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Accusim Tutorial

This document contains a step-by-step tutorial for simulating an inverter in the Mentor Graphics application Accusim.  Separate documents began the tutorial for other Mentor applications.

General Information

Opening Accusim

General Information

 

General Information

Once you have a design schematic entered in Design Architect, and you wish to run an analog (SPICE) simulation of your circuit to check rise/fall times and/or delays, you need to run AccuSim II.  Accusim is an analog simulation tool that runs a SPICE kernal similar to most other SPICE simulation software, but it interface directly with your schematic from DA.  Once you have created the viewpoints for a cell, you can open that cell in Accusim, set inputs to the schematic pins, select from various analysis types, and perform analog simulation.  This is generally done to confirm timing specification for your cell.  You can simulate directly from your schematic, or you can simulate you extracted results form layout which will include parasitics and give an accurate timing analysis.

Opening Accusim

Be sure to set your working directory using 'swd' command before To start the analog simulator Accusim, type

      accusim inv/accusim &

you launch accusim.

Accusim Simulation

  1. Once AccuSim II is loaded, you should see your schematic.

If you are doing the post-layout simulation, you will get to see the annotations (in red color) that IC extract placed on your design.

The first thing that we need to do is to tell the simulator what the models are for your FETS. The model names are "p" and "n" for the P- and N-FETS, respectively. You can use any spice models for these that you would like. There is a model file in $ADK/technology/accusim for each technology supported in the ADK. We are using ami05.mod file for this course.

To load a model file, use the File->Auxiliary Files->Load Model Library menu. Use the navigator to load the above file or another that you have created.  You do not need to set any other options in this dialog box.

  1. Next, we must tell the simulator what type of simulation to perform.  Do this using the ‘Setup Analysis’ icon in the main palette menu. We wish to see how the circuit operates over time with different inputs, so we will perform a transient analysis.  You need to press the Transient button to get the dialog box for setting up a transient analysis. You should use a time step of 1 ns(1N) and a stop time of 100 ns. Leave everything else at its default value.

  1. Now you should set the input forces.  Select signal in and then use the Add Force icon or menu to add a force. This should be a pulse type force with an initial value of 0 V and a pulsed value of 5 V. The pulse width can be 50 ns with no delay and a period of 100 ns.

  1. To see a trace of the run while it is progressing, select both inputs and the output and press the trace button on the palette menu. A trace window will open with your selected signals in it.
  1. Now type run in any window to run the simulation (or use Ctrl-F1). You can ignore the warning about the version parameter in the model being ignored.

  1. After the simulation is complete, check to be sure your gate is working properly. If it is not, you can go back to DA and fix any errors, then use File->Design->Load DA Changes to update your design in AccuSim II. 
  2. Once your simulation is working properly, save your setup for use later. Do this via the File->Simulation->Save Setup Data Only menu.  Save your setup to the viewpoint with a descriptive name like "accusim_setup."

  1. Also save your WDB to the viewpoint with File->Waveform DB->Save option. Save the forces WDB to your viewpoint and call it "forces."

 

10. Exit Accusim.