frozenduck
Newbie level 4
For a folded cascoded two stage opamp,
Q1:
Typically, we just add one CMFB from 2nd stage output to 1st stage current source. Why don't we add 1 CMFB for each stage? Is there any drawback?
Q2:
If we just need one CMFB, why do we sense the 2nd stage output instead of 1st stage output? The 2nd stage is just pseudodifferential, is that correct?
Q3:
For CT CMFB, we need to break the loop at the CMFB input and run AC analysis to check the PM and UGB for stability.
1. The UGB should be equal to or few less than that of the main amp. and PM≥60°. Is that right?
2. But how can we make sure it works during main opamp operation?
Q4:
Fro SC CMFB, it cannot be simulated in AC analysis.
1. Run Tran. and save the data, and then run AC.
2. Use PSS analysis.
Which one is correct? Is there any tutorial to do this? I can't find it in the Internet.
Q1:
Typically, we just add one CMFB from 2nd stage output to 1st stage current source. Why don't we add 1 CMFB for each stage? Is there any drawback?
Q2:
If we just need one CMFB, why do we sense the 2nd stage output instead of 1st stage output? The 2nd stage is just pseudodifferential, is that correct?
Q3:
For CT CMFB, we need to break the loop at the CMFB input and run AC analysis to check the PM and UGB for stability.
1. The UGB should be equal to or few less than that of the main amp. and PM≥60°. Is that right?
2. But how can we make sure it works during main opamp operation?
Q4:
Fro SC CMFB, it cannot be simulated in AC analysis.
1. Run Tran. and save the data, and then run AC.
2. Use PSS analysis.
Which one is correct? Is there any tutorial to do this? I can't find it in the Internet.