What is amplification? With a circuit diagram, explain the working of npn transistor as an amplifier in CE configuration.

Explanation

The circuit of an n-p-n transistor as an ampliffer in CE-configuration is shown in the above figure. The EB-junction is forward biased with the batter `V _(B B) and CB`-junction is revers biased with the batter `V _(C C).` A suitable load resistor `R _(L)` is connected in the output circuit. The ac singnal to be amplified is applied betwen bae and emitter. Thge amplified output is take between collector and emitter.
The circuit of an n-p-n transistor an an amplifier in CE-configuration is shown in the above figure. The EB-juctin is forward biased witht the better `V _(B B) and CB-`junction is reverse biased with the battery `V _(C C).` A suitable load resistor `R _(L)` is connected in the output circuit. The ac signal to be amplified is applied between bae and emitter. The amplified output is taken between collector and emitter.
When the current `I _(C )` flows through the load resistor `R _(L),` the output voltage is given by.
`V _(0) = V _(C ) - I _(C)R _(L)`
During positive half cycle of input ac signal, the forward bias of EB-junction increases. Due to this the emitter current increases and hence the collector current also increases. According to the above equation, as the collector current increases output voltage V. decreases. Since the collector is connected to the positive terminal of the battery Vco the decrease in collector voltage means the collector becomes less positive (or negative with respect to the initial value). Thus during positive half cycle of input ac voltage, the output signal varies through a negative half cycle. During negative half cycle of input ac signal, the forward bias of EB-junction decreases. Due to this the emitter current decreases and hence the collector current also decreases. According to eqn (2), the collector voltage `V_(C C)` increases and the collector become more positive. This indicates that during the negative half cycle, the output signal varies through positive half cycle. Thus in Common emitter amplifier, the input voltage and output voltages are 180° out of phase as shown in the figure.