ELECTRONICs signal for a set amount of time is converted to a number represented by for example 16 pulses of fixed duration and amplitude The audio signal as a whole is transmitted as a series of such 16 pulse codes Most electronic devices use digital sig nals In these signals the numbers are almost always represented in binary code that is instead of using a number system based on 10 as is used in writing numbers and manual arithmetic electronic systems use numbers based on 2 There are only two basic numbers in this system 0 and 1 with 1 being repre sented by a pulse and o by the absence of a pulse or some similar arrangement A digital computer for example can rec ognize only two states in each of its millions of circuit switches on or off or high voltage or low voltage By assigning binary numbers to these states such as I for on and o for off and linking many switches together a computer can represent any type of data from numbers to letters to musical notes This process is called digitization SEMICONDUCTING DEVICES Electronic devices that manipulate digital and analog signals today are predominantly 12
THE REVOLUTIONARY FIELD OF ELECTRONICs In In the Semiconductor wafer Semiconductors are instrumental in operating a digital and analog signals Bloomberg via Getty Images 13 TTI HUI
ELECTRONICs semiconductors A semiconductor is a mate rial that conducts electricity but only under certain conditions in contrast with conduc tors that always conduct well and insulators that always conduct poorly Semiconductors are generally made of silicon or silicon com pounds that are doped or treated with certain impurities to alter their electrical properties The basic semiconductor device is the transistor invented in 1947 by U S sci entists William B Shockley Walter H American scientists John Bardeen William B Shockley and Walter H Brattain invented the transistor in 1947 Yale Joel Time Life Pictures Getty Images 14
THE REVOLUTIONARY FIELD OF ELECTRONICs Brattain and John Bardeen The typical transistor consists of three semiconductor materials bonded together In the so called n p n type the first part called the emit ter is doped to give it an excess of negative charges the second the base is doped to give it excess positive charges and the third the collector is doped to give it an excess of negative charges The voltage applied between the emit ter and collector is fixed and relatively TRANSISTOR case base emitter collector In a transistor the current flowing from emitter to collector varies with and is amplified by the signal flowing in the base Copyright Encyclopaedia Britannica Inc rendering for this edition by Rosen P Educational Services 15 TTI HUI
