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Quiescent Output Voltage
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isaacnewton



Joined: 13 May 2004
Posts: 158
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Location: Earth Village
Post08 Jul 2005 22:23   

Quiescent Output Voltage
The attached is a schematic of a simple op amp. I have question about the Quiescent Output Voltage of this op amp (open loop) or the Base voltage of Q6. How to calculate it by hand. It looks like the quiescent output voltage of this op amp is not well controlled.

Thank you in advance.

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willyboy19



Joined: 15 Feb 2004
Posts: 158
Helped: 10
Post09 Jul 2005 8:26   

Re: Quiescent Output Voltage
Your understanding is correct: the base of Q6 is the high impedance node of the Opamp whose voltage level can not be well controlled (open loop wise). As a matter of fact, any small current imbalance between the upper PNP and lower current sink would result in large excursion of this output node voltage.
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funster



Joined: 30 Jun 2005
Posts: 234
Helped: 12
Post09 Jul 2005 11:27   

Re: Quiescent Output Voltage
you can't use a high gain amplifier in open loop operating mode.

it will saturate quickly.

to control output voltage, you must use negaive feedback

to construct amplifier into inverting amplifier or

noninverting amplifier.


best regards




isaacnewton wrote:
The attached is a schematic of a simple op amp. I have question about the Quiescent Output Voltage of this op amp (open loop) or the Base voltage of Q6. How to calculate it by hand. It looks like the quiescent output voltage of this op amp is not well controlled.

Thank you in advance.
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