101. The hexadecimal equivalent of binary number 11010110 is
A) D6
B) B5
C) A4
D) C7
Answer: A
Explanation: Group binary in 4 bits → 1101 = D, 0110 = 6 → D6₁₆.
102. The Boolean expression for a NOR gate is
A) (A + B)’
B) (AB)’
C) A’ + B’
D) A’B’
Answer: A
Explanation: NOR = NOT(OR) = (A + B)’
103. In digital logic, a “word” refers to
A) A single bit
B) A group of bits
C) An ASCII character
D) A byte only
Answer: B
Explanation: A word is a fixed-size group of bits processed as one unit.
104. The binary equivalent of the decimal number 255 is
A) 11111110
B) 11111111
C) 11111100
D) 11110000
Answer: B
Explanation: 255 = 2⁸ – 1 = 11111111₂.
105. The Boolean function A’B + AB’ is equivalent to
A) XOR
B) XNOR
C) NAND
D) NOR
Answer: A
Explanation: A’B + AB’ = A ⊕ B (Exclusive-OR).
106. The output of a logic gate is 1 when all inputs are 0. The gate is
A) AND
B) NAND
C) NOR
D) OR
Answer: C
Explanation: NOR gate gives 1 only when all inputs are 0.
107. Which of the following gates cannot be used to construct an XOR gate directly?
A) AND
B) OR
C) NAND
D) EX-NOR
Answer: D
Explanation: XOR is basic; EX-NOR is complement of XOR.
108. The 2’s complement of binary 1001 is
A) 0110
B) 1111
C) 0111
D) 1001
Answer: C
Explanation: 1’s complement of 1001 = 0110; add 1 → 0111.
109. The logic gate that provides output 0 only when inputs are different is
A) AND
B) NOR
C) XNOR
D) XOR
Answer: D
Explanation: XOR outputs 1 when inputs differ, 0 when same.
110. Which device stores binary data temporarily?
A) ROM
B) RAM
C) PROM
D) EPROM
Answer: B
Explanation: RAM (Random Access Memory) stores temporary data.
111. What is the function of an encoder?
A) Converts binary to decimal
B) Converts decimal to binary code
C) Stores data
D) Adds numbers
Answer: B
Explanation: Encoder converts multiple input lines to coded binary output.
112. The most commonly used logic family in VLSI circuits is
A) TTL
B) CMOS
C) ECL
D) RTL
Answer: B
Explanation: CMOS is preferred for low power and high density.
113. The term “noise immunity” refers to
A) Power dissipation
B) Ability to tolerate voltage fluctuations
C) Output current capacity
D) Clock stability
Answer: B
Explanation: Noise immunity = tolerance against unwanted voltage variations.
114. The function of a parity generator is
A) Detect errors
B) Correct errors
C) Generate error
D) Amplify signal
Answer: A
Explanation: Parity generator adds an extra bit to detect transmission errors.
115. A shift register can
A) Store data
B) Shift data left or right
C) Delay data
D) All of the above
Answer: D
Explanation: Shift registers can store and shift data — used as delay elements too.
116. The output of a JK flip-flop remains unchanged when
A) J=0, K=0
B) J=1, K=1
C) J=1, K=0
D) J=0, K=1
Answer: A
Explanation: JK flip-flop holds previous output when both inputs are 0.
117. Which circuit can perform both addition and subtraction?
A) Full adder
B) Half adder
C) Parallel adder-subtractor
D) Decoder
Answer: C
Explanation: Adder-subtractor circuit can perform both by using control signal.
118. An edge-triggered flip-flop changes state
A) Only during level high
B) Only during level low
C) Only at the edge of clock pulse
D) Never changes
Answer: C
Explanation: Edge-triggered FF changes output only on rising/falling clock edge.
119. The binary representation of decimal 37 is
A) 100101
B) 110001
C) 101011
D) 111111
Answer: A
Explanation: 37₁₀ = 32 + 4 + 1 = 100101₂.
120. The hexadecimal of binary 11110000 is
A) F0
B) 0F
C) FF
D) F1
Answer: A
Explanation: 1111 = F, 0000 = 0 → F0₁₆.
121. Which flip-flop is called a “data latch”?
A) T
B) D
C) JK
D) SR
Answer: B
Explanation: D flip-flop stores the input data until next clock trigger.
122. A combinational circuit has
A) Memory
B) Feedback
C) No memory
D) Sequential behavior
Answer: C
Explanation: Output depends only on present input — no feedback or memory.
123. Which law is represented by A + AB = A?
A) Absorption law
B) De Morgan’s
C) Distributive
D) Associative
Answer: A
Explanation: A + AB = A is Boolean absorption law.
124. In BCD code, decimal number 9 is represented as
A) 1001
B) 1111
C) 1010
D) 1100
Answer: A
Explanation: BCD(9) = 1001.
125. A 4-input AND gate gives 1 only when
A) One input is 1
B) All inputs are 1
C) Any input is 0
D) Any two inputs are 1
Answer: B
Explanation: AND gate gives high only when all inputs are high.
126. Which number system is most suitable for digital computers?
A) Binary
B) Decimal
C) Octal
D) Hexadecimal
Answer: A
Explanation: Computers operate on binary logic (0 and 1).
127. The full form of PROM is
A) Programmable Read Only Memory
B) Primary Read Only Memory
C) Peripheral Read Only Memory
D) Protected Read Only Memory
Answer: A
Explanation: PROM is user-programmable but read-only afterward.
128. EEPROM can be
A) Electrically erased
B) Erased by UV light
C) Not erased
D) Magnetically erased
Answer: A
Explanation: EEPROM = Electrically Erasable Programmable ROM.
129. The basic element in a digital circuit is
A) Resistor
B) Logic gate
C) Transistor
D) Transformer
Answer: B
Explanation: Logic gates form the core of all digital circuits.
130. A binary counter is also known as
A) Incrementer
B) Register
C) Shift register
D) Decoder
Answer: A
Explanation: Counters increment or decrement binary numbers sequentially.
131. The number of unique states in an n-bit counter =
A) n
B) n²
C) 2ⁿ
D) 2n
Answer: C
Explanation: Each bit has 2 states, total = 2ⁿ combinations.
132. The output of a NOR gate is 0 when
A) Any input = 1
B) All inputs = 0
C) Inputs unequal
D) Inputs same
Answer: A
Explanation: NOR = NOT(OR) → output 0 if any input = 1.
133. A flip-flop is a ______ device.
A) Combinational
B) Sequential
C) Linear
D) Analog
Answer: B
Explanation: Flip-flops are sequential — depend on clock and previous state.
134. A 3-bit Gray code sequence has how many codes?
A) 4
B) 6
C) 7
D) 8
Answer: D
Explanation: n-bit Gray code → 2ⁿ combinations → 8.
135. A half subtractor circuit has
A) 1 input, 2 outputs
B) 2 inputs, 2 outputs
C) 3 inputs, 2 outputs
D) 2 inputs, 1 output
Answer: B
Explanation: Inputs: A, B; Outputs: Difference and Borrow.
136. The output of a full subtractor has
A) 1 output
B) 2 outputs (Diff, Borrow)
C) 3 outputs
D) None
Answer: B
Explanation: Full subtractor produces Difference and Borrow outputs.
137. The XOR gate is called
A) Exclusive OR
B) Extended OR
C) Even OR
D) Equal OR
Answer: A
Explanation: XOR = Exclusive-OR, outputs 1 for unequal inputs.
138. Which logic family offers the lowest noise margin?
A) CMOS
B) ECL
C) TTL
D) DTL
Answer: B
Explanation: ECL operates at small voltage swings → lowest noise margin.
139. A multiplexer performs
A) Encoding
B) Selection
C) Decoding
D) Comparison
Answer: B
Explanation: Multiplexer selects one input among many.
140. A 16-to-1 multiplexer requires how many select lines?
A) 3
B) 4
C) 5
D) 6
Answer: B
Explanation: 2⁴ = 16 → 4 select lines.
141. The propagation delay of a logic gate depends on
A) Load capacitance
B) Input voltage
C) Gate type
D) All of the above
Answer: D
Explanation: Delay depends on load, input, and internal gate characteristics.
142. The Boolean equation (A + B)(A + B’) = A demonstrates
A) Absorption
B) Consensus
C) Distributive
D) Idempotent law
Answer: A
Explanation: Simplifies to A → Absorption law.
143. The maximum clock frequency of a counter is limited by
A) Number of bits
B) Propagation delay
C) Input voltage
D) Supply voltage
Answer: B
Explanation: Propagation delay through flip-flops limits maximum clock rate.
144. A monostable multivibrator has
A) One stable state
B) Two stable states
C) No stable state
D) Three stable states
Answer: A
Explanation: Monostable = one stable, one quasi-stable state.
145. A bistable circuit has
A) One stable state
B) Two stable states
C) No stable state
D) None
Answer: B
Explanation: Bistable (flip-flop) has two stable states: 0 and 1.
146. A comparator is used to
A) Compare two binary numbers
B) Count pulses
C) Add numbers
D) Convert code
Answer: A
Explanation: Comparator outputs high when two inputs are equal.
147. In digital systems, metastability occurs in
A) Counters
B) Asynchronous circuits
C) Synchronous circuits
D) Latches
Answer: B
Explanation: Metastability arises when asynchronous inputs violate setup/hold times.
148. The main function of clock in sequential circuits is
A) Synchronization
B) Power supply
C) Noise reduction
D) Amplification
Answer: A
Explanation: Clock synchronizes flip-flops and sequential events.
149. Which number system uses digits 0 to 7?
A) Binary
B) Octal
C) Decimal
D) Hexadecimal
Answer: B
Explanation: Octal system base = 8 → digits 0–7.
150. The output of NAND gate is high if
A) All inputs are low
B) All inputs are high
C) Any input is low
D) Both A & C
Answer: D
Explanation: NAND = NOT(AND); gives high if any input = 0.
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