Walt Jung(?) tube opamp

[peranders]

I found this opamp made of tubes in the Walt Jung "brick book". Just a little candy for the tube dudes.

 

[Fred Dieckmann]

ummmmm......

I count 8 bipolar transistors (and not even good ones) in this "tube" op amp. Kind of defeats the whole purpose doesn't it?
Q1 to Q4 are a folded cascode stage with another cascode stage on the bottom of it before somebody inevitably ask.

 

[peranders]

I think this was more like a design idea rather than a ready solution.

 

[phase_accurate]

I do not ask anything but inevitably complain that the thingie on the bottom looks damn close to a current mirror.

Regards

Charles

 

[peranders]

I'm afraid Fred is right. The lower part is the load of the differential stage and the tubes are stealing current from the differential transistors and these transistors have their inputs connected to constant DC voltage.

 

[Tube_Dude]

The current mirror...

I do not ask anything but inevitably complain that the thingie on the bottom looks damn close to a current mirror.

They are a current mirror!!!

Cheers

 

[peranders]

Sorry, I didn't read to well, correct, folded cascode with current mirror as collector load at the bottom.

 

[Tube_Dude]

Curiosity??

Hi paranders

For what is the out 2??...with a high open loop output impedance??