A multiplexer, commonly called a MUX, is a fundamental digital circuit component. It functions as a data selector that can choose one input from multiple input signals and route it to a single output line. Think of it as an electronic switch that can select between different data sources based on control signals.
A typical 4-to-1 multiplexer has four data input lines labeled I0 through I3, two select lines S1 and S0, and one output line. The select lines work together to form a 2-bit binary code that determines which input is connected to the output. When S1 S0 equals 00, input I0 is selected. When it's 01, I1 is selected, and so on. This binary addressing system allows us to select any one of the four inputs.
The internal structure of a multiplexer consists of logic gates working together. Each input line connects to an AND gate. The select lines control these AND gates, enabling only one at a time based on the binary select code. The outputs of all AND gates feed into a single OR gate. Since only one AND gate is enabled at any moment, only one input signal passes through to the OR gate and becomes the final output.
Let's see the multiplexer in action. When the select lines are set to 00, input I0 is chosen and its value appears at the output. Changing the select to 01 routes I1 to the output instead. Similarly, 10 selects I2, and 11 selects I3. Notice how only the selected input path is active while all others remain disconnected. This demonstrates the fundamental switching behavior of a multiplexer.
Multiplexers have numerous practical applications in digital systems. In computer memory systems, they route data from multiple memory banks to the CPU based on address signals. In communication networks, they allow multiple data streams to share transmission channels. They're essential in microprocessors for selecting between different data sources and in digital signal processing for channel selection. This versatility makes multiplexers fundamental building blocks in modern digital electronics.