THEORY EXAMINATION (SEM–IV) 2016-17 ELECTRONIC CIRCUITS

Subject: Electronic Circuits (EC401MTU)

Exam Type: Theory
Semester: IV (4th Semester)
Session: 2016–17
Time: 3 Hours
Maximum Marks: 100

Section A – Short Answer Questions (10 × 2 = 20 Marks)

This section evaluates the student's understanding of basic electronic circuit concepts, op-amps, transistors, and oscillators.

Topics Covered:

Calculation of maximum op-amp gain given slew rate and input signal.

Integrator circuit – circuit diagram and output expression.

Definitions of slew rate and CMRR (Common Mode Rejection Ratio) in op-amps.

Hybrid-π model and T-model of an NPN transistor.

Explanation of Barkhausen criterion for sustained oscillations.

Operating conditions for NMOS and PMOS in triode and saturation regions.

Calculation of new gain and bandwidth of an amplifier with negative feedback.

Circuit, frequency formula, and conditions for oscillation in a Colpitts oscillator.

Principle of operation of a crystal oscillator.

Identification and explanation of internal capacitances in a BJT.

Section B – Descriptive / Analytical Questions (5 × 10 = 50 Marks)

This section focuses on derivations, design analysis, and circuit behavior of amplifiers and oscillators.

Key Questions Include:

Inverting Amplifier: Derive expression for closed-loop gain assuming finite open-loop gain.

Series–Series Feedback Amplifier: Derive formulas for gain, input, and output resistance.

RC Phase Shift Oscillator (Op-Amp Based): Derive expression for frequency and condition of oscillation.

(i) Explain Hartley Oscillator with circuit and working.
(ii) Differentiate between DMOSFET and EMOSFET construction and characteristics.

DC Biasing of NPN Transistor: Derive Q-point and stability factor expressions.

MOS Differential Pair: Perform small signal analysis to find differential and common-mode gain.

(i) For an enhancement-type NMOS transistor (Vt = 0.7V, Vg = 1.5V):
Determine region of operation for VD=0.5V,0.9V,3VV_D = 0.5V, 0.9V, 3VVD​=0.5V,0.9V,3V.
(ii) Explain construction and working of an N-type enhancement MOSFET.

(i) Draw input and output characteristics of a common-emitter amplifier.
(ii) State ideal op-amp properties (infinite gain, infinite input resistance, zero output resistance, etc.).

Section C – Long Analytical Questions (2 × 15 = 30 Marks)

This section involves detailed analysis and derivations on amplifiers, op-amp limitations, and feedback networks.

Questions Include:

Small-Signal Analysis of Common Emitter Amplifier:

Derive expressions for:                           Input resistance

Voltage gain (base to collector)             Overall voltage gain (source to load)

Open-circuit voltage gain                      Output resistance

Finite Loop Gain and Bandwidth Effects:

Discuss how non-ideal op-amp parameters affect performance.

Define input offset voltage and input offset current.

Feedback Topologies:

Explain all four (Voltage–Series, Voltage–Shunt, Current–Series, Current–Shunt) with block diagrams.

Explain the working of an LC Tank Circuit used in oscillators.

Major Topics Covered

Operational Amplifiers (parameters, limitations, and applications)

Feedback amplifiers (types, advantages, gain derivations)

Transistor models (Hybrid-π, T-model) and biasing analysis

Small-signal analysis of amplifiers

MOSFET and BJT operation

Oscillators (RC, LC, Colpitts, Hartley, Crystal)

Frequency response and stability analysis

Purpose of the Paper

This paper evaluates both theoretical understanding and analytical capability in designing and analyzing analog electronic circuits.
It integrates semiconductor device behavior with practical amplifier and oscillator design, providing a foundation for advanced subjects like analog communication and integrated circuit design.