Effect of removing bypass capacitor: In a silicon transistor amplifier, the capacitors Cc and CE are assumed short at signal frequency. If the emitter bypass capacitor CE is disconnected, which statement is TRUE?

Introduction / Context:In small-signal transistor amplifiers, bypass capacitors are used to stabilize gain and control input resistance. Removing the emitter bypass capacitor alters feedback conditions, which directly impacts amplifier characteristics.

Given Data / Assumptions:

• Silicon transistor amplifier with emitter resistor RE.
• At signal frequencies, coupling capacitor Cc is short, but CE is disconnected (open).
• We ignore output resistance r0.

Concept / Approach:

With CE present, RE is bypassed, providing high gain and no AC feedback. Without CE, RE introduces negative feedback: this increases input resistance (since base sees β+1 times RE) and reduces AC voltage gain (due to degeneration).

Step-by-Step Solution:

Verification / Alternative check:

This effect is used deliberately in amplifier design to trade gain for linearity and input resistance stabilization.

Why Other Options Are Wrong:

• (b) Wrong: input resistance increases, not decreases.
• (c) Wrong: input resistance does not decrease.
• (d) Wrong: gain decreases, not increases.
• (e) Wrong: gain is not unchanged; emitter degeneration always reduces gain.

Common Pitfalls:

• Assuming bypass capacitor only affects DC bias; it strongly affects AC small-signal behavior.
• Mixing up input resistance trends when degeneration is added.

Final Answer:

The input resistance Ri increases and the magnitude of voltage gain Av decreases