love_analog wrote on Feb 18th, 2012, 5:45pm:I am curious how people are finding their transistor parameters for analog design 28nm and below
Do you still use gm=2*I/(Vgs-Vt). and I=K*W/L*(Vgs-Vt)^2.
Working with recent college grads - they just put the structure together and parameterize all the transistors and run optimization routines.
This for an opamp with gain, BW specs.
Typically - and independant on process - I am doing normally this:
- If you know you need highest speed, use min L, and find W e.g. to achieve a certain Vdsat or drive-strength.
- If you know matching is important, then better use non-minimum-L and start with meaningful L, find suited W for good matching, Vdsat and noise. Best make some technology investigations on these parameters vs Id, L, W.
- Especially the for current source better use never min-L. Look mostly at Vdsat and matching.
- Of course also the Id needs to be selected, just to fit power budget, noise, drive strength, bandwidth, etc.
- The more experiences you have the closer usually the starting point on Id, L, W is to the optimum values. Number of fingers, etc. I set usually to make the transistor not looking too extreme, best not far away from quadratic. More care is needed for special applications like RF and power-amps.
Bye Stephan