17EC34
Visvesvaraya Technological University, Belagavi
MODEL QUESTION PAPER
3rd Semester, B.E (CBCS 2017-18 Scheme) EC/TC
Course: 17EC34- Digital Electronics, Set no. 1
Time: 3 Hours Max. Marks: 100
Note: (i) Answer Five full questions selecting any one full question from each Module.
(ii) Question on a topic of a Module may appear in either its 1st or/and 2nd question.
Module-1
1 a. Design a combinational logic circuit which takes two, 2-bit binary numbers as its input and
generates an output equal to 1, when the sum of the two number is odd.(06 Marks)
b. Convert the given boolean function into
i) f(a,b,c) = (a+b)(b+c) minterm canonical form
ii) f(a,b,c) = a+ac(b+c) maxterm canonical form (06 Marks)
c. Find all the prime implicants and essential prime implicants for the given function using k-
mapmethd. f(a,b,c,d) = Σm(0,3,6,7,8,9,10) + dc(2,5,11,12,15) (08 Marks)
OR
2 a. Define the following terms:
Minterm, Maxterm, CSOP, CPOS, POS. (05 Marks)
b. Simplify the given function using K-map method.
f(a,b,c,d,e) = Σm(3,7,11,12,13,14,15,16,18) + dc((24,25,26,27,28,29,30,31) (05 Marks)
c. Find the prime implicants and essential prime implicants using Quine-McCusky method and
verify the result using k-map.
F(a,b,c,d) = Σm(7,9,12,13,14,15) + dc(4,11) (10 Marks)
Module-2
3 a. What is magnitude comparator? Design a two bit digital comparator by writing TT,
relevant expression and logic diagram. (10 Marks)
b. Implement the following functions using 3:8 decoder(IC-74138)
i) f1(a,b,c,d) = πM(2,4,5,7,9,10,13,14)
ii) f2(a,b,c,d) = Σm(1,3,5,8,12,14,15)(10 Marks)
OR
4 a. Explain Carry look ahead adder with neat diagram and relevant expressions. And also
briefly explain how it is better than parallel adder.(10 Marks)
b. Implement f(a,b,c,d) = Σm(0,1,5,6,10,12,14,15) using
i) 8:1 MUX with a,b,c as select lines.
ii) 4:1 MUX with a, b as select lines. (10 Marks)
Module-3
5 a. What is flip-flop. Discuss working principle of SR flip-flop with its TT. Also highlight role
of SR latch in switch debouncer circuit. (10 Marks)
b. What is significance of edge triggering? Explain working of negative edge triggered D flip-
flop with their functional table and waveforms.(10 Marks)
1 0f 2
OR
6 a. Explain the working of Master-Slave JK flip-flop with functional table and timing diagram.
Show how race around condition is overcome. (12 Marks)
b. Obtain characteristic equation for the following flip-flops.
i) JK f/f ii) SR f/f (08 Marks)
Module-4
7 a. Explain Universal Shift Register with the help of logic diagram, mode control table and
symbol.(10 Marks)
b. Explain the working of 4-bit Johnson counter using positive edge triggered D flip-flop, also
draw the timing diagram. What is the modulus of this counter? (10 Marks)
OR
8 a. Design a Synchronous Mod-6 counter using JK flip-flop. (10 Marks)
b. Explain the working of 4-bit binary ripple up counter using negative edge triggered flip-
flop. Also draw the timing diagram. (10 Marks)
Module-5
9 a. Explain Mealy and Moore models of clocked synchronous sequential circuits with
necessary block diagrams. (10 Marks)
b. Design a cyclic Mod-8 synchronous binary counter using JK flip-flop. Give state diagram,
transition table and excitation table. (10 Marks)
OR
10 a. Construct mealy state diagram that will detect input sequence 10110, when input pattern
is detected, z is asserted high. Give state diagram for each state. (10 Marks)
b. Analyze the following sequential circuit shown in Fig Q10(b), and obtain
i) Flip-flop input and output equation ii) Transition equation
iii) Transition table iv) State table v) Draw the state diagram. (10 Marks)
Fig Q10(b)
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