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22-Elec-B5 Advanced Electronics: December 2019

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

  1. Question 1 MOS Differential Amplifier — Bias, Transconductance, Full Current Switching and Input Offset
  2. Question 2 Common-Source Amplifier — Mid-Band Gain and Design of the Coupling and Bypass Capacitors
  3. Question 3 Class B Output Stage — Output Power, Device Dissipation and Efficiency
  4. Question 4 Op-Amp with a Diode-Connected Transistor in the Feedback Path — A Logarithmic Amplifier
  5. Question 5 Common-Gate Amplifier inside a Voltage-Series Feedback Loop — Input and Output Resistance

Start with Question 1 →

Paper format. National Exams, December 2019 — 16-Elec-B5 Advanced Electronics. Three hours; CLOSED BOOK, an approved Casio or Sharp calculator permitted. Five questions, ALL to be answered, 20 marks each. Op-amps are ideal and the supplies are ±15 V unless a question states otherwise; in schematics ground and chassis are common. Where a question leaves an interpretation open, the paper's own Note 1 invites the candidate to state the assumption inside the answer — every such assumption below is flagged in a check callout.

Reference texts. A. S. Sedra and K. C. Smith, Microelectronic Circuits, 8th ed. — Ch. 7 (transistor amplifiers and biasing), Ch. 8 (differential and multistage amplifiers, offset voltage), Ch. 10 (frequency response, short-circuit time constants), Ch. 11 (output stages and power amplifiers), Ch. 12 (feedback topologies). B. Razavi, Fundamentals of Microelectronics, 2nd ed., Ch. 8 (operational amplifier as a black box, non-linear feedback elements) and Ch. 10 (differential amplifiers). P. Gray, P. Hurst, S. Lewis and R. Meyer, Analysis and Design of Analog Integrated Circuits, 5th ed., Ch. 3 (single-transistor amplifiers) and Ch. 8 (feedback).

Check — the paper's own MOSFET convention. The formula sheet printed with Question 1 defines the saturation current as $i_{DS}=\tfrac12 K\,(v_{GS}-V_{TH})^2$ with $K=K'(W/L)=\mu C_{ox}(W/L)$, and that convention is used throughout Questions 1 and 5. Question 2 is the one place where it does not close: with $K=1\ \text{mA/V}^2$ and $V_{GS}=2$ V the sheet would give $I_D=0.5$ mA, whereas the bias network of Question 2 fixes $I_D=1$ mA by three independent routes (the gate divider, $V_S/R_S$, and the stated $V_D$). The bias data therefore governs there, and the transconductance is taken as $g_m=2I_D/V_{ov}$, which is convention-free. Both readings are quoted in Question 2, Step 2.