Question

A n–p–n transistor is used as an amplifier in (a) common–base (b) common–emitter configuration. The voltage gain in two cases is A₁ and A₂ respectively. The phase difference between input and output in the two cases is δ₁ and δ₂ respectively which of the following is correct?

(1) δ₁ = δ₂ = -π; A₁ = A₂

(2) δ₁ = 0;δ₂ = -π; A₁ < A₂

(3) δ₁ = -π;δ₂ = 0; A₁ > A₂

(4) δ₁ = 0;δ₂ = +π; A₁ = A₂

Answer 1

(2) δ₁ = 0;δ₂ = -π; A₁ < A₂

The common base configuration in an amplifier, the output and input are in phase i.e. δ₁ = 0. However in common–emitter amplifier output is out of phase with input and output lags behind input i.e. δ₂ = -π. The voltage gain in common–emitter configuration is more than in common–base configuration i.e. A₁ > A₂ .