🧠 Introduction

A Demultiplexer (DEMUX) is a combinational logic circuit that takes a single input and routes it to one of many outputs, depending on the select lines.

👉 You can think of it as the reverse of a multiplexer:

MUX: Many inputs → One output
DEMUX: One input → Many outputs

Thus, a Demultiplexer is also known as a “data distributor.”

🎯 Purpose of Demultiplexer

To transmit a single data input to one of the many outputs.
Used where one source needs to be connected to multiple destinations at different times.

⚙️ Working Principle

It has one input line, n selection lines, and 2ⁿ output lines.
The selection lines decide which output line gets the input signal.

🛠️ Basic Structure

No. of Outputs	No. of Select Lines	Example
2	1	1×2 DEMUX
4	2	1×4 DEMUX
8	3	1×8 DEMUX
16	4	1×16 DEMUX

General Rule:

For m outputs, we need n selection lines, where m = 2ⁿ.

📈 Block Diagram of a Demultiplexer

Input: Data (D)
       |
Select Lines (S₀, S₁, ..., Sn)
       |
     [ DEMUX ]
     /   |    \
Outputs: O₀  O₁  ... On

Only one output is active at a time, depending on the select line combination.

📑 Example: 1×4 Demultiplexer

Input: D
Select Lines: S₁, S₀
Outputs: Y₀, Y₁, Y₂, Y₃

Truth Table:

S₁	S₀	Active Output
0	0	Y₀ = D
0	1	Y₁ = D
1	0	Y₂ = D
1	1	Y₃ = D

✅ Only one output carries the input signal D, others remain 0.

🧩 Circuit Diagram of 1×4 DEMUX

Logical Expressions:

Y₀ = D ⋅ ¬S₁ ⋅ ¬S₀
Y₁ = D ⋅ ¬S₁ ⋅ S₀
Y₂ = D ⋅ S₁ ⋅ ¬S₀
Y₃ = D ⋅ S₁ ⋅ S₀

where:

(⋅) = AND
(¬) = NOT (inverted)

🧠 Important Points

Only one output is activated at a time based on select inputs.
Others remain inactive (0).
It is mainly used for data distribution.

🌟 Applications of Demultiplexer

Application	How it’s used
Data Routing	Distributing data from one source to multiple destinations
Communication Systems	Channelizing signals to different channels
Memory Management	Connecting CPU to memory blocks
Serial-to-Parallel Data Conversion	Convert serial data to parallel
Logic Circuits	Implementation of logical expressions

🔥 Advantages of Demultiplexer

Saves wiring when one input needs to reach many outputs.
Simplifies design for data distribution systems.
Flexible control using selection lines.
Efficient for multi-point communication.

🎯 Summary

Feature	Demultiplexer
Purpose	Distribute one input to multiple outputs
Input Lines	1
Output Lines	2ⁿ outputs
Control Signals	n select lines
Major Components Used	AND, OR, NOT gates

✏️ Example Problem

👉 Design a 1×4 Demultiplexer.

Inputs: D
Select Lines: S₁, S₀

Outputs:

Y₀ = D ⋅ ¬S₁ ⋅ ¬S₀
Y₁ = D ⋅ ¬S₁ ⋅ S₀
Y₂ = D ⋅ S₁ ⋅ ¬S₀
Y₃ = D ⋅ S₁ ⋅ S₀

✅ Implement using AND, NOT gates!

📢 Real-Life Analogy

Think of a Demultiplexer like a water tap distributor 🚰:

One pipe (input) brings water.
The control valve (select line) decides which outlet the water will flow through (output).

📌 Key Differences between MUX and DEMUX

Feature	Multiplexer (MUX)	Demultiplexer (DEMUX)
Inputs	Multiple inputs	One input
Outputs	One output	Multiple outputs
Function	Select one input	Select one output
Also Called	Data Selector	Data Distributor

Demultiplexers