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Design >> Analog Design >> analog design 28nm and below - poll
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Message started by love_analog on Feb 18^th, 2012, 5:45pm

Title: analog design 28nm and below - poll
Post by love_analog on Feb 18^th, 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.

Title: Re: analog design 28nm and below - poll
Post by raja.cedt on Feb 19^th, 2012, 1:49am

hello,
this equations even don't work at 180nm as well...better trust the simulator for finding parameters called gm,gds... and use this parameters to find opamp gain and BW...

Title: Re: analog design 28nm and below - poll
Post by loose-electron on Feb 21^st, 2012, 4:28pm

For CMOS Academic equations have never worked properly.

Academic simplifications.

Run a set of bias curves, use those
for approximate bias locations
(geometry scaling to set Id aftger setting up Vds and Vgs)

After that use a simulator.

Title: Re: analog design 28nm and below - poll
Post by weber8722 on Apr 20^th, 2012, 7:11am

love_analog wrote on Feb 18^th, 2012, 5:45pm:

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