CMFB loop gain and phase margin

[yixiusky]

loop gain cmfb

I would like to ask one question:

when i check the stability of CMBF loop. There is peak shows in both loop gain and phase margin plot. I can not know the reason. Could you help me ?

thank you very much

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[meanture]

cmfb loop gain

me too

 

[lwjbh]

pole zero doublet gain boosting

waiting for the answers

 

[JoannesPaulus]

It might be a pole-zero doublet. Are you using gain boosting in the main amplifier?

 

[yixiusky]

thank you for your answer . but i did not use gain boosting method.

 

[fanatic]

thank you for your answer . but i did not use gain boosting method.

how about your cm loop? make clear that if there is zero in your cm loop.

 

[varunkant_2k]

Peak always shows the high energy level or in other words One or more poles are dominating the frequency response.
Try to add any zero in the feed forward path by adding any buffer or by resistance in such a way it occures exactly at the dominant pole.

 

[LvW]

Re: loop gain cmfb

I would like to ask one question:

when i check the stability of CMBF loop. There is peak shows in both loop gain and phase margin plot. I can not know the reason. Could you help me ?

As the peaks occur at relatively high frequencies (100 MHz region) it seems to be a result of parasitic capacitive feedbacks. But - is it a problem for you resp. for the proper function of the system?
(By the way: it is not a "phase margin" plot - it`s simply a plot of the phase response).

 

[raj_shekar]

If if occurs after UGB there is no issue

 

[love_analog]

It is typically means there are 2 parasitic poles close to each other (unless you managed to create a zero somehow). Think of an LC oscillator. You will see large Q and peak in the magnitude plot at the resonant frequency. Also you'll see 180 degree phase shift.