continuous cmfb circuit reduce UGB?

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ljy4468

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Hi all~

i made an opamp(folded cascode) with UGB=500Mhz, Av=50.
and made an booster with an continuous CMFB
and applied it to main opamp

So, i simulated it, and the result is UGB=400Mhz, Av=120

But I saw many paper about opamp with booster, and there is no change IN UGB before and after applying booster.
why my amp's UGB is falling down.
all node's voltage is correct as i expected
Somebody could help me
I'm going crazy hhhhh

and another question
how can i know my cmfb's operating well in HSPICE
how can I simulate it?

Thanks
Good day~
 

THe UGB will shrink if the CMFB loop is not designed properly. Refer to "A fast-settling CMOS op amp for SC circuits with 90-dB DC gain" by Klaas Bult in 1990 for more details
 

from my experience,you should simulate your booster seperately.
found the UGB of the booster.
then if you simulate your gain-boosted opamp in the open loop.then you must confirm that the GB(main opamp)<UGB(booster)<second pole(main opamp).if the relationship is satisfied,then the UGB of the main opamp should be the same as the gain-boosted opamp.
ps:av=50db i think should be
hehe

 

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