Analog Tutorial 4: Post Layout Simulation of an Inverter

Table of Contents

Overview

Setting up the Simulation

Creating a New Configuration

Simulation

Overview

This tutorial covers simulating the inverter that was created with the Virtuoso Layout Editing tool. More specifically, it covers setting up and executing a transient simulation, using the schematic that was used to simulate the inverter previously built. It also includes creating a configuration cell view to customize your settings.

Setting up the Simulation

Start the Cadence tools by typing "icfb &" from your cadence directory, in a shell window. When first simulating the inverter schematic, we set up a different cell called "invertersim". Open up the schematic view of this cell to setup the simulation of the extracted layout cell of the inverter.

First, change the source of the inverter to the pulse source used before. Set the parameters as follows:

Next, copy the inverter, and place the copy directly above or below the existing inverter. Ensure that the pulse source is connected to the inputs of both inverters. Add an output pin to the new inverter and name it "OUTPUT_LAY". Check and save the schematic.

Creating a New Configuration

In the Library Manager window, create a new cell view for the invertersim cell. Go to File -> New -> Cell View ... In the Create New File window that appears, type config in the "View Name" field and the "Tool" field should automatically change to Hierarchy-Editor. If not, change the "Tool" field manually. Select OK.

Two windows will appear. In the New Configuration window, select Use Template...

In the Use Template window that appears, select "spectreS" in the "Name" field drop-down list. Select OK.

Back in the New Configuration window, change the "View" field from myview to schematic. Select OK.

The Cadence hierarchy editor will now appear as its default table format.

Select View -> Tree and the new Tree View will appear below.

There are two inverters listed. One of them is the new inverter that we copied from the existing inverter in the schematic view of invertersim. In this case, this inverter is I4. Right click on I4 and select Set Instance View -> analog_extracted.

Next, save these settings by selecting View -> Update and File -> Save. Close the Cadence hierarchy editor window.

Simulation

Now you are ready to simulate. From the Virtuoso Schematic Editing window, select Tools -> Analog Environment. When the Cadence Analog Design Environment window appears, verify that the simulator is "spectreS". To ensure that the configuration that was set up in the "config" cell view is simulated, select Setup -> Design ... For "invertersim", select config instead of schematic.

Choose a 500ns transient analysis and select the input and two outputs to plot.

Run the simulation and you should then see the three plots. Seperate them using the Switch Axis Mode icon if you'd like. You can see that the extracted layout of the inverter is working correctly (as an inverter) and is slightly different than the other inverter. You can observe the differences by zooming in or using the calculator to measure the rise, fall, and delay times. For more information on using the calculator, see tutorial 2: Simulating an Inverter.