Answer to Question #109526 in Electrical Engineering for Bharti

Question

Show that the voltage gain of an emitter follower circuit is close to unity.

Answer 1

An emitter follower circuit and its equivalent are shown below:

The voltage gain is

$$A=\frac{(\beta+1)[R_ER_L/(R_E+R_L)]}{(R_s+r_{bc})+(\beta+1)[R_ER_L/(R_E+R_L)]}.$$

The term $(R_s+r_{bc})<<(\beta+1)[R_ER_L/(R_E+R_L)].$ Therefore, the voltage gain is positive, close to unity but it is smaller than unity.