A common emitter amplifier has »small signal gain of 65. What will happen if the emitter bypass capacitor is removed

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. Cµ and Cπ 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.