Demultiplexer or Demux is a combinational circuit that accepts data from one input line and distributes over multiple output lines. Hence it is also called as line Converter or Distributor. This post will give you a brief idea about what is Demultiplexer, its types, Cascading of Demultiplexers, applications, advantages and disadvantages.
What is Demultiplexer
Demultiplexer is a combinational circuit that accepts multiplexed data and distributes over multiple output lines. In other words, the function of Demultiplexer is the inverse of the multiplexing operation. Similar to Multiplexer, the output depends on the control input.
The control input or the ‘select’ input decides which output line is connected to the input. Let us consider 1:4 Demultiplexer as shown in Fig.1 below where: D is the input, S0 and S1 are the control inputs, I0, I1, I2, I3 are the 4 output lines and the data is transmitted to one of the four outputs.
Fig. 1 – Schematic Diagram of 1:4 Demux
If S1S0 = 00, then I0 output of Demultiplexer receive the input data.
If S1S0 = 01, then output I1 receives the input data.
If S1S0 = 10, then input data is distributed to I2.
If S1S0 = 11, then output I3 receives the input data.
Hence, the logic equations for the outputs are:
- I0 = S’1 S’0 D
- I1 = S’1 S0 D
- I2 = S1 S’0 D
- I3 = S1 S0 D
Types of Demultiplexer
There are several types of Demultiplexers and few basic ones are listed as follows:
- 1:2 Demultiplexer
- 1:4 Demultiplexer
- 1:8 Demultiplexer
- 1:16 Demultiplexer
The 1:2 Demux consists of 1 data input, 1 control bit and 2 output bits. I0 and I1 are the two output bits, S is the control bit or the select bit and D is the input bit.
Fig (2) illustrates the block diagram and circuit diagram of 1:2 Demux.
Fig. 2 – (a) Block Diagram of 1:2 Demux (b) Circuit Diagram of 1:2 Demux using Logic Gates
The 1:4 Demux consists of 1 data input bit, 2 control bits and 4 output bits. D is the input bit, I0, I1, I2, I3 are the four output bits and S0 and S1 are the control bits.
Fig (3) illustrates the block diagram and circuit diagram of 1:4 Demux.
Fig. 3 – (a) Block Diagram of 1:4 Demux (b) Circuit Diagram of 1:4 Demux using Logic Gates
The 1:8 Demux consists of 1 data input bit, 3 control bits and 8 output bits. I0, I1, I2, I3, I4, I5, I6, I7 are the eight output bits, S0, S1 and S2 are the control bits and input D.
Fig (4) illustrates the block diagram and circuit diagram of 1:8 Demux.
Fig. 4 – (a) Block Diagram of 1:8 Demux (b) Circuit Diagram of 1:8 Demux using Logic Gates
The 1:16 Demux consists of 1 data input bit, 4 control bits and 16 output bits. I0, I1, I2, I3, I4, I5, I6, I7, I8, I9, I10, I11, I12, I13, I14, I15 are the sixteen output bits, S0, S1, S2 and S3 are the control bits and D is the input bit.
Fig (5) illustrates the block diagram and circuit diagram of 1:16 Demux.
Fig. 5 – (a) Block Diagram of 1:16 Demux (b) Circuit Diagram of 1:16 Demux using Logic Gates
Cascading of Demultiplexers
Cascading refers to a process where large Demuxes can be designed and implemented using smaller Demuxes.
Example: 1:8 Demux can be designed using two 1:4 Demuxes and similarly 1:16 Demuxes can be designed using one 1:2 Demux and two 1:8 Demultiplexers as shown in the figure.
Fig. 6 – (a) 1:8 Demux Designed Using Two 1:4 Demuxes (b) 1:16 Demux Designed Using Two 1:8 Demuxes
Applications of Demultiplexers
The applications include:
- Demultiplexers are used in clock data recovery solutions.
- Demultiplexer along with multiplexer is necessary for any communication system for data transmission.
- Demultiplexers are used in ATM packets broadcasting.
- The output of Arithmetic Logic Unit is stored in respective registers using Demultiplexers.
- They act as Serial to Parallel converter.
- They are also used in Wavelength routers.
Fig. 7 – Applications of Demultiplexer
Advantages of Demultiplexers
The advantages include:
- Transmission of Audio/Video signals requires combination of Multiplexers and Demultiplexers.
- They are also used as decoders in security systems like banking sectors.
- Combination of Demuxes with Muxes increases the efficiency of the communication system.
Disadvantages of Demultiplexers
The disadvantages include:
- Wastage of Bandwidth might occur.
- Delays might occur due to synchronization of signals.