THEORY EXAMINATION (SEM–IV) 2016-17 ANALOG AND DIGITAL ELECTRONICS

The B.Tech Analog and Digital Electronics (NEC409A) question paper from the 2016–17 IV Semester Theory Examination is a 100-mark, 3-hour extensive assessment covering semiconductor devices, feedback amplifiers, oscillators, operational amplifiers, digital logic circuits, sequential circuits, and regulated power supplies. The paper is divided into three structured sections, each designed to test conceptual knowledge, analytical reasoning, circuit design skills, and numerical problem-solving abilities.

SECTION A – Short Answer Technical Questions (20 Marks)

This section contains 10 brief questions, each carrying 2 marks, assessing the student’s grasp of fundamental concepts in analog and digital electronics.

Key topics include:

Why Silicon and Germanium are not used in LEDs

Definition and V-I characteristics of a Tunnel diode, highlighting the negative resistance region

Advantages of negative feedback in amplifiers

Need for frequency response analysis in amplifiers and circuits

Barkhausen criteria for sustained oscillations

Two piezoelectric materials used in crystal oscillators

State transition diagram of an R–S flip-flop

Realizing a 16×1 multiplexer using two 8×1 multiplexers

Why photodiodes operate only in reverse bias

Applications of a multiplexer

These short questions test quick recall and conceptual clarity across analog & digital domains.

SECTION B – Descriptive & Numerical Questions (Any 5 × 10 = 50 Marks)

This section contains medium-length questions requiring theoretical explanation, diagrammatic analysis, and circuit-based numerical calculations.

Key areas include:

1. Photodiode Construction & Working

Semiconductor structure

Reverse-bias operation

Applications in sensing and communication

2. Feedback Amplifier Properties

Details of series–shunt and shunt–shunt feedback topologies with properties such as input resistance, output resistance, and gain stability.

3. Negative Feedback Effects

Students list five key characteristics modified by negative feedback, such as reduced distortion, improved bandwidth, increased stability, etc.

4. Colpitts Oscillator

Derivation of oscillation frequency when inductor includes series resistance

5. Numerical Problem on Colpitts Oscillator

Using given values (L = 100 mH, C1 = 10 pF, C2 = 100 pF, r = 50Ω, R0 = 2.2Ω), calculate:

Frequency of oscillation

Minimum gain required

6. Wien Bridge Oscillator

Explanation and derivation of the frequency of oscillation.

7. Digital Logic Fundamentals

(i) Difference between encoder and decoder
(ii) Excitation table of JK Flip-Flop

8. Astable Multivibrator Using Op-Amp

Operation, waveform description, and expression for cutoff frequency.

9. Transistor as a Switch

Using output characteristic curves to explain switching action.

SECTION C – Long, Analytical Questions (Any 2 × 15 = 30 Marks)

This section contains in-depth circuit-level questions requiring extensive explanations, diagrams, and sometimes derivations.

Q3 – Voltage Regulators

Explaining:

What voltage regulators are

Operation of Shunt voltage regulators (constant voltage control using shunt element)

Operation of Series op-amp based voltage regulators

Q4 – Schottky Diode Construction & Characteristics

Students differentiate between:

Schottky barrier diode vs conventional p–n junction diode
Then explain:

Construction

Working principle

V–I characteristics (fast switching, low forward voltage drop)

Q5 – Short Notes on Feedback Topologies

Series–Series topology

Shunt–Series topology

Detailed explanation of input/output resistance variations, voltage/current mixing arrangements, and their application areas.