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1990-11-05
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N O V A Circuit Analysis Program
General Information
NOVA is a program that can be used to analyze most linear (AC) circuits. It
can calculate voltage, phase, and delay at any circuit point (node) at any
frequencies. Most (AC) circuit analysis programs can only give useful results
for low frequencies (below 10 Mhz). NOVA can do this but it can also be used
for RF and microwave circuits. Microwave circuits require the analysis be done
in terms of S-parameters, rather then AC voltages. NOVA does AC, time domain,
and S-parameter analysis.
Components at RF, have parasitic reactances that have a significant effect on
the performance. Programs that have "ideal" components give only a theoretical
analysis. To get real world results, at high frequencies, you need a program
that has accurate component models.
With full screen editing, nodal circuit notation, and single key stroke
commands, NOVA is easier to use and easier to learn that any other circuit
analysis program.
This version has S-parameter (data) devices. Virtually any Rf device:
transistors, fiber optic links, cables, filters, amplifiers, equalizers, etc.
can be characterized by S-parameter data files. These data devices behave in
the circuit exactly like the real device models. For example: if you have a
transistor characterized by S-parameter data and put a resistor in the emitter
or from collector to base, you will see the response and impedance of the
circuit change just as you would with the regular transistor model. If one
characterizes a RF cable as S-parameter data, puts it in the circuit and then
puts a mismatch on the end of the cable, one will see a reflection from the
S-paramerter transmission line model. In other words, the S-parameter data
model acts quite suprisingly like a real device.
The data format of S-parameter files that NOVA can read is similar to the S-
parameter files of the major circuit analysis programs but not identical. It
is relatively easy to convert these files to the NOVA format. There are
hundreds of RF device files available from many sources.
This version of NOVA has circuit tweaking while in the graph mode. You may
find it extremely useful. Vary a component and watch the response, return
loss, and delay change. With the co-processor version circuits can be tuned in
virtually "real" time. With a 16 Mhz, 386SX machine, SUPER NOVA will calculate
and plot, a 200 point graph, of S21, S11 and group delay, in 2 seconds.
* * * F E A T U R E S * * *
* Magnitude, phase, delay, input impedance, S21, S12, S22, and S11
calculations. * Nodal notation * Full screen circuit editing. *
Library of components * Accurate component models. * Graphics with
CGA, EGA, VGA, or Hercules modes. * Circuit tweaking. * Automatic
graph scaling. * Analysis modes: S-parameter, AC, and Time domain.
* Component types: Resistors, Capacitors, Inductors, Transformers,
Bi-polar transistors, FETs, Op-amps, Transmission lines, Two-port
devices. * Fast. * Easy to use. * Log and linear sweep. * Filter
scaling. *
Robert Stanton
15 Church Street
Oneonta, New York 13820
Phone: 607+432-4112 or 215+443-8382
------------------------------------------------------------------------------
NOVA is now being distributed as "Shareware". Registration is $69.95.
With registration you will receive a copy of SUPER NOVA (the math co-processor
version), plus supplemental written instructions.
The next version of NOVA (expected to be completed in 1991) will have
circuit optimization. Registered owners of the present version will receive a
free copy of the next version (optimization) , when it becomes available.
U.S. companies may phone in a purchase order number for immediate delivery of
SUPER NOVA. Shipped U.S. mail priority delivery (no extra charge).
------------------------------------------------------------------------------
NOVA Instructions
Copyright 1990
by Robert Stanton
Circuit Analysis
The circuit is fed from one signal source. The signal source always outputs
1.0 Volt AC. Voltages are calculated relative to ground. S-parameters are
calculated at the termination node(s). The circuit may have more then one
termination. Thus, one can analyze diplex filters and other circuits with
more then one output point.
With NOVA's full screen editing, circuit components, their values and their
connection points (nodes) are displayed on the screen. Components can be
added, deleted, or moved on this screen.
Getting Started
1) Load Dos 2.0 or higher. (512K of memory required)
2) Insert the NOVA disk.
3) Enter: NOVA (or SUPER if you have the math coprocessor version)
------------------------------------------------------------------------------
Using the Program
After the program is loaded, the editing screen will come up. This is the
central screen of the program. From here one can: enter a circuit, save a
circuit to disk, get a circuit from disk, do AC analysis, change frequencies,
run a graph, change the parameters of components, scale a filter, or do time
domain analysis.
At the bottom of the screen, is a list of the operations that can be done form
the editing screen. You will also see on the screen, some help messages such
as: "Press down arrow to enter first component".
The edit screen works somewhat like a spreadsheet. The cursor is moved by the
arrow keys. Components may be added, deleted, changed in value, or connected
to different nodes, by changing the values on this screen.
Editing Screen Commands
Below is an explanation of the commands shown at the bottom of the editing
screen:
1) "F" To set analysis frequencies.
2) "S" To save a circuit on disk.
3) "G" To get a circuit from disk.
4) "N" To change the "output" node. The node where the voltage is shown.
5) "Q" To change the parameters of the components, such as: inductor Q,
transistor Ft, op-amp gain, etc
6) "*" Clears editing screen for a new circuit.
7) "+" Calls the library of active components.
8) "a" Runs sweep analysis. Gives tabular output of S21 and S11.
8a) "A" Runs S12 and S22.
9) "j" Gives graphic output of S21 and S11.
9a) "J" Gives graphic output of S12 and S22.
10) "W" Calls time domain analysis routines.
11) "!" Exits program.
Entering a Circuit
Here is and example of how to enter a circuit. The circuit will be a
single stage, transistor amplifier.
The schematic looks like this:
Collector
___________________ _____ Output
| Node 3 |
| |
| |
Base 1___| |
In __ ________________1 2n2222 |
| Node 1 1___ R
| 1 | Emitter R = 1000 ohms
| | Node 2 R
Gen = 1.0 Volt R |
| R = 100 ohms |
| R |
| | |
|____________________|___________________|
| Node 0
|
Ground
It is necessary to number the node points on the schematic. You will notice
that the four nodes of the circuit are numbered.
(A node is a point on a circuit where two or more components connect.)
Use the following three rules when numbering nodes:
1) The output of the generator (source) is always node # 1.
2) All grounds are node # 0.
3) Circuit nodes may be numbered in any order, but don't skip a number.
Entering the Circuit:
To enter the first component, press the down arrow, this will open up the
first line.
The transistor, is entered by pressing key "T". Then enter the nodes the
three leads of the transistor connect to. Then press the down arrow to open up
the next line.
Resistors are entered by pressing key "R".
After you have entered the components your editing screen should look like the
example below:
Comp. Type Value Node Node Node Node
1 Generator 0 Ohms 0 1
2 Transistor 2n2222 2 1 3
3 Resistor 100.000 2 0
4 Resistor 1000.00 3 0
To change component value or node number, press "space-bar"
Analysis: A, Save cir.: S, Get cir.: G, Freq.: F, Out Node: N, = ( 3 )
Time Dom.: W, Graph: J, Parm: Q, Sca: Z, New: *, Lib: +, Exit: !
_____________________________________________________________________________
If you made a mistake, it can be easily corrected. Put the cursor on the
number to be corrected and press the space bar. This erases the old value.
Then enter the correct number.
Running a Circuit Analysis
If the circuit has been entered correctly, it is ready for analysis.
To run the analysis, press key "A".
The analysis will run at the default sweep frequencies.
This circuit should show a voltage gain of 9.6 ( 19.6 dB).
If you didn't get these values, you may have entered the circuit incorrectly.
Check your circuit entry against figure 1.
Setting the Frequencies of Analysis.
One may run an analysis or make a graph for any frequency sweep.
From the edit page press key "F". The frequency page will come up.
You may change the start and stop frequencies, by simply entering in new
values. The frequency steps may be linear or logarithmic. To have linear
steps just enter the size of the frequency steps, as a positive number.
Example: You want the analysis to run from 1 KHz to 20 KHz in steps of
1 KHz, the frequency screen should look end up like this:
Start frequency: 1000 Hz.
Stop frequency: 20000 Hz.
Steps: 1000 Hz.
IF you want log frequency steps: enter at "Steps" number preceded by a "-".
For example:
Start frequency: 1000 Hz.
Stop frequency: 20000 Hz.
Steps: -18
(This will give 18 log steps for 1 kHz to 20 kHz)
Generating a Graph of Circuit Response
NOVA can draw a graph of: S11[dB], S21[dB], S12[dB], S22[dB] and delay.
To plot a graph: Press key "J".
Once you are in the graph screen, the following key commands work:
Graph Command Keys:
"S" To change the vertical scale. You may set the "top of scale" and
the "bottom of scale" in dB. Phase will plot to the same scale
numbers as voltage. The limits are +- 180 (dB or degrees). The
vertical scale may be expanded to any degree.
"F" You may set any start and stop frequencies. The number of steps
plotted is determined by the size of the frequency step. It is
generally better to use a defined number of logarithmic steps for
graphs. For a log sweep, enter a negative number of steps. For
example, entering a -50 will produce a graph of fifty, log spaced,
frequency points.
"D" A menu will come up, asking what parameters are to be plotted.
Parameters such as S21, S11, phase, or delay may be selected.
TUNING (tweaking) A CIRCUIT
Some engineers prefer to optimize by tweaking. It gives a good intuitive
understanding of the circuit.
The arrow keys are primarly use for tweaking. It up and down arrows select
the component to be tweeked. Pressing the up arrow selects the component
above, the down arrow selects the component below, or uou could go back to the
editing screen, put the cursor on the component to be tweaked and then press
"j" . (for graph screen).
Once you have selected the component to be tweaked you may select the amount
of tweak you want. The "<" and ">" key change the percentage the component is
tweaked. The tweak may be as low as 1% or as high as 20%.
To tweak a component to a higher value, press the "right arrow" key. To tweak
lower press the "left arrow" key. A new graph will be drawn overlayed on the
old graph. A family of curves may be created. If the screen gets too messy
press key "C" to clear the screen.
Saving a Circuit On Disk
From the editing page, press key "S".
You will be asked to enter a name for the circuit file.
Enter the circuit's name without the extension ".nap".
Getting a Circuit from a Disk
From the editing page, press key "G".
NOVA will list the names of all circuits saved on the disk.
Enter the name of the circuit, without the extension ".nap".
S-parameter Analysis
At RF frequencies S-parameter are used to define circuit performance.
If the source impedance of the Generator is 1 Ohm or greater, and if the
output node is terminated with a resistor, NOVA will do an S-parameter
analysis. If the source impedance of the Generator is less then 1 Ohm, NOVA
will do an AC analysis of the circuit.
You can override the S-parameter analysis mode by pressing key "/". This will
force the program into AC analysis. AC analylsis is a voltage calculation. (If
the generator voltage is 1.0 Volt, the voltage at Node (x) is:)
Pressing key "a" will run tabular (S21 and S11).
Pressing key "A" will run a tabular (S12 and S11).
C o m p o n e n t T y p e s
Component type are: R (resistor)
L (inductor)
C (capacitor)
T (bipolar transistor)
F (field effect transistor)
O (op-amp)
X (transformer)
U (transmission line)
% (Two-port S-parameter device)
Component Models
To accurately predict real circuit performance, for RF and microwave, the
physical characteristics of components need to be taken into account by the
program. Even at relatively low frequencies accurate component models are
important. For example, active filters made of op-amps are effected by the
op-amps' open loop gain and phase performance. NOVAs' models are very accurate
and because "real world" characteristics of the components may be entered.
Actual results are always close to the NOVA predictions.
A real resistor is not a pure resistance. It has body inductance, lead
inductance, and shunt capacatance. At RF and microwave frequencies the
parameters interact in complex ways.
Inductors have capacitance. Capacaitors have inducatance. Both have
resistance, (which gives then Q).
The written instruction show the model for each of the NOVA components.
Using the Component Library
1) On the edit page, put the cursor on the line where you want the
transistor or op-amp to be placed.
2) Press key "+". (The LIBRARY will load.)
3) Pick the library component you want, by putting the cursor on it.
4) Press key "+" again. (The component will be put in your circuit).
(Two-port devices are not stored in the NOVA component library. They are
stored as separate ASCII files on the disk.)
Adding a New Component to the Library
Since one can change all the parameters of a transistor or op-amp, one can
create new component models. If, for example, one wanted to add a new type
op-amp to the library, he can do it as follows:
Look up the parameters of the new op-amp in a data book.
From the edit page, press key "+". This calls the library.
Move the cursor to a blank line and press key "O". A standard op-amp circuit
model will be put on that line.
Press key "Q". Change the parameters to those of the new op-amp type wanted.
Press key "+" to save the change.
Two-port S-parameter Component Models
The two-port component is completely different then the other models provided
with NOVA. The other components: resistor, transistor, capacitor, etc.
are created from formulas in the inside the program. The two-port component is
created from a data file, of the component measured performance. The data
type used is: S-parameters.
A simple ASCII file is written, from S-parameter data supplied by manufactures
or measured on your test equipment. The file is has the name of the component
type. For example, if you are writing in data of a LT1001 transistor, save the
file under the name LT1001.two. (The extension ".two" tells NOVA the file is a
two port file.)
When the analysis is run, NOVA reads that data and constructs an imaginary
component that has the exact performance specified by the data, (at the
frequencies of the data file). Between frequencies NOVA must interpolate
(guess at) the performance of the device.
The advantage using two-port components is the data file can be of any two-
port RF or Microwave device that can be measured by S-parameters, such as:
transistor, FETS, or even fiber optic devices. Conventional component types
are limited by the accuracy of the program's component models, to 1 or 2GHz.
Two-port models are limited in frequency only by the accuracy of the data
used.
Making a Two-port Model
There are now hundreds of device files available in public domain or from
other sources. There are written in ASCII and with a fairly standard format.
You may wish to create your own device files, or convert existing files to a
form that can be read by NOVA. Below is an example of a NOVA device file:
! Monolithic Microwave IC
! MAR-8 (minicircuits)
Z=50
dB
MHz S11 S21 S12 S22
50 -3.92 -11 32.00 171 -50.00 30 -3.65 -11
100 -5.92 -21 33.00 162 -40.00 38 -4.73 -24
500 -8.18 -77 27.80 109 -27.96 52 -9.37 -96
1000 -11.37 -113 23.00 80 -24.44 51 -13.56 -147
1500 -11.70 -139 19.40 62 -21.94 46 -14.89 174
2000 -10.46 -155 16.90 47 -20.00 41 -15.39 153
2500 -9.63 -180 14.80 32 -18.42 32 -14.42 127
3000 -8.87 167 12.9 20 -17.72 27 -17.08 111
3500 -7.54 153 11.4 6 -17.08 21 -17.72 107
4000 -6.94 141 9.8 -5 -16.48 14 -19.17 106
The first two lines are comments. (preceded by "!")
"Z=50" Specifies the impedance of the S-parameters. ( 50 is the default)
"dB" Magnitude are in dB. (linear mag is the default)
"MHz" The frequencies are in MHz. (GHz is the default)
(These commands have to be at the start of a line, and printed exactly as
you see them.)
The S-parameters are in Mag (or dB) and angle.
The maximum number of frequencies is 60.
Be careful, entering data, small data errors can create large analysis
errors.
Printing Out a Graph:
Graphs may be outputed to your printer, if you have a CGA, EGA or VGA graph
cards.
Hercules can be displayed on the CRT but can not be printed directly to the
line printer. Simulate CGA programs are avaiable that can be used with
computers that have a Hercules card.
To print graphs to various types of line prints, with various types of
graphics card, you will need to refer to the written instructions.
TIME DOMAIN ANALYSIS
To run time domain analysis press key "W".
For time domain analysis NOVA can apply a square wave signal, to the input
of the circuit. It will then draw a graph of the output waveform of the
circuit.
(A square wave may be considered as composed of a fundamental frequency and
an infinite number of odd harmonics. If any square wave has less then an
infinite number of harmonics, it will have a finite rise time.)
The default input square wave created by NOVA is the sum of a fundamental and
odd harmonics up to the 101st harmonic. Thus it has a finite rise time.
Increasing the number of harmonics improves the rise time. You may command
NOVA to use up to 1001 harmonics.
Time Domain Command Keys
"O". Causes the program to calculate and draw graph of the time domain
(square-wave) response of the circuit.
"I" Causes the input wave to be drawn. The input wave has an amplitude of
+/- 1.0 volt. (2 Volts peak to peak)
"R" Used to change both the graph resolution of the display and the number
of harmonics that composes the input square wave.
"F" To change the input square wave frequency.
"T" To change the start and stop times for the graph.
"S" To change the scales on the graph.
Example:
Enter the circuit below:
1000 Ohms
1 >-----------------R R R------------------< 2 Out
| |
| |
| |
| C
Gen C = 1.0 uf
| C
| |
| |
|__________________________________|
0 |
Ground
Your editing screen should look like this:
Comp. Type Value Node Node Node Node
1 Generator 0 Ohms 0 1
2 Resistor 1000.00 1 2
3 Capacitor 1.00000 uF 2 0
To change component value or node number, press "space-bar"
Analysis: A, Save cir.: S, Get cir.: G, Freq.: Q, Out Node: N, = ( 2 )
Time Dom.: W, Graph: J, Parm: X, Sca: Z, New: *, Lib: +, Exit: !
_____________________________________________________________________________
Running a time-domain analysis:
1. Now that the circuit is entered, press key "W" .
2. The time domain screen will come up.
3. Before we run the analysis, we'll select an input square-wave frequency.
4. Press key "F".
5. Specify a frequency. (100 Hz is good)
6. To see the output wave form press key "O".
7. If you wish to see the input wave form press key "I"
You might try running the analysis at various square wave frequencies.
A coprocessor increases the speed of time-domain analysis by about ten to
twenty times.
Limitations of the Program
The maximum number of components, in a circuit can be eighty.
The maximum number of nodes is forty.
Only one signal source is used.
All node voltages are calculated only relative to ground.
Example Circuits Included with this Disk
RC
It is a simple series resistor and capacitor. This is a good circuit to
start with. Change the values of the components, run a graph, do time domain
analysis, etc.
Ellipfilt
This is an RF elliptical low pass filter. Because this is an RF circuit NOVA
will present the analysis in terms of S-parameters, rather then AC voltages.
The filter was designed by taking the normalized values from a filter book
and entering them into NOVA. Once the normalized filter was in NOVA the
response was run to verify that it was entered correctly. It was then scaled
to it's present impedance and cutoff frequency by using key "Z".
Run a time domain analysis. Press key "W". When the time domain screen comes
up, press key "O" (for output wave). Without a coprocessor it takes about
five minutes for NOVA to compute the output waveform. With a coprocessor it
takes only 30 seconds. (You must have SUPER NOVA to utilize the coprocessor)
Quadhybd
This is a 90 degree quadrature hybrid transformer. It only works at 10.7 MHz.
This outputs ports are 3 dB down, and the other port, called the isolation
port, has no output. The phase shift of one port is 45 deg. and the other -45
deg. So what! At first glance it doesn't look like this circuit would be good
for anything. Actually it is useful for phase modulators and demodulators,
and probably some other stuff.
Difamp
This transistor amplifier is kind of out of date, as op-amps do the job
better, but it is an interesting circuit to experiment with, and to learn
from.
Tonecont
This is a good three band audio tone control. You can play with this control
by "turning the pots". The pots are simulated with two resistors. If you
change one resistor of the "pot", then change the other by the same amount,
the opposite way. You can make the response change.
Running a time domain analysis will show what happens to a square-wave when it
is run through a tone control.
TLDC (transmission line, directional coupler)
An RF directional coupler made up of 1/4 wave transmission lines. It only
works near the 1/4 frequency of the lines. At that frequency, because it
is a true directional coupler, it has isolation on one port. By looking a the
various ports you can see the directional characteristics.
TLBPF (transmission-line coupled, bandpass filter)
Narrow band RF filters are commonly made up of resonate circuits coupled
by capacitors or inductors. This filter is coupled by transmission lines.
This gives it better performance the a bandpass filter coupled by capacitors
or inductors. Of course, a low frequencies it could get rather large.
Actfilt
This is a dual amplifier audio bandpass filter. You will find that for this
type of filter to work properly, the unity-gain frequency of the op-amp must
be much higher then the passband frequency. If you wish to experiment, you
may change the unity-gain frequency of the op-amp with the parameter command.
This is a good audio bandpass filter circuit. It's stable and maintains a gain
of around 2, even with various types of op-amps.
Two_Port
This circuit is just the two-port device and a termination. However, there
are several two-port data files on the demo disk. To put another two-port
device in this circuit, put the cursor on the old device, press the space-bar
to erase. You may now enter the name of any two-port file, on the disk. (if
you press "?", instead of entering a file name, you will get a list of the
available two port files.)
Limitation of Liability:
NOVA is not warranted to meet your requirements nor is the operation of
the program warranted to be totally error free or uninterrupted.
In no event will there be liability for any damages, including any lost
profits, lost savings, or other incidental or consequential damages arising
out of the use, or inability to use, this program.
------------------------------------------------------------------------------
5. Specify a frequency. (100 Hz is good)
6. To see