The document discusses crossover distortion that can occur in a class B push-pull amplifier if it is not properly biased. It explains that the transistors do not turn on at zero voltage, leading to distortion. To avoid this, the circuit is biased beyond cutoff using resistors R1 and R2. It then describes the construction and working of a complementary symmetry class B push-pull amplifier, which uses two transistors with identical but opposite parameters. The input signal is applied to the common base, and during the positive half cycle one transistor conducts while the other is reverse biased, and vice versa for the negative half cycle.

1. B.Sc II Sem III
- Prof.D.B.Bobade

2. CROSSOVER DISTORTION IN CLASS B PUSH
PULL AMPLIFIER

3. • In this amplifier, if there is no proper biasing then crossover distortion occurs as
shown above.
• Also, bases of the transistor does not turn ON at zero voltage.
• Hence, to avoid crossover distortion, the circuit is biased beyond the cutoff and
biasing is provided by resistors R1 and R2.
• COMPLIMENTARY SYMMETRY CLASS B PUSH PULL AMPLIFIER:
• CONSTRUCTION:
The circuit is as shown uses two
transistors with identical parameters
but compliment of each other. Hence,
called as complimentary symmetry
power amplifier.
The emitter and bases of both the
transistors are connected together.
The RL is connected between the
common emitter terminal and the
signal source. The i/p signal is applied
to the common base terminal.

4. • The collector of QR is connected to the positive terminal of voltage source VCC
and collector of Q2 is connected to the negative terminal of VCC.
• WORKING:
• When the i/p signal is applied, then during positive half cycle, EB junction of Q1
becomes forward biased hence conduct i.e. IC1 flows through load resistor RL.
• At the same time, Q2 becomes reverse biased. Hence, does not conduct i.e. IC2 =
0.
• Similarly, during negative half cycle, EB junction of Q2 becomes forward biased.
• Hence, conduct i.e. IC2 flows through load resistor RL.
• At the same time, EB junction of Q1 becomes reverse biased. Hence, does not
conduct. i.e. IC1 = 0.
• In this way, amplified o/p is obtained due to the combination of IC1 and IC2.