EX-403 Digital Electronics & Logic Design (DELD) - Dec 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aState and Prove Demorgan's theorem. Convert $(A5D8)_{16}$ into BCD number.
   How to answer

   • State both De Morgan theorems with Boolean expressions
   • Prove using truth table or algebraic laws
   • Convert (A5D8)16 to binary then to decimal
   • Convert decimal to BCD code
2. 7 Marks
   bSimplify the logic function using K-map: $Y=\Sigma m (0, 2, 3, 4, 6, 7, 9, 11, 16, 18, 19, 20, 22, 23, 25, 27).$
   How to answer

   • Plot 5-variable K-map with given minterms
   • Form largest possible groups of 1s
   • Write prime implicants for each group
   • Obtain minimized SOP expression for Y
3. 7 Marks
   aImplement a full adder using NAND gates.
   How to answer

   • Write truth table and expressions for Sum and Carry of full adder
   • Express Sum and Carry in NAND-only form
   • Draw NAND-gate implementation diagram
   • Explain operation
4. 7 Marks
   bImplement the function $F=\Sigma m(0,1,3,4,7,8,9,11,14,15)$ using 8:1 MUX.
   How to answer

   • Determine select lines and data inputs for 8:1 MUX for 4-variable function
   • Derive implementation table relating MSB variable to MUX inputs
   • Assign 0,1,D,D' to MUX data inputs
   • Show final circuit connection
5. 7 Marks
   aExplain positive edge triggered D-flip-flop with the help of circuit diagram and waveforms.
   How to answer

   • Show circuit diagram of positive edge triggered D flip-flop
   • Explain master-slave or edge-detector operation
   • Show waveforms for CLK, D and Q
   • State characteristic table/equation Q+=D on rising edge
6. 7 Marks
   bDesign a sequential circuit with two Flip Flops, A & B and one input $x$. When $x=0$, the State of the circuit remains the same when $x=1$ the circuit passes through the state transitions from 00 to 01 to 11 to 10 back to 00 & repeat.
   How to answer

   • Draw state diagram for 00->01->11->10->00 when x=1 and self-loop when x=0
   • Select flip-flop type and derive excitation/state table
   • Simplify flip-flop input equations using K-map
   • Draw final sequential circuit diagram
7. 7 Marks
   aDesign and explain the working of a 4 bit synchronous binary counter and draw its timing diagram.
   How to answer

   • Show 4 JK/D flip-flops with common clock and combinational gating
   • Derive counter input equations for binary up-count
   • Explain synchronous counting operation
   • Sketch timing diagram for Q0-Q3 and clock
8. 7 Marks
   bUsing D flip flops design a synchronous counter which counts in the sequence 000, 001, 010, 011, 100, 101, 110, 111, 000.
   How to answer

   • List present-state to next-state table for 000 to 111 sequence
   • Determine D inputs as D=next state using D excitation
   • Simplify D equations
   • Draw 3 D flip-flop synchronous counter circuit
9. 7 Marks
   aExplain memory decoding. How long will it take to erase UV erasable EPROM completely?
   How to answer

   • Define memory decoding and address decoding concept
   • Explain full/partial decoding with decoder example
   • State UV EPROM erasing method and typical time
10. 7 Marks
    bDescribe the principle of operation of a successive approximation ADC.
    How to answer

    • Show block diagram with DAC, comparator, SAR, control logic
    • Explain binary search successive approximation steps
    • Give conversion example over n clock cycles
    • Mention end-of-conversion operation
11. 7 Marks
    aA line printer is capable of printing 132 characters in a single line and each character is represented by ASCII code. How many bits are required to print each line?
    How to answer

    • Recall ASCII code is 7-bit code per character
    • Multiply 132 characters by bits per character
    • Compute total bits per line
    • State result
12. 7 Marks
    bHow is carry look ahead adder faster than a ripple carry adder? Explain in detail with neat sketches.
    How to answer

    • Explain ripple carry delay propagation problem
    • Derive generate-propagate carry look-ahead expressions
    • Show CLA logic diagram with neat sketches
    • Compare delay: O(n) vs O(log n)/2-level
13. 7 Marks
    aDiscuss the working of a 4 bit Johnson counter with neat block diagram.
    How to answer

    • Show 4 D flip-flops in shift register with inverted feedback
    • List 8 distinct states of Johnson sequence
    • Explain 2n states and decoding
    • Give block diagram and waveforms
14. 7 Marks
    bImplement the functions using PAL $W=\Sigma m(2,12,13)$, $X=\Sigma m(7,8,9,10,11,12,13,14,15)$, $Y=\Sigma m(0,2,3,4,5,6,7,8,10,11,15)$, $Z=\Sigma m(1,2,8,12,13)$.
    How to answer

    • Simplify each function W,X,Y,Z to minimal SOP
    • Map product terms to PAL AND-OR structure
    • Show PAL fuse/programming diagram
    • Explain shared product terms if any
15. 14 Marks
    Write Short notes on any **two** the following:

    1. a)Parity generator & checkers
    2. b)Priority encoder
    3. c)Master slave flip-flop
    4. d)R/2R D to A converter
    How to answer

    • Select any two topics from list
    • Give definition/principle with block/circuit diagram
    • Explain working with key expressions
    • Mention applications