The COMMON-COLLECTOR CONFIGURATION (CC) is used as a current driver for
impedance matching and is particularly useful in switching circuits. The CC is also referred to as an
emitter-follower and is equivalent to the electron-tube cathode follower. Both have high input impedance
and low output impedance.
In the CC, the input is applied to the base, the output is taken from the emitter, and the collector is
the element common to both input and output.
GAIN is a term used to describe the amplification capabilities of an amplifier. It is basically a ratio
of output to input. The current gain for the three transistor configurations (CB, CE, and CC) are ALPHA
(a), BETA (b), and GAMMA (g), respectively.
The TRANSISTOR CONFIGURATION COMPARISON CHART gives a rundown of the
different properties of the three configurations.