Editing Common emitter (section)

=== Low-frequency voltage amplifier ===
A typical example of the use of a common-emitter amplifier is shown in Figure 3.

[[File:Complete common emitter amplifier.png|thumb|280px|Figure&nbsp;3: Single-ended ''npn'' common-emitter amplifier with emitter degeneration. The AC-coupled circuit acts as a level-shifter amplifier. Here, the base–emitter voltage drop is assumed to be 0.65&nbsp;volts.]]

The input capacitor C removes any DC component of the input, and the resistors R<sub>1</sub> and R<sub>2</sub> bias the transistor so that it will remain in active mode for the entire range of the input. The output is an inverted copy of the AC component of the input that has been amplified by the ratio ''R''<sub>C</sub>/''R''<sub>E</sub> and shifted by an amount determined by all four resistors. Because ''R''<sub>C</sub> is often large, the [[output impedance]] of this circuit can be prohibitively high. To alleviate this problem, ''R''<sub>C</sub> is kept as low as possible and the amplifier is followed by a voltage [[buffer amplifier|buffer]] like an [[emitter follower]].