Digital electronics consists of combinational circuits and sequential circuits. Combinational circuit elements are the ones whose output depends on the present inputs and do not depend on the past inputs. Logic gates, decoder, encoder, etc. are examples of the combinational circuit element. Here, we are going to discuss two of such circuit elements.
Multiplexer and Demultiplexer are two combinational circuit elements. In this article, we will discuss the difference between multiplexer and demultiplexer.
Difference between Multiplexer and Demultiplexer in tabular form
| Multiplexer | Demultiplexer |
| The multiplexer is a combinational circuit element that chooses one out of many inputs as output depending on the input(s) of selection line(s) | The demultiplexer is a combinational circuit element that is used to channel the input to one of the many output lines depending on the input(s) of the selection line(s). |
| It has multiple input pins. | It has only one input pin apart from selection lines. |
| It has only one output pin. | It has multiple output pins. |
| If a multiplexer has 2n number of input lines then it will have n number of selection lines or vice versa. | If a demultiplexer has n number of selection lines then it will have 2n number of output lines or vice versa. |
| Multiplexer acts as a digital switch. | Purpose Multiplexer acts as a digital switch. Demultiplexer acts as a signal allocator. |
| A multiplexer is used for multiplexing purposes, in communication schemes such as TDM, in parallel to serial converter, etc. | A demultiplexer is used for demultiplexing purposes, in communication schemes such as TDM, in serial to parallel converter, etc. |
What is Multiplexer?
A multiplexer, also known as MUX is a combinational circuit element that is used to choose one among many inputs as its only output depending on the input given to the selection line. Multiplexer acts as a digital switch. It is used to switch the value of the output from one input value to another depending on the value of selection inputs.
If a MUX has 2n number of input lines then it must have n number of selection line pins, i.e., if a MUX has 8 = 23 number of input pins then it must have 3 selection lines. Multiplexers are expressed as 2n:1 multiplexer such as 2:1 MUX, 4:1 MUX, 8:1 MUX, 16:1 MUX etc. Here 2n is the number of inputs, 1 denotes the number of outputs and n is the number of selection line. Block diagram of an 8:1 MUX is given below:
The truth table of an 8:1 MUX is given below:
| S2 | S1 | SO | Output (F) |
| 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 |
Where, S2, S1, S0 are the selection inputs,
And, I0, I1, I2, I3, I4, I5, I6, I7 are the input lines.
A multiplexer is a very important component of electronics. It is used as a digital switch, parallel to serial converter, for multiplexing signals in TDM and many more purposes.
What is a Demultiplexer?
Demultiplexer, also known as DeMUX is a combinational circuit element that is used to channel the input to one of the many outputs depending on inputs of the selection lines. DeMUX acts as an allocator. It channels its input to one of its many outputs depending on the values of the selection line.
If a DeMUX has n number of selection line then it will have 2n number of output lines i.e., if a DeMUX has 3 number of selection lines then it will have 23 = 8 number of output lines. DeMUX is expressed as 1:2n DeMUX such as 1:2 DeMUX, 1:4 DeMUX, 1:8 DeMUX, 1:16 DeMUX, etc. where 2n denotes the number of output lines, n denotes the number of selection line and 1 denotes the number of the input pin. Block diagram of a 1:8 DeMUX is given below:
The truth table of a 1:8 DeMUX is Given below:
| S2 | S1 | S0 | F0 | F1 | F2 | F3 | F4 | F5 | F6 | F7 |
| 0 | 0 | 0 | IP | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | IP | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 1 | 0 | 0 | 0 | IP | 0 | 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 | 0 | 0 | IP | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | IP | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | IP | 0 | 0 |
| 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | IP | 0 |
| 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | IP |
F0, F1, F2, F3, F4, F5, F6, F7 are the output lines, Where, S2, S1, S0 are the selection inputs,
And, IP is the Input.
Demultiplexers are also very important in electronics. They are used to convert serial data into parallel data, used the receiver section of TDM to demultiplex the multiplexed signals, etc.
Conclusion
We can say that multiplexer and demultiplexer are complementary in nature. Their properties and working complement each other. Both of them are widely used in combinational circuits.
Author
Subhrajyoti Choudhury
