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GATE 2014 EE (EE1) – Question 33

Analog and Digital Electronics · Amplifiers: biasing, equivalent circuit and frequency response · 1 mark · Multiple choice

Find the magnitude of mid-band voltage gain of the circuit shown, assuming transistor h_fe = 100.

Diagram for GATE 2014 EE (EE1) question 33
  1. 1
  2. 10
  3. 20
  4. 100

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Show answer and explanation

Correct answer: (D) 100

Explanation

At midband the coupling and emitter-bypass capacitors are treated as shorts. Under the additional intended approximation that transistor input resistance hieis negligible relative to the series10kΩ, ib≈vi/10kΩ. Then vo≈−hfeib×10kΩ, giving **|vo/vi|≈100,D**. With finite hie,the gain is100×10k/(10k+hie), and a forward-active bias point is required but not shown.