A small-signal voltage amplifier in a common emitter configuration was working satisfactorily. Suddenly its emitter-bypass capacitor (CE) got disconnected Its:

1. Voltage gain will decrease

2. Voltage gain will increase

3. Bandwidth will decrease

4. Bandwidth will increase

Concept:

When an emitter bypass capacitor present then while performing AC analysis the effect of emitter resistance got nullify because in AC analysis the capacitor behaves as a short circuit.

EFFECT of removing emitter-bypass capacitor:

• Voltage gain reduces
• Input resistance improves
• Current gain improves
• Bandwidth increases (since gain bandwidth product should be constant).
• Common-mode gain decreases
• CMRR (common-mode rejection ratio) increases.

Important Points

• Effect of a bypass capacitor, coupling capacitor only present in the low-frequency region
• Effect of the internal capacitor of transistor i.e. C_µ and C_π present at a higher frequency.
• During the mid-frequency region no effect of capacitor present.

REMEMBER:

For differential gain, there is no effect of bypass capacitor so therefore CMRR increases only because of a decrease in common-mode gain.