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Question 20272
JEE Physics · Hard

Semiconductors: BJT Configurations Summary MCQ

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BJT Configurations SummaryHardQuestion 20272

Question

Which BJT configuration has the lowest input impedance?
  1. A
    Common Emitter (CE)
  2. B
    Common Collector (CC)
  3. C
    Common Base (CB)
    Correct
  4. D
    All are equal

Correct answer

Common Base (CB)

Explanation

CB configuration: input at emitter, output at collector. Input impedance ≈ r_e = V_T/I_E ≈ 26mV/I_E — very low (tens of ohms). CE has moderate Zin (~1 kΩ); CC (emitter follower) has high Zin (~β × R_E). Low Zin of CB makes it useful for matching to low-impedance sources (antennae, RF amplifiers).

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