Feedback in the Emitter Follower

The emitter follower can be seen to be an example of negative feedback when the relationship

is put in the form

which when compared to

shows that B=1. The gain with feedback is

The gain of 1 can be seen as a result of all the output being fed back to the input.

R Nave

Feedback in the Common Emitter

The input/output relationships:

can be combined in the form

which when compared to the form

gives

The application of negative feedback in this case with the value of B shown leads to an amplification

which corresponds to the approximate voltage gain obtained by other approaches:

R Nave