I am trying to apply two-port feedback analysis to a circuit similar to the one shown below. I can't represent the forward amplifier as a two-port network because the input signal and feedback signal go to different inputs.
Is it a valid operation to refer the feedback signal to the non-inverting input of the forward amplifier to form a two-port network as shown in the second figure?
Then I can calculate the forward amplifier gain and the feedback quantity, and the summing node is clear. Referring the feedback signal to the non-inverting input can be done using equations for the ideal inverting and non-inverting gains of the forward amplifier, because the non-ideality (i.e. finite loop gain) is the same for both gains.