Multiplexer / The Multiplexer (MUX)

Multiplexer is the general term used to describe the process of sending one or more analog or digital signals over a common transmission line at different times or speeds, and therefore, only the device we use to do this is called a multiplexer.

Shortened to "MUX" or "MPX", the Multiplexer is a combinational logic circuit designed to pass one of several input lines to a single common output line with the application of a control signal. Multiplexers work like very fast-moving rotary switches that connect or control multiple input lines called "channels" one by one to the output.

Multiplexers can be digital circuits made from high-speed logic gates used to modify digital or binary data. There may be analog types that use transistors, MOSFETs or relays to adjust one of the voltage or current inputs to a single output.

Basic Plurality Key

Basic Plurality Key

Since each layer of the switch is known as a wafer, the rotary switch, also called a wafer switch, is a mechanical device that rotates a shaft and selects the input. In other words, the rotary switch is a manual switch that you can use to select individual data or signal lines by translating their inputs as "on" or "off".

In digital electronics, multiplexers are also known as data selectors, because they can "select" each input line, they are constructed from individual analog switches coated in a single IC package, unlike "mechanical" type selectors such as normal traditional switches and relays.

They are used as a method of reducing the number of logic gates required in a circuit design, or when a single data line or bus is required to carry two or more different digital signals. For example, a single 8-channel Multiplexer, etc.

In general, the selection of each input line in a multiplexer is controlled by an additional input set called Control lines. Depending on the binary state of these control inputs, the appropriate data entry of "high" or "low" is connected directly to the output. Normally, a Multiplexer has a double number of 2n data entry lines and a series of "control" entries corresponding to the number of data entries.

Note that multiplexers are different from encoders. Encoders can pass an n-bit input pattern to multiple output lines that represent the binary encoded (BCD) output equivalent of the active input. As shown, basic logic we can create multiplexer from a simple 2 lines to 1 line (2 to 1) through NAND doors.

2-Input Multiplexer Design

2-Input Multiplexer design

The A input of this simple 2-1 line Multiplexer circuit, built from standard NAND doors, moves to check which input (I0 or I1) is transmitted to the output in Q.

From the accuracy table above, when logic A is low in 0, we can see that input I0 is blocked when passing the input I1's data from the NAND gate Multiplexer circuit to the output. Therefore, with a logic "0" or a logic "1" application in A, we can choose the appropriate input, I0 or I1, with the circuit acting as a single-pole double shot (SPDT) switch.

Since we only have one control line, then we can change only 21 inputs, and in this simple example, the 2-input Multiplexer connects one of the two 1-bit sources to a common output and produces a Multipler of 2 to 1 line. We can confirm this in the Boolean statement below.

Boolean expression

4×1 Channel Multiplexer

4×1 Channel Multiplexer

For this 4×1 Multiplexer above, the Boolean expression with inputs A to D and data selection lines A, B is given as follows:

4×1 Channel Multiplexer

In this example, only one of the four analog switches is turned off at any time. Connects only one of the input lines, A to D, to the only output in Q. Which key is turned off depends on the addressing entry code on lines "A" and "B". Therefore, in this example, to select input B to the output in Q, the binary input address must be "A" = logic "1" and "B" = logic "0". Thus, we can show the selection of data through the multiplexer as a function of data selection bits, as shown.

Multiplexer Input Line Selection

Multiplexer Input Line Selection

By adding more control address lines, (n) it will allow the multiplexer to control more entries as it can change 2n entries. However, each control line configuration will only connect one input to the output.

4-Channel Multiplexer Using Logic Gates

4-Channel Multiplexer Using Logic Gates

Multiplexer Symbol

Multiplexer Symbol

Multiplexers are not limited to migrating a number of different input lines or channels to a common single output. There are also types that can change their input to multiple outputs and have configurations such as 4×2, 8×3 or even 16×4, etc.

At this point, we also recommend that you know more about FET's, which are one of the infrastructures of multiplexer circuits. In this way, the issues will sit even more in your head.