Question

In a common emitter amplifier the input signal is applied across
A) Anywhere
B) Emitter-collector
C) Collector –base
D) Base- emitter.

Answer 1

Hint- Here, the emitter of the transistor is common to both input and output circuits and hence the name common emitter connection. The emitter is heavily doped and moderate size, base is lightly doped and very thin and collector is moderately doped and large in size.

Complete step by step answer:
In a transistor there are three terminals namely emitter, base and collector. To construct a transistor, we require four terminals; two for the input and two for the output. This difficulty is solved by making one terminal of the transistor common to both input and output terminals. The input is fed between this common terminal and one of the two terminals. The output is produced between the common terminal and the remaining terminal. Accordingly; a transistor can be connected in a circuit in the following three configurations.
-Common base (CB) configuration.
-Common emitter (CE) configuration.
-Common collector (CC) configuration.
The CE configuration is the most widely used configuration and n-p-n transistors are the most commonly used transistors.
$180$
Common emitter transistors are used most widely, because a common emitter transistor amplifier provides high current gain, high voltage gain and high power gain. This type of transistor gives for a small change in input there is small change in output. The output voltage is degree out of phase with the input voltage. In common emitter configuration, input is applied between base and emitter and output is taken from the collector and emitter.
In CE amplifier. input signal to be amplified is applied between the base-emitter circuit and the output amplified signal is taken across the emitter-collector circuit. The emitter-base junction is forward biased using a DC voltage source VBB and the collector-base junction is reversed biased using the DC voltage source ${V_{CC}}$.

$\therefore$ Correct option is (D).

Note:
-An input characteristic is a curve between base current and base emitter voltage at constant collector emitter voltage.
-An output characteristic is the curve between collector current and collector-emitter voltage at constant base current.
-An amplifier is a device that increases the amplitude of an AC signal. and this process is called amplification.