The multiplexer is a combinational logic circuit designed to switch one of several input lines to a single common output line by the application of a control logic. The input has a maximum of 2N data inputs (where N = selection or control lines) and single output line.
In short, Multiplexer is also known as Mux or data selector or many to one circuit or universal logic circuit or parallel to serial circuit.
The relation between the selection/control lines and the input lines is given as
M = 2N
In simple language, a multiplexer is a circuit that selects only one output from multiple inputs. Figure 2(a) shows 2×1 mux symbol. Figure 2(b) shows its equivalent circuit.
4×1 Multiplexer
number of selection/control input, N = 2 (S1 & S0)
number of data inputs =2N = 22 = 4 (I3, I2, I1 & I0)
number of output = 1 (Y)
One of these four inputs (I3, I2, I1 & I0) will be connected to the output (Y) based on the combination of inputs present at these two selection lines (S1 & S0). The truth table of 4×1 Mux is as follows.
| Selection/Control Lines | Output | |
| S1 | S0 | Y |
| 0 | 0 | I0 |
| 0 | 1 | I1 |
| 1 | 0 | I2 |
| 1 | 1 | I3 |
As from Truth table, we can directly write the Boolean function for output, Y as
4×1 Mux can be implemented by using Inverters, AND gates & OR gate as shown in figure 3.
Applications of Multiplexer
Mux is implemented in various domains where there is a necessity of transmitting a large amount of data with the use of single line.
1. Communication System
A Mux is implemented in this system to increase efficiency. Using a single transmission line, various types of data (audio, video, etc.) are transmitted at the same instant.
2. Computer Memory
In a computer, the huge quantity of memory is implemented by means of the Mux. It also has an advantage of a reduction in the number of copper lines which are used for the connection of memory to other parts of the computer.
3. Computer System of a Satellite Transmission
Mux is used for the data signals to be transmitted from spacecraft or computer system of a satellite to the earth by means of GPS.
4. Telephone Network
In a telephone network, the multiple audio signals are brought into a single line and transmitted with the implementation of a Mux. By this way, the numerous audio signals are made isolated and ultimately the recipient will receive the required audio signals.
Advantages of Multiplexer
1. Mux makes the transmission circuit economical and less complex.
2. Analog switching current is low of order 10mA-20mA. Due to such a low magnitude of the current, the heat dissipation is very low.
3. The ability of Mux to switch digital signals can be extended to switch to a video signal, audio signals etc.
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