Classification of Amplifiers:
In the Classification of Amplifiers, the transistor amplifiers may be classified in several ways such as on the basis of transistor configuration used, active device used, output, frequency range of operation, input, the number of stages used, coupling methods, mode of operation (biasing conditions) and on the basis of bandwidth.
On the basis of active device used, the amplifiers may be classified as BJT amplifiers and FET amplifiers.
On the basis of output the amplifiers may be classified as voltage amplifiers and power amplifiers. The former primarily increases the voltage level of the input signal whereas the latter increases the power level of the input signal.
On the basis of frequency range of operation the amplifiers may be classified as dc amplifiers (from 0 to about 10 Hz), audio-frequency amplifiers (20 Hz to 20 kHz) and radio frequency amplifiers (a few kHz to hundred of MHz).
On the basis of the input the amplifiers may be classified as small signal amplifiers and large signal amplifiers.
On the basis of number of stages, the amplifiers may be classified as single stage amplifiers and multistage amplifiers. The multistage amplifiers, on the basis of coupling methods, may further be classified as R-C coupled amplifiers, transformer-coupled amplifiers, L-C coupled amplifiers and direct-coupled amplifiers.
On the basis of mode of operation the amplifiers may be classified as class A, class B, class AB and class C amplifiers. This classification depends on the portion of the input signal cycle during which collector current is expected to flow. In class A operation collector current flows for the entire ac signal, in class B operation collector current flows only during positive half cycle of the input ac signal, in class AB operation the collector current flows for appreciably more than half but less than entire cycle of the input ac signal whereas in class C operation the collector flows for less than half cycle of ac signal.
On the basis of bandwidth, the classification of amplifiers are narrowband amplifiers (normally RF amplifiers or tuned amplifiers) and wideband amplifiers (normally video amplifiers).