CBSE Class 12 · 2009 · SemiconductorsShort Answer

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Give a circuit diagram of a common emitter amplifier using an n-p-n transistor. Draw the input and output waveforms of the signal. Write the expression for its voltage gain.

Solution

Circuit: an n-p-n transistor with the base-emitter junction forward biased by a base resistor and the collector-emitter output reverse biased through a collector load

R_{C}

; the ac signal is applied to the base and output taken at the collector.
When the signal increases the forward bias,

I_{C}

rises and the collector voltage falls, so the output is

18 0^{\circ}

out of phase with the input.
Voltage gain:

A_{V} = \frac{V _{0}}{V _{i}} = β \frac{R _{C}}{R _{B}} .

A_{V} = β \frac{R _{C}}{R _{B}} (output 18 0^{\circ} out of phase).

CBSE Class 12 Board · 2009 · Subjective

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