Need for Biasing in Transistor

NEED FOR BIASING

When an input AC signal only is applied to the circuit (without any DC) as shown in fig.3.53 (a). During positive half cycle of input (V_in > V) then input junction becomes forward biased results in current flows from emitter to base then base to collector circuit.

During negative half cycle of input the junction becomes reverse biased so, no current flows in the circuit, results in negative cycle is not amplified as shown in fig.3.53 (b).

To obtain faithful amplification the following three conditions needs to be satisfied.

(i) Emitter Base junction should be forward biased.

(ii) Collector Base junction should be reverse biased.

(iii) There should be proper zero signal collector current

The proper flow of zero signal collector current and the maintenance of proper collector-emitter voltage during the passage of signal is known as transistor biasing. It is important that the AC input voltage should be smaller than the biasing voltage, otherwise the above mentioned problem repeats at every cycle.