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Simple Cadence Software Tutorial Part 6

Simulating the Inverter

This final part of the tutorial deals with simulating the inverter that has been made in the previous sections.  To test out inverter, we will make a new schematic of a network with the inverter in it.  To create a new schematic, we need a new cell view.  We can create a new library entirely, but for simplicity, we will create a cell view within our current library.  This is done in the same manner in which it was done in all of the previous steps.  We will call the new cell view inv_test.  Make sure that the selected tool is Composer-Schematic.In the new schematic, we need to add the inverter, two DC voltage supplies, a ground connection, and a capacitor.  First we will add the inverter.  Click Add->Instance, change the library to your library, and select inv.  Place it in the center of the schematic.  Next we will add the two voltage supplies.  The first we will add is the input supply.  Click Add->Instance, change to NCSU_Analog_Lib, click Voltage Supplies, and select vdc.  Place the first supply to the left of the in pin on the inverter.  You may want to rotate the supply so that it is horizontal with the positive terminal closest to the in pin.  Before placing the next supply (the vdd supply) we need to change a parameter for the supply.  In the Add Instance window, set the DC Voltage to 5 V.  Place the supply at the top of the schematic.

Figure 15. Add instance of 5V DC voltage supply

Next we need to add the ground connection below the vss pin of the inverter.  We also need to add a capacitor at the output of the inverter to act as a load.  When all of the components are placed, we need to add a pin at the output of the circuit.  Add a pin called out.  This pin should be an INPUToutput pin as have all of the previous pins.  The finished circuit should look similar to the one below:

Figure 16. The test schematic

Simulating the Test Circuit

We are now ready to simulate this schematic.  Click Tools->Analog Environment to open the window that gives access to the simulation tools.
Figure 17. The Analog Environment Window

By default, the simulator will be set to spectre.  Before we can simulate the circuit we need to setup the simulator first.  The simulator needs to know what model libraries should be read for this simulation.  Click Setup->Model Library, which will bring up a window in which you enter the path to all libraries that were used in this schematic.  All libraries supplied by NCSU are in/opt/cadence/NCSU_1.2/local/models/spectre/standalone/.  The exact file name will then need to be entered after the path.  Press Add to add the library to the list in the window.  This must be done every time the Analog Environment window is opened.  The list of library files is below:

ami06N.m – For use with the AMI06 selected tech library
ami06P.m – For use with the AMI06 selected tech library
ami16N.m – For use with the AMI16 selected tech library
ami16P.m – For use with the AMI16 selected tech library
hp14tbN.m – For use with the HP14TB selected tech library
hp14tbP.m – For use with the HP14TB selected tech library
tsmc25N.m – For use with the TSMC30 selected tech library
tsmc25P.m – For use with the TSMC30 selected tech library
tsmc35N.m – For use with the TSMC40 selected tech libraries
tsmc35P.m – For use with the TSMC40 selected tech libraries

Figure 18. Model Library Setup for spectreOnce the models have been entered we need to specify what we want to do with our simulation.  We first need to specify our analysis, click Analysis->Choose.  In the window that appears, select dcand click Component Parameter.  Next double click Select Component, so that you can select the input DC voltage source on the schematic.  This will bring up and other window in which you need to select the parameter of the source that will be used in the analysis.  Select dc.

Figure 19. Select Component Parameter

Next enter the starting and stopping voltages for the supply (Start: 0V, Stop: 5V).  Select linear for Sweep Type and make the Step Size 0.1.  The Analysis window should appear similar to the one below:

Figure 20.  Analysis Setup Window

Click Ok to close the window.  The next step is to select the outputs.  Click Outputs->To Be Plotted->Select On Schematic.  This will bring the schematic window to the front.  Select the nodes at the input and output of the inverter.

Figure 21. Test Schematic with input and output nodes selected

This is done by clicking them once.  Minimize the schematic and return to the Analog Environment window.  This window should now look like the one below.

Figure 22. Analog Environment Window after simulation setup

Finally, we are ready to run our simulation.  Click Simulation->Netlist and Run.  This will run the simulation and should produce an output file and a plot of the inverter’s input and output.

Figure 23. Input/Output plot for the inverter

Figure 24. Spectre output file

This is the end of the basic tutorial.  Return to the Table of Contents for more options.

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