Question

In a common emitter amplifier circuit using n-p-n transistor, the phase difference between the input and output voltages will be

• A. \(180^{\circ }\)
• B. \(135^{\circ }\)
• C. \(90^{\circ }\)
• D. \(45^{\circ }\)

Hint:

In a common emitter amplifier, a rise in input voltage lowers the collector voltage, so the output is inverted.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
In a common emitter amplifier the output is taken from the collector, where \(V_C=V_{CC}-I_CR_C\).

Step 2: What happens to the signal
When the input voltage rises, the base current and the collector current rise. The drop \(I_CR_C\) increases, so the collector voltage falls.

Step 3: Result
The output goes down when the input goes up, so the signal is inverted. This is a phase difference of \(180^{\circ}\).

Final Answer:
The input and output voltages differ in phase by 180 degrees, which is option (A). \[ \boxed{\text{(A) }180^{\circ}} \]