Hi everyone,
I was reviewing analog circuits and was studying common-emitter amplifier from Art of Electronics (3rd edition) but I got confused analyzing a circuit. The book states that when looking at the input impedance of a common-emitter amplifier as shown below, it would be R1 || R2 || (B*R_E) where B is the current gain of the NPN.
However, why wouldn't input see the R_C resistance? The "Ohm model" of the NPN transistor is as shown above, so it makes sense to me that at the input node (i.e., base of the NPN), it would see R_C resistance as part of the input resistance. Is it not included because you don't include any impedance at the output node of the circuit?