Question

In a common base transistor circuit, the current gain is $0.98$. The current gain of common emitter transistor circuit is
A) $0.2$
B) $98$
C) $20$
D) $49$

Answer 1

Hint: The typical base amplifier is designed in a very different way than the other electronic circuit architecture setups. In general, the signal input is applied to the base, but this connexion is grounded in the case of the common base and is occasionally referred to as the grounded base circuit design.

Complete step by step solution:
The common base amplifier for the three transistor amplifier configurations is the least widely used. The common emitter and collector configurations (emitter follower) are much more widely used since they usually have more useful features.

For both NPN and PNP circuits, the input is applied to the transmitter and the output is taken from the collector for the common base amplifier circuit. The base of both circuits is the common terminal. The foundation is centred on the signal, but the DC potential is above the ground for biasing purposes.

The common configuration of the base amplifier is not used as extension settings. However, it considers applications for amplifiers requiring low input impedance. One application is for preamplifiers of moving coil microphones-they have very low impedance levels.

In a common base transistor, current gain is given by,
$\beta = \dfrac{{\Delta {I_C}}} {{\Delta {I_B}}} = 0.98 $
Where, ${I_C} $ is the collector current and ${I_B} $ is the base current.

The current gain of the common emitter transistor,
$\alpha = \dfrac{{\Delta {I_C}}} {{\Delta {I_E}}} $
${I_E} $ Is the Emitter current
$\alpha = \dfrac{\beta} {{1 - \beta}} $
$\alpha = \dfrac{{0.98}}{{1 - 0.98}} = 49$
$\alpha = 49$

The correct option is (D).

Note: As a part of the grounding, the setup further enhances stability. The fact that it is grounded for RF signals reduces the level of unforeseen fake feedback on the circuit design with the electrode that is between the emitter and the collector. It should be remembered that there is always less than unity in the present gain of a typical base amplifier. The tensile gain however more than this is, but is based on the input and output resistance of the emitter-base crossover (and also its internal resistance). As a consequence, a standard-base amplifier will achieve a high voltage gain.