How can I determine the dominant pole of an opamp by hand calculation?

[Hackson]

How can I determine the dominant pole of an opamp by hand calculation?

I am confused with associating each node with a time constant and things like that......where can I find good reference about that? I read Razavi's book....it simply does all the calculation and I don't really get any insight of the circuits......any idea? Thanks a lot.

 

[duncan94022]

Re: Opamp dominant pole

A great discussion for a 741 is in Gray Analysis and Design of Analog Integrated Circuits. You can buy one used for less than $25. Check https://www.bookfinder.com. Basically you are generally going to find the dominant pole in the stage with the most gain, usually the input stage. The miller capacitance on the input stage will generally set the dominant pole unless the amp is inernally compensated. Then the compensation cap will dominate.

 

[flatulent]

Re: Opamp dominant pole

To further amplify (sorry for the pun) on the post above, look at the schematic for the extra lumped capacitance added to the circuit. It will usually be across the input/output of one of the stages. The Miller effect stated in the previous post is used to make the time constant larger than if the capacitance was across a lumped resistor.

 

[sadfish]

Opamp dominant pole

Find the point: where the loading cap and AC resistor are larger.

 

[santhoshv78]

Re: Opamp dominant pole

find the high inpedance node of the circuit.