is a return to Main Command level.
LENA - Page 46 of 46
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