Multiplexer (MUX) and Demultiplexer (DEMUX) Applications
Key Takeaways
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A multiplexer is also called a data selector, as it utilizes ‘SELECT’ inputs to route the desired data input to the output.
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Multiplexers can easily replace logic gates and implement logic with the advantage of changing the function whenever required.
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Multiplexer and demultiplexer applications are present in data acquisition systems, sensor arrays, multi-channel systems, etc.
MUX and DEMUX
Multiplexers (MUX) and demultiplexers (DEMUX) play a crucial role in reducing complexity in wireless systems, satellite applications, space communication, and high-speed optical circuits. Their applications include digital systems, computer networks, and communication systems.
In most designs, MUX and DEMUX devices work as a pair. The multiplexer combines multiple signals onto a single line. The demultiplexer separates them back out at the other end. These components reduce the cost, space, and power requirements in electronic circuits.
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System Optimization With Multiplexers and Demultiplexers |
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Feature |
Multiplexer |
Demultiplexer |
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Cost Saving |
When a single device needs to process multiple input signals, a multiplexer can be used to select and route the signals to a common processing unit. Using multiplexers eliminates the need for multiple processing units, keeping overall costs down. |
Whenever data from one source needs to reach multiple devices, a demultiplexer can send it to the right destination. Demultiplexers enable the transmission of data to different output channels such as video, audio, etc. They also eliminate the need for duplicate hardware, reducing overall system cost. |
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Space Saving |
Consolidate multiple signals onto a single transmission line, therefore reducing the number of lines or devices needed and frees up valuable board space. |
Complements by distributing a single signal across multiple channels, eliminating the need for multiple input ports on connected devices. Together, both components help shrink the overall footprint of a design. |
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Power Saving |
Processes multiple signals through a single device, which directly reduces power consumption and improves overall efficiency. |
Contributes by removing the need for duplicate hardware across output channels, they help keep power draw low. |
Most MUX and DEMUX applications use CMOS semiconductor devices or Heterojunction Bipolar Transistors (HBT). The applications requiring low power consumption focus on CMOS-based implementation, whereas high-speed and high-frequency applications are better realized using HBT technology. The sections below give two examples of MUX and DEMUX applications.
Multiplexer (MUX) and Demultiplexer (DEMUX) Application Examples
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Logic circuit |
Application |
Description |
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Multiplexer |
Logic generator |
Replaces the combination of logic gates and implements logic functions with the provision of changing the function easily. |
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Parallel-to-serial data converter |
Enables conversion of parallel data to serial form and transmits over a single output line. |
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Demultiplexer |
Serial-to-parallel data converter |
Serial data is converted to parallel data and distributed to multiple devices. |
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Single-source to multiple destinations |
Data can be sent from a single source to multiple destinations chosen based on the select signal. |
Multiplexers as Logic Generators
One of the most practical advantages of multiplexers is their ability to replace combinations of discrete logic gates. Instead of wiring up several AND, OR, and NOT gates to build a Boolean expression, a single MUX IC can implement the same function. Multiplexers make it easy to implement logic and offer the added advantage of quickly changing the function whenever required. A single multiplexer IC, can handle even complex logic expressions efficiently while reducing circuit complexity and saving space.
For example, consider the function F = A ⊕ B ⊕ C . This function uses three input variables: A, B, and C. Implement it by selecting a multiplexer with three data select inputs: S0, S1, and S2. The three data select inputs make it an 8-to-1 MUX, as they allow eight possible input combinations. You can then use a truth table to map these input combinations to the desired output.
Truth table of the function F = A ⊕ B ⊕ C and implementation using MUX
From the truth table, it is clear the function equals 1 only when ABC corresponds to 001, 010, 100, and 111. Data inputs D1, D2, D4, and D7 are connected to binary 1 and the rest of the data inputs to 0. This approach is used in function generators, arithmetic logic units, control units, digital signal processors, memory systems, I/O interfaces, etc.
Parallel-to-Serial Data Conversion With Multiplexers
Parallel data can be converted to serial data using a multiplexer circuit. The multiplexer and counter enable parallel to serial data conversion. The output of the counter is connected to the select inputs of the multiplexer. The parallel data is applied to the multiplexer inputs sequentially as the counter counts.
When the counter finishes one complete count sequence (say 000 to 111), the parallel data is converted into serial data and is given to the output line. The multiplexer functioning as a parallel-to-serial-data converter is used in UART interfaces, I2C, and SPI protocol-based systems.
Serial-to-Parallel Data Conversion With Demultiplexers
While a multiplexer performs parallel to serial data conversion, demultiplexers convert serial data to parallel data. Computer systems and networks routinely depend on this capability, making demultiplexers a key component in modern digital design.
A practical example is high-speed serial communication interfaces such as PCIe buses. Here, demultiplexers receive incoming serial data as inputs and break it into parallel streams. Each stream is routed to its intended destination, whether that's a storage device, GPU, CPU, etc.
Single Source to Multiple Destination Applications
Consider a scenario where a single computer needs to send data to multiple peripheral devices. This could be anything from a fax machine, pen plotter, or printer for example. Dedicating a separate data line to each device is inefficient and costly. Instead, a DEMUX allows the system to route data from one source to multiple destinations over a single shared line.
The select signal acts as the controller. It determines which output channel is active at any given time, allowing the system to switch between connected devices quickly and without additional hardware. This principle also scales well. In more complex systems, a single input line can serve dozens of destinations, reducing board space and simplifying routing without adding design complexity.
Cadence Supports MUX and DEMUX Applications
From data acquisition systems and sensor arrays to multi-channel systems, multiplexers and demultiplexers are central to how modern digital systems move and manage data. Designing these systems accurately requires tools that can handle the complexity of routing, timing, and integrity all in one place. Cadence’s suite of PCB design and analysis tools gives engineers the precision and control needed to design digital systems employing multiplexers and demultiplexers.
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