Digital electronics multiplexers demultiplexers

Multiplexer And De-multiplexer

1. Multiplexer (data Selectors)
•Definition : 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.
•Several data input lines
•Some select line (less than the no. of input lines)
•Single output line
•If there are n data input lines and m select lines, then
2
m
= n

2. Functional Diagram Of a Multiplexer

3. 2 : 1 Multiplexer
S Z
0 I
0
1 I
1

4. 4 : 1 Multiplexer
S
0
S
1
Z
00I
0
01I
1
10I
2
11I
3

5. 8 : 1 Multiplexer
S
0
S
1
S
3
Z
000I
0
001I
1
010I
2
011I
3
100I
4
101I
5
110I
6
111I
7

6. Multiplexer Tree
•The Multiplexers with more number of inputs can be obtained by
cascading two or more multiplexers with less number of inputs.
•Below is a design of 16:1 MUX using 4 4:1 MUXs :-

7. Demultiplexer (Data Distributor)
•Definition : A DEMULTIPLEXER (DEMUX) basically reverses
the multiplexing function. It takes data from one line and
distributes them to a given number of output lines. For this
reason, the demultiplexers is also known as a data
distributor.
•Single data input lines
•Some select line (less than the no. of output lines)
•Several output line
•If there are n data output lines and m select lines, then
2
m
= n

8. Functional Diagram Of a Demultiplexer

9. 1 : 2 Demultiplexer
S
0
Y
0
Y
1
0D0
10D

10. 1 : 4 Demultiplexer
S
0
S
1
D
0
D
1
D
2
D
3
00D 0 0 0
010 D 0 0
100 0 D 0
110 0 0 D

11. 1 : 8 Demultiplexer

12. 1 : 8 Demultiplexer (Truth Table)
S
0
S
1
S
3
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
000D 0 0 0 0 0 0 0
0010 D 0 0 0 0 0 0
0100 0 D 0 0 0 0 0
0110 0 0 D 0 0 0 0
1000 0 0 0 D 0 0 0
1010 0 0 0 0 D 0 0
1100 0 0 0 0 0 D 0
1110 0 0 0 0 0 0 D

13. Demultiplexer Tree
F
0
F
1
F
3
F
2
F
4
F
5 F
6
F
7
S
0
S
1
S
2
1:2 Demux
1:2 Demux
1:2 Demux
1:2 Demux
1:2 Demux
1:2 Demux 1:2 Demux
INPUT
0
1
0
0
0
0
0
0
1
1
1
1
1 1
S
S
S
S
S
S
S
Below is a design of 1:8 MUX using 7 1: MUXs :-

14. Implementation Of Logic Functions
using Multiplexer
ABCF
0000
0011
0100
0110
1000
1010
1101
1111
f(a, b, c) = a’b’c + ab
0
0
0
1
0
0
1
1
ABC
S
2
S
0
S
1
F
8:1 MUX
0
4
3
1
2
5
6
7

15. ABCOF
0000
C
0011
0100
0
0110
1000
0
1010
1101
1
1111
C
0
0
1
BC
S
0
S
1
F
4:1 MUX
0
1
2
3
f(a, b, c) = a’b’c + ab

16. A B C D O F
0 0 0 0 0
D
0 0 0 1 1
0 0 1 0 0
D
0 0 1 1 1
0 1 0 0 1
D’
0 1 0 1 0
0 1 1 0 0
0
0 1 1 1 0
1 0 0 0 0
0
1 0 0 1 0
1 0 1 0 0
D’
1 0 1 1 1
1 1 0 0 1
1
1 1 0 1 1
1 1 1 0 1
1
1 1 1 1 1
f(a, b, c) = F=A’B’C’D + A’B’CD + A’BC’D’ + AB’CD +
ABC’D’ + ABC’D + ABCD’ +ABCD
D
0
1
ABC
S
2
S
0
S
1
F
8:1 MUX
0
4
3
1
2
5
6
7
D’

17. THANK YOU