Gain

Gain is the increase in the strength of a signal. Expressed in dB. 3 dB is about doubling.

A gain of more than 1 is called amplification, while a gain of less than 1 is called attenuation.

Class

Transistors may be biased in a variety of classes. A trade off of linearity and power consumption is usually made where a Class A

Class A

The transistor is "on" all the time. We say 360 degrees of conduction, representing an entire period of the sine waveform. Idealy this class produces very little distortion, however consumes a lot of power.

Class AB

The transistor is "on" for more than half the cycle of a sine wave. We say >180 of conduction. The bias produces both odd and even order distortion, however uses less power than class A.

Class B

The transistor is "on" for only half the cycle of a sine wave. We say 180 degrees of conduction. Idealy this class produces only even order distorion. In narrow-band systems such as radios this distortion is easily filtered out. In wide-band systems such as audio it is believed that 2nd order distortion sounds good. It is difficult to build an ideal class B amplifier and hence class AB is more popular.

Class C

The transistor is "on" less than half the cycle of a sine wave. We say <180 of conduction. This class produces both even and odd order distortion, however is very efficient.

Amplifier

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Coupling

ways of regulating voltage

Diode. DC voltage drop. When AC passes only allows half the waveform through. This is useful for constructing a power supply.

Capacitive coupling. DC does not pass through capacitors, but AC does. At low frequencies capacitors have high resistance, and at high frequencies capacitors have low resistance.

Transformer coupling. Inductor based. DC does not pass through inductors, but AC does. Low resistance at low frequencies and high resistance at high frequencies.