Transistor as an Amplifier

Transistor as an Amplifier

The transistor improves the strength of a weak and low signal and hence it also acts an amplifier. The transistor work as an amplifier circuit is shown in the figure below. As we already know that the transistor has three terminals namely emitter, base, and collector. As shown below it is common base configuration and emitter and base of the transistor are connected in forward biased and the collector base region is in reverse bias.

The input signal or low and weak signal is applied across the emitter-base and the output is obtained to the load resistor R_C which is connected in the collector circuit. The DC voltage that is V_EE is applied to the input circuit with the input signal to achieve the amplification. The DC voltage V_EE makes the emitter-base junction under the forward biased and is known as a bias voltage. When a low signal is applied to the input, a small variation in signal voltage causes a big variation in emitter current (for an example change of 0.1V in signal voltage causes a change of 1mA in the emitter current) because the input circuit has very low resistance. This change is almost equivalent in collector current because of the transmitter action and negligible base current. In this circuit, a load resistor R_C of high value is connected. When collector current flows through such a high resistance, it produces a large voltage drop across it and it amplifies a weak signal of input. Thus, a weak signal (0.1V) applied to the input circuit appears in the amplified form (10V) as an output in the collector circuit.