MOSFET characteristics can vary across multiple wafers.
If we wanted to make sure a sensitive analogue design worked across all process variations, we would want to simulate these variations and check the results were still within our specification.
Some of the most common variations affect the strength or speed of the MOSFET switching, and we have both P and N type MOSFETS.
The corners represent the most extreme variations of these parameters. By combining them, we get these combinations:
- FF (fast fast)
- SF (slow fast)
- SS (slow slow)
- FS (fast slow)
- TT (typical typical)
We have SPICE models of the different corners provided in the Skywater PDK.
For my basic simulations, I often remove all the corner libraries except TT, to speed up the simulation time.
For more information, check this Wikipedia page: https://en.wikipedia.org/wiki/Process_corners
Having the formal verification part additionally felt nice, that I could have something that I know is going to be functional instead of just guessing for a long time and then looking at waveforms and then not knowing what hell I'm doing!