Digital Circuits Questions and Answers – Demultiplexers (Data Distributors) – 1

This set of Digital Electronics/Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Demultiplexers (Data Distributors) – 1”.

1. The word demultiplex means ___________
a) One into many
b) Many into one
c) Distributor
d) One into many as well as Distributor

Explanation: The word demultiplex means “one into many” and distributor. A demultiplexer sends a single input to multiple outputs, depending on the select lines. It is clear from the diagram:

2. Why is a demultiplexer called a data distributor?
a) The input will be distributed to one of the outputs
b) One of the inputs will be selected for the output
c) The output will be distributed to one of the inputs
d) Single input to Single Output

Explanation: A demultiplexer sends a single input to multiple outputs, depending on the select lines. For one input, the demultiplexer gives several outputs. That is why it is called a data distributor.

3. Most demultiplexers facilitate which type of conversion?
b) Single input, multiple outputs
c) AC to DC
d) Odd parity to even parity

Explanation: A demultiplexer sends a single input to multiple outputs, depending on the select lines. Demultiplexer converts single input into multiple outputs.

4. In 1-to-4 demultiplexer, how many select lines are required?
a) 2
b) 3
c) 4
d) 5

Explanation: The formula for total no. of outputs is given by 2n, where n is the no. of select lines. Therefore, for 1:4 demultiplexer, 2 select lines are required.

5. In a multiplexer the output depends on its ___________
a) Data inputs
b) Select inputs
c) Select outputs
d) Enable pin

Explanation: A demultiplexer sends a single input to multiple outputs, depending on the select lines. As the select input changes, the output of the multiplexer varies according to that input.

6. In 1-to-4 multiplexer, if C1 = 0 & C2 = 1, then the output will be ___________
a) Y0
b) Y1
c) Y2
d) Y3

Explanation: It can be calculated from the figure shown below:

For C0 =1 and C1 =0, Y1 will be the output as 0 and 1 are the bit combinations of 1.

7. In 1-to-4 multiplexer, if C1 = 1 & C2 = 1, then the output will be ___________
a) Y0
b) Y1
c) Y2
d) Y3

Explanation: It can be calculated from the figure shown below:

For C0 =1 and C1 =0, Y3 will be the output as 0 and 1 are the bit combinations of 1.

8. How many select lines are required for a 1-to-8 demultiplexer?
a) 2
b) 3
c) 4
d) 5

Explanation: The formula for total no. of outputs is given by 2n, where n is the no. of select lines. In this case n = 3 since 23 = 8.

9. How many AND gates are required for a 1-to-8 multiplexer?
a) 2
b) 6
c) 8
d) 5

Explanation: The number of AND gates required will be equal to the number of outputs in a demultiplexer, which are 8.

10. The output Q4 of this 1-to-8 demultiplexer is ____________

a) Q2.(Q1)’.Q0.I
b) Q2.Q1.(Q0)’.I
c) Q2.(Q1)’.(Q0)’.I
d) Q2.(Q1).Q0.I

Explanation: The logic gates for Q4 implement the function Q2.(Q1)’.(Q0)’. This means:
Q2 should be high (1).
Q1 should be low (0) – denoted by the ‘ symbol after Q1.
Q0 should be low (0) – denoted by the ‘ symbol after Q0.
When the input I is high (1), the output Q4 will also be high (1) because all the conditions for Q4 are met (Q2 is high, Q1 is low, and Q0 is low).

Therefore, the output Q4 of the demultiplexer is correctly represented by Q2.(Q1)’.(Q0)’.I.

11. Which IC is used for the implementation of 1-to-16 DEMUX?
a) IC 74154
b) IC 74155
c) IC 74139
d) IC 74138

Explanation: IC 74154 is used for the implementation of 1-to-16 DEMUX, whose output is inverted input.

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