About this previous year paper
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.