Amplifiers are used in radios, communication equipment, and many other electronic devices. Power amplifiers handle large voltage and current (power = voltage * current) signals. The classes of amplifiers are grouped to 4 different types:
- Class A: Amplifiers in general amplify different signals differently. Some amplifiers can amplify Direct Current (DC) signals, others amplify Alternate Current (AC) signals, and some amplify both AC and DC signals. The DC offset in any input signal to the amplifier can alter the output from the amplifier if input signal is not properly coupled. Amplifiers operate on certain bias points. This bias point is analogical to the built in pressure inside the spray paint cylinder. The input signal is analogical to the pressing of your finger on the spray nozzle. The output is analogical to the paint sprayed outside. If the amplifier is not biased properly (has built in pressure) it will not produce an output (spray paint) no matter how strong is your input signal (pressure you apply by your finger).
Class A amplifier is biased in a way to provide an output (spray paint) for full range of input (full 360 degree cycle). See figure below. This amplifier consumes the most of power among rest of classes and is therefore the least efficient (less than 25%). It is like spraying large and small amounts of paint while varying your finger pressure (high and low pressure on the spray nozzle from your fingers.)
- Class B: Class B amplifies input signals (such as voice, audio, video, or wired or wireless data) for half the signal period of 180 degrees (assuming AC sinusoidal signal). This is analogical to spraying paint (see above analogy) for half the input period or cycle. Also see figure below. This class is also more efficient but less power consuming.
- Class AB: This class is positioned between the above two classes A and B.
- Class C: This class amplify signals for periods less than half the input cycle, see figure below. They consume much less power and therefore are more efficient than class A and B. This amplifier is mainly used to amplify signals without the need of having the knowledge of the entire signal cycle. Applications include tuned class C amplifiers, FM radio amplifier, and AM modulation circuits. This amplifier is also not good to use for linear applications because it amplifies only small portion of the entire signal. See figure below.
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