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1990-09-13
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1,710 lines
P C - E C A P
Version 1.10
Program Reference Manual
Copyright (c) 1990 by Peter Volpa
All Rights Reserved
_______
____|__ | (tm)
--| | |-------------------
| ____|__ | Association of
| | |_| Shareware
|__| o | Professionals
-----| | |---------------------
|___|___| MEMBER
Peter Volpa
Circuit Systems
418 Church Road
Sicklerville, NJ 08081-1727 page 1
License
PC-ECAP is distributed as "shareware". It is NOT public
domain or free software.
Non-registered users of this software are given the
opportunity to evaluate the complete PC-ECAP software
package for 30 days with no obligation. If, after the
evaluation period, you find PC-ECAP to be suitable for your
needs, you must register your copy or discontinue using
PC-ECAP.
What we're saying is if you use this program, then you
should pay for your copy. That way Circuit Systems will be
able to provide updates, support, and generally stay in
business.
PC-ECAP is distributed in two forms: a registered version
and an unregistered version. The unregistered version is a
fully-functional program that has all the features of the
registered version. However, the unregistered version
requires the user to go through an initialization procedure
each time PC-ECAP is started. The initialization procedure
requires the user to enter a random 4-digit number before
PC-ECAP will run. The registered version does not have this
initialization procedure.
The REGISTERED version of PC-ECAP is LICENSED TO THE SINGLE
PERSON WHO REGISTERED THE PROGRAM AND MAY NOT BE DISTRIBUTED
IN ANY MANNER.
All users are granted a limited license to copy the
UNREGISTERED version of PC-ECAP for the trial use of others.
This license does NOT include distribution or copying of
this software:
* In conjunction with any other product or service.
* In general use within a company or school.
* For any "disk fee" other than a small (generally
$2.00 to $5.00) copying charge.
* For distribution in any modified form. The file
containing this license information MUST be
included along with full documentation and all
the files that make up this software package.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 2
Ordering Information
A PC-ECAP registration licenses you to use the product on a
regular basis. Registration also entitles you to technical
support, update notices, and enables you to get future
releases of PC-ECAP at a minimal price.
Individual registrations come in two forms. The first,
registration only, costs $69 (plus $2.00 shipping and
handling). Upon receipt of your paid registration form, we
will send you the latest registered version of PC-ECAP with
documentation on the disk. We also offer PC-ECAP with a
printed manual. For $79 (plus $3.00 shipping and handling)
we will send you the latest registered version of PC-ECAP
along with a professionally printed bound manual. New
Jersey residents should include 7% sales tax.
Educational institutions may apply a 35% discount to all
prices. PLEASE include your educational institution
letterhead (with your title) when you order.
Site licensing is also available. Prices are based on the
estimated number of users. Please write for more
information.
A PC-ECAP registration form is included in the distribution
package for your convenience. It is in the file ORDERFRM.
Please take time to fill it out and return it. If you would
like high-quality software to continue to be made available
on a try-first basis and for a reasonable cost, it is up to
YOU to support such programs.
Please send your registration form, suggestions and any
comments that you might have to:
Peter Volpa
Circuit Systems
418 Church Road
Sicklerville, NJ 08081-1727
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 3
DISCLAIMER
ALTHOUGH WE HAVE EXTENSIVELY TESTED PC-ECAP AND BELIEVE IT
WILL GIVE ACCURATE RESULTS IF USED CORRECTLY, WE SUPPLY THIS
PROGRAM AS IS. CIRCUIT SYSTEMS DISCLAIMS ALL WARRANTIES,
EXPRESSED OR IMPLIED, THAT THIS PROGRAM IS FIT FOR ANY
PURPOSE. CIRCUIT SYSTEMS ALSO ASSUMES NO LIABILITY FOR ANY
DAMAGES EITHER DIRECT OR CONSEQUENTIAL, WHICH MAY RESULT
FROM THE USE OF THIS PROGRAM.
Trademarks
MS-DOS is a registered trademark of Microsoft Corporation.
PC-DOS, PC/AT, PC/XT, and PS/2 are registered trademarks of
IBM Corporation.
Compaq is a registered trademark of Compaq Computer Corp.
Hercules is a registered trademark of Hercules Computer
Technology.
Association of Shareware Professionals
This program is produced by a member of the Association of
Shareware Professionals (ASP). ASP wants to make sure that
the shareware principle works for you. If you are unable to
resolve a shareware-related problem with an ASP member by
contacting the member directly, ASP may be able to help. The
ASP Ombudsman can help you resolve a dispute or problem with
an ASP member, but does not provide technical support for
members' products. Please write to the ASP Ombudsman at P.O.
Box 5786, Bellevue, WA 98006 or send a Compuserve message
via easyplex to ASP Ombudsman 70007,3536.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 4
Introduction
PC-ECAP is an easy to use AC circuit analysis program which
analyzes circuits consisting of resistors, capacitors,
inductors, transformers, transistors (both bipolar and
FET's), operational amplifiers and transconductance
amplifiers.
Totally integrated in one package, it contains a full screen
text editor for preparing analysis input, an electronic
circuit analyzer that calculates your circuit's frequency
and phase response, a high resolution display plotter that
supports all common graphics adapters and a high resolution
plotter for IBM/Epson compatible printers.
Features:
* Completely menu driven - very easy to use.
* Can analyze circuits with up to 40 nodes - no
limit on the number of components.
* Built in full screen editor with on-line help
function.
* Free input format - common abbreviations such as
P, U, N, M, K, MEG, G are recognized. For
example if your circuit has a 47pf capacitor, all
you need to enter for its value is 47pf.
* Supports CGA, EGA, VGA, Hercules and even the
Monochrome Display Adapter.
* All calculations are done in double precision -
14 digits of BCD.
* High resolution plots on IBM/Epson compatible
printers.
* Program may be configured to send its output to
LPT1, LPT2, LPT3 or a disk file.
* Bipolar transistor model maker. Just enter your
transistor's operating parameters and PC-ECAP will
create a Hybrid-Pi model for your transistor.
* Does not need a numeric coprocessor.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 5
System Requirements:
* IBM PC, XT, AT, PS/2 or compatible.
* PC or MS-DOS 2.0 or later.
* One floppy disk drive.
* 182K of free memory - that is, 182K in addition to
the operating system and any resident programs
that you may have loaded.
* A CGA, EGA, VGA or Hercules compatible graphics
card is recommended for best performance. But if
all you have is a monochrome display adapter,
PC-ECAP will even graph its results on that -
though the resolution will be much lower.
* An IBM/Epson compatible printer, if hard copy is
desired. Most printers used with IBM and IBM
compatible computers support this standard. Be
sure "IBM" mode is selected (usually by means of a
dip switch).
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 6
Before You Begin
The very first thing that you should do before going any
further is to make a backup copy of your distribution disk.
To do this just use the DOS command DISKCOPY. This will
work whether or not you have two floppy disk drives. It
also doesn't matter if the diskette that you want to copy to
is formatted or not. DISKCOPY will format it for you.
From the DOS prompt type this:
DISKCOPY A: B:
You will be asked to "Insert source diskette in drive A:"
This should be your original PC-ECAP disk. Continue to
follow the directions on the screen and you will have your
backup copy.
Installing PC-ECAP
We have included an "Install" program with PC-ECAP to make
installation very easy. The Install program will not do
anything "funny". It will not modify your AUTOEXEC.BAT or
your CONFIG.SYS files. All it will do is create a
subdirectory on your hard drive called "\ECAP". Then it
will copy all the needed PC-ECAP files from your floppy
drive to that subdirectory. That's all. It is strictly for
your convenience. The default "from" drive is drive A: and
the default "to" drive is drive C:. These may be changed to
any other drives as needed.
If you don't have a hard drive, you don't need to proceed
any further. Skip the rest of this section and use your
backup copy as your working disk.
To use the install program, insert your backup copy of
PC-ECAP into your floppy drive and type:
INSTALL
Follow the directions and before you know it, you will have
PC-ECAP on your hard drive.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 7
Quick Start
Although there is no substitute for reading this entire
manual, I know there are those of you who can't wait to try
a new program. So for those who like to try-first-read-
later, this will give you a taste of what PC-ECAP can do.
Start PC-ECAP by typing:
ECAP
at the DOS prompt.
From the main menu choose the "Select input file"
selection. Select EXAMPLE1.DAT as your input file. The
circuit described by EXAMPLE1.DAT is a simple RC low-pass
filter and is shown below.
1 1.59K 2
------/\/\/\/\------*---------
|
|
input ___|___ .1uf output
_______
|
|
0 |
--------------------*----------
Now from the main menu choose "Analyze circuit". The
analysis will begin and you will see the results as the
program progresses. When the analysis is complete, the
results will be plotted on your display. First you will see
a plot of Magnitude vs. Frequency. If you press any key
other than ESC you will get a plot of Phase vs. Frequency.
Pressing any key (other than ESC) again will show you
Magnitude again. When you are finished, press ESC to return
to the main menu.
As I said, this is a taste - for the details read on.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 8
Getting Started
PC-ECAP is started by typing the following command at the
DOS prompt:
ECAP [ options ]
The optional command line switches should not be needed by
99% of computers, and therefore are covered separately in
appendix A.
When PC-ECAP is started, you will first see the main menu.
The program has been designed to be very easy to use, and
the menu system plays an important part in reaching this
goal. All menu choices may be selected in either one of two
ways. First, a selection may be made by typing the first
letter of an item. These are highlighted so they stand out.
Selection may also be made by using the cursor keys (up
arrow, down arrow, home and end) to highlight a choice.
When "ENTER" is pressed the selection is made. The program
will do its best to logically anticipate your next choice.
For example, after editing a circuit description and
returning to the main menu, the choice "Analyze circuit"
will be highlighted - assuming that after editing, you most
likely will want to analyze your circuit.
MAIN MENU Descriptions
Select input file
This selection will display an alphabetically sorted
list of all the circuit description files in your
current directory. Use the cursor keys to select a
file to use. If you see "more . . ." displayed at the
beginning or end of the list, this means that there are
additional files on another page. You can use the PgUp
or PgDn keys in addition to the up arrow, down arrow,
left arrow, right arrow, home and end keys to view
them. Once your choice is highlighted just press ENTER
to select it.
If you want to select a file that is not listed (for
example - a new circuit description that you want to
input) press F2. A window will appear asking for the
filename. Type the filename and press ENTER. All
filenames should be eight characters or less in length.
If you type in more than eight, only the first eight
will be accepted. A file extension is optional, if it
is omitted the extension ".DAT" will be appended to the
filename. If a filename has an extension other than
".DAT", the ".DAT" extension will be substituted in its
place.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 9
If at any time you want to abort the current operation,
pressing the ESC key will return you one level up in the
program.
Edit input file
This starts the built-in full screen editor. The file
that you want to edit must be selected first. If no
file is selected, you will be sent to the "Select input
file" screen and then returned to the editor.
The editor is very straight forward to use, just type
each line followed by the ENTER key. When in the
editor these keys have special meaning:
Right Arrow - move one character to the right.
Left Arrow - move one character to the left.
Home - move to the beginning of the line.
End - move to the end of the line.
Up Arrow - move one line up.
Down Arrow - move one line down.
Cntrl Home - move to the beginning of the file.
Cntrl End - move to the end of the file.
PgDn - move 20 lines down.
PgUp - move 20 lines up.
Del - will delete the character directly above
the cursor.
Backspace - will delete the character to the left of
the cursor.
Ins - will toggle between the insert and
replace modes. In the insert mode the
cursor will change to a block cursor and
any characters typed will be inserted
between any characters already on the
screen. When in replace mode, any
characters typed will type over those on
the screen.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 10
In addition to these special keys, five function keys
have special meaning.
F1 Help
One of the features that has been added to make
PC-ECAP easy to use is the on-line help. When F1
is pressed a window will appear containing useful
information on items such as circuit element
description formats, analysis range and sweep
type, value types and examples. You can move
through these with the PgUp and PgDn keys. When
you are ready to continue editing, pressing F1
again or the ESC key will close the window and let
you edit.
F2 Model Maker
The model maker allows you to more accurately
model bipolar transistors. The transistor model
used is the Hybrid-Pi model. Despite its
simplicity, this model gives quite good results
for analysis up to about one half of the
transistor's cutoff frequency (Ft).
When the model maker is activated, a window will
appear. You will first be asked for the node
numbers of the transistor. Enter these pressing
the ENTER key after each entry for base, emitter,
and collector. You next have to answer four
questions. You will be asked (and need to know)
the following:
Transistor DC collector current - hopefully you
will know this. If not, try your best guess.
Transistor current gain or Beta - since the gain
of bipolar transistors varies with collector
current, the number that you enter here should be
at the collector current specified above for best
results. Usually it is available in the data
sheet for the transistor.
Transistor Gain-Bandwidth product (Ft) - this also
should be at the collector current entered above
(check the data sheet).
Transistor common base output capacitance - this
is just the base to collector capacitance.
Usually it is listed as Cobo in the transistor
data. (Which means output capacitance common base
with the emitter open).
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 11
After all the information is entered, the window
will close and components for the model will be
inserted into your circuit description after the
current cursor line.
F3 Insert Line
Pressing F3 will insert a blank line above the
current cursor line and move the cursor line and
all lines below it down.
F4 Delete Line
Pressing F4 will delete the current cursor line
and move all lines below it up.
F5 Find Component
The Find Component feature is useful to find
circuit elements in your circuit description file.
Just press F5, enter the element to be found, and
the line containing the element will be
highlighted with the cursor positioned there. If
the element does not exist, a "Component not
found" message will appear.
Leaving The Editor
When you are finished with your editing, press the ESC
key. If you have made any changes to the file, you
will be asked, "Save Changes (Y/N or <CR> for Yes)?".
Answer "Y" to save all changes, or "N" to ignore all
changes. A carriage return will save all changes.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 12
Analyze circuit
This choice will begin the actual analysis of the
circuit selected. If a file containing the circuit
description has not been selected, you will first be
sent to the "Select input file" screen and then
returned to begin analysis.
PC-ECAP will subject your circuit to a 1 volt signal at
the selected input node and then calculate the
magnitude and phase response at the selected output
node. The input signal is from an ideal AC voltage
source and therefore it can drive any impedance. Any
output node selected will not be loaded by PC-ECAP.
This analysis is repeated for each of the frequencies
in the specified input range. The number of
frequencies within the input range that PC-ECAP will
subject your circuit to, is controlled by the "Change
the number of sample points" option under the "Change
program settings" choice of the main menu. Its use
will be fully explained under that heading. As PC-ECAP
progresses, it will display magnitude and phase results
on the screen. The results of the analysis are also
saved in a disk file. The file will have the same name
as the circuit description file but will have a file
extension of ".OUT".
When the analysis is finished, the results will be
plotted on your display. For all display adapters
other than VGA, PC-ECAP will use the highest resolution
that your display adapter supports. VGA adapters will
be run in EGA mode (640 x 350). The resolution used
will be as follows:
CGA 640 x 200
EGA 640 x 350 enhanced display
640 x 350 monochrome display
640 x 200 color display
Hercules 720 x 348
VGA 640 x 350 monochrome or color
MDA 80 x 25
Pressing any key other than ESC will toggle between the
display of "Magnitude vs. Frequency" and "Phase vs.
Frequency". Pressing ESC will return to the main menu.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 13
View output data
This selection allows you to view the results of
circuits that have been previously analyzed. The
results will be listed in tabular form on the display.
You can use the cursor keys to move through them. The
cursor keys that are active under this selection are
the following:
Up Arrow - scroll up one line.
Down Arrow - scroll down one line.
PgUp - scroll up 19 lines.
PgDn - scroll down 19 lines.
Home - display the first 19 lines.
End - display the last 19 lines.
The analysis results can also be plotted on the display
by pressing the F1 function key. Plotting works the
same way as described in the "Analyze circuit" section.
Pressing any key except ESC will toggle between the
magnitude and phase displays. Pressing ESC will return
you to the tabular listing of the data. Press ESC again
to return to the main menu.
Output to printer
This choice will normally send the results of an
analysis to a printer selected under the "Change
program settings" option. If desired, the results can
instead be sent to a disk file for printing later. The
file will have a filename that is the same as the file
selected, but with a file extension of ".PRN".
In either case the output will consist of a listing of
the circuit description at the time of analysis, a
tabular listing of the analysis results, and high
resolution plots of Magnitude and Phase vs. frequency.
It is necessary to have a printer that is IBM/Epson
compatible if printed output is desired. Most printers
used with IBM compatible computers support this
standard, although in a few cases it may be necessary
to select this mode by means of a switch on the
printer.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 14
Change program settings
PC-ECAP allows you to configure certain aspects of its
operation. The configuration information is saved in a
disk file that is read every time the program is run.
The name of this file is "PC-ECAP.CFG". If this file
is not present it will be created. This should only be
necessary the very first time you run PC-ECAP. The
file will have as defaults, 70 sample points for
analysis and LPT1 selected as the output destination.
Both of these may be changed by means of this menu.
Change the number of sample points
When an analysis is performed, the desired frequency
range is divided into a number of sample points. The
number of points may be set to 35, 70, 140, 280 or 560.
It should be noted that you must obviously make a
choice between the high analysis resolution provided by
selecting 560 sample points and the faster
computational speed offered by selecting 35 points.
The number of points you select really depends on the
circuits that you analyze. I have found that for most
circuits 70 sample points works quite well. You should
increase the number of points if you have a circuit
that has abrupt changes in magnitude or phase. You may
also want to increase the number of points if you
analyze circuits over a very wide frequency range.
Select output destination
The output from PC-ECAP can be sent to a printer
designated as LPT1, LPT2, or LPT3. Alternately output
may be sent to a disk file for later printing. For
printed output, select the port that you have your
printer attached to (normally this will be LPT1).
Write changes to disk
This selection will write any changes in configuration
to the "PC-ECAP.CFG" file. Select this option to make
the changes you have made carry over to the next
session of PC-ECAP. If the changes are not written to
disk, they will be in effect only for your current
session.
Return to main menu
Returns you to the main menu.
Quit this program
Ends your current session with PC-ECAP and returns you
to DOS.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 15
Analyzing a Circuit Using PC-ECAP
The first step in analyzing any circuit is to draw the
circuit on a piece of paper. Next number all the nodes in
the circuit. A node is any connection of 2 or more
components. Node numbers must be non-negative integers.
There are two rules that you must follow when numbering
nodes, first ground or the common connection between input
and output must always be designated as node number 0.
Secondly, although the nodes may be numbered in any order,
none may be skipped. PC-ECAP has a limit of 40 nodes but no
limit on the number of components.
Input Format
The input format of a PC-ECAP circuit description is easy to
learn and remember. Fields describing a component are of
the free format type and are simply separated by spaces.
Circuit element names should begin with a letter designating
the type of circuit element and may optionally be followed
by up to 15 additional alphanumeric characters.
Values used to describe a circuit element may be integer
(100), floating point (1000.45), either an integer or
floating point number followed by an integer exponent
(1E-3, 4.7E6) or either an integer or floating point number
followed by one of the following scale factors:
P=1E-12 N=1E-9 U=1E-6 M=1E-3 K=1E3
MEG=1E6 G=1E9
Letters immediately following a number that are not scale
factors are ignored, and letters immediately following a
scale factor are ignored. So 10, 10ohms and 10Hz all
represent the same number, and u, uf and umhos all represent
the same scale factor. Note that 1000, 1000.0, 1000Hz, 1E3,
1.0E3, 1K and 1KHz all represent the same number.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 16
Circuit Element Description
Resistors
RXXXX N1 N2 Value
N1 and N2 are the two element nodes. Value is the
resistance in ohms.
Examples:
R1 1 2 100
RLOAD 12 15 1K
Capacitors
CXXXX N1 N2 Value
N1 and N2 are the two element nodes. Value is the
capacitance in farads.
Examples:
C4 8 9 1uf
COSC 2 3 22pf
Inductors
LXXXX N1 N2 Value
N1 and N2 are the two element nodes. Value is the inductor
value in henries.
Examples:
L3 7 0 10mh
LTANK 4 5 56uh
Transformers
TXXXX +Pri -Pri +Sec -Sec N
+Pri and -Pri are the nodes for the transformer primary.
+Sec and -Sec are the nodes for the transformer secondary.
N is the turns ratio between primary and secondary (Np/Ns).
The + and - signs denote the phasing of the windings,
e.g. the +Pri node will be in phase with the +Sec node.
Example:
T1 3 0 4 5 10turns
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 17
Bipolar Transistors (both NPN and PNP)
BXXXX NB NE NC Beta Rbe
NB, NE, and NC are the base, emitter and collector nodes
respectively. Beta is the Transistor current gain. Rbe is
the equivalent base-emitter resistance (in ohms) used in the
Hybrid-Pi transistor model.
Example:
B1 9 0 11 100 1250
Field Effect Transistors (both JFETs and MOSFETs)
FXXXX NG NS ND Gm
NG, NS, and ND are the gate, source, and drain nodes
respectively. Gm is the FET transconductance in mhos
(Amps/Volt).
Example:
F2 3 4 0 2000umhos
Operational Amplifiers
OXXXX N+ N- NO Gain Rout
N+, N-, and NO are the non-inverting input, inverting input
and output nodes respectively. The opamp output is
referenced to ground (node 0). Gain is the open loop gain
of the opamp, usually somewhere between 10,000 and 1 million
times. Rout is the open loop output resistance for the
opamp. Real opamps usually have an output resistance
between 10 and 150 ohms.
Example:
O1 1 2 2 100k 75
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 18
Transconductance Amplifiers
GXXXX N+ N- NO+ NO- Gm
N+ and N- are the non-inverting input and inverting input.
NO+ and NO- are the non-inverting output and the inverting
output. Please note that these outputs are floating. In
other words the actual output is not from either output to
ground, but is developed between the outputs. Either output
(but not both) may be tied to ground if a single ended
output is desired. Gm is the amplifier transconductance in
mhos (Amps/Volt). The transconductance amplifier may be
used in its own right or it may be used to perform a voltage
to current conversion, sometimes useful when simulating
other devices.
Example:
GXXXX 1 2 3 0 100mmhos
A Few Words About Transconductance Amplifiers
Although most people are familiar with bipolar transistors
and operational amplifiers, not as many know about
transconductance amplifiers. These amplifiers are another
variation of a dependent source. The common bipolar
transistor is a current controlled current source; A small
current entering the base controls a much larger current
flowing between the collector and emitter. The opamp is a
voltage controlled voltage source; A very small input
voltage effectively controls a much larger voltage swing at
the output. With this said, a transconductance amplifier
can be described as a voltage controlled current source; A
small voltage difference between the two inputs controls a
current flowing either into or out of the output. In our
case this current will flow from one output to the other.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 19
Specifying Analysis Parameters
Once your circuit has been described you need to determine
how it will be analyzed. PC-ECAP will subject your circuit
to a 1 volt signal at the selected input node and then
calculate the magnitude and phase response at the selected
output node. The frequency of the input signal can be swept
over the specified range in either a linear or logarithmic
fashion.
The PLOT statement is used to tell PC-ECAP which node of
your circuit will be used for the input, which node will be
used for the output, the frequency range that you want to
analyze and the sweep mode (linear or logarithmic).
This is the format for the PLOT statement:
PLOT NI NO Start-frequency Stop-frequency Plot-mode
PLOT may optionally be abbreviated to P. NI is the
circuit's input node. NO is the circuit's output node.
Start-frequency is simply the beginning frequency for the
analysis. Stop-frequency is the upper frequency limit of
the analysis. Plot-mode specifies whether a linear or a
logarithmic frequency sweep is to be performed. This may be
abbreviated to 3 letters (LIN or LOG) if desired.
As an example, we might have a circuit where node 2 is the
input and node 5 is the output. The lowest frequency that
we want to look at is 100 Hz and the highest frequency is
10 KHz. Also lets sweep this range logarithmically.
This PLOT statement will specify all this:
PLOT 2 5 100HZ 10KHZ LOG
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 20
An Example Please!
It's about time now to look at an example circuit. We will
analyze a simple RC low-pass filter. The circuit is shown
below.
1 1.59K 2
------/\/\/\/\------*---------
|
|
input ___|___ .1uf output
_______
|
|
0 |
--------------------*----------
This circuit has 3 nodes and they have been numbered.
Notice that we have numbered the common node between the
input and the output as node 0. This is required.
The next thing to do is to describe the circuit to PC-ECAP
so that it will know just what is connected to what and the
component values associated with each part. The next two
lines will completely describe this circuit:
R 1 2 1.59K
C 2 0 .1UF
The first line says to PC-ECAP that a resistor is connected
between nodes 1 and 2 and has a value of 1.59K (notice that
you don't have to enter 1500 for the resistor value, PC-ECAP
understands what "K" means).
The second line reads "a capacitor is connected between
nodes 2 and 0 and has a value of .1uf". Now all we have to
tell PC-ECAP is where we want to put the input signal, where
we want to look for the output and what frequency range we
want to cover. This is done with the PLOT statement. For
this circuit we want node 1 to be our input and node 2 to be
our output. Also we want to sweep the input frequency from
100Hz to 10KHz in a logarithmic fashion. The next line will
tell PC-ECAP all this.
PLOT 1 2 100 10KHZ LOG
On your distribution disk (or in the archive file if you got
this program from a BBS) you will find EXAMPLE1.DAT. This
file contains the circuit description for this circuit.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 21
If you haven't started PC-ECAP yet do so now. From the
main menu choose the "Select input file" selection. Select
EXAMPLE1.DAT as your input file. Next from the main menu
choose "Edit input file". The editor will load EXAMPLE1.DAT
and you will see the following:
; Example1.dat - RC low-pass filter with a cutoff frequency
; of 1 KHz.
R 1 2 1.59k
C 2 0 .1UF
PLOT 1 2 100 10KHZ LOG
This circuit description tells PC-ECAP all that it needs to
know about this circuit and how you want to analyze it.
Press ESC to get back to the main menu and now choose
"Analyze circuit". The analysis will begin and you will see
the results as the program progresses. When the analysis is
complete, the results will be plotted on your display.
First you will see a plot of Magnitude vs. Frequency. If
you press any key other than ESC you will get a plot of
Phase vs. Frequency. Pressing any key (other than ESC)
again will show you Magnitude again. If you have an EGA
with 256K of memory or a Hercules or VGA card, both pages of
graphics memory will be used and the change from Phase to
Magnitude and back will be instantaneous.
Another Example
We have included a few other sample circuits with PC-ECAP.
EXAMPLE2.DAT is a 75 ohm high-pass filter that can be used
to reject television interference. EXAMPLE3.DAT is a
band-pass filter for use as a modem receive filter. If
you'd like, take a look at them and run an analysis. You
may want to draw them on a piece of paper first to really
see what you are doing.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 22
For our last example we're going to take a look at
EXAMPLE4.DAT. This circuit is a single stage transistor
amplifier made with a 2N3904 NPN transistor. We will
demonstrate the use of the "Model Maker" that is part of the
full screen editor. Here's the circuit:
+10 volts
0 |
\ R4
/ 470 ohms
\
/
R3 |
8.2K | 3
+--\/\/\/\----*---------
| | output
| /
R1 | | /
1 270 ohms | 2 |/ 2N3904
-------/\/\/\/\---*---------|
| |\
input R2 \ | \
1.2K / _\/
\ |
/ |
| 0 |
------------------*-------------*---------
As you can see the first thing you need to do is to number
the nodes. Please take a look at the top of R4. This end
of the resistor connects to the +10 supply voltage but we
have numbered it as node 0. This is an important point.
Any node that has a DC voltage connection should always be
connected to ground. For the sake of an AC analysis, any DC
voltage source is the same thing as ground.
Now that we have numbered the nodes, we can describe the
circuit:
R1 1 2 270
R2 2 0 1.2K
R3 2 3 8.2K
R4 3 0 470
Alright, now we are ready for the NPN transistor. The
transistor that we are using is a 2N3904. We could use a
simple one line description for this transistor, but that
wouldn't show what happens to the transistor at high
frequencies. What we need is a more sophisticated
transistor model. One that will change its characteristics
as the frequency changes like a real transistor.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 23
PC-ECAP has the capability to create just such a model. But
first you need to know some information about the transistor
that you want to model. This is what is required:
DC collector current -
For this circuit about 10 milli-amps flows
from the collector to emitter.
Transistor current gain -
At 10 ma. this is a minimum of 100. This is
the same as Beta (the current gain at DC).
Transistor Gain-bandwidth product -
For the 2N3904 with a collector current of 10
ma. this is 300 MHz minimum. This is also
known as Ft.
Common base output capacitance -
This is just the capacitance from the base to
the collector. For the 2N3904 it is 4 pf
maximum.
Now that we have the required information we can make a
transistor model. Please note that it doesn't matter for an
AC analysis whether the transistor is NPN or PNP.
From the editor press F2. This will start the Model Maker
function. A window will appear and ask first for the node
numbers for base, emitter and collector. You would just
enter 2, 0, and 3. Then you will be asked for the
information mentioned above. After answering all the
questions your model will be created and inserted into your
circuit description on the line following the cursor.
For this circuit we might want to know just how good a
frequency response we have, so let's sweep a frequency range
of 1 KHz to 100 MHz. And let's do it logarithmically. With
node 1 as the input and node 3 as the output, this line
should make PC-ECAP do what we want:
P 1 3 1KHZ 100MEG LOG
As you might notice, PLOT can be abbreviated to P.
That's all there is to it. Run an analysis and see what
kind of amplifier we have. You should also try changing
some component values to see what happens. What happens if
you decrease R1? Or increase it?
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 24
Models
The circuit models that PC-ECAP uses for Transformers,
Bipolar transistors, FET's, Operational Amplifiers, and
Transconductance Amplifiers are ideal models. If you
desire, you can easily create models that are more complex.
For Bipolar transistors if your need a better model just use
the "Model Maker" feature in the editor. As previously
discussed, a Hybrid-Pi transistor model will be created and
inserted into your circuit description.
For the transformer, the addition of two inductors will make
a transformer that is quite "real". You can add an inductor
in parallel with the primary to model the transformer's
magnetizing inductance. This inductor should be equal to
the transformer's primary inductance. The transformer's
manufacturer can supply the inductor value for this or you
can measure it yourself (the secondary should be open for
this test). A second inductor can be added in series with
the primary winding (and the inductor paralleling the
primary). This inductor will model the transformer's
"leakage" inductance. This inductance is due to the
magnetic field that does not couple the primary and
secondary windings. Again, the transformer's manufacturer
can supply this or you can measure it (measure the primary
inductance as before, but this time short out the
secondary). By adding these two inductors, you will create
a transformer that has a finite bandwidth. The parallel
inductor affects the low frequencies and the series inductor
will affect the high frequencies.
For FET's, the addition of a capacitor to model the gate to
source capacitance and a second one to model the gate to
drain capacitance will improve accuracy at high frequencies.
You can get the appropriate values from your transistor's
data sheet. Also the Siliconix Low Power Discretes data
book is an excellent source for more information on this.
For FET's: Cgs = Ciss - Cgd = Ciss - Crss
Cgd = Crss
Operational Amplifiers today are usually frequency
compensated internally. Most of the time a method called
"dominant pole compensation" is used. This method inserts a
pole in the opamp's frequency response at a very low
frequency. This pole will dominant the response (hence the
name) and roll off at a 20 db/decade rate. The opamp model
that PC-ECAP uses is not frequency dependent. The open-loop
gain that you ask for is the gain that you will get for all
frequencies. It's not that difficult to make an opamp model
that will decrease its gain as frequency increases. Such a
model is included on your disk as OPAMPMOD.DAT. Please take
a look at it.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 25
References for Modeling
Although we have tried to give you some useful information
to use for modeling circuit elements, a full treatment of
the subject is beyond the scope of this manual. For those
of you who are interested, a good college library should
have several books that might help. Two references that may
be more readily available for many people are:
"National Semiconductor Linear Applications Handbook" from
National Semiconductor Corporation
2900 Semiconductor Drive
Santa Clara, CA 95052-8090
This handbook has an excellent paper entitled "The
Monolithic Operational Amplifier: A Tutorial Study". This
paper tells you just about everything that you would want to
know about the inner workings of opamps.
A good reference for FET's in general is:
"Siliconix Low Power Discretes Data Book" by
Siliconix Incorporated
2201 Laurelwood Rd.
Santa Clara, CA 95054-1516
They have several interesting application notes on the use
of FET's.
Parting Comments
A considerable amount of time and effort was expended to
develop PC-ECAP. We sincerely hope that you feel it was all
worth it. We want you to know that we don't intend to stop
here. We have several ideas for enhancements that we would
like to add in future releases. But it is you that will
make it possible. By registering your copy of PC-ECAP, you
will help make the possible into reality. Thanks for your
support.
Revision History
Version 1.10 - added the option of 35 sample points to the
select number of sample points menu. Greatly increased the
number of plot ranges available when displaying results.
Magnitude now spans .1 db/div to 80 db/div and Phase now
spans 22.5 degrees/div to 720 degrees/div.
Version 1.02 - first release widely distributed.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 26
Appendix A - Command Line Switches
PC-ECAP will automatically determine the type of video
display adapter that your computer uses and will set itself
accordingly. There are a few situations where it is not
possible to accurately determine the adapter type. For
example, if a monochrome monitor is used with a CGA card,
the program has no way of knowing that. Also, there are
some advanced EGA cards that will change their display mode
to match a given program. Since PC-ECAP is trying to change
its mode to match the video adapter, there can be no
guarantee as to what you will actually wind up with.
In order to accommodate these situations (as well as others
that may be unforeseen at this time) PC-ECAP has a series of
optional command line switches that can be used to set the
video display mode.
To start PC-ECAP with a command line option, type this at
the DOS prompt:
ECAP [ option ]
Where "option" is one of the following:
/H Hercules Monochrome Graphics card (or
compatible).
/C Color/Graphics Adapter with color monitor.
/CM Color/Graphics Adapter with monochrome
monitor. For use with Compaq monochrome
display or computers having LCD displays.
/E Enhanced Graphics Adapter with EGA monitor.
/EC Enhanced Graphics Adapter with CGA monitor.
/EM Enhanced Graphics Adapter with monochrome
monitor.
/M Monochrome Display Adapter.
/N Non-compatible video. PC-ECAP normally
writes directly to video RAM for the fastest
possible screen display. If the /N option is
specified, all screen writes will go through
the BIOS. Also, any on screen plotting will
be done using character graphics. Use this
mode only if no other mode works on your
machine.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 27
Appendix B - Error Messages
ABORT -- Too many circuit nodes
You have 1 or more circuit nodes with a number greater
than 40, either because you actually have a circuit
with more than 40 nodes or you have made a typo and
have inadvertently skipped some.
CAUTION! Conflicting transistor parameters supplied
The data that you have entered for your transistor
doesn't make any sense. For example - you may have
said that your transistor has a very high cutoff
frequency and then specified a huge base to collector
capacitance. Or you may have specified a very low
collector current and a high cutoff frequency. Things
that contradict each other. Recheck your data and
change if necessary.
HERC.DRV is not found
You have a Hercules or Hercules compatible graphics
card, and the required driver HERC.DRV is missing.
This driver is needed to display text when PC-ECAP is
in graphics mode. If you have DOS version 3.0 or
greater, PC-ECAP will look for this file in the same
directory that contains ECAP.COM. This may be
different than the directory that contains your circuit
files. Otherwise, ECAP.COM and HERC.DRV should be in
the current directory.
Input File Size Limit Reached
PC-ECAP allocates a 4K buffer for its text editor.
Your circuit description file has exceeded this amount.
The only way this should happen is if you have filled
your circuit description file with comments or other
none essential information. Remove the extra data. If
you really believe that 4K is insufficient, let us
know.
Insufficient disk space
Well, what can we say, your disk is full. Delete those
files that you really don't need or get a bigger disk.
PC-ECAP Reference Manual (c) 1990 Circuit Systems page 28
LPT1, LPT2 or LPT3 is not ready
You requested PC-ECAP to print something but your
printer isn't ready. Check to see that your printer's
power is turned on. Also check to see if your
printer's cable is connected. You will also get this
message if you try to print on a printer that does not
exist.
No files found. Enter name of new file.
When you tried to select an input file, PC-ECAP didn't
find any that had the extension ".DAT". If you
actually believe that there should be circuit
description files in you current directory, quit
PC-ECAP and check to see if you are in the correct
directory.
Please create this file or select another
You have asked for an analysis of a circuit that does
not exist. Use the text editor to create a circuit
description file for your circuit.
Please run an analysis or select another
You have asked to see the results of a circuit that you
haven't analyzed yet. Run an analysis.
Your copy of PC-ECAP has been illegally modified!
Someone or something (another program perhaps) has
changed your copy of ECAP.COM. PC-ECAP checks itself
every time it runs and this check has failed.
Reinstall the program.
PC-ECAP Reference Manual (c) 1990 Circuit Systems
