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how to choose the optimal OPAMP structure ?

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patato

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I mean, when given certain spec such as slew rate,bandwidth, gain etc.,I start to implement my circuit, following steps on the textbooks.

But what if a two-stage or fold-cascode doesn't fit in? Textbooks only tell me that "if u are using A structure, you can blah blah blah". The real problem is how do i know if A is the best(or worsest) structure for my target?is it simply try & error to get the right solution? or there's a table or something can be used for reference?

it's confusing me quite some time.
I really need some advice about it.:|
 

Yes, it is confusing...

It is basically a trial and error problem I think. You can use some intuition + previous expereiences to help you choose. But for a 1st time, I think there is no clear rule as to which structure to use.

Maybe the only clear thing is that two stage amplifiers are problematic in terms of stability. Single stage amplifiers are generally faster and more immune to large capacitive loads.

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generally if you need high bandwidth and single pole settling you go with folded cascode. for switched cap that is most common.
if you want high output swing then two stage.
if you need to drive resistive load then class AB.
there are many other criteria that you would know from experience.
 

from my own learning experience, it is quite overwhelming and confusing to begin with when choosing the right topology for an opamp. the book would tell you which topology to choose for different requirements. but the best way to learn is to try building your own circuit. try building some simple circuit consists of different opamp topology (i.e., bandgap, constant current reference, etc) and then u will realize why one topology works better than the other one in certain cases.
 

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