Common Emitter Transistor Amplifier

 

• 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

• 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 V_CC remains constant.

       V_CE = V_CC – i_cR_C

• 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 Formula

    V_CE = V_CC – i_cR_C

Differential above equation

    dV_CE = 0 – di_cR_C

    dV_CE = – di_cR_C

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

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