Which transistor configuration amplifier’s current gain is lowest?

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RRB ALP CBT 2 Electronic Mechanic Previous Paper: Held on 23 Jan 2019 Shift 1

Answer 1

The DC current gain of a common collector is given by the ratio of emitter current to the base current, i.e.

\(\gamma=\frac{I_E}{I_B}\)

The DC current gain for a common emitter configuration is defined as:

\(\beta=\frac{I_C}{I_B}\)

The DC current gain for a common base configuration is defined as:

\(\alpha=\frac{I_C}{I_E}\)

IE = Emitter Current

IB = Base Current

I_C = Collector Current

The comparison of the various configuration of Amplifiers is as shown:

Parameter	Common-Base	Common-Emitter	Common-Collector	CE (Darlington)
Input Current	IE	IB	IB	IB
Output Current	IC	IC	IE	IC
Current Gain	\({\alpha _{dc}} = \frac{{{I_C}}}{{{I_E}}}\)	\({\beta _{dc}} = \frac{{{I_C}}}{{{I_B}}}\)	\(\gamma = \frac{{{I_E}}}{{{I_B}}} = \left( {1 + {\beta _{dc}}} \right)\)	\({\beta _{dc}} = {\beta _1}{\beta _2}\)
Voltage Gain	Medium	Medium	Less Than 1	Medium

Hence the correct increasing order of their Current Gain is:

CB < CE < CC < Darlington pair