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CBSE Class 12-science Answered

 Draw the circuit diagram of a common-emitter amplifier using an n-p-n transistor. What is the phase difference between the input signal and output voltage ? Draw the input and output wave forms of the signal. Write the expression for its voltage gain. State two reasons why a common emitter amplifier is preferred to a common base amplifier  
Asked by Topperlearning User | 01 Jul, 2014, 11:21: AM
answered-by-expert Expert Answer

The circuit of a common-emitter amplifier using an n-p-n transistor is shown below :

 

In a common emitter amplifier circuit, the input signal voltage and output collector voltage are in opposite phase. i.e 180° out of phase. Thus the phase difference between the input signal and output voltage is 180°.

The input and output wave forms are shown in fig.

where β is the current gain , RL the load resistance and Ri the input resistance.

Reasons for using a common emitter amplifier over common base amplifier:

(i) Voltage gain is quite high without any phase change of signal voltage.

(ii) Voltage gain is uniform over a wide frequency range or power gain is high .

 

Answered by | 01 Jul, 2014, 01:21: PM

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