Digital Logic Circuits and Components MCQ Questions and Answers
1. Which of the following number systems is base 16?
A) Binary
B) Decimal
C) Hexadecimal
D) Octal
2. A digital circuit that performs arithmetic and logical operations is called a:
A) Control Unit
B) ALU (Arithmetic Logic Unit)
C) Register
D) Decoder
3. The output of an AND gate is 1 only when:
A) All inputs are 0
B) All inputs are 1
C) Any input is 1
D) Inputs are alternating
4. The Boolean expression for a NOR gate is:
A) A + B
B) A′ + B′
C) A · B
D) (A + B)′
5. In Boolean algebra, the expression A + A′B simplifies to:
A) A + B
B) AB
C) A′ + B
D) A
6. A logic circuit that implements the sum of minterms is called:
A) Product of Sums
B) Sum of Products
C) Exclusive OR
D) Half Adder
7. Which law states that A + 0 = A?
A) Identity Law
B) Null Law
C) Idempotent Law
D) Absorption Law
8. A K-map with 3 variables will have:
A) 2
B) 4
C) 8
D) 16 cells
9. A combinational circuit that performs addition of three bits is called a:
A) Half Adder
B) Full Adder
C) Decoder
D) Encoder
10. Which gate can be used to realize all basic logic operations?
A) AND
B) NAND
C) OR
D) XOR
11. A full subtractor has how many inputs and outputs?
A) 3 inputs, 2 outputs
B) 2 inputs, 2 outputs
C) 3 inputs, 1 output
D) 2 inputs, 1 output
12. The output of an XOR gate is 1 when:
A) All inputs are 1
B) Inputs are different
C) Inputs are the same
D) Both inputs are 0
13. In a 4-variable K-map, adjacent cells differ in:
A) 2 bits
B) 3 bits
C) 1 bit
D) 4 bits
14. Simplify the Boolean expression A(A′ + B).
A) AB
B) A′ + B
C) AB
D) A + B
15. A circuit that converts binary data from n inputs to 2ⁿ outputs is a:
A) Decoder
B) Encoder
C) Multiplexer
D) Demultiplexer
16. The device used to select one input from many and forward it to the output line is a:
A) Multiplexer
B) Decoder
C) Encoder
D) Demultiplexer
17. A D flip-flop stores data on:
A) Rising edge of clock
B) Falling edge of clock
C) Clock edge (depending on design)
D) Input change
18. The master-slave flip-flop is used to:
A) Eliminate race condition
B) Increase speed
C) Reduce power
D) Increase delay
19. A JK flip-flop behaves as a T flip-flop when:
A) J = 0, K = 1
B) J = 1, K = 0
C) J = K = 1
D) J = K = 0
20. Sequential circuits depend on:
A) Present inputs only
B) Present inputs and past outputs
C) Clock only
D) Inputs and propagation delay
21. A counter that counts both up and down is called:
A) Up/Down Counter
B) Ring Counter
C) Johnson Counter
D) Ripple Counter
22. The binary counter that resets automatically after a fixed count is known as:
A) Mod-n counter
B) Ripple counter
C) Decade counter
D) Shift register
23. A 4-bit register can store:
A) 2 values
B) 4 bits of data
C) 8 bits of data
D) 16 bits
24. A shift register that circulates data back to its input is known as a:
A) Ring counter
B) Johnson counter
C) Ripple counter
D) Asynchronous counter
25. In an asynchronous counter, flip-flops are triggered:
A) By previous flip-flop output
B) Simultaneously
C) By clock directly
D) By reset signal
26. The propagation delay in sequential circuits affects:
A) Logic level
B) Timing performance
C) Number of gates
D) Voltage level
27. An SR latch becomes invalid when:
A) S = 1 and R = 1
B) S = 0 and R = 1
C) S = 1 and R = 0
D) S = 0 and R = 0
28. A circuit that holds data temporarily is called:
A) Counter
B) Register
C) Decoder
D) Encoder
29. In integrated circuits, SSI stands for:
A) Small Scale Integration
B) Simple System Integration
C) Serial Signal Interface
D) Standard Semiconductor Integration
30. Which memory is non-volatile?
A) RAM
B) Cache
C) Register
D) ROM
31. The memory that loses data when power is turned off is:
A) Volatile memory
B) Non-volatile memory
C) Secondary memory
D) Static memory
32. The Boolean expression (A + B)(A + B′) simplifies to:
A) A + B
B) A
C) AB
D) B
33. A logic gate that performs the inverse of OR operation is:
A) NOR gate
B) XOR gate
C) NAND gate
D) XNOR gate
34. The fan-in of a logic gate refers to:
A) Number of inputs
B) Number of outputs
C) Speed of operation
D) Power dissipation
35. The fan-out refers to:
A) Number of inputs
B) Number of gates driven by output
C) Number of flip-flops used
D) Speed factor
36. Binary code 1011 represents which decimal number?
A) 11
B) 10
C) 12
D) 13
37. Gray code differs from binary code because:
A) Only one bit changes between successive numbers
B) Two bits change
C) All bits change
D) No bit changes
38. The process of reducing Boolean expressions is called:
A) Transformation
B) Simplification
C) Translation
D) Encoding
39. The minimum SOP form of A + AB is:
A) A
B) B
C) AB
D) A + B
40. A decoder with 3 inputs will have how many outputs?
A) 4
B) 6
C) 8
D) 10
41. In Boolean algebra, the complement of A + B is:
A) A + B′
B) A′ + B′
C) A′B′
D) (A + B)
42. The Boolean identity A + AB = A demonstrates which law?
A) Absorption law
B) Idempotent law
C) De Morgan’s law
D) Associative law
43. A demultiplexer performs the reverse operation of a:
A) Decoder
B) Multiplexer
C) Encoder
D) Comparator
44. A comparator is a combinational circuit that:
A) Compares two binary numbers
B) Adds two binary numbers
C) Stores data
D) Multiplies two values
45. Which of the following is a universal gate?
A) XOR
B) NAND
C) OR
D) XNOR
46. The term edge-triggered in flip-flops means:
A) The output changes at clock transition
B) The output changes continuously
C) The flip-flop has no clock
D) The output is asynchronous
47. A monostable multivibrator has:
A) Two stable states
B) One stable state
C) No stable state
D) Three stable states
48. A bistable circuit can store:
A) 1 bit
B) 2 bits
C) 4 bits
D) 8 bits
49. The setup time of a flip-flop is:
A) Minimum time before clock when input must be stable
B) Time after clock edge
C) Propagation delay
D) Hold time
50. A Johnson counter is a type of:
A) Ripple counter
B) Binary counter
C) Ring counter
D) Synchronous counter
51. In an SR flip-flop, if both inputs are 0, the output:
A) Holds previous state
B) Becomes 0
C) Becomes 1
D) Toggles
52. The Boolean expression of an XNOR gate is:
A) A′B + AB′
B) AB + A′B′
C) (A + B)′
D) (AB)′
53. A half adder has how many outputs?
A) 3
B) 2
C) 1
D) 4
54. Which of the following circuits can be used as a parity generator?
A) XOR gate
B) AND gate
C) NOR gate
D) OR gate
55. The maximum number of minterms for 4 variables is:
A) 16
B) 8
C) 4
D) 32
56. A binary decoder converts binary information into:
A) One active output line
B) Multiple active outputs
C) Binary input
D) Arithmetic output
57. Which flip-flop has no race-around condition?
A) D flip-flop
B) JK flip-flop
C) SR flip-flop
D) T flip-flop
58. The memory cell in static RAM is made up of:
A) Capacitor and transistor
B) Flip-flop
C) Decoder
D) Counter
59. Dynamic RAM stores data using:
A) Capacitors
B) Resistors
C) Flip-flops
D) Shift registers
60. ROM is primarily used for storing:
A) Firmware
B) Temporary data
C) Counters
D) Buffers
61. The Boolean equation A + A′B′ simplifies to:
A) A + B′
B) AB
C) B
D) A′
62. A 4-to-1 multiplexer requires how many selection lines?
A) 4
B) 2
C) 1
D) 3
63. A priority encoder assigns priority to:
A) The highest order input
B) The lowest order input
C) Random input
D) All inputs equally
64. A BCD counter counts from:
A) 0000 to 1001
B) 0000 to 1111
C) 0001 to 1010
D) 0000 to 0111
65. In a synchronous counter, all flip-flops are triggered by:
A) Common clock
B) Previous output
C) Random signal
D) Reset line
66. The propagation delay of a gate is measured between:
A) Input change and output response
B) Clock pulse width
C) Input setup time
D) Hold time
67. A decoder is also called a:
A) Demultiplexer with enable input
B) Encoder
C) Counter
D) Comparator
68. Which gate is known as the inverting buffer?
A) NOT gate
B) AND gate
C) OR gate
D) XOR gate
69. A 1-of-8 decoder activates:
A) One output line at a time
B) All lines together
C) Random output
D) Multiple outputs
70. The output enable signal in a decoder:
A) Controls whether outputs are active
B) Adds extra outputs
C) Multiplies outputs
D) Disables inputs
71. An 8-bit register can hold how many different combinations?
A) 128
B) 256
C) 512
D) 1024
72. A down counter counts:
A) 0 to maximum
B) Maximum to 0
C) Randomly
D) In binary gray code
73. The output of a latch changes:
A) When inputs change
B) Only at clock edges
C) Randomly
D) Never
74. Which logic family offers the lowest power dissipation?
A) TTL
B) RTL
C) CMOS
D) DTL
75. In a TTL NAND gate, transistors are used as:
A) Switching devices
B) Amplifiers
C) Resistors
D) Capacitors
76. A hazard in combinational circuits refers to:
A) Undesired transient output change
B) Clock failure
C) Power overload
D) Input noise
77. A 4-bit ripple counter can count up to:
A) 8
B) 15
C) 16
D) 12
78. A look-up table (LUT) in an FPGA acts as a:
A) Combinational logic block
B) Sequential logic block
C) Decoder
D) Register
79. A PLA (Programmable Logic Array) implements:
A) SOP or POS expressions
B) Only AND functions
C) Only OR functions
D) Arithmetic circuits
80. The Boolean expression AB + A′B simplifies to:
A) B
B) A
C) A + B
D) AB
81. The carry look-ahead adder is faster than ripple carry because:
A) It computes carry in parallel
B) It uses fewer gates
C) It uses delay elements
D) It ignores carries
82. A tri-state buffer can output:
A) 0 and 1
B) 0, 1, or high-impedance
C) Only 1
D) Only 0
83. Which type of memory is used in cache systems?
A) SRAM
B) DRAM
C) ROM
D) PROM
84. The main characteristic of sequential logic is:
A) Dependence on previous states
B) Dependence only on inputs
C) No clock dependency
D) Continuous analog behavior
85. A programmable ROM (PROM) can be:
A) Written once
B) Rewritten multiple times
C) Used as RAM
D) Only volatile
86. Which is the fastest memory in a computer system?
A) DRAM
B) Flash
C) Register
D) Cache
87. The number of flip-flops required for a mod-16 counter is:
A) 4
B) 8
C) 16
D) 5
88. In Boolean logic, A · 1 = ?
A) A
B) 0
C) A′
D) 1
89. A 4-bit comparator has how many input lines?
A) 4
B) 8
C) 16
D) 12
90. A decoder with an enable input acts as:
A) Fixed decoder
B) Controlled decoder
C) Register
D) Encoder
91. A JK flip-flop toggles when:
A) J = 1, K = 1
B) J = 0, K = 1
C) J = 1, K = 0
D) J = 0, K = 0
92. A shift register can be used for:
A) Serial-to-parallel conversion
B) Multiplexing
C) Decoding
D) Counting only
93. The Boolean function A′B + AB′ represents which gate?
A) OR
B) XOR
C) NOR
D) XNOR
94. Which flip-flop is most commonly used in counters?
A) T flip-flop
B) D flip-flop
C) JK flip-flop
D) SR flip-flop
95. In a 3-to-8 decoder, the number of enable inputs is usually:
A) 0
B) 1
C) 2
D) 3
96. A two-level logic circuit corresponds to:
A) Sum of Products or Product of Sums
B) Half adder
C) Decoder
D) Counter
97. A flip-flop can be viewed as a:
A) One-bit memory cell
B) Decoder
C) Multiplexer
D) Encoder
98. Which of the following memories uses magnetic material?
A) Hard disk
B) Flash memory
C) ROM
D) DRAM
99. In logic circuits, fan-out determines:
A) Maximum load the gate can drive
B) Speed of clock
C) Gate delay
D) Power consumption
100. In Boolean algebra, A + A = ?
A) A
B) 1
C) 0
D) A′