[SOLVED] Question on the book "Analog Design Essential"

[petelee]

Question on folded cascode opamp

Hi,

The comment in the following picture. ==> "There is no way that DC current could flow out, even if the output node would be connected to ground."

The output node is VOUT, isn't it? If so and the VOUT is connected to GND, I expect the current is flowing out to GND node. Am I wrong? I might misinterpret the author's intention.

Could anybody please help me out? ~~~

 

[crutschow]

Few probably have that book. If you could post a picture of the schematic it would help.

 

[petelee]

Re: Question on folded casecode opamp



Dear Crutschow, Thanks for looking at my post. Here's the one attached.

 

[LvW]

Hi petelee, I suppose both supply voltages are chosen so that the output node is at a dc potential of 0 volts.
(We have a similar situation for all - ideal - opamps with symmetric split supply).

 

[petelee]

Re: Question on folded cascode opamp

Thanks LvW for commenting about it.

Do you mean that it's like VDD/VSS=2v/-2v for example?

 

[crutschow]

It's not entirely clear but I think he's talking only about the amplifier bias current and not signal current. Any signal current obviously would flow in or out of the output node.