- The demultiplexer is a type of electronic circuit that receives a single input signal and chooses one of several possible output routes to which the signal is transmitted.
- A demultiplexer is a circuit that can distribute or deliver multiple outputs from a single input (also known as a demux or data distributor). A demultiplexer can function as a single input device with multiple output switches. The output lines of the demultiplexer are numbered ‘n,’ the select lines are numbered’ and n = 2m. The control signal or select input code determines which output line the input must be sent to.
- The demux also functions as a binary to the decimal decoder. The data input line should be logic 1, and the binary input is sent to the select input lines. The output will be displayed on the corresponding line. This circuit is useful in the design of multiple combinational circuits. A demultiplexer circuit performs the opposite function of a multiplexer (hence the name).
Types of Demultiplexer
- There are various types of demultiplexers available depending on the output configuration, such as 1 to 2, 1 to 4, 1 to 8, and 1 to 16. These demultiplexers come in a variety of IC packages. The 74139 IC is a dual 1 to 4 Demux, the 74138 IC is a 1 to 8 Demux, the 74237 IC is a 1 to 8 Demux with address lines, the 74154 IC is a 1 to 16 Demux, and the 74159 IC is an open collector 1 to 16 Demux. As a result, Demux ICs are also referred to as Decoder ICs.
- 1:2 Demultiplexer
- 1:4 Demultiplexer
- 1:8 Demultiplexer
1. 1:2 Demultiplexer
- The 1 to 2 De-multiplexer has only two outputs, Y0 and Y1, one selection line, S0, and a single input, A. The input will be connected to one of the outputs based on the selection value. The 12 multiplexer’s block diagram and truth table are shown below.
Block Diagram:
Truth Table:
| In | C | Out1 | Out2 |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 |
| 0 | 1 | 0 | 0 |
| 1 | 1 | 0 | 1 |
- The logical expression of the term Y is as follows:Y0=S0′.A
Y1=S0.A - The following is the logical circuit of the above expressions.
2. 1×4 De-multiplexer:
- A single input (D), two selection lines (S1 and S0), and four outputs comprise a 1-to-4 demultiplexer (Y0 to Y3). For a specific combination of select lines, the input data is routed to any of the four outputs at any given time.
Block Diagram:
Truth Table:
| S1 | S0 | O |
|---|---|---|
| 0 | 0 | I0 |
| 0 | 1 | I1 |
| 1 | 0 | I2 |
| 1 | 1 | I3 |
The following is the logical expression for the term Y:
Y0=S1′ S0′ A
Y1=S1′ S0 A
Y2=S1 S0′ A
Y3=S1 S0 A
- The following is the logical circuit of the above expressions:
3. 1:8 Demultiplexer
- The 1-to-8 demultiplexer has a single input D, three select inputs S2, S1, and S0, and eight outputs Y0 to Y7. Because of its three select input lines and eight output lines, it is also known as a 3-to-8 demultiplexer. Depending on the combination of select inputs, it distributes one input line to one of eight output lines.
Block Diagram:
Truth Table:
- It sends one input line to one of the eight output lines based on the select input combinations, for example, input ‘D’ is connected to one of the outputs from X0 to X7 based on the S0, S1 & S2 select lines. Demux the truth table from 1 to 8.
| S2 | S1 | S0 | Y7 | Y6 | Y5 | Y4 | Y3 | Y2 | Y1 | Y0 |
|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | D |
| 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | D | 0 |
| 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | D | 0 | 0 |
| 0 | 1 | 1 | 0 | 0 | 0 | 0 | D | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 | D | 0 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 | 0 | D | 0 | 0 | 0 | 0 | 0 |
| 1 | 1 | 0 | 0 | D | 0 | 0 | 0 | 0 | 0 | 0 |
| 1 | 1 | 1 | D | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
- The following is the logical expression for the term Y:X0 = S2’ S1’ S0’ D
X1 = S2’ S1’ S0 D
X2 = S2’ S1 S0’ D
X3 = S2’ S1 S0 D
X4 = S2 S1’ S0’ D
X5 = S2 S1’ S0 D
X6 = S2 S1 S0’ D
X7 = S2 S1 S0 D - The following is the logical circuit of the above expressions.
Advantages of Demultiplexer
- Transmission of audio/video signals necessitates the use of multiplexers and demultiplexers.
- The combination of Demuxes and Muxes improves the communication system’s efficiency.
Disadvantages of Demultiplexer
- Bandwidth waste is possible.
- Delays may occur as a result of signal synchronization.
Applications of Demultiplexer
- Clock data recovery solutions employ demultiplexers.
- A demultiplexer, in conjunction with a multiplexer, is required for data transmission in any communication system.
- ATM packet broadcasting makes use of demultiplexers.
- Demultiplexers are used to store the output of the Arithmetic Logic Unit in the appropriate registers.
- They function as a serial-to-parallel converter.
- Wavelength routers also make use of them.
