Answer to Question #111908 in Electric Circuits for HH

Question

Which type of amplifier is used for obtaining both current and voltage gains? Draw a
circuit of such amplifier in fixed bias condition using a p-n-p transistor. (Clearly indicate
the polarities of biasing voltages.) What are the limitations of fixed biasing? How are
these limitations overcome by using universal bias?

Answer 1

1) Common emitter amplifier is used for obtaining both crrent and voltage gain. The circuit of pnp transister in common emitter is drawn in the figure.

2)Limitation of fixed biaing:

Stability factor is very high(of the order of 100)

Succeptible to temperature variation

3)These limitations are overcome by universal bias by using a voltage divider to nullify the effect of temperature variation ehich affect Vce. By using universal bias, stability factor reaches near to unity.

The diagram is as attached

Thanks