Combinational Logic Quizzes: Test Your Understanding

Question 1

Which of the following is a defining characteristic of combinational logic circuits?

Accepted Answer

Output depends solely on current inputs

Answer

Stores data in memory cells

Answer

Uses sequential logic gates

Answer

Performs computations based on past inputs

Question 2

A combinational logic circuit has two binary inputs and one binary output. What is the minimum number of logic gates required to implement the circuit?

Accepted Answer

2

Answer

1

Answer

3

Answer

4

Question 3

Which of the following is NOT a type of combinational logic gate?

Accepted Answer

Register

Answer

AND

Answer

OR

Answer

NAND

Question 4

A 4-to-1 multiplexer has 'n' select lines. What is the value of 'n'?

Accepted Answer

2

Answer

1

Answer

3

Answer

4

Question 5

Which of the following Boolean expressions represents the output of an XOR gate?

Accepted Answer

A XOR B

Answer

A + B

Answer

A . B

Answer

A / B

Question 6

A 3-bit adder circuit has three inputs (A, B, and Cin) and two outputs (Sum and Cout). What is the purpose of the Cin input?

Accepted Answer

To store the carry-in

Answer

To generate the carry-out

Answer

To represent the least significant bit of the sum

Answer

To invert the input signals

Question 7

A combinational logic circuit implements the following function: F = (A . B) + (C XOR D). Which of the following logic gates is NOT required to implement this function?

Accepted Answer

NAND

Answer

AND

Answer

OR

Answer

XOR

Question 8

Which of the following is not a logical operator used in Boolean algebra?

Accepted Answer

IF

Answer

AND

Answer

OR

Answer

XOR

Question 9

What is the primary function of a decoder in combinational logic?

Accepted Answer

Selecting one output line based on input combinations

Answer

Converting binary code to decimal code

Answer

Converting decimal code to binary code

Answer

Generating all possible output combinations for a given input

Question 10

Which of the following logic gates has a truth table with only one '1' output?

Accepted Answer

NAND

Answer

AND

Answer

OR

Answer

NOR

Question 11

What is the output of a 3-to-8 decoder with inputs A=0, B=1, and C=0?

Accepted Answer

00000010

Answer

00000001

Answer

00000100

Answer

00001000

Question 12

What is the key distinction between combinational and sequential logic circuits?

Accepted Answer

Sequential circuits use memory, while combinational circuits do not

Answer

Combinational circuits use memory, while sequential circuits do not

Answer

Combinational circuits can be reprogrammed, while sequential circuits cannot

Answer

Sequential circuits can be reprogrammed, while combinational circuits cannot

Question 13

Which of the following is a significant benefit of using field-programmable gate arrays (FPGAs) in digital circuit design?

Accepted Answer

Flexibility and reconfigurability

Answer

Reduced circuit size

Answer

Increased speed

Answer

Lower power consumption

Question 14

What is the purpose of a multiplexer in combinational logic?

Accepted Answer

Selecting one output line from multiple input lines

Answer

Selecting one input line from multiple output lines

Answer

Generating all possible output combinations for a given input

Answer

Converting binary code to decimal code

Question 15

Which of the following logic gates has the truth table: 000, 001, 010, 011, 100, 101, 110, 111?

Accepted Answer

OR gate

Answer

AND gate

Answer

NOT gate

Answer

XOR gate

Question 16

What is the primary function of a multiplexer?

Accepted Answer

To select one of several input signals

Answer

To amplify a signal

Answer

To store data

Answer

To perform arithmetic operations

Question 17

Which Boolean expression correctly represents the logical NOR operation?

Accepted Answer

¬(A + B)

Answer

A + B

Answer

A * B

Answer

A ^ B

Question 18

A half adder is used to add two:

Accepted Answer

1-bit numbers

Answer

2-bit numbers

Answer

3-bit numbers

Answer

4-bit numbers

Question 19

Which of the following is a universal logic gate that can implement all other logic gates?

Accepted Answer

NAND gate

Answer

AND gate

Answer

OR gate

Answer

NOT gate

Question 20

A Karnaugh map is a graphical tool used to simplify the:

Accepted Answer

Design of combinational logic circuits

Answer

Analysis of sequential logic circuits

Answer

Implementation of digital systems

Answer

Testing of logic gates

Question 21

The output of a 3-input XOR gate is:

Accepted Answer

1 if an odd number of inputs are 1

Answer

1 if an even number of inputs are 1

Answer

1 only if all inputs are 1

Answer

0 only if all inputs are 0

Question 22

A multiplexer is a combinational logic circuit that performs:

Accepted Answer

Data selection

Answer

Data storage

Answer

Data transmission

Answer

Data conversion

Question 23

The canonical sum-of-products form of a Boolean expression represents:

Accepted Answer

All possible combinations of the input variables

Answer

Only the combinations that produce a 1 output

Answer

Only the combinations that produce a 0 output

Answer

The minimal form of the expression

Question 24

A truth table is a tabular representation that displays all possible:

Accepted Answer

Input and output combinations of a logic function

Answer

States of a sequential logic circuit

Answer

Design steps of a digital system

Answer

Test cases for a logic gate

Question 25

Design and implement the logic function F(A, B, C) = AB + AC' + BC' using a hardware description language (HDL) of your choice. Include a testbench to verify the circuit's functionality.

Accepted Answer

Provide correct HDL code and a testbench.

Answer

Provide HDL code with errors.

Answer

Provide HDL code for a different logic function.

Answer

Provide HDL code without a testbench.

Question 26

Which Boolean expression represents the XOR gate?

Accepted Answer

A ⊕ B

Answer

A + B

Answer

A · B

Answer

A ⊗ B

Question 27

Identify the universal logic gate.

Accepted Answer

NAND gate

Answer

AND gate

Answer

OR gate

Answer

NOT gate

Question 28

What is the key distinction between combinational and sequential logic circuits?

Accepted Answer

Sequential circuits have memory, while combinational circuits do not.

Answer

Combinational circuits have memory, while sequential circuits do not.

Answer

Combinational circuits are asynchronous, while sequential circuits are synchronous.

Answer

Sequential circuits are asynchronous, while combinational circuits are synchronous.

Question 29

Explain the difference between a half-adder and a full-adder.

Accepted Answer

Half-adders handle two 1-bit numbers, while full-adders handle three 1-bit numbers.

Answer

Full-adders handle two 1-bit numbers, while half-adders handle three 1-bit numbers.

Answer

Half-adders only handle positive numbers, while full-adders handle both positive and negative numbers.

Answer

Full-adders only handle positive numbers, while half-adders handle both positive and negative numbers.

Question 30

Simplify the Boolean expression AB + A'B using Boolean algebra.

Accepted Answer

1

Answer

A

Answer

B

Answer

0

Question 31

Determine the truth table for the logic circuit: (A ∧ B) ∨ (¬A ∧ ¬B).

Accepted Answer

| A | B | Output |
|---|---|--------|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |

Answer

| A | B | Output |
|---|---|--------|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |

Answer

| A | B | Output |
|---|---|--------|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |

Answer

| A | B | Output |
|---|---|--------|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |

Question 32

Which characteristic defines combinational logic circuits?

Accepted Answer

Output solely depends on current inputs

Answer

Employ memory elements

Answer

Output can vary over time

Answer

Exhibit sequential operation

Question 33

Which logic gate produces an output that is TRUE only when all of its inputs are TRUE?

Accepted Answer

AND

Answer

XOR

Answer

OR

Answer

NAND

Question 34

What is the primary function of a decoder in combinational logic?

Accepted Answer

To convert binary code into specific output signals

Answer

To amplify digital signals

Answer

To perform arithmetic operations

Question 35

A 4-bit binary adder is a combinational logic circuit that adds two 4-bit binary numbers. How many full adders are required to construct it?

Accepted Answer

3

Answer

2

Answer

4

Question 36

What is the primary function of a multiplexer in combinational logic?

Accepted Answer

To select one input signal from multiple inputs based on a select signal.

Answer

To store digital data

Answer

To amplify analog signals

Question 37

Which of the following logic families is known for its low power consumption and high speed?

Accepted Answer

CMOS

Answer

NMOS

Answer

TTL

Answer

ECL

Question 38

What is the fundamental difference between a combinational logic circuit and a sequential logic circuit?

Accepted Answer

Combinational logic circuits have no memory, while sequential logic circuits have memory elements.

Answer

Combinational logic circuits are more complex to design than sequential logic circuits.

Answer

Combinational logic circuits operate at higher speeds than sequential logic circuits.

Question 39

Which of the following tools is commonly used for designing and simulating combinational logic circuits?

Accepted Answer

Logic synthesis software

Answer

Presentation software

Answer

Word processors

Answer

Spreadsheets

Question 40

Find the canonical representation of the Boolean function F(A,B,C) = A'B + BC.

Accepted Answer

A' + BC

Answer

A + BC'

Answer

A' + B'C

Answer

AB + BC

Question 41

Which logic gate can be used to implement any other logic function?

Accepted Answer

NAND gate

Answer

AND gate

Answer

OR gate

Answer

NOT gate

Question 42

What is the primary function of a multiplexer in a combinational logic circuit?

Accepted Answer

To select and pass one of multiple input signals to the output.

Answer

To store data

Answer

To amplify input signals

Question 43

Which type of flip-flop is commonly used in sequential logic circuits?

Accepted Answer

D flip-flop

Answer

Capacitor

Answer

Resistor

Question 44

Which of the following is a defining characteristic of combinational logic circuits?

Accepted Answer

The output depends exclusively on the present inputs.

Answer

The output relies on both current and past inputs.

Answer

The output is retained and can be retrieved later.

Question 45

What is the main purpose of using logic diagrams in combinational logic design?

Accepted Answer

To graphically represent the circuit's logic functionality.

Answer

To simulate the circuit's behavior using software

Answer

To provide a detailed layout for manufacturing the circuit.

Question 46

The key difference between sequential and combinational logic circuits lies in:

Accepted Answer

Sequential logic circuits have memory.

Answer

Sequential logic circuits are more complex to design

Answer

Sequential logic circuits are faster

Answer

Sequential logic circuits use more logic gates

Question 47

What is the truth table output for A AND (B OR C) when A = 0, B = 1, and C = 0?

Accepted Answer

0

Answer

1

Answer

x (undefined)

Answer

-1

Question 48

What is the minimum number of 2-input NAND gates required to implement the logic function F = (A + B)(C + D')?

Accepted Answer

2

Answer

3

Answer

4

Answer

1

Question 49

What is the purpose of a multiplexer?

Accepted Answer

To select one of several input signals based on a control signal

Answer

To store data

Answer

To amplify a signal

Question 50

What is the difference between a decoder and an encoder?

Accepted Answer

A decoder converts binary code to specific outputs, while an encoder converts specific inputs to binary code.

Answer

A decoder is used for digital-to-analog conversion, while an encoder is used for analog-to-digital conversion.