# RF Wireless World

## Home of RF and Wireless Vendors and Resources

One Stop For Your RF and Wireless Need

## Amplifier classes-class A,class B,Class AB,Class C

This page provides comparison between amplifier classes viz.class A,class B,Class AB and Class C.

### Amplifier class-A operation

• In this class-A, amplifier operates in active region at all the times(2*π).
• Stage efficiency = PL(max)/ PS x 100 %
Where PS is DC input power.
•  Load Power = PL = (VL)2 /RL = (VPP)2/8*RL

### Amplifier class-B operation

• In this class-B, current flows for half of the input cycle(π).
• Q point is located at cutoff the DC and AC load lines.
VCEQ = VCC/2
•  AC load power of class-B push pull amplifier,
PL = (VPP)2/8*RL

### Amplifier class-AB operation

• In this class-AB, amplifier operates between half and full input cycle(between π to 2*π).

### Amplifier class-C operation

• In this class-C, amplifier operates for less than half of the input cycle(less than π).
• It is basically a tuned amplifier.
•  AC load power for class-C amplifier is,
PL = (VPP)2/8*RL
Where, VPP is peak to peak load voltage and RL is load resistance

Following table mention difference between Class-A,Class-B,Class-AB and Class-C with respect to important parameters.

 Amplifier Class type Q point Iq Conduction Angle Maximum Efficiency Class A 0.5 0.5 2*pi 50% Class B 0 0 pi 78% Class AB 0-0.5 0-0.5 pi-2*pi 50-78% Class C <0 0 0-pi approaches to 100%

In order to operate transistor (FET) for a certain class, the gate and drain DC voltages have to be biased carefully to the certain operating point which is called as Quiescent point or Q-point.

Class A offers least distortion, while Class C offers maximum distortion of the output signal.