
#19
Feb2212, 11:35 AM

P: 3,842

In real life( not the model), the noise current actually comes out of the input of the opamp. The current become a voltage through the external impedance. Remember the opamp has high open loop gain, the output will change to make the input goes to zero. So if the input noise current create a noise voltage, the output of the opamp with generate an output to neutralize the noise so to make the input back to zero. As you can see the article I posted in post #9, equation 3.3 gave Req=R1//Rf only, the input impedance is not in it. That's is also what I studied before. 


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