1.Combinational Circuit 2. Sequential Circuit 3. Multiplexer (Data Selectors) 4. Functional Diagram Of a Multiplexer 5. 2 : 1 Multiplexer 6. 4 : 1 Multiplexer 7. 8 : 1 Multiplexer 8. Multiplexer Tree 9. Demultiplexer (Data Distributor) 10. Functional Diagram Of a Demultiplexer 11. 1:2 DeMultiplexer 12. 1:4 DeMultiplexer 13. 1:8 DeMultiplexer 14. Demultiplexer Tree 15. Implementation Of Logical Function using Multiplexer

1. Digital Electronics
Combinational Circuit
Sequential Circuit
Prepared by
Sweta Kumari Barnwal
Assistant Professor
Arka Jain University
Sweta Kumari Barnwal 1

2. Combinational Circuit
 A combinational circuit that consists of logic gates
whose outputs, at any time, are determined by
combining the values of the present inputs.
 For n input variables, there are 2n possible binary
output combinations.
 For each binary combination of the input variables,
there is one possible output.
 A combinational circuit can be described by:
a) A truth table that lists the output values for
each combination of the input variables, or
b) m Boolean functions, one for each output
variable.
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3. Continued….
n i/p m o/p
Lines lines
Here, m = 2n
 It has not any memory/storage unit therefore its output does not
depend upon the previous input output.
 Examples: Multiplexer, Demultiplexer, Adder, Subtractor,
Encoder, Decoder etc.
Combinational
Circuit
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4. Sequential Circuit
Sequential circuits consist combinational logic circuit as well as
memory elements (used to store certain circuit states). Hence,
outputs depend on BOTH current input values and previous
input values (kept in the storage elements).
Examples: Flip Flop, Latch, Counter, Register etc.
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5. Multiplexer (DataSelectors)
 It 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.
 In single line we can say that it is a logical device/circuit having
many input lines & only one output line.
Severalnumberofdata input lines
Someselect lines (<input lines)
Singleoutput line
If there data input lines = n
(where n is 2k and k is integer, k = 1,2,3,4,5………)
then number of selectlines = m
Therefore, 2m = n
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6. Functional DiagramOfaMultiplexer
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7. 2 : 1Multiplexer
S
0
1
Y
I0
I1
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8. 4: 1Multiplexer
S1 S0 Y
0 0 I0
0 1 I1
1 0 I2
1 1 I3
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9. 8: 1Multiplexer
S0 S1 S2 Y
0 0 0 I0
0 0 1 I1
0 1 0 I2
0 1 1 I3
1 0 0 I4
1 0 1 I5
1 1 0 I6
1 1 1 I7
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10. Multiplexer Tree
•
The Multiplexers with more number of inputs can be obtained
by cascading two or more multiplexers with less number of
inputs.
Below diagram is showing 16:1 MUX using four 4:1 MUXs :-•
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11. Demultiplexer (DataDistributor)
 It basicallyreverses the multiplexing function. It takesdata from
one line and distributes them to a given number of output lines.
For this reason, the demultiplexer is also known as a data
distributor.
 In short, it has single input and multiple output lines.
Severalnumberofdata output lines
Someselect lines (<output lines)
Singleinput line
If there data output lines = n
(where n is 2k and k is integer, k = 1,2,3,4,5………)
then number of selectlines = m
Therefore, 2m = n
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12. Functional DiagramOf a Demultiplexer
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13. 1: 2Demultiplexer
S0 Y0 Y1
0 D 0
1 0 D
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14. 1 : 4Demultiplexer
S1 S0 D0 D1 D2 D3
0 0 D 0 0 0
0 1 0 D 0 0
1 0 0 0 D 0
1 1 0 0 0 D
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15. 1 : 8Demultiplexer
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16. 1: 8Demultiplexer (TruthTable)
S2 S1 S0 D0 D1 D2 D3 D4 D5 D6 D7
0 0 0 D 0 0 0 0 0 0 0
0 0 1 0 D 0 0 0 0 0 0
0 1 0 0 0 D 0 0 0 0 0
0 1 1 0 0 0 D 0 0 0 0
1 0 0 0 0 0 0 D 0 0 0
1 0 1 0 0 0 0 0 D 0 0
1 1 0 0 0 0 0 0 0 D 0
1 1 1 0 0 0 0 0 0 0 D
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17. DemultiplexerTree
Below isadesignof 1:8 DeMUXusingseven1: 2 DeMUXs:
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18. Implementation Of LogicalFunction usingMultiplexer
A B C F
0 0 0 0
0 0 1 1
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 1
F(A, B, C) = A’B’C + AB
0
1
0
0
0
0
1
1
S2 S1 S0
A B C
F
0
1
2
3 8:1 MUX
4
5
6
7
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19. A B C Y
0 0 0 0
0 0 1 1
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 1
F
C
0
0
1
C
0
0
1
A B
S S1 0
F
0
1 4:1MUX
2
3
F(A, B, C) = A’B’C + AB
A B F
0 0 C
0 1 0
1 0 0
1 1 1
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20. A B C D Y
0 0 0 0 0
0 0 0 1 1
0 0 1 0 0
0 0 1 1 1
0 1 0 0 1
0 1 0 1 0
0 1 1 0 0
0 1 1 1 0
1 0 0 0 0
1 0 0 1 0
1 0 1 0 0
1 0 1 1 1
1 1 0 0 1
1 1 0 1 1
1 1 1 0 1
1 1 1 1 1
F
D
D
D
0
0
D
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
A B C
S S S2 1 0
F
0
1
2
3 8:1 MUX
4
5
6
7
D’
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21. THANKYOU
Sweta Kumari Barnwal 21