BJT Transistor Biasing

TRANSISTOR BIASING

The main function of transistor is to do amplification. The weak signal is applied to the base of the transistor and amplified output is obtained from the collector circuit. The main requirement during amplification process is that only the magnitude of the signal should increase and signal shape should not get change. This increase in magnitude of the signal without any change in original signal shape is called as faithful amplification.

To achieve this, input circuit (i.e. base-emitter junction) of the transistor remains forward biased and output circuit (i.e. collector base junction) always remains reverse biased during all parts of the signal. It is called as transistor biasing.

Need for biasing:

The primary purpose of transistor biasing is to keep the base-emitter junction properly forward biased and collector-base junction properly reverse biased during the application of signal. It can be achieved with a bias battery or associating a circuit with a transistor. The circuit which provides transistor biasing is known as biasing circuit. The transistor biasing is very essential for the proper operation of transistor in linear region or active region.

1. Transistor Biasing - Operating region

Applying external voltage of correct polarity and magnitude to the two junction. of the transistor is called Biasing

Based on the external voltage polarity, the transistor will be operated in three different regions.

That is

(i) Active region

(ii) Cutoff region and

(iii) Saturation region