Digital Logic Design MCQs

This comprehensive set of Digital Logic Design MCQs is designed to cover all essential topics required for success in exams related to digital circuits and systems. Focused on key subjects such as Boolean algebra, logic gates, combinational and sequential circuits, flip-flops, multiplexers, and counters, these MCQs are crafted to help students build a strong foundation in digital logic design concepts and techniques.

Who should practice Digital Logic Design MCQs?

Students preparing for courses in electrical engineering, computer science, or IT that include digital logic design and circuit theory.
Individuals aiming to strengthen their understanding of logic gates, Karnaugh maps, combinational circuits, and sequential circuit design.
Candidates preparing for competitive exams or certifications that assess knowledge of digital electronics and system design.
Learners interested in mastering topics such as flip-flops, registers, finite state machines, and arithmetic circuits like adders and subtractors.
Professionals focused on improving their skills in digital system design, circuit optimization, and hardware description languages like VHDL or Verilog.
Suitable for all aspirants seeking to enhance their knowledge and performance in digital logic design for academic or professional success.

1. What is a logic gate?

A) A device that performs basic logical operations
B) A storage device for digital data
C) A type of memory unit
D) A form of network protocol

View Answer

2. Which of the following is a universal gate?

A) AND
B) OR
C) NAND
D) NOT

View Answer

3. What is the output of an AND gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

4. What is the binary equivalent of the decimal number 10?

A) 1010
B) 1001
C) 1100
D) 1111

View Answer

5. What is a flip-flop used for in digital logic circuits?

A) To store binary information
B) To perform addition
C) To decode data
D) To display information

View Answer

6. Which of the following gates will output 0 when both inputs are 1?

A) AND
B) OR
C) XOR
D) NAND

View Answer

7. What does the term “fan-out” refer to in digital logic design?

A) The number of gates a single gate can drive
B) The number of inputs a gate can accept
C) The speed of a gate
D) The power consumption of a gate

View Answer

8. What is the purpose of a half-adder?

A) To add two single-bit binary numbers
B) To store a single bit of data
C) To multiply binary numbers
D) To shift binary data

View Answer

9. What is the base of the hexadecimal number system?

A) 2
B) 8
C) 10
D) 16

View Answer

10. How many flip-flops are needed to construct a 4-bit binary counter?

A) 2
B) 4
C) 6
D) 8

View Answer

11. What is a multiplexer (MUX)?

A) A device that selects one input from several and outputs it
B) A device that stores binary data
C) A device that performs subtraction
D) A device that generates clock signals

View Answer

12. What is the primary function of a decoder in digital logic?

A) To convert coded information into a familiar form
B) To add binary numbers
C) To store data
D) To count pulses

View Answer

13. What does the term “propagation delay” refer to in logic circuits?

A) The time taken for a signal to travel through a gate
B) The speed of the clock signal
C) The maximum frequency of operation
D) The time taken to reset a flip-flop

View Answer

14. Which of the following logic gates produces an output of 1 only when the inputs are different?

A) AND
B) OR
C) XOR
D) NAND

View Answer

15. What is a D flip-flop used for?

A) Storing a single bit of data with the clock input
B) Performing logical operations
C) Shifting data
D) Adding binary numbers

View Answer

16. What is the purpose of an ALU in a digital system?

A) To perform arithmetic and logical operations
B) To store data
C) To control the system clock
D) To perform input/output operations

View Answer

17. What does the truth table of a NOR gate show?

A) The output is 0 when any input is 1
B) The output is 1 when both inputs are 1
C) The output is 1 when both inputs are 0
D) The output is always 0

View Answer

18. Which of the following is an example of a sequential circuit?

A) AND gate
B) OR gate
C) Counter
D) XOR gate

View Answer

19. How many inputs does a full-adder have?

A) 1
B) 2
C) 3
D) 4

View Answer

20. What is the binary representation of the hexadecimal number A?

A) 1010
B) 1001
C) 1110
D) 1100

View Answer

21. What does a JK flip-flop do when both J and K inputs are 1?

A) Toggle the output
B) Set the output to 1
C) Reset the output to 0
D) No change in output

View Answer

22. What is the decimal equivalent of the binary number 1101?

A) 11
B) 12
C) 13
D) 14

View Answer

23. Which gate is used to detect if two binary inputs are different?

A) AND
B) OR
C) XOR
D) NOR

View Answer

24. What is the purpose of a shift register in digital circuits?

A) To store and shift data
B) To perform logical operations
C) To add binary numbers
D) To decode binary data

View Answer

25. How many different output combinations are possible with a 3-input truth table?

A) 2
B) 4
C) 6
D) 8

View Answer

26. What is the output of a NOR gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

27. What does the term “race condition” refer to in sequential circuits?

A) When two signals arrive at the same point at different times
B) When multiple outputs are set to the same value
C) When flip-flops are toggled too quickly
D) When signals interfere with each other

View Answer

28. What is a counter in digital logic design?

A) A sequential circuit that counts pulses
B) A combinational circuit
C) A memory storage device
D) A logic gate

View Answer

29. What is the hexadecimal equivalent of the binary number 1101 0110?

A) D6
B) C5
C) A7
D) B9

View Answer

30. What is a Moore machine in digital logic design?

A) A finite state machine where the output depends only on the current state
B) A machine where output depends on both the state and the input
C) A type of adder circuit
D) A memory unit

View Answer

31. Which of the following gates is used to invert a binary input?

A) AND
B) OR
C) NOT
D) XOR

View Answer

32. What is the binary addition of 1011 + 1101?

A) 11000
B) 10100
C) 10010
D) 11100

View Answer

33. How many states does a 3-bit counter have?

A) 3
B) 4
C) 6
D) 8

View Answer

34. What is the purpose of Karnaugh maps in digital logic design?

A) To simplify Boolean expressions
B) To store binary data
C) To perform addition
D) To measure propagation delay

View Answer

35. What is the primary function of a demultiplexer (DEMUX)?

A) To direct data from one input to one of many outputs
B) To perform arithmetic operations
C) To store binary data
D) To generate clock signals

View Answer

36. What is a T flip-flop?

A) A flip-flop that toggles its state on every clock pulse
B) A flip-flop that stores two bits of data
C) A flip-flop that resets automatically
D) A flip-flop that performs addition

View Answer

37. What is the binary equivalent of the decimal number 25?

A) 11001
B) 10110
C) 11100
D) 11010

View Answer

38. What is the key difference between a latch and a flip-flop?

A) A latch is level-triggered, while a flip-flop is edge-triggered
B) A latch stores multiple bits, while a flip-flop stores one bit
C) A flip-flop operates faster than a latch
D) A latch uses more power than a flip-flop

View Answer

39. What is a synchronous counter?

A) A counter where all flip-flops are triggered by the same clock signal
B) A counter where each flip-flop has its own clock
C) A counter that stores multiple bits of data
D) A counter that adds binary numbers

View Answer

40. What does the term “glitch” refer to in digital logic circuits?

A) A short, unwanted change in a digital signal
B) A method of encoding data
C) A type of logic gate
D) A way to synchronize circuits

View Answer

41. What is the binary equivalent of the hexadecimal number 3F?

A) 111111
B) 101010
C) 110110
D) 100101

View Answer

42. What is the output of an XOR gate when both inputs are 0?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

43. What does the term “asynchronous counter” refer to in digital logic?

A) A counter where flip-flops are triggered at different times
B) A counter where all flip-flops are triggered simultaneously
C) A counter used to store data
D) A counter that performs multiplication

View Answer

44. What is the function of a parity bit in digital systems?

A) To detect errors in transmitted data
B) To perform binary addition
C) To encode data
D) To control clock signals

View Answer

45. What is the decimal equivalent of the binary number 1110?

A) 12
B) 13
C) 14
D) 15

View Answer

46. How many select lines are needed for an 8-to-1 multiplexer?

A) 2
B) 3
C) 4
D) 8

View Answer

47. What does the term “setup time” refer to in flip-flop operations?

A) The minimum time before the clock edge that the input must be stable
B) The maximum time before the clock edge that the input can change
C) The time taken for the output to change
D) The time taken for the flip-flop to reset

View Answer

48. What is the output of a NOT gate when the input is 0?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

49. What is a synchronous binary counter?

A) A counter where all flip-flops are triggered by the same clock signal
B) A counter that operates without a clock signal
C) A counter that counts only even numbers
D) A counter that uses latches

View Answer

50. What is the binary equivalent of the decimal number 9?

A) 1000
B) 1001
C) 1010
D) 1100

View Answer

51. What is the function of a decoder in a digital system?

A) To convert binary data into readable information
B) To perform binary multiplication
C) To add binary numbers
D) To store data

View Answer

52. Which of the following is a combinational logic circuit?

A) Flip-flop
B) Counter
C) Multiplexer
D) Shift register

View Answer

53. How many different combinations are possible with a 4-bit binary number?

A) 8
B) 12
C) 16
D) 24

View Answer

54. What is a half-adder?

A) A circuit that adds two single-bit numbers
B) A circuit that subtracts two binary numbers
C) A circuit that multiplies binary numbers
D) A circuit that divides binary numbers

View Answer

55. What does the term “hold time” refer to in flip-flop operations?

A) The minimum time the input must be stable after the clock edge
B) The maximum time before the clock edge the input can change
C) The time taken for the output to stabilize
D) The time taken for the input to reset

View Answer

56. What is a full-adder?

A) A circuit that adds two binary digits and a carry bit
B) A circuit that stores data
C) A circuit that shifts data
D) A circuit that decodes binary data

View Answer

57. What is the output of a NOR gate when both inputs are 0?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

58. What is the primary function of an encoder?

A) To convert information into coded format
B) To perform binary addition
C) To store data
D) To decode binary information

View Answer

59. What is the binary equivalent of the hexadecimal number B?

A) 1010
B) 1011
C) 1100
D) 1111

View Answer

60. Which of the following gates is considered a universal gate?

A) AND
B) OR
C) XOR
D) NAND

View Answer

61. What is the primary purpose of a clock signal in digital circuits?

A) To synchronize operations
B) To store binary data
C) To perform binary addition
D) To amplify signals

View Answer

62. How many outputs does a 3-to-8 decoder have?

A) 2
B) 4
C) 6
D) 8

View Answer

63. What is the difference between a combinational and sequential circuit?

A) A combinational circuit does not have memory, while a sequential circuit does
B) A sequential circuit is faster than a combinational circuit
C) A combinational circuit performs more operations than a sequential circuit
D) A sequential circuit uses fewer logic gates

View Answer

64. What is the binary equivalent of the decimal number 15?

A) 1000
B) 1100
C) 1111
D) 1010

View Answer

65. What is the primary function of a latch in digital systems?

A) To store one bit of data
B) To perform logical operations
C) To count pulses
D) To shift binary data

View Answer

66. How many states does a 4-bit binary counter have?

A) 8
B) 10
C) 12
D) 16

View Answer

67. What is the purpose of a clocked D flip-flop?

A) To store data based on clock input
B) To decode binary data
C) To perform binary multiplication
D) To amplify signals

View Answer

68. What is the hexadecimal equivalent of the binary number 1110?

A) A
B) B
C) C
D) E

View Answer

69. Which of the following best describes a Moore machine?

A) A finite state machine where the output depends only on the current state
B) A finite state machine where the output depends on both the state and input
C) A combinational circuit
D) A counter

View Answer

70. What is the function of a JK flip-flop when both inputs are 1?

A) Toggle the output
B) Reset the output
C) Set the output to 1
D) No change in output

View Answer

71. What is the decimal equivalent of the binary number 1011?

A) 9
B) 10
C) 11
D) 12

View Answer

72. How many logic gates are required to implement a full adder?

A) 4
B) 5
C) 6
D) 9

View Answer

73. What does the term “fan-out” refer to in digital circuits?

A) The number of inputs a gate can handle
B) The number of outputs a gate can drive
C) The propagation delay of a gate
D) The maximum frequency of a circuit

View Answer

74. What is the hexadecimal equivalent of the decimal number 15?

A) A
B) B
C) C
D) F

View Answer

75. What is the primary function of a shift register?

A) To shift data in or out of a circuit
B) To perform binary addition
C) To count binary pulses
D) To decode binary data

View Answer

76. What is the characteristic equation of a D flip-flop?

A) Q(t+1) = D
B) Q(t+1) = D’
C) Q(t+1) = JQ’
D) Q(t+1) = JK’

View Answer

77. Which of the following is an application of multiplexers?

A) Data selection
B) Binary addition
C) Signal amplification
D) Clock synchronization

View Answer

78. How many select lines are required for a 16-to-1 multiplexer?

A) 2
B) 3
C) 4
D) 5

View Answer

79. What is the function of a binary counter?

A) To count pulses in binary form
B) To store multiple bits of data
C) To perform logical operations
D) To amplify digital signals

View Answer

80. What is the propagation delay in a logic gate?

A) The time it takes for an input change to affect the output
B) The time it takes to switch between two logic levels
C) The time taken to reset a circuit
D) The time required to store data

View Answer

81. What is the binary equivalent of the decimal number 18?

A) 10010
B) 10100
C) 11010
D) 11100

View Answer

82. What is the primary advantage of a CMOS over a TTL gate?

A) Lower power consumption
B) Faster switching time
C) Higher noise margin
D) Larger size

View Answer

83. What is the sum output of a half-adder when both inputs are 1?

A) 0
B) 1
C) 2
D) Undefined

View Answer

84. What is the function of a JK flip-flop when both inputs are 0?

A) No change in output
B) Toggle the output
C) Set the output
D) Reset the output

View Answer

85. How many different states can a 3-bit binary counter represent?

A) 4
B) 6
C) 8
D) 10

View Answer

86. Which of the following gates can be used to construct any other logic gate?

A) XOR
B) AND
C) OR
D) NAND

View Answer

87. What is the primary function of an SR latch?

A) To store a single bit of data
B) To perform binary addition
C) To amplify signals
D) To decode binary information

View Answer

88. What does the term “noise margin” refer to in digital circuits?

A) The tolerance of a circuit to voltage noise
B) The amount of heat generated by a circuit
C) The time taken for a signal to propagate
D) The maximum frequency of operation

View Answer

89. What is the output of a NAND gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

90. What is the decimal equivalent of the hexadecimal number 2A?

A) 32
B) 40
C) 42
D) 44

View Answer

91. How many inputs does a full adder require?

A) 2
B) 3
C) 4
D) 5

View Answer

92. Which of the following is a characteristic of sequential logic circuits?

A) They use memory elements to store previous states
B) They perform only logical operations
C) They are faster than combinational circuits
D) They do not require a clock signal

View Answer

93. What is the primary function of an ALU (Arithmetic Logic Unit)?

A) To perform arithmetic and logical operations
B) To store binary data
C) To decode instructions
D) To manage memory

View Answer

94. What is the hexadecimal equivalent of the binary number 1010?

A) 9
B) A
C) B
D) C

View Answer

95. What is the function of an OR gate?

A) The output is 1 if at least one input is 1
B) The output is 0 if both inputs are 0
C) The output is 1 only if both inputs are 1
D) The output is 1 if both inputs are 0

View Answer

96. How many flip-flops are required to build a 4-bit binary counter?

A) 2
B) 4
C) 6
D) 8

View Answer

97. What is the binary equivalent of the decimal number 7?

A) 111
B) 101
C) 110
D) 100

View Answer

98. What is a ring counter?

A) A type of counter where the output of the last flip-flop is fed back to the input of the first
B) A counter that stores multiple bits
C) A counter that multiplies binary numbers
D) A counter used to amplify signals

View Answer

99. What is the main characteristic of a ripple counter?

A) Flip-flops are triggered sequentially, causing a ripple effect
B) All flip-flops are triggered simultaneously
C) It performs only addition
D) It has a very short propagation delay

View Answer

100. What is the primary function of a tri-state buffer?

A) To control data flow by providing three output states: high, low, and high-impedance
B) To perform binary addition
C) To decode binary data
D) To shift data between registers

View Answer

101. What is the output of an AND gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

102. How many select lines are required for a 4-to-16 decoder?

A) 2
B) 3
C) 4
D) 5

View Answer

103. What is the function of a Johnson counter?

A) A type of ring counter where the output is fed back in inverted form
B) A counter that stores data
C) A counter used to perform multiplication
D) A counter that amplifies digital signals

View Answer

104. What does the term “setup time violation” refer to in digital circuits?

A) The input changes too close to the clock edge, causing incorrect operation
B) The input is stable before the required time
C) The clock signal is too fast for the flip-flop
D) The output does not change fast enough

View Answer

105. What is the binary equivalent of the decimal number 25?

A) 11001
B) 10100
C) 10011
D) 11110

View Answer

106. What is the main difference between a latch and a flip-flop?

A) A latch is level-triggered, while a flip-flop is edge-triggered
B) A latch uses more power than a flip-flop
C) A latch stores more data than a flip-flop
D) A flip-flop does not use a clock signal

View Answer

107. What is the output of a NOR gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

108. How many flip-flops are required to create a 3-bit synchronous counter?

A) 1
B) 2
C) 3
D) 4

View Answer

109. What is the decimal equivalent of the binary number 1111?

A) 12
B) 13
C) 14
D) 15

View Answer

110. What does the term “hold time violation” refer to in digital circuits?

A) The input does not remain stable long enough after the clock edge
B) The input is held too long before the clock edge
C) The output changes too quickly
D) The clock signal is unstable

View Answer

111. What is the hexadecimal equivalent of the decimal number 255?

A) FF
B) AA
C) F0
D) 00

View Answer

112. What is the function of a binary encoder?

A) To convert data into binary form
B) To add binary numbers
C) To amplify binary signals
D) To store data

View Answer

113. What is the primary use of a multiplexer in digital circuits?

A) To select one input from several inputs
B) To perform binary subtraction
C) To store multiple bits
D) To decode binary data

View Answer

114. How many bits are required to represent a hexadecimal digit?

A) 2
B) 4
C) 6
D) 8

View Answer

115. What is the main advantage of a synchronous counter over an asynchronous counter?

A) All flip-flops are triggered simultaneously, resulting in faster operation
B) It uses fewer logic gates
C) It consumes less power
D) It does not require a clock signal

View Answer

116. What is the binary equivalent of the decimal number 5?

A) 101
B) 110
C) 100
D) 111

View Answer

117. What is the output of a NAND gate when both inputs are 0?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

118. What is the purpose of a half subtractor?

A) To subtract two binary digits
B) To add two binary digits
C) To multiply two binary digits
D) To divide two binary digits

View Answer

119. How many outputs does a 3-to-8 decoder have?

A) 4
B) 6
C) 8
D) 10

View Answer

120. What is the binary equivalent of the hexadecimal number A?

A) 1010
B) 1011
C) 1100
D) 1000

View Answer

121. What is the function of a JK flip-flop when both inputs are 1?

A) Toggle the output
B) Reset the output
C) Set the output to 1
D) No change in output

View Answer

122. What is the decimal equivalent of the binary number 1001?

A) 7
B) 8
C) 9
D) 10

View Answer

123. How many select lines are required for an 8-to-1 multiplexer?

A) 2
B) 3
C) 4
D) 5

View Answer

124. What is the primary function of a clock signal in a flip-flop circuit?

A) To synchronize data changes
B) To amplify data
C) To decode binary numbers
D) To store data

View Answer

125. What is the primary function of a D flip-flop?

A) To store a single bit of data
B) To perform binary addition
C) To amplify signals
D) To decode binary data

View Answer

126. What is the binary equivalent of the decimal number 20?

A) 10100
B) 11001
C) 11100
D) 10011

View Answer

127. What is the function of a full subtractor?

A) To subtract two binary digits with borrow
B) To add two binary digits
C) To multiply two binary digits
D) To divide two binary digits

View Answer

128. What is the hexadecimal equivalent of the binary number 1110?

A) A
B) B
C) C
D) E

View Answer

129. What is the output of an XOR gate when both inputs are 1?

A) 0
B) 1
C) Undefined
D) Floating

View Answer

130. What is the primary function of a decoder in digital logic?

A) To convert binary input into a specific output
B) To store binary data
C) To amplify signals
D) To perform binary addition

View Answer