Hello,

How can I identify poles,zeros and gain in an analog circuit. Do i have to replace MOSFETs with their equivalent and find the transfer function?

Thank you

 

Please show the circuit in question.

 

Hello,

How can I identify poles,zeros and gain in an analog circuit. Do i have to replace MOSFETs with their equivalent and find the transfer function?

Thank you

It sort of depends on what you hope to accomplish? Can you let us in on your thinking?

 

For example, in the following circuit which are the poles and zeros?What is the methodology to find them ?

 

I don't know if there is a way to do it analytically, If there is I am not familiar with it. If you can simulate the circuit which looks like a differential amplifier with a current mirror and some output capacitance, then you might be able to identify the number of poles from the slope of the rolloff, and take a stab at finding the corner frequency.

 

It can be done analytically. Using a simple AC model for the main diff fets, assume the current mirrors
have no freq dependencies

http://aries.ucsd.edu/NAJMABADI/CLASS/ECE102/12-F/NOTES/ECE102_F12-LecSet-7A.pdf


Regards, Dana.

 

For example, in the following circuit which are the poles and zeros?What is the methodology to find them ?

It looks like the link in post #6 might be a good place to start, but to find the poles and zeros you will need to add more specific information to the mosfet models such as the capacitances. It make get a little complicated with three capacitors per mosfet. You might gain this info from a spice model or data sheet.
It may be a lot easier though to just do simulations using a simulator.
You might also want to state the reason you want to find the poles and zeros.

 

Thank you @danadak ,very interesting presentation. @MrAl basically what I want to learn is which capasitances affect zeros and poles the most and if its possible to predict the frequency response of the circuit before simulation.