Computer Science Illuminated, 7th Edition

4.3 Constructing Gates

Before we examine how gates are connected to form circuits, let’s examine, at an even more basic level, how a gate is constructed to control the flow of electricity.

Transistors

A gate uses one or more transistors to establish how the input values map to the output value. A transistor is a device that acts, depending on the voltage level of the input signal, either as a wire that conducts electricity or as a resistor that blocks the flow of electricity. A transistor has no moving parts, yet it acts like a switch. It is made of a semiconductor material, which is neither a particularly good conductor of electricity (such as copper) nor a particularly good insulator (such as rubber). Usually silicon is used to create ...