Simulating a Design Using Accusim
1.
Setting the Working Directory
4.
Setting up Transient Analysis
10.
Setting up a Monte Carlo Analysis
11.
Setting up the DC Sweep Analysis
12.
Reloading Design Changes in Accusim
13.
Running the Monte Carlo Analysis
The
AccuSim II is an analog circuit simulator that allows you to test the design
you created in Design Architect in a Spice flavor fashion. By just substituting
the lowest level gate cell in the spice netlist, it is quite convenient to
perform timing analysis using the same gate design. A CMOS inverter is going to
be used as an example to illustrate the steps for building and verifying analog
components. Since procedures for DC and AC analysis are similar to those of
time transient analysis, transient analysis and DC sweep analysis will be
focused in this tutorial.
1. Setting the Working Directory
From the UNIX
terminal, navigate to the directory where your Design Architect Schematic is located. In this case we have called the design inv
and it should be located in your home directory, i.e. just under your user
name.
disk2/acc/xxx
Where xxx represents your user name.
If you
are not already in this directory, navigate to this directory. Set this as the working directory using the swd command.
To invoke
accusim enter the following into the console.
accusim design_name/accusim
Where
design_name is the name of your design, in this case we used inv.
The schematic
should open by itself.
Invoke the following
command
File -> Auxiliary Files -> Load Mode
Library
The following
dialog box will appear. Complete the file name as shown below. Then click OK.
4. Setting up Transient Analysis
Select from the right hand palette
Setup Analysis
A dialog box as shown below will appear. Click on Transient for time transient analysis. Enter 0.1n for Time Step box and 20n for Stop Time field. Then click on OK.
There are two ways to assign test signal to input ports; the first way is to assign input signals right in Accusim (recommended), and the other way is to specify the input signals in a file. The first method is going to be used in this tutorial.
To assign input signal in Accusim, select in port from the schematic. Then click on ADD FORCE from the Time Mode palette. A force dialog box will appear as shown in Figure 4. Click on PULSE to form the test signal. Activate View Force then enter the pulse parameters for the rest of the fields as shown in Figure 4. Click on OK.
To specify input signals in a file: The format for input
signals file is exactly the same as SPICE
syntax. Say, you have a file named input1.sig
with input signal as following: (Note that lines starting with * will be
considered as comment lines).
***************Input Signal in with a period of 10ns
******************************
Vin in 0 pulse (0 5 5n 0.1n 0.1n 5n 10n)
*************** Alternative for input signal in with a
period of 20 ns************
Vin in 0 pulse (0 5 10n 0.1n 0.1n 10n 20n)
Select from the main menu bar;
File -> Auxilary
Files -> Load Netlistfiles..
A Load Netlistfile
dialog box will appear. Enter the complete path and filename or use Navigator
to locate input1.sig file.
If you are familiar
with PSPICE netlist format, you can check the netlist before you run it by selecting
from the main menu bar.
Report ->
Netlist
To probe circuit nodes, in the schematic window, select the
input and output ports, then click Trace
on the right hand side palette. A trace window will be opened. (Select wires
to trace voltages and nodes to trace currents) See Figure 6.
To run your circuit, click on Run icon from the right side palette. It takes a couple of seconds
to run the simulation. The result is shown in Figure 7.
You can check the
rise time, fall time and delay time from the results palette. To get this
information follow the steps given below.
In the schematic, first select the in port.
Click WF MEASURE
on the Result palette. A pop up
menu will appear.
Select Rise Time, and then click on OK. You will see the rise time information of your design. After this is complete repeat using the out port.
See Figure 8 for reference.
Other information can also be obtained by using WF MEASURE in the Result palette.
You can measure a
number of parameters with measure commands in the Measure palette.
Sweep analysis can
be performed to sweep a transistor's length, width, and model parameters:
Choose the Time
palette
Choose Setup Sweep Corner
Enter the parameters
as shown below to sweep the width (w) of transistor /I$203 from 2 um to 10um in
Increments of 1
um. Activate the Add Sweep Definition button to save it in the
sweep table.
Set up the Setup Analysis and Add Force dialog
boxes.
To the right of the Multiple Run button: selection
choose Sweep.
Activate the Run command.
Choose Chart to show the results of the sweep (enter
signal name, referenced to //gnd, and sweep run to observe).
10. Setting up a
Choose the Time palette
Choose
Enter the parameters as shown below to do a
with the default distribution, and varied individually.
Activate the Add
Specification button to save the specification.
To the right of the Multiple Run button: selection
choose
Activate the Run command.
Choose Chart to show the results of the
11. Setting up the DC Sweep Analysis
Select input port in
from the schematic. Then from the main menu bar:
Setup -> Analysis
A dialog box will appear as shown in Figure 9. Click on DC Sweep for DC Sweep analysis. Fill
in the dialog box as shown in Figure 9. Click on OK.
Note: if you are
familiar with Spice Netlist, you can check the netlist by selecting from the
main menu bar:
Report -> Netlist
Before you run your
circuit remember to keep the data of all the circuit nodes by selecting from
the main menu bar:
Add -> Keeps
Click on All for
the Add Keeps dialog box then
click on OK.
To run your circuit, click on Run icon from the right side palette. It takes a couple of seconds
to run the simulation. After that, select output port out from the schematic. Click on Chart on the right side palette. The output waveform chart will be
created in another window as shown below.
12. Reloading Design Changes in
Accusim
You can change instance properties
(width, length, etc.) directly in accusim. Activate the Design Chng
palette, choose the instance
on the schematic to change, then
activate the Change Property command and choose the property to
change. The property will
be displayed in red on the schematic indicating it has been changed.
The design can be changed in Design Architect and then
reloaded in Accusim without exiting from it.
Reload design in Accusim after modifying it, select:
File ->Design
->Load DA Changes
From the main menu bar. Then click OK to execute.
13. Running the
To perform a
the value of the capacitor enter the parameters as shown below.
Activate the Add Specification button. (Your instance number will be different, use Change
Selection to enter the instance number
for your capacitor, or instance you want to change.)
Next activate the Define Distribution button and the
following dialog box will appear.
Active the Edit button and change the Region from
+-10% to the desired number. Activate
the Add Distribution button when complete.
Close both dialog boxes.
Activate the parameter to the left of the MultiRun
command as shown below (top right of
Choose
Then activate the Run command. The following
dialog will appear.
Enter the Number of Runs desired and the Collection Name.
OK the box to perform the analysis.
Select the output signal in the schematic and activate the Chart
command.
You should see the results of the analysis; zoom in to see
the details.
Choose the Results->Chart->Envelop Curves from the pull-down menus to plot the minimum, average,
and maximum values of the
analysis. You can use the Measurement commands to calculate rise
and fall times.
Click Here To Continue to Schematic Driven
Layout Using IC - Station