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All Rights reserved. In the future, more circuits will be fab- Integrated circuits will be used less in the ricated using insertion technology and future.
Summary 1. Digital signal processing uses computers to enhance 3. The number of states or voltage levels is limited in signals. Block diagrams give an overview of electronic 4. An analog circuit has an infinite number of voltage system operation. Schematic diagrams show individual part wiring 5. In a linear circuit, the output signal is a replica of and are usually required for component-level the input.
All linear circuits are analog, but not all analog Troubleshooting begins at the system level. Some analog circuits distort Alternating current and direct current signals are signals.
Analog signals can be converted to a digital format Digital-to-analog converters are used to produce a The quality of a digital representation of an analog signal is determined by the sampling rate and the number of bits used. Chapter Review Questions Determine whether each statement is true or false. Most digital circuits can output only two states, Digital circuit outputs are usually sine waves. Block diagrams are best for component-level troubleshooting.
The output of a linear circuit is an exact replica What could go wrong with capacitor C2 in two wires but will selectively signal two differ- Fig. Contrast between an LED light source and incandescent lamps. Learning Outcomes This chapter will help you to: E lectronic circuits used to be based on the flow of electrons in devices called vacuum tubes.
Today, almost all electronic Identify some common electronic materials circuits are based on current flow in semi- as conductors or semiconductors. The mechanics of cur- Predict the effect of temperature on semiconductors. Some current carriers currents in semiconductors. High temperatures create Identify the majority and minority carriers in additional carriers in semiconductors.
These N-type semiconductors. The transistor is P-type semiconductors. It is a semiconduc- tor device. Diodes and integrated circuits are also semiconductors. This chapter covers the basic properties of semiconductors. At the cen- ter of any atom is a small, dense core called the nucleus. Copper, like all atoms, has an equal Electron number of protons and electrons. Thus, the net atomic charge is zero.
It is called the valence orbit. In the case of Valence orbit copper, there is only one valence electron. A copper atom can be simplified as shown Copper atom in Fig. Even a very small copper wire contains billions of atoms, each with one valence elec- tron.
These electrons are only weakly attracted to the nuclei of the atoms. They are very easy to move. Since there are so many valence electrons and since they are so easy to move, we can expect tremendous num- bers of electrons to be set in motion by even a small voltage. Thus, copper is an excellent elec- Low resistance tric conductor. It has very low resistance. Heating a copper wire will change its resis- a Bohr model of the copper atom not to scale tance.
As the wire becomes warmer, the valence electrons become more active. They move farther away from their nuclei, and they move more rap- idly. This activity increases the chance for colli- sions as current-carrying electrons drift toward the positive end of the wire. These collisions absorb energy and increase the resistance to current flow. As they be- Positive come hotter, they conduct less efficiently, and temperature Fig.
Such materials are coefficient said to have a positive temperature coefficient. This simply means that the relationship between Conductors form the fundamental paths Conductor for electronic circuits. Figure shows how Valence electron a copper wire supports the flow of electrons. The valence. Figure a shows carbon in electronics. Most of the wire used in elec- arranged in the diamond structure.
With this Printed circuit tronics is made from copper. Figure b solder. This makes it very popular. Here, the valence electrons are free to as good as copper. Aluminum is less expensive than from carbon. One insulates, and the other copper, but it is difficult to solder and tends to does not. It is simply a matter of whether the corrode rapidly when brought into contact with valence electrons are locked into the struc- other metals.
Carbon in graphite form is used to make Silver is the best conductor because it has resistors and electrodes. So far, the diamond the least resistance. The structure of carbon has not been used to make high cost of silver makes it less widely applied electrical or electronic devices.
Gold is a good conductor. It is very stable and does not corrode as badly as copper and silver. This makes the con- tacts very reliable. In an insulator, the valence electrons are tightly bound to their parent atoms.
They are not free to move, so little or no current flows when a voltage is applied. Practically all insula- tors used in electronics are based on compounds. Compound A compound is a combination of two or more a Diamond different kinds of atoms.
Some of the widely applied insulating materials include rubber, plastic, Mylar, ceramic, Teflon, and polystyrene. Silver is not often used in electronic 1. Aluminum is not used as much as copper 2. Copper has one valence electron. In conductors, the valence electrons are to solder. The current carriers in conductors are the valence electrons. These and other Diode components make modern electronics possible. This bundle is called the nucleus of the atom.
The first orbit has two elec- trons. The last, or outermost, orbit has four electrons. The outermost or valence orbit is the most impor- tant atomic feature in the electrical behavior of materials. Remember that there are four electrons in the valence orbit. Materials with four valence electrons are not stable. They tend to combine chemically with other materials. They can be called active mate- Active material b A simplified silicon atom rials.
The dots represent valence electrons. Doping graphene with lithium can produce superconductivity. Crystal tend to form combinations that will make eight Select one of the internal nuclei as represented electrons available in the valence orbit. Eight is by a circled N. You will count eight electrons. Thus, the silicon crystal is very stable.
At room One possibility is for silicon to combine temperature, pure silicon is a very poor conduc- with oxygen. A single silicon atom can join, tor. If a moderate voltage is applied across the Silicon dioxide or link, with two oxygen atoms to form silicon crystal, very little current will flow.
The valence Ionic bond dioxide SiO2. This linkage is called an ionic electrons that normally would support current bond. The new structure, SiO2, is much more flow are all tightly locked up in covalent bonds. Pure silicon is sometimes called Intrinsic silicon Silicon dioxide is stable chemically. It does not intrinsic silicon. Intrinsic silicon contains very react easily with other materials.
It is also sta- few free electrons to support the flow of current ble mechanically. It is a hard, glasslike mate- and therefore acts as an insulator. Finally, it is stable electrically. One way to improve its conduction is to tegrated circuits and other solid-state devices. Heat is a form of energy. A valence elec- SiO2 insulates because all of the valence elec- tron can absorb some of this energy and move trons are tightly locked into the ionic bonds. The high-energy electron They are not easy to move and therefore do not has broken its covalent bond.
Figure shows support the flow of current. This Thermal carrier Sometimes oxygen or another material is not electron may be called a thermal carrier. It available for silicon to combine with. Now, if a voltage is placed across the electrons. If the conditions are right, silicon atoms crystal, current will flow.
Covalent will arrange to share valence electrons. This pro- Silicon has a negative temperature coef- bonding cess of sharing is called covalent bonding. The ficient. As temperature increases, resistance. The big difference between germanium and silicon is the amount of heat energy needed to N N N Free move one of the valence electrons to a higher electron orbit level, breaking its covalent bond.
This is far easier to do in a germanium crystal. A com- Broken parison between two crystals, one germanium covalent and one silicon, of the same size and at room N N N bond temperature will show about a 1, ratio in resistance. The silicon crystal will actually have 1, times the resistance of the germa- nium crystal.
So even though the resistance of Heat energy silicon drops more rapidly than that of germa- nium with increasing temperature, silicon is still going to show greater resistance than ger- Fig. Circuit designers prefer silicon devices for decreases in silicon. It is difficult to predict most uses. The thermal, or heat, effects are usu- exactly how much the resistance will change ally a source of trouble.
Temperature is not easy in a given case. However, all circuits are changed in temperature. Good designs minimize that The semiconductor material germanium is change. Germanium used to make transistors and diodes, too. Ger- Sometimes heat-sensitive devices are nec- manium has four valence electrons and can essary. A sensor for measuring temperature form the same type of crystalline structure as can take advantage of the temperature coeffi- silicon.
It is interesting to observe that the first cient of semiconductors. So the temperature transistors were all made of germanium. The coefficient of semiconductors is not always a first silicon transistor was not developed until disadvantage.
Now silicon has almost entirely replaced Germanium started the solid-state revolu- germanium. One of the major reasons for this tion in electronics, but silicon has taken over. Germanium also has a negative electronic equipment today. It is not practical to response temperature coefficient.
The rule of thumb for make integrated circuits from germanium, but germanium is that the resistance will be cut in silicon works well in this application. An electron that is freed from its covalent 8. Silicon is a conductor. Silicon has four valence electrons. Germanium has less resistance than silicon. Silicon dioxide is a good conductor. Silicon transistors and diodes are not used A silicon crystal is formed by covalent as often as germanium devices.
Integrated circuits are made from High tem- were another silicon atom. It is a free plications, there is a better way to make them electron as far as the crystal is concerned. This semiconduct.
It can Doping Doping is a process of adding other mate- serve as a current carrier. Silicon with some rials called impurities to the silicon crystal to arsenic atoms will semiconduct even at room change its electrical characteristics. One such temperature. Arsenic impurity material is arsenic.
Arsenic is known Doping lowers the resistance of the sili- as a donor impurity because each arsenic atom con crystal. When donor impurities with five donates one free electron to the crystal. Arse- N-type are produced. Since electrons have a negative nic is different from silicon in several ways, but semiconductor charge, we say that an N-type semiconductor the important difference is in the valence orbit.
Arsenic has five valence electrons. When an arsenic atom enters a silicon crys- tal, a free electron will result. Figure shows. Si Si Si Extra electron. N Si As Si. Si Si Si. Self-Test Supply the missing word in each statement. Free electrons in a silicon crystal will serve as current.
Arsenic is a impurity. When silicon is doped, its resistance Arsenic has valence electrons. The driver of that car takes the opportunity to do so, and this Doping can involve the use of other kinds of makes a space for directly behind it. The driver impurity materials. Figure shows a simpli- of the second car also moves up one position. Note that boron has only three Boron atom This continues with the third car, the fourth car, valence electrons. If a boron atom enters the and so on down the line.
The cars are moving silicon crystal, another type of current carrier from left to right. Note that the space is moving will result. A hole may be considered as Figure shows that one of the covalent a space for an electron. This is why hole current bonds with neighboring silicon atoms cannot is opposite in direction to electron current. This produces a hole, or missing Hole, or missing electron.
The hole is assigned a positive charge electron since it is capable of attracting, or being filled by, an electron. Boron is known as an acceptor impurity. Each boron atom in the crystal will create a hole that is capable of accepting an electron. Holes serve as current carriers. But in a P-type semiconduc- tor, the holes move toward the negative termi- Si Si Si nal of the voltage source. Hole current is equal to electron current but opposite in direction.
Figure illustrates the difference between N-type and P-type semiconductor materials. P-type In Fig. Doping a semiconductor crystal with boron will produce current carriers called Boron is an impurity. Boron has valence electrons. Electrons will drift toward the positive An unwanted hole will exist in the crystal. Minority carrier are made, the doping levels can be as small as This hole is called a minority carrier. The free 1 part per million or 1 part per billion. Only electrons are the majority carriers.
They are in the majority. A few It is not possible to make the silicon crystal free electrons might also be present. Thus, it is easy to imagine be the minority carriers in this case. Niels Bohr and the Atom Today very high-grade silicon can be manu- Scientists change the future by factured. This high-grade material has very improving on the ideas of others.
Although this keeps Niels Bohr proposed a model of atomic structure in that the number of minority carriers to a minimum, applied energy levels quantum their numbers are increased by high tempera- mechanics to the Rutherford tures. This can be quite a problem in electronic model of the atom.
Bohr also circuits. To understand how heat produces mi- used some of the work of Max nority carriers, refer to Fig. As additional Planck. Each broken bond produces both a free electron and a hole. If the crystal was made as P-type material, then the important areas where the compound semi- thermal holes join the majority carriers and the conductors offer advantages are at very high thermal electrons become minority carriers.
The heat also produces mi- transmission of light , and in hostile environ- nority carriers. In the making of N-type semiconductor A free electron in a P-type crystal is called Heat increases the number of minority a majority carrier.
A hole in an N-type crystal is called a minority carrier. By controlling the Silicon accounts for almost all of the devices cur- amount of germanium, the amount of strain rently being made.
Improvements of carrier mobility increases are becoming more difficult to achieve. Transistors are introduced in Chap. Now, they have become semiconductor. These devices use semiconduct- small enough so that atomic interactions are ing and sometimes conducting materials that are beginning to interfere with proper operation. Slower rier mobility, that is, get the holes and electrons than silicon, but more flexible and potentially to move faster.
Mobility can be improved by much cheaper, organic electronics has already using other materials, such as gallium arsenide. Or- effect transistor. GASFETs are used in very ganic displays might compete with liquid crystal high-frequency applications.
In a semiconductor, such as silicon, the energy Strained silicon is formed by the growth of a difference between the top of the valence band silicon-germanium layer on top of a traditional and the bottom of the conduction band is called silicon wafer. Wafers of silicon are the basic raw the band gap. Or it is the amount of energy, in material used in the manufacture of integrated electron volts eV , required to free a valence circuits, which is covered in Chap.
Then, duction level. The larger crystalline lattice exerts amounts to a force of 1 newton applied over a distance of 1 meter, or to a current of 1 am- pere through a 1-ohm resistor for 1 second. Silicon carbide devices can safely handle thousands of volts. Conduction band Band gap Dopant band Valence band. Conductor Insulator Intrinsic silicon Doped silicon. In fact, the bands overlap is to convert as much sunlight as possible into as shown in red.
An insulator has a large band electricity. This means that it is very difficult to move The photon energy of light varies according a valence electron into the conduction band. The However, it can be done. This is why insula- entire spectrum of sunlight, from infrared to tors can break down and conduct if subjected ultraviolet, covers a range from about 0. Now, look at the graph to about 2.
For example, red light has an for intrinsic silicon. The band gap is smaller energy of about 1. Most solar cells cannot for most applications. Finally, look at doped use about 55 percent of the energy of sunlight, silicon.
The electrons provided by the dopant because this energy is either below the band material green fall just below the conduction gap of the material or is excessive. There is band. The band gap is small for doped semicon- currently intense interest in finding new semi- ductors. This is important for the operation of conductor materials to improve the efficiency devices such as diodes and solar cells, both of and lower the cost of solar cells.
It is possible which are explained in the next chapter. A key to obtaining an efficient solar cell. Self-Test Determine whether each statement is true or If a photon has more energy than the band false. The band gap of materials is measured in Doping semiconductors increases their volts. The band gap for copper or silver is zero. The electron volt is a unit of work or energy.
Good conductors, such as copper, contain a large Free electrons serve as current carriers. Acceptor impurities have three valence electrons 2. In a conductor, the valence electrons are weakly and produce holes in the crystal. Holes in semiconductor materials serve as current 3. Heating a conductor will increase its resistance. This response is called a positive temperature Hole current is opposite in direction to electron coefficient. Silicon atoms have four valence electrons.
They can Semiconductors with free holes are classified as form covalent bonds that result in a stable crystal P-type materials. Impurities with five valence electrons produce 5.
Heat energy can break covalent bonds, making N-type semiconductors. This Impurities with three valence electrons produce gives silicon and other semiconductor materials a P-type semiconductors. Holes drift toward the negative end of a voltage 6. At room temperature, germanium crystals have source.
Electrons are majority carriers for N-type material. This makes germanium diodes and Holes are majority carriers for P-type material. Holes are minority carriers for N-type material. Electrons are minority carriers for P-type material. The process of adding impurities to a semiconductor The number of minority carriers increases with crystal is called doping.
Doping a semiconductor crystal changes its To move a valence electron to the conduction band, electrical characteristics. Donor impurities have five valence electrons and band gap must be applied. This forms N-type semiconductor material. Silicon does not semiconduct unless it is doped or heated. The current carriers in conductors such as Silicon has five valence electrons.
A silicon crystal is built by ionic bonding. It is easy to move the valence electrons in Semiconductors have a negative temperature sistance goes up as temperature goes down. Silicon is usually preferred to germanium Holes are current carriers and are assigned a When a semiconductor is doped with arsenic, positive charge. If a P-type semiconductor shows a few free N-type material has free electrons available to electrons, the electrons are called minority support current flow.
Doping a crystal increases its resistance. If an N-type semiconductor shows a few free Doping with boron produces free electrons in holes, the holes are called minority carriers.
Suppose that you could perfect a method of How could these crystals lems in many, but not all, electronic products. Hint: Diamonds are Can you think of an application where their noted for their extreme hardness and ability to temperature sensitivity is desired? You have learned that conductors and semicon- Some semiconductors, such as gallium arsenide, ductors have opposite temperature coefficients.
That How could you use this knowledge to design a is, the carriers move faster in the crystal. What circuit that remains stable over a wide tempera- kinds of devices could benefit from this?
Diodes are very important in electronic circuits. Your study of diodes Interpret volt-ampere characteristic curves will enable you to predict when they will be for diodes. You will be Identify the cathode and anode leads of some diodes by visual inspection. Figure shows a Diode representation of a PN-junction diode. Notice PN-junction that it contains a P-type region with free holes diode and an N-type region with free electrons.
The diode structure is continuous from one end to the other. It is one complete crystal of silicon. The junction shown in Fig. It does not represent a mechanical joint. In other words, the junction of a diode is that part of the crystal where the P-type material ends and the N-type material begins.
When a diode is manufactured, some of the free electrons cross the junction to fill some of the holes. Figure shows this effect. The result is the P-type side, that atom becomes a negative that a depletion region is formed.
The electrons ion. The ions form a charge that prevents any Depletion that have filled holes are effectively captured more electrons from crossing the junction. With the electrons gone the electrons cross the junction to fill some of and the holes filled, no free carriers are left. The depletion region will not continue to This negative charge is called the ionization grow for very long.
Now that we know what happens when a Figure shows why this potential is PN junction is formed, we can investigate how formed. Any time an atom loses an electron, it it will behave electrically. That is also true with certain radio-frequency measurements that can be made with a PC. This edition covers wireless network troubleshooting and presents more information about digital modulation methods.
Last but not least, there is now more troubleshooting information. In addition to using software and PCs, methods of using basic calculations to predict circuit performance are discussed.
For example, a regulated power supply circuit is analyzed to determine normal voltage readings. This is becoming more important as fewer voltage readings and fewer waveforms are supplied with schematics.
Technicians are forced to become more self-reliant and better educated about the circuit principles and theory that are covered here. The practicality of this book has always been very strong and has continued to evolve over time.
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