classA and opamp

[revenant]

How can an op amp be said to operate in class A when some of its inner circuits are of class ab or b design.Are there now on the market chips that are purely class A.?

 

[jan.didden]

How can an op amp be said to operate in class A when some of its inner circuits are of class ab or b design.Are there now on the market chips that are purely class A.?

Generally when people talk about putting their opamp in class A with an external resistor or current source, they refer to the output stage only because that is the only one accessible.

But your point is a good one.

Jan

 

[Mooly]

Most opamps operate in class AB. Depending on the particular opamp and the signal currents involved, the opamp can run in Class A up to the point that the signal forces it into AB mode.

In other words for normal line level signals into moderate impedances the majority of 'audio opamps' will be running in Class A.

 

[29285]

I would assume that all voltage amplification done by differential pairs feeding current sources as well as current mirrors normally operates in class A. Only the current amplifying output stage may be class A/AB/B/C.