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constant-gm bias circuit
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promach:
For https://designers-guide.org/forum/Attachments/Improvements_in_biasing_and_compensation_of_CMOS_opamp.pdf#page=3 , how to derive expression (14) ?
David Hess:
They don't they implement constant Gm the same way it is done in bipolar circuits by adjusting the bias current levels?  Or is that what they are proposing?  It was not clear to me.
silverback:
To obtain constant GM the bias current Id or Ic for transistors should be proportional to absolute temperature, Iptat.
David Hess:

--- Quote from: silverback on April 26, 2019, 12:17:46 pm ---To obtain constant GM the bias current Id or Ic for transistors should be proportional to absolute temperature, Iptat.
--- End quote ---

Exactly, and doing exactly that was an early innovation in bipolar circuit design.

Why isn't the same thing done in their example?  Is there something about CMOS which makes it untenable?

Thinking about it now, I never noticed such a thing in published CMOS operational amplifier designs but I assumed like later published bipolar designs, they just left that part out.
promach:
Do you guys know how to come up with the equation for RDS4C  ?
 
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