Question

In a common emitter amplifier circuit using an NPN transistor, the phase difference between the input and the output voltages will be:

• A. $45°$
• B. $90°$
• C. $135°$
• D. $180°$

Answer 1

The correct option is D

$180°$

CE amplifier:

1. A Common emitter transistor can be an NPN transistor or PNP transistor with an emitter grounded.
2. The input will be between the base and the emitter and the output is taken from the collector.

In the case of an NPN transistor, the formula for the output voltage is given by $V_{out}=-\frac{R_C}{R_E}{V}_{in}$

Where $R_C=$Collector resistance, $R_E=$Emitter resistance, $V_{in}=$Input voltage,

⇒ Since the sign is negative, the output voltage is completely out of phase with the input voltage

⇒ Therefore, the phase difference is $180°$

Hence, the correct answer is option D.