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Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

Q1: To obtain the Boolean function Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)the inputs PQRS in the figure should be (2024)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) 1010
(b) 1110
(c) 0110
(d) 0001
Ans:
(b)

Q2: A counter is constructed with three D flip-flops. The input-output pairs are named (D0, Q0), (D1, Q1) and (D2, Q2), where the subscript 0 denotes the least significant bit. The output sequence is desired to be the Gray-code sequence  000, 001, 011, 010, 110, 111, 101 and 100, repeating periodically. Note that the bits are listed in the Q2 Q1 Q0 format. The combinational logic expression for D1 is (2021)
(a) Q2Q1Q0
(b) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(c) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (c)
Sol: Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q3: Consider the following circuit which uses a 2-to-1 multiplexer as shown in the figure below. The Boolean expression for output F in terms of A and B is (SET-1 (2016))
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) ABA ⊕ B
(b) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(c) A+BA + B
(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

Ans: (d)
Sol: In the given multiplexer,
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Select = B
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q4: A Boolean function f(A, B, C, D) = Π(1, 5, 12, 15) is to be implemented using an 8x1 multiplexer (A is MSB). The inputs ABC are connected to the select inputs S2S1S0 of the multiplexer respectively.  Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Which one of the following options gives the correct inputs to pins 0, 1, 2, 3, 4, 5, 6, 7 in order? (SET-2(2015))
(a) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(b) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(c) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (b)
Sol: Boolean function f(A, B, C, D) = Π(1, 5, 12, 15) is implemented with 8 x 1  MUX
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q5: In the 4 x 1 multiplexer, the output F is given by F = A ⊕ B. Find the required input ' I3 I2 I1 I0'.  (SET-1(2015))
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) 1010
(b) 0110
(c) 1000
(d) 1110
Ans: 
(b)
Sol: F = A ⊕ B
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)⇒ I= 0, I1 = 1, I2 = 1, i3 = 0
I3 I2 I1 I0 = 0110

Q6: A 3-bit gray counter is used to control the output of the multiplexer as shown in the figure. The initial state of the counter is 0002. The output is pulled high. The output of the circuit follows the sequence   (SET-3 (2014))
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) I01,1,I1,I3,1,1,I2I01, 1, I1, I3, 1, 1, I2 
(b) I0, 1, I1, 1, I2, 1, I3, 1
(c) 1, I0, 1, I1, I2, 1, I3, 1
(d) I0, I1, I2, I3, I0, I1, I2, I3 
Ans:
(a)
Sol: For Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
MUX is enabled and output is I0
For Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
MUX is disable and output is '1'
similarly, for
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q7: The output Y of a 2-bit comparator is logic 1 whenever the 2-bit input A is greater than the 2-bit input B. The number of combinations for which the output is logic 1, is (2012)
(a) 4
(b) 6
(c) 8
(d) 10
Ans:
(b)
Sol:
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q8: A 3-line to 8-line decoder, with active low outputs, is used to implement a 3-variable Boolean function as shown in the figurePrevious Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE) The simplified form of Boolean function F(A, B, C) implemented in 'Product of Sum' form will be (2008)
(a) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(b) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(c) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (a)
Sol: Let us consider active high input
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)F = Σ(1, 3, 5, 6) = ΠM(0, 2, 4, 7)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q9: A (4 × 1) MUX is used to implement a 3-input Boolean function as shown in figure. The Boolean function F(A,B,C) implemented is (2006)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE) (a) F(A, B, C) = Σ(1, 2, 4, 6)
(b) F(A, B, C) = Σ(1, 2, 6)
(c) F(A, B, C) = Σ(2, 4, 5, 6)
(d) F(A, B, C) = Σ(1, 5, 6)
Ans:
(a)
Sol: Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)= Σ(1, 2, 4, 6)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q10: Figure shows a 4 to 1 MUX to be used to implement the sum S of a 1-bit full adder with input bits P and Q and the carry input Cin. Which of the following combinations of inputs to I0, I1, I2 and I3 of the MUX will realize the sum S ?  (2003)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(b) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(c) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (c)
Sol: For a 4:1 mux
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)where sum of full adder is = A ⊕ B ⊕ C
Truth table of Full adder
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Q11: The output f of the 4-to-1 MUX shown in figure is (2001)
Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)(a) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(b) X + Y
(c) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

(d) Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)
Ans: (b)
Sol: ∵F = Σmin(1, 2, 3)
∴ Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE)

The document Previous Year Questions- Combinational Logic Circuits | Analog and Digital Electronics - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Analog and Digital Electronics.
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FAQs on Previous Year Questions- Combinational Logic Circuits - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is a combinational logic circuit?
Ans. A combinational logic circuit is a type of digital circuit where the output is solely determined by the current input values, with no memory element involved in the process.
2. What are the basic building blocks of combinational logic circuits?
Ans. The basic building blocks of combinational logic circuits are logic gates such as AND, OR, NOT, XOR, NAND, and NOR gates.
3. How do you design a combinational logic circuit?
Ans. To design a combinational logic circuit, one needs to analyze the problem, create a truth table based on the input-output requirements, simplify the Boolean expressions using Karnaugh maps or Boolean algebra, and finally implement the circuit using the appropriate logic gates.
4. What is the difference between combinational and sequential logic circuits?
Ans. In combinational logic circuits, the output is solely dependent on the current input, whereas in sequential logic circuits, the output is influenced by both the current input and the previous state of the circuit.
5. How do you test a combinational logic circuit?
Ans. Combinational logic circuits can be tested using techniques such as simulation, fault simulation, and functional testing to ensure that the circuit behaves as expected under different input conditions.
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