Combinational Logic Circuits: Master the Fundamentals of Digital Logic Design

Question 1

Which of the following is NOT a fundamental logic gate?

Accepted Answer

Flip-Flop

Answer

AND

Answer

NAND

Answer

OR

Question 2

What is the primary purpose of a multiplexer?

Accepted Answer

Selecting one of multiple input signals based on a control signal

Answer

Amplifying analog signals

Answer

Generating clock pulses

Answer

Performing complex mathematical operations

Question 3

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

Accepted Answer

Output solely determined by current inputs

Answer

Employs feedback mechanisms to determine output

Answer

Involves sequential operations such as storing data

Answer

Requires a clock signal to operate

Question 4

What is the primary advantage of using programmable logic devices (PLDs) in digital logic design?

Accepted Answer

Enhanced flexibility and reprogrammability

Answer

Significantly higher speed compared to traditional logic gates

Answer

Reduced power consumption

Answer

Lower manufacturing cost

Question 5

Identify the primary operations performed by a 4-bit subtractor and a 4-bit adder, explaining how they differ.

Accepted Answer

Adders perform addition, while subtractors perform subtraction.

Answer

Both adders and subtractors perform multiplication.

Answer

Subtractors perform division, while adders perform addition.

Answer

Both adders and subtractors perform logical operations like AND and OR.

Question 6

Which of the following is NOT a function of a multiplexer?

Accepted Answer

Demultiplexing

Answer

Data selection

Answer

Combining multiple data lines

Answer

Signal routing

Question 7

What is a key advantage of using programmable logic devices (PLDs) over discrete logic gates in combinational logic circuit design?

Accepted Answer

Increased flexibility and reduced circuit complexity through reconfigurability.

Answer

Lower cost

Answer

Improved reliability

Question 8

In a combinational logic circuit, the output depends only on which input(s)?

Accepted Answer

Present inputs

Answer

Previous inputs

Answer

Future inputs

Answer

A specific sequence of inputs

Question 9

Which of the following types of combinational logic circuits is designed to perform arithmetic operations?

Accepted Answer

Adder

Answer

Flip-flop

Answer

Timer

Answer

Register

Question 10

What is the primary purpose of using De Morgan's theorem in combinational logic design?

Accepted Answer

Simplifying complex logic expressions by converting between AND-OR and OR-AND forms.

Answer

Increasing the speed of the circuit.

Answer

Converting sequential logic to combinational logic.

Answer

Reducing the number of logic gates required.

Question 11

In a combinational logic circuit, a 'don't care' condition occurs when:

Accepted Answer

The output is unspecified or irrelevant for a particular input combination.

Answer

The output is always 1.

Answer

The output is always 0.

Question 12

Which of the following gates can be used to implement all other logic gates (i.e., it is a universal logic gate)?

Accepted Answer

NAND

Answer

AND

Answer

NOT

Answer

OR

Question 13

What is the primary function of a multiplexer?

Accepted Answer

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

Answer

To convert analog signals to digital

Answer

To amplify incoming signals

Question 14

Which Boolean expression represents an XOR gate?

Accepted Answer

AB' + A'B

Answer

(A + B')(A' + B)

Answer

A'B + AB'

Answer

AB + A'B'

Question 15

What is the key difference between combinational and sequential circuits?

Accepted Answer

Combinational circuits have no memory, while sequential circuits utilize memory elements

Answer

Combinational circuits exclusively use AND gates, while sequential circuits exclusively use OR gates

Answer

Combinational circuits are more complex than sequential circuits

Question 16

To design a full adder, which logic gates are required?

Accepted Answer

AND, OR, XOR

Answer

AND, OR, NOT

Answer

NAND, NOR, EX-OR

Answer

NOT, NAND, EX-NOR

Question 17

Which of the following is a type of multiplexer?

Accepted Answer

8-to-1 MUX

Answer

Decoder

Answer

Comparator

Answer

Flip-flop

Question 18

In a combinational logic circuit, the output is determined by:

Accepted Answer

Current inputs only

Answer

Previous inputs and feedback signals

Answer

Random factors and circuit history

Answer

Clock signals and stored data

Question 19

Which of the following techniques is used to optimize combinational logic circuits?

Accepted Answer

Logic minimization

Answer

Linear programming

Answer

Numerical analysis

Answer

Statistical modeling

Question 20

What is the output of the logic circuit represented by the expression: (A NAND B) NOR (C XOR D)?

Accepted Answer

NOT ((A NAND B) OR (C XOR D))

Answer

(A NAND B) AND (C XOR D)

Answer

(A XOR B) NOR (C AND D)

Answer

NOT ((A OR B) NOR (C XOR D))

Question 21

Which combinational logic circuit compares two binary numbers and outputs a '1' if they are equal?

Accepted Answer

Comparator

Answer

Flip-flop

Answer

Adder

Answer

Multiplexer

Question 22

In a combinational logic circuit, the output is determined solely by:

Accepted Answer

The present inputs

Answer

Random factors

Answer

Past inputs

Answer

A clock signal

Question 23

In a multiplexer circuit, which input line is selected by the control inputs?

Accepted Answer

Data input line

Answer

Output line

Answer

Ground line

Answer

Control input line

Question 24

What is a key advantage of using combinational logic circuits?

Accepted Answer

Fast operation

Answer

Limited applications

Answer

High power consumption

Answer

Complex design

Question 25

In a combinational logic circuit, a feedback loop is:

Accepted Answer

Not present

Answer

Required for clock synchronization

Answer

Essential for stable operation

Answer

Used to store data

Question 26

Determine the output of a 2-input AND gate when one input is 1 and the other is 0.

Accepted Answer

0

Answer

Z

Answer

X

Answer

1

Question 27

Which circuit is designed to compare two binary numbers?

Accepted Answer

Comparator

Answer

Multiplexer

Answer

Adder

Answer

Decoder

Question 28

What is the primary function of a multiplexer?

Accepted Answer

To select one of several data inputs

Answer

To store data in memory

Answer

To amplify digital signals

Answer

To convert analog to digital signals

Question 29

What is the minimum number of logic gates required to implement a full adder?

Accepted Answer

10

Answer

8

Answer

14

Answer

12

Question 30

Identify the logic gate with only one output.

Accepted Answer

Inverter

Answer

NAND

Answer

OR

Answer

AND

Question 31

Which of the following is NOT classified as a type of combinational logic circuit?

Accepted Answer

Flip-flop

Answer

Adder

Answer

Comparator

Answer

Multiplexer

Question 32

State the primary advantage of using combinational logic circuits.

Accepted Answer

Simplicity and high speed

Answer

High reliability

Answer

Flexibility in design

Answer

Low power consumption

Question 33

Identify the logic gate that is NOT considered a basic gate used in the construction of all other combinational circuits.

Accepted Answer

XOR Gate

Answer

OR Gate

Answer

AND Gate

Answer

NOT Gate

Question 34

What is the name of a circuit that adds two binary numbers together?

Accepted Answer

Full Adder

Answer

Multiplexer

Answer

Decoder

Question 35

Which type of circuit selects one out of several input lines based on a control signal?

Accepted Answer

Multiplexer

Answer

Encoder

Answer

Comparator

Answer

Demultiplexer

Question 36

What is the Boolean expression for a 2-input XOR gate?

Accepted Answer

A'B + AB'

Answer

A'B'

Answer

AB

Answer

A + B

Question 37

A circuit that compares two binary numbers and outputs whether they are equal is called a:

Accepted Answer

Comparator

Answer

Subtractor

Answer

Encoder

Answer

Adder

Question 38

Which of the following is NOT a characteristic of a combinational logic circuit?

Accepted Answer

Output depends on past inputs and current inputs.

Answer

No memory elements are involved.

Answer

Output changes instantaneously with changes in input.

Answer

Output is determined solely by the current inputs.

Question 39

In a full adder, how is the sum output generated?

Accepted Answer

Using an XOR gate with inputs from the two input bits and the carry-in.

Answer

Using an OR gate with inputs from the two input bits and the carry-in.

Answer

Using an AND gate with inputs from the two input bits.

Question 40

What type of circuit converts a BCD (Binary Coded Decimal) input into a 7-segment display output?

Accepted Answer

BCD to 7-segment decoder

Answer

Demultiplexer

Answer

7-segment to BCD encoder

Answer

Multiplexer

Question 41

Which of the following is a method for simplifying Boolean expressions?

Accepted Answer

Karnaugh Map

Answer

Flip-Flop

Answer

Full Adder

Answer

Sequential Logic

Question 42

Which of the following statements is **NOT** a characteristic of a combinational logic circuit?

Accepted Answer

The output depends on both the current and past inputs.

Answer

Combinational circuits do not contain memory elements.

Answer

The output is solely determined by the current input values.

Answer

The output changes instantaneously with input changes.

Question 43

What logic gates are required to implement a half-adder, which adds two single-bit inputs and produces a sum and a carry-out bit?

Accepted Answer

XOR and AND gates

Answer

AND and NOT gates

Answer

OR and NOT gates

Answer

XOR and OR gates

Question 44

How can a 4-bit binary subtractor be implemented using full adders?

Accepted Answer

By taking the 2's complement of the subtrahend and adding it to the minuend.

Answer

By using a separate subtractor circuit.

Answer

By directly subtracting the subtrahend from the minuend.

Question 45

Which of the following is **NOT** a typical output of a comparator circuit, which compares two binary numbers and indicates their relationship?

Accepted Answer

The sum of the two numbers

Answer

Less than

Answer

Greater than

Answer

Equal

Question 46

In a multiplexer (MUX), which component determines which of the multiple inputs is selected and outputted to a single output?

Accepted Answer

Select lines

Answer

Control lines

Answer

Output lines

Answer

Data lines

Question 47

A 4-to-1 MUX has 4 data inputs (D0-D3) and 2 select lines (S0, S1). What is the output (Y) when S0=1 and S1=0?

Accepted Answer

D2

Answer

D3

Answer

D1

Answer

D0

Question 48

Which of the following is **NOT** a common application of combinational logic circuits?

Accepted Answer

Memory storage

Answer

Data routing and selection

Answer

Data comparison

Answer

Arithmetic operations

Question 49

What information does a truth table provide regarding a logic circuit?

Accepted Answer

The output for every possible input combination.

Answer

The physical implementation of the circuit.

Answer

The logic gates used in the circuit.

Answer

The timing diagram of the circuit.

Question 50

What is the main advantage of using Karnaugh maps (K-maps) to simplify Boolean expressions and design logic circuits?

Accepted Answer

K-maps visually identify adjacent minterms, allowing for grouping and simplification.

Answer

They provide a graphical representation of logic gates.

Answer

They automate the process of circuit design.