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.
