In digital electronics, multiplexers (MUX) and demultiplexers (DEMUX) are crucial for data routing. They perform opposite functions but work together in many systems. Let’s explore their differences with practical examples to understand them better.
What is a Multiplexer (MUX)?
A multiplexer (MUX) selects one input from multiple sources and forwards it to a single output line based on select lines.
Key Features of a MUX:
- Multiple Inputs (2ⁿ), One Output
- “Data Selector” – Chooses which input goes to the output
- Used in: Communication systems, memory addressing, data routing
Example: 4:1 Multiplexer
A 4:1 MUX has:
- 4 inputs (I₀, I₁, I₂, I₃)
- 2 select lines (S₁, S₀)
- 1 output (Y)
Truth Table:
| S₁ | S₀ | Selected Input → Output (Y) |
| 0 | 0 | I₀ → Y |
| 0 | 1 | I₁ → Y |
| 1 | 0 | I₂ → Y |
| 1 | 1 | I₃ → Y |
Practical Use Case:
Imagine a TV remote control that selects between multiple input sources (HDMI, USB, AV, TV Tuner). The MUX acts like a source selector, sending only one signal to the TV screen.
What is a Demultiplexer (DEMUX)?
A demultiplexer (DEMUX) does the opposite of a MUX. It takes one input and routes it to one of multiple outputs based on select lines.
Key Features of a DEMUX:
- Single Input, Multiple Outputs (2ⁿ)
- “Data Distributor” – Sends input to a selected output
- Used in: Memory systems, communication networks, ALU circuits
Example: 1:4 Demultiplexer
A 1:4 DEMUX has:
- 1 input (D)
- 2 select lines (S₁, S₀)
- 4 outputs (Y₀, Y₁, Y₂, Y₃)
Truth Table:
| S₁ | S₀ | Active Output (Input D goes to…) |
| 0 | 0 | Y₀ = D |
| 0 | 1 | Y₁ = D |
| 1 | 0 | Y₂ = D |
| 1 | 1 | Y₃ = D |
Practical Use Case:
Think of a post office sorting system where a single conveyor belt (input) distributes packages to different bins (outputs) based on their destination codes (select lines).
Key Differences Between MUX and DEMUX
| Feature | Multiplexer (MUX) | Demultiplexer (DEMUX) |
| Function | Selects one input → one output | Routes one input → many outputs |
| Inputs | Multiple (2ⁿ) | Single (1) |
| Outputs | Single (1) | Multiple (2ⁿ) |
| Select Lines | Chooses which input to pass | Chooses which output to send to |
| Applications | Data routing, signal transmission | Memory addressing, data distribution |
Combined Example: MUX + DEMUX in Communication
In telecommunication systems, MUX and DEMUX work together:
- Sender Side (MUX): Combines multiple signals (voice, video, data) into one transmission line.
- Receiver Side (DEMUX): Separates the combined signal back into individual channels.
Example:
At a TV broadcasting station:
- MUX combines multiple channels into a single cable signal.
- DEMUX in your set-top box splits them back into separate channels.
Conclusion
- MUX = Data Selector (Many → One)
- DEMUX = Data Distributor (One → Many)
- Both use select lines to control routing.
- Often used together in communication & computing systems.
