Test: Large Signal Amplifiers - Electronics and Communication Engineering (ECE) MCQ

The O-point of class-A amplifier is located in active region i.e. at the mid-point of dc load line as shown below.

Compared to class A operation, class B operation has

• higher efficiency (r| = 78.5%)
• greater output power 
• more distortion and noise interference.
• negligible power loss at no input signal i.e. no power drain since transistor in class B operation will not consume any power if signal is not applied.

Hence, statements 1,2 and 4 are correct.

We know that,

or

Concept:

1. Crossover distortion is the term given to a type of distortion that occurs in push-pull class AB or class B amplifiers. 
2. It happens during the time when one side of the output stage shuts off, and the other turns on.
3. If there is a difference in timing of on and off of two stages of the transistor, cross-over distortion occurs.
4. The cross-over distortion in the class B power amplifier is eliminated by the Class AB power amplifier which uses diodes at the bases of transistors to reduce forward bias voltage at bases i.e. by biasing the transistors slightly above the cut-off.

The maximum theoretical efficiency of a class A amplifier is 50%. 

The power dissipated by the transistor is

For series-fed load, overall efficiency,

For transformer-coupled load, overall efficiency,