IT-305 Digital Circuits and Systems - 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
   aConvert the following numbers as directed (any two):

   1. i)$(9A)_{16}$ to Binary
   2. ii)$(745)_{8}$ to Decimal
   3. iii)$(1101011)_{2}$ to Hexadecimal
   How to answer

   • State base conversion method (hex to binary: 4 bits per hex digit, octal to decimal, binary to hex grouping)
   • Convert any two of the three numbers with steps
   • Write final converted values with base subscript
   • Verify by reverse conversion
2. 7 Marks
   bExplain BCD, Excess-3 and Gray codes. Write their applications.
   How to answer

   • Define BCD, Excess-3 and Gray codes with bit structure
   • Give example encoding for decimal digits
   • List properties (weighted/unweighted, self-complementing, cyclic)
   • State applications (displays, arithmetic, error minimization, shaft encoders)
3. 7 Marks
   aExplain Full Adder with truth tables and logic diagrams. Design a full adder using two half adders.
   How to answer

   • Define full adder with block diagram and truth table for A, B, Cin
   • Derive Sum and Cout expressions
   • Show logic diagram using gates
   • Show construction using two half adders with OR gate
4. 7 Marks
   bSimplify the following Boolean function using K-map and implement it using NAND gates: $F(A, B, C) = \Sigma(0, 2, 3, 5, 7)$
   How to answer

   • Plot 3-variable K-map for $\Sigma(0,2,3,5,7)$
   • Group minterms and obtain simplified SOP expression
   • Show conversion to NAND-only form using De Morgan
   • Draw NAND-gate implementation diagram
5. 7 Marks
   aDesign a 4-to-16 decoder using 3-to-8 decoders and explain its operation.
   How to answer

   • State principle of expanding 3-to-8 to 4-to-16 using MSB as enable
   • Show block diagram with two 3-to-8 decoders and enable logic
   • Explain addressing for 16 outputs
   • Mention enable / select operation
6. 7 Marks
   bExplain Shift Registers and their types with applications.
   How to answer

   • Define shift register and clocked shifting
   • Describe types: SISO, SIPO, PISO, PIPO with diagrams
   • Explain shifting operation
   • List applications (data storage, transfer, counters)
7. 7 Marks
   aExplain Counters. Describe Johnson counter and Ring counter with timing diagrams.
   How to answer

   • Define counters and classification
   • Explain Johnson (twisted ring) counter operation with states
   • Explain Ring counter operation with states
   • Draw timing diagrams showing sequence and modulus
8. 7 Marks
   bCompare NMOS, PMOS and CMOS logic in detail.
   How to answer

   • Describe NMOS, PMOS device structure and operation
   • Describe CMOS complementary structure
   • Compare on power, speed, noise margin, fan-out, area
   • Conclude with summary table
9. 7 Marks
   aDesign a 2 input TTL NAND gate and explain its working.
   How to answer

   • Draw 2-input TTL NAND circuit with multi-emitter transistor, phase splitter and totem-pole output
   • Explain operation for input combinations 00,01,10,11
   • Give truth table and output levels
   • Mention current sourcing/sinking
10. 7 Marks
    bWrite a short note on 7-segment LED display.
    How to answer

    • Describe 7-segment structure with segments a-g and common anode/cathode
    • Show segment patterns for digits 0-9
    • Explain LED drive and current limiting
    • State applications in displays
11. 7 Marks
    aExplain Multivibrators. Describe Monostable multivibrators with diagrams.
    How to answer

    • Define multivibrator and its three types
    • Explain monostable operation with trigger and quasi-stable state
    • Draw circuit/waveforms showing pulse width timing
    • Give formula for pulse duration and applications
12. 7 Marks
    bExplain Analog to Digital Converters. Describe any one ADC in detail.
    How to answer

    • Define ADC, resolution, sampling and quantization
    • Classify ADC types
    • Describe any one ADC (e.g., successive approximation / flash / dual-slope) with block diagram
    • Explain conversion steps and applications
13. 7 Marks
    aWhat does edge triggered and level triggered mean?. Differentiate between Edge triggered and Level triggered flip- flops.
    How to answer

    • Define edge triggering vs level triggering with waveforms
    • Explain positive/negative edge and high/low level response
    • Compare on clock response, transparency, timing
    • Give examples of flip-flops using each
14. 7 Marks
    bDraw AND, OR and NOT gates using NOR gate only.
    How to answer

    • Recall NOR as universal gate with basic NOT/OR/AND relations
    • Show NOT using single NOR with inputs tied
    • Show OR using NOR followed by NOT
    • Show AND using inverted inputs to NOR
15. 14 Marks
    Write a short note on (Any Four)

    1. a)Draw 8*1 MUX using 2x1 Mux
    2. b)Schmitt trigger circuit
    3. c)Gray to binary code conversion
    How to answer

    • For chosen four topics give definition/principle
    • Draw relevant circuit/logic diagram and conversion steps
    • Give truth table / equations where applicable
    • Mention applications