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CHAPTER

ELECTRONIC FUNDAMENTALS

CHAPTER OUTLINE

Semiconductor Devices ........................................................................................................................ 24

Diodes .................................................................................................................................. 27

Zener Diode .......................................................................................................................... 29

Electro Optics ...................................................................................................................................... 30

Photo Conductor .................................................................................................................... 31

Photo Diode .......................................................................................................................... 32

Light Generating Diode .......................................................................................................... 34

Laser Diode ........................................................................................................................... 34

Rectifier Circuit ................................................................................................................................... 35

Communications Applications of Diodes .................................................................................. 37

Transistors ............................................................................................................................ 37

Field-Effect Transistors .......................................................................................................... 45

FET Theory .......................................................................................................................................... 47

FET Amplifier ........................................................................................................................ 50

Integrated Circuits ............................................................................................................................... 52

Operational Amplifiers ........................................................................................................... 53

Use of Feedback in Op-Amps ................................................................................................................ 54

Summing Mode Amplifier ...................................................................................................................... 56

Comparator ........................................................................................................................... 57

Zero-Crossing Detector ........................................................................................................... 58

Phase-Locked Loop ................................................................................................................ 58

Sample and Zero-Order Hold Circuits ...................................................................................... 60

Zero-Order Hold Circuit .......................................................................................................... 63

Bidirectional Switch .............................................................................................................. 64

Digital Circuits ..................................................................................................................................... 66

Binary Number System ......................................................................................................................... 68

Logic Circuits (Combinatorial) .............................................................................................................. 69

AND Gate ............................................................................................................................. 70

OR Gate ............................................................................................................................... 70

NOT Gate ............................................................................................................................. 70

Boolean Algebra .................................................................................................................... 71

Understanding Automotive Electronics. http://dx.doi.org/10.1016/B978-0-12-810434-7.00002-8

Exemplary Circuits for Logic Gates .......................................................................................... 71

Combination Logic Circuits ..................................................................................................... 75

Logic Circuits with Memory (Sequential) ............................................................................................... 77

R-S Flip-Flop ........................................................................................................................ 77

JK Flip-Flop .......................................................................................................................... 78

D Flip-Flop ........................................................................................................................... 79

Timer Circuit ......................................................................................................................... 80

Synchronous Counter ........................................................................................................................... 83

Register Circuits .................................................................................................................... 83

Shift Register ........................................................................................................................ 84

Digital Integrated Circuits ..................................................................................................................... 86

The MPU ............................................................................................................................................. 87

This chapter is for the reader who has limited knowledge of electronics. It is intended to provide

an overview of the subject so that discussions in later chapter s about the operation and use of automo-

tive electronics control systems will be easier to understand. The chapter discusses electronic

devices and circuits having applications in electronic automotive instrumentation and control systems.

Topics include semiconductor devices analog circuits, digital circuits, and fundamentals of integrated

circuits.

SEMICONDUCTOR DEVICES

All of the active circuit devices (e.g., diodes and transistors) from which electronic circuits are built are

fabricated from so-called semiconductor materials. A semiconductor material in pure form is neither a

good conductor nor a good insulator. The ability of a material to conduct electric current is character-

ized by a property called conductivity. A model for current flow in semiconductor materials and an

explanation for electric conductivity are developed later in this chapter. A metal such as copper, which

is a good conductor, has a relatively high conductivity such that current flows in response to relatively

low applied voltage. An insulator such as mica has a relatively low conductivity such that essentially

zero current flows in response to an applied voltage. A semiconductor material has conductivity some-

where between that of a good conductor and that of a good insulator. Therefore, this material (also

called semiconductor material) and devices made from it are semiconductor devices (also called

solid-state devices).

There are many types of semiconductor devices, but transistors and diodes are two of the most im-

portant automotive electronics. Furthermore, these devices are the fundamental elements used to con-

struct nearly all modern integr ated circuits. Therefore, the discussion of semiconductor devices will be

centered on these two. Semiconductor devices are made primarily from silicon or germanium (although

other materials, e.g., gallium arsenide, are also in use) that is purposely infused with impurities that

change the conductivity of the material.

The conductivity of a pure semiconductor can be varied in a predictable manner by diffusing precisely

controlled amounts of very specific impurities into it. The process of adding impurities to silicon is called

“doping.” Boron and phosphorus are often used as impurity source materials to alter the conductivity of

24 CHAPTER 2 ELECTRONIC FUNDAMENTALS

silicon. When boron is used, the semiconductor material becomes a so-called p-type semiconductor.

When phosphorus is used, the semiconductor material becomes an n-type semiconductor.

In order to understand the operation of these transistors and diodes, it is helpful to understand the

basic physical mechanism of electric conductivity in both n-type and p-type semiconductor materials.

The flow of an electric current through any material is due to the motion of electrons in the material in

response to an applied electric field. This electric field results from the application of a voltage at the

external terminals of the corresponding structure. The variable called an electric field in this chapter is a

component of the general theory that is known as “electromagnetic field theory.” This theory forms the

basis of modeling all electric phenomena. This electric field is represented by a vector that is known as

electric field intensity and denoted as



E in this book. Although the advanced details of electromagnetic

field theory are beyond the scope of this book, somewhat simplified theoretical models are presented in

later chapters (e.g., Chapter 5). For the purpose of explaining electric properties of semiconductor ma-

terials, we present the simplest model of electric field intensity in which the magnitude varies in pro-

portion to applied voltage and inversely with the distance between the electrodes to which the voltage is

applied. The electrons that move in response to this electric field originate from the individual atoms

that make up the material.

For a basic understanding of conductivity, it is helpful to refer to Fig. 2.1 that depicts a relatively

long, thin slab of semiconductor material across which a voltage is applied.

In this figure, the electric field intensity is a vector denoted as



E that is x-directed. In this book,

vectors are indicated by a bar over the symbol for the vector as exemplified by the electric field inten-

sity



E. A voltage v is applied to a pair of conducting (e.g., Cu) electrodes. For this relatively long, thin

semiconductor material, the magnitude of the electric field intensi ty E is approximately constant over

the semiconductor and is given approximately by

E ¼

The vector



E is given by



E ¼ E

where

x ¼unit vector in the x direction.

Electrode

FIG. 2.1 Illustration of current conduction in semiconductor.

25SEMICONDUCTOR DEVICES

Also shown in Fig. 2.1 is the current density vector



J, which is also an x-directed vector. The current

density vector is propor tional to the electric field intensity:



J ¼ σ



¼ σE

(2.1)

where σ is the conductivity of the material. The magnitude of the current density J is the current per unit

cross-sectional area (which by the assumption of essentially constant E is constant) and is given by

J ¼

(2.2)

where A

is the cross-sectional area of the slab in the y, z plane. The reciprocal of conductivity is known

as the resistivity ρ of the material:

ρ ¼

(2.3)

The explanation of electron flow in any material is based upon the “band theory of electrons.” This

theory is a major com ponent in modern atomic physics. According to this theory, the energy of the

electrons associated with the atoms making up a material is constrained to certain ranges called bands.

Any given electron will have an energy within one of these bands, and no electron can have energy

outside these bands. Within each band, the electrons can have only discrete energy levels, and only

one electron can “occupy” a given energy level. Consequently, the number of electrons within each

band for any atom is constrained to the number of “allowed” energy levels. An electron can only move

in response to an applied electric field and contribute to current flow if there is an unoccupied energy

level to which it can move as its energy changes due to the electric field intensity force acting on it.

All of the energy levels of the lower energy bands of an atom are filled such that there is no energy

level to which an electron can move in response to an applied electric field. Thus, these lower band

electrons cannot contribute to current flow in response to an applied voltage. The electrons in the out-

ermost band, known as the conduction band, are the least tightly bound, and for a material such as Si,

they are few in number relative to the number of energy levels in that band. These outer band electrons

can move to an adjacent energy level and effectively move freely in response to an applied electric

field. These electrons are called “free electrons.” Doping Si with phosphorus impurity results in an

excess of fre e electrons relative to pure Si. The doped material is said to be an “n-type” semiconductor

and has a conductivity that is greater than the undoped Si.

The next lowest energy band from the outermost is called the “valence band” since it is associated

with the chemical valence of the material (in this case Si). The energy levels of this band are nearly (but

not completely) filled. However, doping a semiconductor with a p-type impurity (e.g., doping Si with

boron) yields a relative excess of energy levels in this valence band. The resulting doped material is

called a p-type semiconductor. Electrons in this band can move to the available energy levels created by

doping in response to an electric field, thereby contributing to current flow. However, functionally, this

p-type material behaves as though it had excess of positively charged particles called “holes.” The

model for current flow in a semiconductor and the explanation of semiconductor devices use the fic-

titious holes and their response to an applied field as a basis for the contribution they make to current

flow. The terminology used to describe these charge carriers is as follows: in n-type material electrons

are called “majority carriers” and holes called “minority carr iers”; the reverse is true in p-type material.

26 CHAPTER 2 ELECTRONIC FUNDAMENTALS

Doping a semiconductor material changes the relative densities of holes and electrons. However,

there is a basic relationship between these densities, which is preserved regardless of the doping con-

centrations. If one starts with an intrinsic semiconductor such as Si that has an equal concentration of

“free” electrons and holes (since each free electron leaves a “hole” in the valence band for an intrinsic

semiconductor), we denote this concentration n

¼1.510

/cm

Doping Si with either a p-type or an n-type impurity changes the concentrations. Denoting electron

density n, and hole density p, the following equation expresses the relationship between these concen-

trations under thermal equilibrium:

np ¼ n

(2.4)

There is another basic aspect of semiconductor physics that plays a role in the electric characteristics of

semiconductor electronic components. Whenever a voltage V is applied to a slab of semiconductor

material, it creates an electric field that is represented by the electric field intensity vector



E as de-

scribed above (in this text, the over bar for a variable is the notation indicating that the variable is

a vector).

In a semiconductor material, any electric field due to an external potential causes the electrons and

holes to move with mean velocity vectors



and



, respectively. These velocities are given by



¼ μ



¼ μ



where μ

is the electron drift mobility and μ

is the hole drift mobility.

These mean velocities yield electron and hole current densities



and



, respectively:



¼ nq



¼ pq



where q is the charge on an electron (1.6  10

19

coulomb). These relationships will appear in models

for various components in this text.

Throughout this book, current flow is taken to be conventional current in which the direction of flow

is from positive to negative, whereas in reality, current consists of electron motion from negative to

positive. This choice of current is merely convenient for notational purposes and has no effect on

the validity of any circuit analysis or design.

DIODES

The first electronic component to be considered is a device called a “diode.” A diode is a two-terminal

electric device having one electrode that is called the anode (a p-type semiconductor) and another that

is called the cathode (an n-type semiconductor). A solid-state diode is formed by the junction between

the anode and the cathode. In practice, a p-n junction is formed by diffusing p-type impurities on one

side of the intended junction and n-type impurities on the other side of a region of an intrinsic semi-

conductor (e.g., Si).

The regi on in which the diode material changes from p-type to n-type material is called the p-n

junction (or simply junc tion). The junction region is relatively short but plays a critical role in the diode

operation. When the junction is formed, elect rons in the vicinity of the junction migrate from the n-type

to the p-type. Similarly, holes in the region migrate from p-type to n-type. This migration leaves behind

27SEMICONDUCTOR DEVICES

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