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# Cmfb Stb

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stb iprobe , iprobe stb , stb stability , stb simulation
8 Threads found on edaboard.com: Cmfb Stb

## need some help about CMFB in three_stage OP

when I do cm stb simulation in three_stage OP,I add L=500p to power and ground. the result shows that a peak in f=9.6G. If I delete L in power and ground,there in no peak in cm stb result. Why? please help me. thanks!

## Capacitive feedback OTA Design Issues in Loop gain

HI I have designed a capacitive feedback OTA ( OTA is folded cascode single stage OTA with ideal cmfb). When I simulate the loop gain of OTA (using iprobe and stb analysis in cadence) I get a 'High Pass' response at low frequencies. I am not sure why this is happening. Please help to solve this issue. Thanks

## The importance of loop gain

Yes you can still use loopgain simulation methodology in cadence. However before running "stb" analysis you have to run transients till your CM is settled. An easier way is to use ideal cmfb circuit and then do can skip the transient analysis part. My answer assumes you already have good background simulation experience in spectre. Let me know if

## How to simulate fully differential ota with sc cmfb

you can run trasient analysis until your cmfb is settled. Now run AC analysis and in its option menu click yes "prevoppt". It should do the trick for you.

## loop gain \measurement

Has anyone done the 'stb' analysis in Virtuoso or used the cmdmprobe component .I need to measure the vcmfb loop gain of a differential amplifier. how to go about it

## Is the method right to judge the CMFB's stability?

The diagram of a full differential opamp with cmfb is in the left I want to know whether it is stable, I broken the point a and make the cmfb point as the input and point a as the output as can be seen in the right. Cla is the load of the point a. Can I judge the stability of the cmfb circuit by seeing the bandwidth and phase

## problem on using cadence stability(stb) analysis

For multi-loop stability analysis, you should check the inner loop first and the outer loop check later. so in your case you should make sure the cmfb has enough of phase margin, then proceed to the RC feedback path. Hope this helps Regards, Smart

## Stability analysis using Spectre

So I am using the stb analysis to check the stability of my cmfb. Is phase of +180 equal to phase of -180? Thanks Added after 9 minutes: So I just read somewhere that cadence computes the loop-phase by shifting it up by 180, so that unity gain frequency for the loop gain would correspond to phase mar