Editing Common emitter (section)

== Applications ==
=== 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]].

=== Radio ===
Common-emitter amplifiers are also used in radio frequency circuits, for example to amplify faint signals received by an [[antenna (electronics)|antenna]].{{dubious|reason=the antenna RF stage is more usually common base, it is the IF and AF stages that are common emitter|date=February 2015}} In this case it is common to replace the load resistor with a tuned circuit. This may be done to limit the bandwidth to a narrow band centered around the intended operating frequency. More importantly it also allows the circuit to operate at higher frequencies as the tuned circuit can be used to resonate any inter-electrode and stray capacitances, which normally limit the frequency response. Common emitters are also commonly used as [[low-noise amplifier]]s.

=== Audio ===

Common-emitter amplifiers are also used for audio amplifiers. For example, a [[do it yourself]] or hobbyist application of the common-emitter amplifier is presented in.<ref>Single-Transistor Audio Amplifier - How the Common Emitter Amplifier Works https://youtube.com/watch/QGInwQa_XEM</ref>