Modern digital systems rely on smooth and efficient ways to transfer data, whether it’s streaming videos or sending signals across a network. Behind the scenes, special switching components help guide data to the right place quickly and accurately. These components help convert signals, reduce wiring, and make data transmission faster. This article explains the difference between multiplexer and demultiplexer, explores how they work in digital communication systems, highlights their applications, and compares their structure and behavior in a computer science context.
Table of Contents:
What is a Multiplexer (MUX)?
A multiplexer, also known as a MUX, is a combinational circuit that has multiple input lines and one output line, allowing you to select your desired output. This is why a MUX is also called a data selector. It selects an input from several inputs and then transmits it in the form of a single line. The multiplexer and demultiplexer in computer networks are used together for transmission.
A MUX consists of
- Input data
- Select Line
- Output data
Based on the number of selected lines, you can calculate the number of data inputs that can be transmitted. You can calculate it using the following formula.
A MUX is represented by N:1 when there are N data inputs, and will be called a N:1 MUX. The diagram shown below represents how a multiplexer is visualized for simplification.
A multiplexer uses gates that are responsible for selecting the desired input to be transmitted as output. The diagram below showcases the logic gate representation of a 4:1 MUX.
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Types of Multiplexers (MUX)
The type of multiplexer is defined by the number of select lines it has.
4:1 Multiplexer (2 Select Lines)
A 4:1 multiplexer has 4 data input lines. By the 2m = N formula, we can calculate that the number of selected lines (m) is 2. Hence, a 4:1 multiplexer looks like this.
8:1 Multiplexer (3 Select Lines)
An 8:1 multiplexer has 8 data input lines and 3 select lines. Again, if we know the value of one, the other can be calculated. It is represented as
You can implement this using two 4:1 multiplexers, like in the figure below.
Note: Remember that the ‘4’ in 4:1 MUX stands for the number of data lines. Beginners usually confuse them with the number of select lines.
Advantages of Using a Multiplexer (MUX)
- Using multiplexers reduces the complexity of the circuit as well as cost of the circuit.
- With the help of a multiplexer, we can implement many combinations of logic circuits.
- Multiplexers act as a central controller. It can switch between different signals, like various video signals, including DVD players, game consoles, etc., or audio. This allows you to choose which one gets sent to your screen or speakers.
Disadvantages of using a Multiplexer (MUX)
- When the multiplexer switches between different inputs, or when a signal goes through it, there is a delay.
- You cannot send two different things through the multiplexer at the exact same moment.
- To tell the multiplexer which input to choose, you need special “select” wires. This means your overall circuit might need a few more connections.
What is a Demultiplexer (DEMUX)?
A demultiplexer is the complete opposite of a multiplexer, as it is a combinational circuit that takes one input and converts it into multiple outputs. Therefore, a demultiplexer is also called a data distributor. It receives a single input line and then converts it into multiple outputs. We will discuss the applications of multiplexers and demultiplexers in the later sections of this article.
A DEMUX consists of
- One input line
- Select lines and
- Output lines.
A demultiplexer is represented by 1:N. For example, if it has one data input and N data outputs, it will be called a 1:N DEMUX. This is how a demultiplexer is drawn and displayed for simplification, but inside, numerous logic gates help distribute the data into multiple data channels.
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Types of Demultiplexer (DEMUX)
Demultiplexers can be categorized based on the number of data it can output or distributed in.
1:4 Demultiplexer (2 Select Lines)
A 1:4 demultiplexer has 4 output lines and 2 select lines. A 1:4 demultiplexer is represented as
1:8 Demultiplexer (3 Select Lines)
A 1:8 demultiplexer has 3 select lines and 8 data output lines. It uses 8 AND gates to implement this combination circuit.
1:16 Demultiplexer (4 Select Lines)
A 1:16 demultiplexer has 4 select lines and 16 data output lines. It can be implemented using two 1:8 demultiplexers like shown in the figure.
Advantages of Using a Demultiplexer (DEMUX)
- To switch between the various signals, like audio and visual, both multiplexers and demultiplexers are required.
- In banking security systems, a demultiplexer (DEMUX) acts like a decoder, helping in directing information to the correct place.
Disadvantages of Using a Demultiplexer (DEMUX)
- DEMUX is prone to bandwidth wastage. If not all output lines are always needed, some of the system’s capacity might not be fully utilized.
- Like multiplexers, demultiplexers also introduce some delay in the complete circuit.
Difference Between Multiplexer and Demultiplexer
Now that you understand what a multiplexer and demultiplexer are, it is quite clear that they are complete opposites of each other. Let us dive deeper into the difference between a multiplexer and a demultiplexer. We will differentiate between the two based on various factors.
1. Functional Role in System Design
- Multiplexer: A multiplexer primarily serves as a data selector, enabling the system to choose one signal from multiple sources for transmission. It is commonly placed at the transmitter end in communication systems to consolidate data before sending it through a shared channel.
- Demultiplexer: A demultiplexer acts as a data distributor, taking a single incoming signal and routing it to one of many destinations. It is typically used at the receiver end to decode and distribute the transmitted data back into its original parallel form.
2. Direction of Data Flow
- Multiplexer: The data flows from many inputs to one output, meaning it follows a many-to-one relationship to select data that it must output.
- Demultiplexer: The data flows from one input to many outputs and hence follows a one-to-many relationship to distribute data into many outputs.
- Multiplexer: A multiplexer is a digital switching device that is designed to take multiple (N) input signals and transmit only one output signal at a time based on the value of the select lines. The selection of which input to route to the output is controlled by log₂N select lines, which determine the active input among the N available options.
- Demultiplexer: A demultiplexer performs the reverse operation of a multiplexer. It takes a single input signal and distributes it to one of the N possible output lines. The decision of which output line will carry the input signal is managed by log₂N select lines, which control how the input is routed among the multiple outputs.
4. Control Signals
- Multiplexer: A MUX uses select lines to control which output line will receive the signal from the single input, distributing data to the correct path based on control logic.
- Demultiplexer: A DEMUX uses select lines to control which output line will receive the signal from the single input, distributing data to the correct path based on control logic.
5. Symbol/Logic Diagram
- Multiplexer: The logic diagram of the MUX is as shown below. The symbol typically shows multiple arrows pointing inwards (inputs), a few lines for control, and a single arrow pointing outwards (output). It represents the 4:1 MUX.
- Demultiplexer: The logic diagram of a DEMUX is as shown below. The symbol typically shows a single arrow pointing inwards (input), a few lines for control, and multiple arrows pointing outwards (outputs). It represents the 1:4 DEMUX.
6. Hardware Complexity
- Multiplexer: A multiplexer requires the implementation of multiple logic gates such as AND, OR, and NOT to correctly process and route the input signals. Their complexity increases proportionally with the number of input lines, as each combination needs to be accurately decoded and mapped to the single output line using the appropriate control logic.
- Demultiplexer: A demultiplexer, on the other hand, relies on a combination of logic gates and a binary decoder circuit to effectively distribute a single input signal to one of the many output lines. The decoder interprets the control signals (select lines) and activates the correct output path, making the hardware design slightly more intricate, especially as the number of outputs increases.
7. Data Transmission Mode
- Multiplexer: A multiplexer converts a parallel stream to serial stream by combining multiple data inputs into a single output line. This approach enhances transmission efficiency and reduces hardware lines, making it ideal for sending grouped signals through limited communication paths.
- Demultiplexer: A demultiplexer converts a serial stream to parallel stream by taking one input and distributing it to several output lines. Based on control signals, it reconstructs the original parallel format, commonly used in receivers to decode incoming compressed data.
8. IC Implementation Examples
- Multiplexer: Some common real-life integrated circuits that implement multiplexers are 74157 (4:1), 74151 (8:1). These are also implemented in FPGAs for signal routing.
- Demultiplexer: 74139 (1:4) and 74138 (1:8) are some common integrated circuits that use demultiplexers. It is also used in microcontrollers for I/O expansion.
Multiplexers vs Demultiplexers: Key Differences
In the table below, we have listed the differences between a multiplexer and a demultiplexer. You can quickly glance and understand them.
| Aspect |
Multiplexer (MUX) |
Demultiplexer (DEMUX) |
| Function |
Selects one input from many |
Sends one input to one of many outputs |
| Data Flow |
Many-to-One |
One-to-Many |
| Inputs/Outputs |
N inputs, 1 output |
1 input, N outputs |
| Select Lines |
Used to pick input |
Used to pick output |
| Application |
Combines data lines |
Distributes data to multiple lines |
Applications of Multiplexers and Demultiplexers
Multiplexer and demultiplexer, together, are widely used in digital systems. Here are some key applications
- Data Routing and Switching: Multiplexers (MUX) send data from multiple sources onto a single path, then demultiplexers (DEMUX) take that single path and accurately route the data to one of many possible destinations. They work together to guide information correctly.
- Data Conversion: Multiplexer and demultiplexer are combinational circuits that convert data from parallel to serial and serial to parallel. MUXes convert data that arrives all at once (parallel) into a single, continuous stream (serial), which is perfect for sending over long distances with fewer wires. DEMUXes then perform the opposite function, taking that single serial stream and turning it back into parallel data at the receiving end.
- Implementing Logic Functions: A multiplexer can be used to build any kind of complex digital logic function you need and customize a circuit. A demultiplexer often serves as a decoder to enable or select specific parts of a system based on a coded input.
- Computer Memory Access: MUX plays a key role in selecting the exact memory location the computer wants to access, which assists in functions like reading from or writing to. Once selected, DEMUX then helps in directing the data to or from the specific chosen memory section.
- Communication Systems: This is the most famous application of multiplexers and demultiplexers combined. MUXs are used to combine multiple separate signals, like many phone calls or internet data streams, into a single, high-capacity communication channel. At the other end of the channel, DEMUXs separate those combined signals back into their original individual streams. Multiplexer and demultiplexer combined together have a term as ‘multiplexing’.
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Conclusion
In this article, we discussed how multiplexers and demultiplexers act as the fundamental building blocks of digital communication. They efficiently combine and separate signals that enable your smartphone’s seamless delivery of diverse media and the robust data transmission across vast computer networks. By understanding their unique yet complementary roles, we can accurately flow of information that powers our modern, connected world.
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Multiplexer and Demultiplexer – FAQs
Q1. What is multiplexer and demultiplexer?
A multiplexer (MUX) selects one input from many and sends it to a single output. A demultiplexer (DEMUX) takes one input and routes it to one of many outputs.
Q2. What is the main purpose of a multiplexer?
The main purpose is to reduce the number of data lines by selecting and transmitting one input at a time.
Q3. What is the function of a demultiplexer?
A demultiplexer takes one input and distributes it to one of many outputs, based on select lines.
Q4. What is 4×1 and 8×1 multiplexer?
A 4×1 MUX selects 1 out of 4 inputs, and an 8×1 MUX selects 1 out of 8 inputs, using 2 and 3 select lines respectively.
Q5. Where is MUX used?
MUX is used in communication systems, data routing, ALUs, and digital circuits for signal selection and transmission.