(SEM III) THEORY EXAMINATION 2021-22 DIGITAL ELECTRONICS

This question paper belongs to B.Tech (Semester III) for the subject Digital Electronics (KOE039), carrying 100 marks with a duration of 3 hours. The exam tests students on the entire spectrum of digital logic design—from number systems and logic gates to sequential circuits, counters, hazards, and programmable logic devices. The structure of the paper ensures evaluation of basic concepts, circuit design skills, analytical understanding, and problem-solving ability.

The paper is divided into three major sections: Section A, Section B, and Section C, each progressively increasing in depth and complexity.

SECTION A – Short Conceptual Questions (20 Marks)

Section A contains 10 short questions (2 marks each). These questions cover fundamental concepts including:

Representation of integers and fractional numbers in binary

BCD addition mechanism

Implementing larger multiplexers using smaller ones

Understanding demultiplexers and decoders

Positive vs negative edge triggering

Delay calculations in ripple counters

Critical and non-critical races in asynchronous circuits

Importance of state assignment in sequential circuit design

Why ECL is faster than TTL

Comparing SRAM and DRAM technologies

This section tests definitions, basic reasoning, and quick conceptual clarity.
 

SECTION B – Analytical & Design-Based Questions (30 Marks)

Students must attempt any three out of five questions (10 marks each). These involve:

Designing 3-input gates using only 2-input gates

Implementing a full subtractor using NAND gates

Realizing Boolean functions using 4:1 multiplexers

Designing and explaining a bi-directional shift register

Designing state diagrams and state tables for circuits with asynchronous inputs

Interfacing TTL with CMOS and understanding logic family parameters

This section evaluates the student’s ability to design circuits, apply Boolean algebra, understand hardware configurations, and interpret sequential behavior.

SECTION C – Long, Design-Oriented & Problem-Solving Questions (50 Marks Total)

Section C contains five main long questions, each with alternate internal choices. Students must attempt one part from each question.

Q3 – Boolean Minimization (10 Marks)

Tabular method (Quine–McCluskey) minimization

K-map reduction and NAND-based implementation

Designing a BCD-to-Decimal decoder

Q4 – Arithmetic & Comparator Circuits (10 Marks)

Designing a complete BCD adder using binary adders + correction logic

Explaining and drawing a 4-bit magnitude comparator

Q5 – Sequential Circuit Design (10 Marks)

Based on the figure on page 2:

Deriving state table and state diagram for a sequential circuit using a full adder + D flip-flop

OR designing a 3-bit Up/Down counter using JK flip-flops

Q6 – Hazards & Asynchronous Transition Tables (10 Marks)

Deriving transition tables for asynchronous sequential circuits

Identifying static and dynamic hazards

Showing static-0 hazard in a POS logic diagram and removing it by adding redundancy

Q7 – Code Conversion & Logic Family (10 Marks)

Designing BCD to Excess-3 code converter using PLA

Drawing the internal diagram of a TTL NAND gate and explaining its operation

This section checks higher-order thinking, including complete understanding of:

Minimization methods

Hardware design logic

Counter design

Hazard identification

PLA implementation

Logic family structures

OVERALL SUMMARY

The Digital Electronics (KOE039) question paper comprehensively tests:

Number systems & arithmetic

Combinational circuits (MUX, DEMUX, decoders, adders, comparators)

Boolean algebra & minimization

Flip-flops & sequential circuits

Counters & registers

Asynchronous circuits & hazards

Logic families (TTL, CMOS, ECL)

Code converters, PLAs

It blends theory, circuit design, numerical calculations, and diagram-based questions to ensure students are well-prepared for practical digital system design.