In the negative feedback system ,why should we consider the feedback block as an isolate block to the amplifying block? Should't we consider about the input resistance of the the amplifying block? If the input resistance of the amplifying block is considered, there will be a complexed problem in the transistor circuit. What should we do while we are analysising the analog negative feedback system? Thanks in advance!
You are absolutely right: the loading on the feedback network will affect performance. If someone told you that in general it will not, you were mislead. However, in a typical operational amplifier system, the feedback section is such low impedance compared with the input impedance of the op amp that the op amp's contribution can be neglected.
Thank you very much!
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