Input Impedance of Emitter Follower
Fig. 1.14 (i) shows the circuit of a loaded emitter follower. The a.c. equivalent circuit with T model is shown in Fig. 1.14 (ii).
As for CE amplifier, the input impedance of emitter follower is the combined effect of biasing resistors (R1 and R2) and the input impedance of transistor base [Zin (base)]. Since these resistances are in parallel to the ac signal, the input impedance Zin of the emitter follower is given by :