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GATE ECE Gateece Devices — practice questions

Explore 5 free Gateece Devices questions in GATE ECE Electronics. Open each question or exercise to read its content, reference answers and available explanation.

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Gateece Devices questions and exercises with answers

Showing questions 1–5 of 5.

In a p-n junction at equilibrium (no applied bias), the net current across the junction is which?Read the answer and worked solution →The transconductance gm of a BJT in active region with collector current IC and thermal voltage VT is which?Read the answer and worked solution →An NMOS transistor in saturation operates when which condition holds (V_DS, V_GS, V_TN)?Read the answer and worked solution →Channel-length modulation in a MOSFET in saturation introduces which effect into the I_D equation?Read the answer and worked solution →The Einstein relation for diffusion and mobility in semiconductors at temperature T is which?Read the answer and worked solution →

Worked practice questions

In a p-n junction at equilibrium (no applied bias), the net current across the junction is which?

  1. Zero (drift exactly balances diffusion)
  2. Equal to the saturation current Is
  3. Equal to V_T / r_s
  4. Infinite due to depletion field
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Correct answer: A. Zero (drift exactly balances diffusion)

At equilibrium: diffusion current (driven by gradient) exactly cancels drift current (driven by built-in field) for both electrons and holes. Net = 0.

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The transconductance gm of a BJT in active region with collector current IC and thermal voltage VT is which?

  1. gm = IC / VT
  2. gm = VT / IC always
  3. gm = IB / β only
  4. gm = VBE / VT only
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Correct answer: A. gm = IC / VT

**Small-signal BJT:** gm = ∂IC/∂VBE = IC/VT. At IC=1 mA, gm ≈ 40 mA/V. Key parameter for small-signal voltage gain in CE amp.

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An NMOS transistor in saturation operates when which condition holds (V_DS, V_GS, V_TN)?

  1. V_GS = V_TN exactly
  2. V_GS < V_TN only at any V_DS
  3. V_DS = 0 V always
  4. V_GS > V_TN and V_DS ≥ V_GS - V_TN
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Correct answer: D. V_GS > V_TN and V_DS ≥ V_GS - V_TN

**NMOS regions:** cutoff V_GS<V_TN triode V_GS>V_TN and V_DS<V_GS-V_TN saturation V_GS>V_TN and V_DS≥V_GS-V_TN. **Saturation:** I_D ∝ (V_GS-V_TN)².

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