design in corners(PVT)

[raziyeh94]

Hello.
I have a delay circuit like a inverter.I designed in TT corner.All result was good.when I simulated in SS corner(temperature:120,voltage:-10%nominal voltage,process: slow) my result became bad .in fact my
circuit didnt work in this corner. How do I do?
should I design a circuit that work in all corners?or I should find worst corner of my circuit? please help me.
thanks

 

[erikl]

should I design a circuit that work in all corners?
... or I should find worst corner of my circuit?

If you want to have it produced, it should of course work in all corners (min/max voltage & temperature limits given by the application).
For good production yield, you should try & find worst working conditions via Monte Carlo analysis.

 

[micpro]

If you want to have it produced, it should of course work in all corners (min/max voltage & temperature limits given by the application).
For good production yield, you should try & find worst working conditions via Monte Carlo analysis.

For yield of small delay circuits in older technologies, local variation Monte Carlo may not be necessary; just run all PVT corners and pick the worst, then tune the circuit for that one.

This procedure works best if you have only one spec, one worst-case corner, and it doesn't change during tuning. Some circuits and specs however are more difficult to tune. For duty cycle lower+upper bound (e.g. 49% .. 51%), you need to keep two corners in mind. If you have multiple specs with trade-offs (duty cycle, speed, power, area, ...) then you end up with a multi-objective optimization problem. A good circuit optimization program can solve that quicker and better than a designer by hand.