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Class AB dumb question

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CAMALEAO

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Hi everyone, can I use a class AB in a 2 stage miller ota? (Diff. input to single output)
If yes, how?
Regards.
 

Seems to contradict OTA design principle of mirroring the diff-pair current into the output node.

What should be the purpose of your design?
 

There is no specific purpose. It was a thought.

What do you mean by contradict (...)? Didn't get.

Thank you.
 

Yes it is. Now say that I wanted to use a classe AB at the output. Would that be possible?

Or maybe the question would be where is the class AB used more often? Which topologies?
 

Yes it is. Now say that I wanted to use a classe AB at the output. Would that be possible?

Or maybe the question would be where is the class AB used more often? Which topologies?
You can create a AB-Class Output Stage after OTA ( Differential Pair)
 

You can create a AB-Class Output Stage after OTA ( Differential Pair)

So, if we look at erikl reference what you are saying is that we could use the circuit from page 11 (method 1 for single output)? Method 2 I guess is for fully differential output amplifier?

- - - Updated - - -

Find here a lecture on CMOS (class AB) output stages appropriate for use as OTA output stage (both together I'd call it an OpAmp).
View attachment 140051 . See pages 210-21 ff. for single ended or differential input from OTA.

erikl, from what I read on those slides, the push-pull structure is actually the class AB? That push-pull structure is the Monticelli one?
 

Find here a lecture on CMOS (class AB) output stages appropriate for use as OTA output stage (both together I'd call it an OpAmp).
That's the point, The overall structure is no longer an OTA, there's no class AB stage in an OTA.
 

From my understanding, Opamp is what is called to an amplifier with current drive capability at the output whereas an OTA is an amplifier without current drive capability. For example a two stage miller amplifier is a OTA which is only suitable to drive capacitors.

Now, I could use a 2 stage miller OTA with the class AB structure, couldn't I? By using the class AB at the output the two stage miller becomes an Opamp.

Can we look at it like that?

That structure on page 21 is the Monticelli one?
 

... That structure on page 21 is the Monticelli one?

Right. Still better to be recognized on page 22:
... with the typical floating current source (M3-M4).
 

OTA is pure class A.
OTA is defined as differential amplifier with high impedance input and output nodes only, while all internal nodes are low impedance ones.
The OTA can work in another class too. There are number of class AB OTA structures in a literature.
 

Can you point onde of those references please?
 

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