Question

In a common base amplifier, the phase difference between the input signal voltage and the output voltage (across collector and base) is
(A) $0$
(B) $\dfrac{\pi }{4}$
(C) $\dfrac{\pi }{2}$
(D) $\pi$

Answer 1

We know that in a common base amplifier the input phase is put equal to the output phase. Then, we will use the formula for phase difference between the input signal voltage and the output voltage (across collector and base). We obtain the phase difference value in the form of difference of output and input voltage.

Complete step by step answer:
We write the formula to find the phase difference between the input signal voltage and the output voltage (across collector and base) in a common base amplifier.
${\rm{Phase difference}}\;{\rm{ = }}\;{\rm{Output voltage}}\; - \;{\rm{Input voltage}}$
Now, we write this formula of phase difference in symbolic form.
$\phi = {V_o} - {V_i}$
As we know that in a common base amplifier the input signal is amplified but remains in phase with the output signal. From this statement, we get to know that the difference of output voltage and input voltage will be equal to zero.
Now, we substitute the difference of output and input voltage that is zero in phase difference formula,
$\phi = 0$
Therefore, the phase difference of the input signal voltage and output voltage is zero

So, the correct answer is “Option A”.

Note:
We should know that a common base amplifier is a type of bipolar junction transistor. The base terminal of this transistor is common to both the input and the output signal. In this amplifier, the output impedance is higher while the input impedance is lower. In normal cases the signal input is applied to the base while in case of common base the connection is grounded. This is the reason we called it as grounded base circuit design.