What "was" input resistance of this voltage-voltage topology amplifier before feedback?
simulate this circuit &ndash; Schematic created using CircuitLab
Closed-loop gain Acl=gRE/(1+gRe)
Loop gain: Aloop=-gRE
Input resistance (without external base divider) rin=h11(1+gRE)
Comment: The &quot;open-loop gain&quot; (Aol=gRE) is a fictitious expression because the circuit cannot be operated without feedback. This is due to the fact that there is no &quot;outer&quot; feedback loop that could be cut. Output and inverting input nodes are identical (internally connected).