Setting up Spectre
Setting up analog simulation
First, you need to specify which simulator to use. Here we will work with Cadence SpectreS, which is a version of Spectre that is integrated into the CDS environment. Select "Setup | Simulator/Directory/Host..." and change to "SpectreS":
Next you need to make sure your transistor models are setup correctly. The path should be set automatically but you always want to double check that. Do "Setup | Model Path..." and verify that at least the following entry is present:
There is probably an additional entry somewhere into your home directory. This allows you to specify your own models but usually you don't want to do that and don't have such a directory so that entry will not do anything.
Setting up stimuli
There is always the option of specifying a text file with stimulus information. This is useful for instance when you have a great many sources and you want to use cut&paste to specify sources. In most cases however, the graphical entry is the preferred way and is syntax free and convinient.
For this circuit, we want to simulate the critical carry path, so we will input a "0" to A1 and A1_b and a "1" to B1 and B1_b as well as "Cin". So no carry is generated and the input carry is propagated to the output. Below, the setups for "Cin" (also use for "B1" and "B2_b") and "A2_b" (also use for "A1") are shown. We use rise/fall times of 100ps which is typical in a submicron process. All signals are delayed by 1n, which will allow for easier measurement afterwards.
After all local sources are specified, change to the "Global" tab and enter the only global source, "VDD". For all sources make sure that "Enabled" is selected, and always hit "Change" to save your modifications. Once everything is setup, close the stimuli window.
Setting up the analysis type