I am working through Razavi mircroelectronics and regarding BJT resistances, there are three master rules:
Rule # 1: looking into the base, the impedance is r_π if emitter is (ac) grounded.
Rule # 2: looking into the collector, the impedance is r_ο if emitter is (ac) grounded.
Rule # 3: looking into the emitter, the impedance is 1/gm if base is (ac) grounded and Early effect is neglected.
But in the circuit below, the Resistance looking into emitter2 is show to be r_π || r_o || 1 / gm (and not just 1/gm).
Why is that?