Showing posts with label Analog Design. Show all posts
Showing posts with label Analog Design. Show all posts

Tuesday, December 21, 2010

Revisit of OP AMP Design

Revisited OP AMP design in a current project to design a single-ended OP amp with low power and narrow bandwidth. Below is a few tips summarized from the design:

1. Open loop is always stable.

2. Maximum loop gain, loop gain, and gain margin.
   Loop gain T=F*A,wk:corresponding to phase margin; F=0 for open loop, F=1 for a unity gain source follower (the worst case for stability);
Maximum loop gain, corresponding to 180 phase; phase margin =0;
gain margin = maximum loop gain - loop gain


3. Current mirror
    cascoded current mirror to improve current source impedance

4. high gain is achieved with telescopic or folded cascode topology;

5. Common mode feed back makes no sense for single-ended output

6. Input offset voltage,CMRR and PSRR to simulate with mismatch

7. Compensation of Op-amp: to move the location of poles.