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Common Emitter Transistor Amplifier

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Common Emitter Transistor

The common emitter transistor amplifier is shown in the figure A. The input signal is applied between base and emitter whereas the output is taken from collector and emitter. The output voltage equation V_CE is given by
V_CE = V_CC – i_cR_C

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As the input voltage increases in the positive half cycle, the base current increases.
As I_C = βI_B, the collector current also increases due to base current increases.
As the collector current increases, the collector to emitter voltage decreases because supply voltage VCC remains constant.

V_CE = V_CC – i_cR_C

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As the signal voltage increases in the positive direction, the output voltage increases in the negative direction. It means that the output signal is 180 degree phase difference with input signal.

Mathematical

V_CE = V_CC – i_cR_C
Differential above equation dV_CE = 0 – di_cR_C
dV_CE = – di_cR_C

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The negative sign indicates that the output voltage is 180 degree out of phase with respect to input voltage.

Phase Reversal

There is 180 degree phase reversal in the common emitter between input signal and output signal is known as phase reversal.
The input positive signal increases in the positive direction, the output signal increases in the negative direction and vice versa in the common emitter transistor amplifier connection.

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Therefore we can say that there is 180 degree phase difference between input signal and output signal.

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Thank You

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