Chapter 3 - Active Components and Integrated Circuits

Abstract

Modern active components are all based on transistors. Before transistors came into extensive use, the main active components for electronic circuits were vacuum tubes (called valves), and these are still used for high-power transmitters. There are two main types of transistors, called bipolar transistors and field-effect transistors (FETs). Most modern electronics systems now are based on the FET, usually in IC form. The transistor is a component that is created using a semiconductor crystal, and in a sense, it is the inevitable result of the use of crystals in radio reception. Bipolar transistors can come in two forms, called NPN and PNP. For NPN, a steady voltage can be connected, with the positive end on the collector lead and the negative (earth) end on the emitter. The field-effect type is used to a much greater extent than the bipolar type, and the most important field-effect type is the metal-oxide-semi-conductor field-effect transistor. This type of transistor needs a voltage signal only, not a current signal, so that the power needed at the input is very much smaller than is needed for a bipolar transistor, almost a negligible amount. Digital circuits have always accounted for a majority of the integrated circuits (ICs) that have been manufactured, but there has always been one particularly important type of linear IC, called the operational amplifier. Digital ICs are the most common variety, mainly because of the vast number of digital devices (not just computers) that make use of these types of ICs.