A multiplexer is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. It has multiple data inputs, a single output, and select lines that determine which input is directed to the output. A demultiplexer performs the opposite function, taking a single input and distributing it to one of multiple outputs based on the select lines. Multiplexers and demultiplexers come in various configurations depending on the number of inputs and outputs, such as 2:1, 4:1, 16:1 or 32:1. They are basic building blocks used in digital systems and communication networks to efficiently route signals.

1. MULTIPLEXERS &
DEMULTIPLEXERS
Dr. Sonali Vyas

2. MULTIPLEXERS
• A multiplexers (MUX) is a device that allows digital
information from several sources to be routed onto a
single line for transmission over that line to a common
destination.
• The basic multiplexers has several data input lines and
a single output line. It also has data- select inputs,
which permit digital data on any one of the inputs to
be switched to the output line.

3. Functional diagram of MUX

4. • A multiplexer selects binary information
present on any one of the input lines,
depending upon the logic status of the
selection inputs, and routes it to the output
line.
• If there are n selection lines, then the number
of maximum possible input lines is 2n and the
multiplexer is referred to as a 2n -to-1
multiplexer or 2n ×1 multiplexer

5. Consider an integer ‘m’, which is
constrained by the following relation:
m = 2n, where m and n are
both integers.
• A m-to-1 Multiplexer has
• m Inputs: I0, I1, I2, ................ I(m-1)
• one Output: Y
• n Control inputs: S0, S1, S2, ...... S(n-1)
• One (or more) Enable input(s)
such that Y may be equal to one of the inputs, depending upon
the control inputs.

6. 6
Example: A 4-to-1 Multiplexer
I0
A 4-to-1 Multiplexer:
I1
I2
I3
S0 S1
Y
1 output
n control inputs
2n inputs
Enable (G)

7. 7
Two-input multiplexer

8. 8
Four-input multiplexer

9. 9
Characteristic Table of a Multiplexer
• If the MUX is enabled,
s0 s1
0 0 Y=I0
0 1 Y=I1
1 0 Y=I2
1 1 Y=I3
Putting the above information in the form of a Boolean equation,
Y =G. I0. S’1. S’0 + G. I1. S’1. S0 + G. I2. S1. S’0 + G. I3. S1. S0

10. Multiplexer come in multiple
variations:
2 : 1 multiplexer
4 : 1 multiplexer
16 : 1 multiplexer
32 : 1 multiplexer

11. Demultiplexers
• A demultiplexer performs the reverse
operation of a multiplexer i.e. it receives one
input and distributes it over several outputs.
• It has only one input, n outputs, m select
input. At a time only one output line is
selected by the select lines and the input is
transmitted to the selected output line.

12. 12
General demultiplexer
Functional diagram:- The large arrow indicates one or more lines.
The select i/p code determines to which
output the DATA input will be transmitted
In other words, the demultiplexer takes
one data input source and selectively
distributes it to 1 of N output channels

13. Block diagram: Truth Table:
Demultiplexers comes in multiple variations.
1 : 2 demultiplexer
1 : 4 demultiplexer
1 : 16 demultiplexer
1 : 32 demultiplexer

14. 14
A 1-line-to-4-line demultiplexer.