14 Basic Electronics In this chapter, we lead you through a study of the basics of electronics. After completing the chapter, you should be able to Understand the physical structure of semiconductors. Understand the essence of the diode function. Understand the operation of diodes. Realize the applications of diodes and their use in the design of rectifiers. Understand the physical operation of bipolar junction transistors. Realize the applications of bipolar junction transistors. Understand the physical operation of field-effect transistors. Realize the application of field-effect transistors. Perform rapid analysis of transistor circuits. REFERENCES 1. Giorgio Rizzoni, Principles and Applications of Electrical Engineering, McGraw Hill, 2003. 2. J. R. Cogdel, Foundations of Electronics, Prentice Hall, 1999. 3. Donald A., Neaman, Electronic Circuit Analysis and Design, McGraw Hill, 2001. 4. Sedra/Smith, Microelectronic Circuits, Oxford, 1998. 1 Basic Electronics 2 14.1 INTRODUCTION Electronics is one of the most important fields in existence today. It has greatly influenced everything since early 1900s. Everyone nowadays realize the impact of electronics on our daily life. Table 14-1 shows many important areas with tremendous impact of electronics. Table 14-1 Various Application Areas of Electronics Area Examples of Applications Automotives Electronic ignition system, antiskid braking system, automatic suspension adjustment, performance optimization. Aerospace Airplane controls, spacecrafts, space missiles. Telecommunications Radio, television, telephones, mobile and cellular communications, satellite communications, military communications. Computers Personal computers, mainframe computers, supercomputers, calculators, microprocessors. Instrumentation Measurement equipment such as meters and oscilloscopes, medical equipment such as MRI, X- ray machines, etc. Microelectronics Microelectronic circuits, microelectromechanical systems. Power electronics Converters, Radar Air traffic control, security systems, military systems, police traffic radars. According to one dictionary, electronics means the physics of electrons and their utilization. In a broader means, it may be defined as the field of manipulating electrical currents and voltages using passive and active devices that are connected together to create electronic circuits. These circuits may contain simple resistors, capacitors, conductors (that are generally called components), diodes, transistors and more complicated devices that contain millions of transistors. In electronics, voltage and current become electrical signals. Signals contain information about a variety of activities in the physical world such as weather, temperature, pressure, speed, etc. This chapter explains the function of semiconductor diodes and transistors. These devices find applications in many practical circuits used in electronic Basic Electronics 3 systems and electric power systems. The emphasis in this chapter is on the basic techniques for the analysis of electronic circuits. 14.2 HISTORY OF ELECTRONICS The field of electronics has long history starting early 1990s. This field is responsible for the development of many important areas such as telecommunication, computers, instrumentation, aviation, medicine, services, etc. It is impossible to imagine what our lives would be like without access electronics. Technologies associated with electronics have made our lives easier. Modern society is indeed unworkable without the existence of electronic devices and appliances. For example, emerging telecommunication services have greatly enhanced the ability of individuals and groups to communicate with each other and have facilitated the speed of information to persons and machines in both urban and rural environments. Table 14-2 includes the history of several important areas of electronics. 14.3 SEMICONDUCTORS A semiconductor is material that is intermediate between a conductor and an insulator. Semiconductors are present in our everyday life. The computer that we use at has more than one electronic chip. Cars, TV’s, coffee machines, washing machines, etc are all equipped with them. 14.3.1 History Although the semiconductor was late in reaching its present development, its history began long before the electron tube. Historically, we may go as far back as 1883 when Michael Faraday discovered that silver sulfide, a semiconductor, which has a negative temperature coefficient. The term negative temperature coefficient is just another way of saying its resistance to electrical current flow decreases as temperature increases. The opposite is true of the conductor. It has a positive temperature coefficient. Another ancestor of semiconductor devices was the crystal detector, used in early wireless radios. This device (patented by a German scientist, Ferdinand Braun, in 1899) was made of a single metal wire touching against a semiconductor crystal. The result was a rectifying diode (so called because it has two terminals), which lets current through easily one way, but hinders flow the other way. By 1930, though, vacuum-tube diodes had all but replaced the smaller Basic Electronics 4 but much quirkier crystal detector. The crystals were left to languish as a kids’ toy in the form of “crystal radios.” Table 14-2 Brief History of Electronics Invention Year: Inventor Application 1904 USA: Sir Ambrose The first rectifier, the diode, Fleming Fleming Valve (Edison effect). 1906 USA: Lee de Forest Invention of the audion tube, a three- element vacuum tube in which the grid controlled the current, which made modern radio possible. 1992 UK Regular radio broadcasting started in Vacuum Tube London. and Radio 1885-1889 Germany: The first to broadcast and receive radio Heinrich Rudolf Hertz waves in the laboratory. 1909 UK: Guglielmo First wireless signal across the Atlantic Marconi Ocean. A3000-km distance between St. John’s (Newfoundland) and Poldhu (Cornwall), on the Southwest tip of England was bridged. 1923 UK: Valdimir Iconoscope: This was used as a TV screen Kosma Zworykyn in the all electronic system developed by EMI. 1926 UK: John Logie Demonstrated the first television. Television Baird 1934 USA: Philo T. First electrical scanning TV camera. Farnsworth 1936 UK: BBC Regular broadcasting TV programs at Alexandra Palace, London. 1982: Sony First flat screen TV. 1935 Scotland: Robert He received his eleventh radio-location Alexander Watson-Watt patent, a device for detecting and locating an approaching aircraft. Radar 1940 USA: Alfred Lee He had already built a working low-power Loomis CW radar for aircraft detection when the British brought the magnetron to the U.S. 1947 USA: Bardeen, Transistor was invented in Bell Brattain and Shockley Laboratories. 1954: Texas Instruments First transistor radio. Transistor 1967: Sony First radio using integrated circuits. Mid-1980s The capability of including one million transistors on silicon chip. Mid-1990s The capability of including ten million transistors on silicon chip. Basic Electronics 5 1946 USA: Brainard, One of the first electronic digital Mauchly, Eckert, computers. Sharpless 1968: Robert Noyce Founded Intel (INTegrated and Gordon Grove Electronics) Corporation. Computers 1970 First commercial microprocessor chip, the Intel 4004 based on small 4-bit digital words. Later Succeeding models expanded the capability to 8-bit, then 16 bit, and finally 32-bit words. In June 1948, a significant breakthrough took place in semiconductor development. This was the discovery of point-contact transistor. Here at last was a semiconductor that could amplify. This discovery brought the semiconductor back into competition with the electron tube. A year later, junction diodes and transistors were developed. The junction transistor was found superior to the point-contact type in many respects. By comparison, the junction transistor was more reliable, generated less noise, and had higher power-handling ability than its point-contact brother. So, during the war, much effort was put into improving the semiconductors, mostly silicon and germanium, used in crystal detectors. 14.3.2 Conduction in Semiconductors This section briefly introduces the mechanism of conduction in a class of materials called semiconductors. Semiconductors are crystals that, in their pure state, are resistive (this means, their electrical properties lie between those of conductors and insulators). When the proper impurities are added (a process often called doping) in trace amounts (often measured in parts per billion), semiconductors display interesting and useful properties. For the sake of comparison, consider the conductivity of through common material. Copper, a good conductor with a very high concentration of free electrons, has a conductivity of 0.59×106 S/cm; glass, an insulator, may range between 10-16 and 10-13 S/cm; and a semiconductor, has a conductivity that varies from 10-8 to 10-1 S/cm. We have said in Chapter 10 that a conducting material is characterized by a large number of conduction band electrons, which have a very weak bond with the basic structure of the material. Therefore, an electric field easily imparts energy to the outer electrons in a conductor and enables the flow of electric current. In a semiconductor, however, we need to consider the lattice structure of Basic Electronics 6 the material, which is characterized by covalent bonding. Figure 14-1 illustrates the lattice structure of silicon, a very common semiconductor. Thermal energy can cause the atoms in the lattice