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Transfer functions in op amps

I have a question regarding finding the transfer functions when dealing with op amps. I do not understand the steps towards going from a general op amp circuit towards getting an the transfer function where you can draw the bode plots for magnitude and phase. Could anyone give me a general step by step tutorial for finding this function or give me a website where they go in depth with these types of problems.
 

Answers and Replies

rbj
2,221
7
first you need to confirm that the op-amp is configured to have negative feedback (that they didn't wire it up backwards), so it's a linear circuit.

then, define the current going into the "+" and "-" terminals is zero (because of the extremely high input impedance) and define that the voltage difference between the "+" and "-" terminals is zero (because of the extremely high gain of the op-amp).

then you apply either the Loop-Current method or Node-Voltage method of circuit analysis, along with the known volt-amp characteristics of every other component in the circuit. this can also be done with the frequency-domain volt-amp characteristics, which is what you want to do if you are seeking frequency-domain behavior (which is what the transfer function is) instead of time-domain behavior (which is what the impulse response or step response are).
 

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