Semiconductor Basics

12VLSI Components

OBJECTIVES OF THIS CHAPTER

We are now ready to talk about more complex electronic system components that are an integral part of microprocessors, computers, cell phones, and many other devices that I discuss in the next couple of chapters. These include multiplexers that select signals from multiple inputs, demultiplexers that do the opposite, registers that store intermediate results, and all type of memories. We already have all the background we need to understand how these larger components work.

12.1 Multiplexers

A multiplexer is a component with many inputs and one output. We call it a MUX for short. It is an essential component in almost all large electronic systems.

The MUX is basically a selector switch, as I show in Figure 12.1.

The selector switch or the rotary switch on the left selects which of the four inputs I want to connect to the output, O. I show the schematic symbol of an electronic multiplexer on the right. In addition to the four inputs and the output, the symbol has two other inputs, the control inputs a and b, which determine the position of the switch arm and selects which of the inputs goes to the output.

Figure 12.1 A MUX selects one of the many inputs, like a rotary switch. The symbol for a MUX is on the right.

Figure ...