ANALOGUE ELECTRONICS I

An amplifier receives a signal from an input source and provides a larger version of the signal to some output device or to another amplifier stage. An input signal is generally small (a few millivolts from a cassette or CD input, or a few microvolts from an antenna) and needs to be amplified sufficiently to operate an output device (speaker or other power-handling device). In small-signal amplifiers, the main factors are usually amplification linearity and magnitude of gain. Since signal voltage and current are small in a small-signal amplifier, the amount of power-handling capacity and power efficiency are of little concern. A voltage amplifier provides voltage amplification primarily to increase the voltage of the input signal. Large-signal or power amplifiers, on the other hand, primarily provide sufficient power to an output load to drive a speaker or other power device, typically a few watts to tens of watts. The main features of a large-signal amplifier are the circuit’s power efficiency, the maximum amount of power that the circuit is capable of handling, and the impedance matching to the output device.

NB: Power amplifiers are those amplifiers that have the objective of delivering power to a load. This means that components must be considered in terms of their ability to dissipate heat.

One method used to categorize amplifiers is by class. Basically, amplifier classes represent the amount the output signal varies over one cycle of operation for a full cycle of input signal.  They are:

i).    Class A

ii).   Class B

iii). Class AB

iv). Class C

v).   Class D