Common Collector Amplifier

The emitter follower: voltage gain just under 1, high input impedance and low output impedance — a buffer.

Intermediate

The output is taken from the emitter, which "follows" the base minus about 0.7 V:

$A_v \approx \frac{R_E}{r_e + R_E} \approx 1 \qquad Z_{in} \approx \beta (r_e + R_E) \qquad Z_{out} \approx r_e + \frac{R_S}{\beta}$

It provides current gain without voltage gain, so it can drive a low-impedance load from a weak source. Push-pull pairs of emitter followers form the output stage of most audio amplifiers.

Spotted a mistake or want to add detail? Suggest an improvement — Content Contributors' edits are reviewed by editors before they go live.

Discussion (0)