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opamp simulation

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promach:
For the Improvements_in_biasing_and_compensation_of_CMOS_opamp (second reference link), why the author break open the connection between gates of M3A and M3B ?

And how to derive the inequality expression (14) in the document ?



Wimberleytech:

--- Quote from: promach on April 16, 2019, 10:32:15 am ---For the Improvements_in_biasing_and_compensation_of_CMOS_opamp (second reference link), why the author break open the connection between gates of M3A and M3B ?

And how to derive the inequality expression (14) in the document ?



--- End quote ---
Set P3 < P1 and simply do the algebra.
Eq 14 appears to have an error...should be gm2b in numerator, not gm2a

promach:

--- Quote ---Set P3 < P1 and simply do the algebra.
Eq 14 appears to have an error...should be gm2b in numerator, not gm2a
--- End quote ---

I will check your advice regarding the inequality expression, but why set P3 < P1 ? Is it dominant pole compensation or something else ?

I try to incorporate the author schematics (Figure 6 in the second reference link) into the opamp, but it resulted in erroneous bode plot

Which part is wrong in the schematics ?



Wimberleytech:

--- Quote from: promach on April 17, 2019, 03:00:49 am ---
--- Quote ---Set P3 < P1 and simply do the algebra.
Eq 14 appears to have an error...should be gm2b in numerator, not gm2a
--- End quote ---

I will check your advice regarding the inequality expression, but why set P3 < P1 ? Is it dominant pole compensation or something else ?

--- End quote ---
yes, essentially

--- Quote ---
I try to incorporate the author schematics (Figure 6 in the second reference link) into the opamp, but it resulted in erroneous bode plot

Which part is wrong in the schematics ?


--- End quote ---
ALWAYS check bias points before even looking at your ac response.  In this case, your biasing is broken. 

promach:
See the following circuit :

I am having problem using the miller lead compensation (M24 mosfet in triode region)

Any help ?

When I saw this 90MHz bandwidth opamp OPA838, I am inspired to do the same, but my current circuit bandwidth is only 10MHz.

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