181 results in Electronics for Physicists
Learning the Art of Electronics
- A Hands-On Lab Course
- 2nd edition
- Thomas C. Hayes, David Abrams, Paul Horowitz
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The much-anticipated new edition of 'Learning the Art of Electronics' is here! Perfect for anyone wanting to learn about different types of circuits and their behavior, the book defines a hands-on course, inviting the reader to try out the many circuits that it describes. Several new topics have been added to the analog half of the book and the digital sections have been rebuilt. An FPGA replaces the less-capable programmable logic devices, and a powerful. ARM microcontroller replaces the 8051 previously used. The new microcontroller allows for more complex programming (in C) and more sophisticated applications, including a lunar lander, a voice recorder, and a lullaby jukebox. A new section explores using an Integrated Development Environment to compile, download, and debug programs. Substantial new lab exercises, and their associated teaching material, have been added, including a project reflecting this edition's greater emphasis on programmable logic.
Electronics
- Analog and Digital
- Barun Raychaudhuri
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Analog and digital electronics are an important part of most modern courses in physics. Closely mapped to the current UGC CBCS syllabus, this comprehensive textbook will be a vital resource for undergraduate students of physics and electronics. The content is structured to emphasize fundamental concepts and applications of various circuits and instruments. A wide range of topics like semiconductor physics, diodes, transistors, amplifiers, Boolean algebra, combinational and sequential logic circuits, and microprocessors are covered in lucid language and illustrated with many diagrams and examples for easy understanding. A diverse set of questions in each chapter, including multiple-choice, reasoning, numerical, and practice problems, will help students consolidate the knowledge gained. Finally, computer simulations and project ideas for projects will help readers apply the theoretical concepts and encourage experiential learning.
Chapter 17 - Microcomputer and Microprocessor
- Barun Raychaudhuri, Presidency University, Kolkata
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Summary
The modern computer is such as electronic gadget where all of the analog and digital electronic devices mentioned in this book are included somewhere or else. This chapter presents a brief idea on the basic principles and architectural blocks of a computer. The role of microprocessor in computer and the fundamentals of programming the microprocessor are interpreted using 8085 as a model.
Evolution of Computer
The modern computer evolved as an electronic instrument and got so much involved in scientific, technical, commercial, and household applications that it gave birth to computer science as a separate subject. Anyway the first computer was not electronic but a mechanical instrument. Indeed performing mathematical calculations with instruments is quite an ancient concept. The word ‘calculate’ is derived from the Latin word calculos, which means stone. Pieces of stone, pebbles, digits of fingers, knot of ropes, nodes of sticks and many other diversified equipment have been employed in arithmetic calculations in different ages of human civilization.
Historical Background
The first known calculating machine is abacus, which was popular in ancient China, Japan, Egypt, and also different countries of Europe. The earlier version of abacus consisted of slotted earthen flats over which pebbles were moved to indicate number positions. The later versions comprised of beads penetrated into framed wires. Table 17.1 outlines a brief sketch of the development of computational concepts and instruments till the middle of the twentieth century.
Charles Babbage, as mentioned in the table, was the first to incorporate all the basic features of a modern computer in his instrumentation. He constructed a large mechanical system named Difference Engine that possessed the following components.
• Mill: It was capable of executing arithmetic processors. It may be compared to the arithmetic logic unit (ALU) of a modern computer.
• Store: It could store numbers, analogous to the memory of today's computer.
• In/Out Ports: There were separate ports for giving instructions and obtaining results, similar to the input and output terminals of a modern computer.
Chapter 10 - Feedback Amplifiers and Oscillators
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Summary
This chapter presents the concept of feedback, which means looping back a portion of the output voltage or current of an amplifier to control the system within itself. Different types of feedback and the advantages of negative feedback are clarified. The relationship between positive feedback and oscillation is explained. Two different categories of oscillator circuits are elucidated, namely the oscillators based on positive feedback and resonant circuit, such as Hartley oscillator, Colpitts oscillator, Wien bridge oscillator, phase-shift oscillator and crystal oscillator, and the switching oscillators, popularly known as multivibrators.
Concept of Feedback
Incorporating feedback to an amplifier changes its gain and other properties. During the feedback process, a portion of either the output voltage or the output current is sampled and returned to the input either in series or in parallel with the original signal. The working principle of feedback implemented to an amplifier can be interpreted with the block diagram of Figure 10.1. It comprises the following elements.
Signal Source: It may be either a voltage source or a current source. The symbol Xs denotes the signal, either the voltage or the current obtained from it.
Mixing Unit: It combines the source signal (Xs) and the feedback signal (Xf) to produce the input signal (Xi) for the amplifier.
Amplifier: It performs the basic job of amplification of a signal. It may be any one of the BJT (Chapters 5 through 8) or the FET (Chapter 9) or any circuit made of those. It may also be an operational amplifier (Chapter 11) circuit. Whatever it may be, the amplifier has a transfer gain (A) and it amplifies the input signal to produce the output of Xo. The transfer gain of the basic amplifier is given by
Sampling Unit: It picks up a fraction of the output signal (Xo) and delivers to the feedback element. The mixing and sampling units are actually series and/or parallel connections of passive elements.
Feedback Element: It is a two-port network, generally made of passive elements, supplying the sampled fraction (Xf/Xo) of the output to the mixing unit. The fraction
is called the reverse transmission factor of the feedback element and is popularly termed as the feedback ratio.
Chapter 13 - Digital Principles and Boolean Algebra
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Summary
The working principles of computers and other digital systems are based on binary and hexadecimal number systems. This chapter introduces different number systems, such as binary, octal, and hexadecimal, and their relationships with our familiar decimal system. Some popular digital codes are also mentioned briefly. Arithmetic operations with binary numbers, development of algebraic techniques with Boolean variables and simplifications of Boolean expressions are illustrated. Indeed this chapter deals with the mathematical and theoretical portion of the digital system. All practical implementations with electronic circuits are included in the subsequent chapters.
The Digital System
The word ‘digital’ originates from digit, meaning separate organs or components like fingers of human hand and each of the keys of a keyboard. In electronic operations, the digit represents two discrete electrical states, such as on/off conditions of a switch or presence/ absence of voltage at a terminal. In the present context, digital refers to those electronic circuits which realize binary numbers in terms of two discrete voltage levels and perform mathematical and logical operations based on the principles of Boolean algebra.
Analog and Digital
The word ‘analog’ is derived from the Greek word analogos, which means ‘according to a certain ratio’. The computation with the operational amplifier, as explicated in Chapter 11, is analog in nature because the voltage values are analogous to numbers. The increment and decrement of numbers is in proportion to the voltage. The following characteristics are the major demarcations between analog and digital systems.
• Continuous and Discrete: An analog device consists of continuously changing quantity. For example, a continuous curve in XY-plane is an analog graph. The voltage change in operational amplifier is continuous. In contrary, a bar chart can be treated as a digital graph. The digital electronic circuits handle only two discrete levels of voltage.
• Size-Dependent Accuracy: The precision of an analog instrument depends on its size, marking of scale and other physical parameters. The least count of a slide calipers and that of a travelling microscope are different. A small size transistor has less power handling capability than that of a larger one. In contrast, the accuracy of a digital instrument does not depend on its size.
Chapter 11 - Operational Amplifier
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Summary
The operational amplifier, abbreviated as op-amp is an amplifier circuit comprised of active and passive components. It has high voltage gain, high input impedance, and wide range of frequency of input signal that it can handle. The most remarkable feature is that the op-amp can be used for the purpose of numerical computations, the numbers being represented by the input and output voltage values. This chapter brings together the basic properties of the op-amp and the most popular circuits constructed with it, such as inverting and noninverting amplifiers, adder, differentiator, integrator, active filter, comparator, Schmitt trigger, and logarithmic amplifier. Also some novel applications of op-amp, such as equation solving and waveform generating are introduced.
A Review on Amplifiers
In Chapters 5 through 10, we have come across different types of amplifiers made of bipolar junction transistors or field-effect transistors. Now we are quite familiar with the fact that the same device may not be suitable for voltage, current, and power amplification and at all frequencies of the input signal. In this chapter, we are about to start a new type of high gain voltage amplifier, known as operational amplifier, abbreviated as op-amp, which is made up of a number of transistors, either bipolar or field-effect or both, combined in a circuit. In this occasion, it may be relevant to have a quick recapitulation on the overall features of a typical amplifier.
Whatever may be the actual circuit configuration, an amplifier can be considered as an electronic circuit comprising one or more active device producing a magnified replica of the input voltage or current. In general, an amplifier has the following properties.
(i) The output signal has generally the same frequency and waveform as that of the input signal. If not, it is a special form of amplifier, known as oscillator or waveform generator.
(ii) The output amplitude is mostly different from the input amplitude and in maximum cases, the former is increased. Sometimes the output amplitude may decrease also when the circuit is called attenuator.
(iii) The phase of the output waveform may or may not change with respect to the input depending on the circuit operation and device property.
(iv) Each amplifier has a certain range of frequency for the input signal over which it can exhibit its properties.
Chapter 12 - IC Technology and Instrumentation
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Summary
This chapter includes two different topics well related to electronic devices and circuits. One is the technology of fabricating integrated circuit (IC) and the other is the construction of measuring instruments, mainly concentrated on cathode ray oscilloscope (CRO).
Integrated Circuit (IC)
An integrated circuit (IC) is a complete miniature circuit comprising active elements, such as diodes and transistors and passive elements, such as resistors and capacitors, all fabricated on a single chip of semiconductor, mostly silicon. American engineer Jack Kilby (1923–2005) and American physicist Robert Noyce (1927–1990) independently invented the principle of IC in 1958 and 1959, respectively. ICs are indispensable components of almost all modern electronic appliances ranging from computer, television, smartphone and other household gadgets to the critical advancing on missiles and artificial satellites.
Use of IC in electronic circuits has a number of advantageous features over the bulky circuits made of interconnected discrete components. The most significant benefits are the followings.
Miniaturization: Fabrication of small-size devices is the most noted advantage of IC. Indeed the word ‘microelectronics’ became popular after the arrival of IC. Accommodating more than 108 transistors within a chip of only 1 cm2 is a very common feature in today's IC technology.
Batch Processing: Millions of ICs can be fabricated at a time from a single piece of semiconductor. The process reduces the cost and provides with good matching among the devices.
Improved Performance: The reliability of the working of ICs is very good because the possible faults due to interconnection of discrete components is eliminated. Small size and light weight make the circuit suitable for airborne, space-based and other vital equipment.
Maintenance: It consumes less power and the entire circuit can be replaced easily at less cost.
In spite of the above benefits, ICs have some limitations, as follows.
• Transistors capable of handling high power cannot be fabricated on IC.
• Inductors and transformers cannot be fabricated on IC.
• IC technology is not suitable for high value capacitors, such as 100–1000 μF.
• Precision resistors having tolerance less than 1% are not possible with IC.
As a whole, the range of IC-fabricated passive components is quite restricted. The power handling capability of IC components is low and the components may be sensitive to voltage and static charge.
Chapter 9 - Field-Effect Transistor (FET)
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This is a separate category of transistor where the output current is controlled by the input voltage. There are two broad categories of such transistors, namely junction field-effect transistor (JFET) and metal–semiconductor field-effect transistor (MOSFET). The device construction, electrical characteristics and the related parameters of JFET and MOSFET are illustrated in this chapter. Different types of amplifier configurations realized with these devices are introduced.
‘Field-Effect’ and ‘Transistor’
Chapters 5 to 8 have gone through various properties of the three-terminal bipolar junction transistor (BJT) where the output current is controlled by another current at the input. The present electronic device is also three-terminal and it can amplify voltage and switch electrical signals. So this is also a transistor. However, unlike the bipolar transistor, the current through the output terminals is controlled by an electric field resulting from the voltage at the third terminal. Indeed the electric field may control the current conducting path of the output circuit without any direct electrical contact between the causing and the resultant parameters. That is why it is named field-effect transistor, abbreviated as FET.
The FET is contemplated in different forms. There is a category of junction FET (JFET) where the input voltage varies the depletion width of a reverse-biased p–n junction. Another group of FET having a metal electrode separated from the semiconductor by an insulator is known as metal-oxide-semiconductor FET (MOSFET). A remarkable difference from BJT is that unlike the participation of both electrons and holes, the output current in a FET is composed of either electrons or holes and accordingly the FET is referred to as unipolar device and majority carrier device. Both the JFET and the MOSFET have the following three terminals.
Source: It is the point through which the majority carriers enter the current carrying semiconductor bar, called channel. The source terminal of the FET may be compared to the emitter of the BJT.
Drain: Through this the terminal, the majority carriers flow out of the channel. The drain is analogous to the collector of a BJT.
Gate: It is the terminal with either a metal (for MOSFET) or a heavily doped region of opposite type semiconductor (p+ for n-channel and vice versa) (for JFET) meant for controlling the drain current. The gate is comparable to the base of the BJT.
Chapter 6 - Transistor Biasing and Amplification
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Summary
As understood from Chapter 5, the bipolar junction transistor is a current amplifier of its own. However, it can be made to amplify voltage also, as will be discussed in this chapter. The key factor for voltage amplification with transistor is the use of external passive elements such as resistors and capacitors in the transistor circuit driven by a single voltage supply. The process is termed as biasing. This chapter illustrates several popular biasing techniques for the common-emitter (CE), common-base (CB) and common-collector (CC) configurations of the transistor.
Load Line and Q-Point
The concept of operating point and load line has been introduced in Chapter 4 in connection with p–n junction diodes. Similar requirements of tracing load line and establishing operating point are realized with the transistor also. The convention remains the same, but the parameters get changed in the case of a transistor.
The operating point for a transistor is commonly named as the Q-point or the quiescent point because it specifies the output voltage and the output current at which the transistor operates steadily. The Q-point of a particular transistor circuit is determined by establishing proper voltage levels at the three terminals using the voltage drops across external resistors, capacitors or inductors and a single electrical power supply. This process is known as biasing, to be discussed in the next section. The fixation of Q-point depends on several factors, such as
• the dc and dc loads of the amplifier,
• the range of the power supply,
• the maximum power rating of the given transistor and
• the allowable distortion in amplification.
Based on the above, there are several different types of classifications of amplifiers, namely class A, class B, class AB, and class C, to be discussed in Chapter 8. In practice, the Q-point of a transistor is determined with reference to output characteristics in the following way.
Figure 6.1(a) shows an n–p–n transistor in CE configuration with an external resistor (RC) in series with the collector terminal. The output characteristics for different base current are sketched in Figure 6.1(b). These are similar to Figures 5.4 (a) and (b), respectively, of Chapter 5 but there is an important difference.
Chapter 3 - p–n Junction Diodes
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Summary
The semiconductor p–n junction is the most fundamental part of many electronic devices including diodes and transistors, and it is a basic element for understanding the working of other semiconductor devices. This chapter brings together the concepts on fabrication of a junction, barrier formation at the junction carrier and transport through it, forward and reverse biased conditions of a p–n junction and the corresponding energy band pictures and the wide variety of diodes that can be constructed using the p–n junction.
Fabrication of p–n Junction
Chapter 2 states that a piece of semiconductor, either n-type or p-type is a solid of variable electrical conductivity depending on the extent of doping. As soon as the combination of p- and n-type materials takes place, the electrical properties change radically. The junction acts a valve allowing current in a single direction. It is capable of converting an alternating input voltage or current to a pulsating direct voltage or current output, the phenomenon being referred to as the rectification.
Though it is called a ‘junction’, the p–n junction is not at all constructed by gluing or soldering two separate n-type and p-type pieces of semiconductors. In order to maintain the regularity of lattice structure, the same piece of intrinsic semiconductor crystal is doped for n- and p-type from two sides. Chapter 12 contains the detailed narration on the construction of p–n junction in connection with integrated circuit (IC) technology. The following are the common techniques of fabricating a p–n junction.
Grown Junction: This technique used to be adopted in the early days of semiconductor technology. In this process, the type of the dopant atom is abruptly changed during the crystal growth. For example, during crystal growth of silicon from melt, phosphorus is added for n-type doping and then boron atoms are added in larger concentration for p-type doping.
Alloyed Junction: This procedure is suitable for small scale production in laboratory. The doped semiconductor is alloyed with the material containing the opposite type of dopant. For example, n-type germanium is heated with indium to form a molten alloy. On cooling, the germanium grows out of the alloy because of redced solubility in solid state. At the interface of the alloy and the separated germanium, a region of germanium exists with high concentration of indium atoms and this germanium becomes p-type. Thus a p–n junction is formed.
Chapter 16 - Analog–Digital Conversion and Memory
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Summary
The digital circuits introduced so far, such as arithmetic, logical, data-processing, and sequential circuits are somehow associated with the core of a digital system, such as, the central processing unit of a computer. Yet there are two other very significant topics, namely analog and digital conversion circuits and different types of memory circuits for storage of digital information. This chapter deliberates upon several digital-to-analog (D/A) and analog-to-digital (A/D) conversion circuits and introduces the classification and fabrication of memory devices in digital systems.
Why D/A and A/D Conversions
A digital system is a special man-made technique whereas most of the natural entities, such as voltage, temperature and light intensity are analog in nature undergoing continuous variation. Indeed the basic unit of a digital circuit, namely the logic gate is made of bipolar transistors or MOSFETs that are analog of their own. These devices are made to operate in two discrete output states so as to comply with the binary system. Hence, for the purpose of interacting with a digital system, it is not sufficient to just convert the nonelectrical entity to a proportional electrical signal. The continuous variation of voltage or current must somehow be converted to a proportional digital change of two discrete states. The two-state response of the digital system also should be translated to a proportional continuous variation. There lies the significance of analog–digital interconversion systems. A few specific examples may be cited.
Printing Computer Outputs: The digital results processed by a computer must be communicated to the analog servomechanism through some equivalent analog signals.
Measuring Nonelectrical Quantities: The digital instruments for measuring nonelectrical quantities, such as temperature, speed or blood pressure first converts the variation of the quantity to a proportional electrical signal using an appropriate transducer. Then the analog electrical signal is converted to equivalent digital code.
Internet Communication: Both way analog–digital conversions are necessary for connecting telephone cables to computers for Internet communications, such as emailing, uploading and downloading data.
Chapter 8 - Transistor Power and Multistage Amplifiers
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Summary
The essential conditions for a bipolar junction transistor to work as power amplifier are illustrated in this chapter. Sometimes the output of an amplifier is used as the input of another amplifier in order to produce larger amplification. Such cascading of two or more amplifier stages is called coupling, which may be done with resistor, capacitor transformer, or with direct connection. Different types of coupling and the resultant multistage amplifiers are discussed. Several classes of amplifier operation, such as A, B, AB and C are introduced. Some specific types of biasing techniques suitable for transistor power amplification, such as push–pull and tuned amplifier are explained.
Need for Power Amplification
In Chapters 5 through 7, we have come across different types of transistor configurations and biasing circuits acting as voltage or current amplifiers. The amplifier converts a portion of the electrical energy obtained from the dc power supply into the energy obtained at the output in proportion to the input. The input signal just controls the mode of conversion. There are wide varieties of amplifier depending on the requirement of
• ac or dc amplification,
• voltage, current, or power amplification,
• amplification over a wide range of frequency of the input signal (wideband amplifier), and
• amplification around only a fixed frequency of the input signal (narrowband or tuned amplifier) and many others.
The loudspeaker in a public address system is a very common example where high level amplification is required for a weak electrical signal. Servomechanisms, such as the movement of the motor in a printer connected to a computer and signal transmissions in radio/television broadcasting are other popular examples where high level amplifications are compulsory. Such large extent of amplification cannot be achieved with the BJT amplifiers discussed in Chapters 6 and 7 because of the following constraints.
(i) Achieving voltage gain is not possible for large signals because the ositive and negative swings of a large (≥ 0.7 V) ac input would drive the Q-point to saturation and cutoff, respectively.
(ii) The current gain can still be achieved because it is the fundamental property of the transistor.
(iii) The nonlinearity in the transistor transfer characteristic becomes predominant for large input signals.
Chapter 4 - Diode Applications
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Summary
The most significant property of the p–n junction diode, as introduced in Chapter 3, is rectification or converting alternating current (ac) to direct current (dc) because the diode conducts under forward bias only. This property is utilized for fabricating rectifier circuits. The three major categories of rectifier namely half-wave, full-wave, and bridge are illustrated in this chapter. The rectifying property of a diode is also implemented to the transmission of a portion of an alternating voltage waveform. Such circuits, known as the clippers are elaborated. Two other important circuits, namely the clamper and the voltage multiplier that use diodes with capacitors are brought together.
Piecewise Linear Model
The diode is, of course, a nonlinear device because the current through it undergoes nonlinear change with voltage. Yet the diode can be approximated as a linear element part-by-part under certain conditions. The concept of such ‘linearizing the diode’, as explained with Figures 4.1(a) and 4.1(b), is quite useful to the analysis of the circuits containing diodes. Both the diagrams symbolize the forward current–voltage characteristic curve of a typical diode but at different scales. Figure 4.1(a) represents the enlarged view for the condition just after cut in. The current is now determined by the junction property and the nonlinearity of the current–voltage curve is quite prominent. The same diode at a forward voltage much higher than the cut-in voltage behaves like that of Figure 4.1(b) where the current is dominated by the bulk resistance of the semiconductor, the nonlinearity below 0.7 V gets squeezed into a small region of the characteristic curve and the major portion of the curve becomes linear.
The above demonstration implies that when the bias voltage becomes much larger than the forward cut-in voltage of the diode, the eBipolar Junction Transistorquivalent circuit can be represented by the combination of the following three pieces of linear circuit elements in series.
•An on/off switch representing the forward/reverse biased condition of the diode.
•A voltage source in lieu of the voltage drop across the diode.
•A resistor denoting the semiconductor bulk resistance.
Therefore, such an equivalent circuit of the diode is termed as the piecewise linear model of the diode. Figure 4.2 illustrates the action of this model. The switch (S) is the proxy of the forward and reverse-biased conditions of the diode.
Chapter 1 - Origin of Electronics
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Summary
Electronics is a subject cultivated at different academic levels of undergraduate and postgraduate science and engineering curriculum. Beyond the classes, it has diversified applications in modern science, technology, economy, society, and daily life. The development of electronics throughout the last century may be treated as a distinct step along the progress of human civilization. This chapter sketches a brief outline of the background, evolution, and widespread applications of electronics. This also introduces the arrangement and relevance of topics in this book.
What Is Electronics
It is understood from our everyday experience that electronics is somehow related to the use of electricity. However, electricity is found in nature also, whereas electronic devices and the use of electricity in those devices are totally man-made. The techniques of electronic devices established several novel aspects in the use of electricity, which were never experienced earlier. Some salient features of electronics are mentioned in the following section.
•Electrical Power Amplification: An electronic device, such as a transistor can be made to amplify voltage and current simultaneously that cannot be achieved with other electrical gadgets, such as a transformer.
•Nonlinear Current–Voltage Relationship: According to Ohm's law, the steady current through a resistor, capacitor, or inductor varies linearly with voltage at a constant temperature. However, the current through electronic devices, such as a diode or a transistor undergoes nonlinear variation with voltage.
•Impedance Transformation: The same electronic device may exhibit different resistances across the input and the output terminals.
All the above characteristics were first realized with triode, a vacuum tube device invented by Lee de Forest in 1906. Therefore the invention of triode may be regarded as the foundation of electronics and we may feel that electronics has been a reliable companion of mankind for more than a century. The continuous research and development throughout this long period has enriched human civilization with innumerable equipment and gadgets like television, mobile phone, satellite communication, Internet, and a metamorphosis of computer from mechanical to electrically operated instrument. The researches on electronics and allied subjects have contributed to other branches of science and technology, and have given rise to new interdisciplinary fields.
Preface
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Summary
‘Electronics’ is quite a familiar word in our daily life. We see around us innumerable electronic gadgets for domestic use and many scientific, engineering, technical, and vocational teaching courses of different academic levels related to electronics. Actually electronics evolved as a part of modern physics almost a century ago and depicted significant contribution to modern science, technology, economy and society.
There is no dearth of excellent reference books on different aspects of electronics. Nevertheless, the University Grants Commission (UGC) guidelines of Choice-Based Credit System (CBCS) curriculum and Learning Outcomes based Curriculum Framework (LOCF), prescribing two full papers of electronics in the core course of undergraduate physics motivated this author to write something on electronics exclusively for young students who have just passed the high school and entered the higher studies. The outcome is this book; Electronics: Analog and Digital, prepared mainly for physics honours/equivalent courses.
The topics of electronic devices, circuits and systems are broadly classified into two categories: analog and digital, as is also specified in the CBCS curriculum. Maintaining the recommended topics, the subject matters are reorganized so as to facilitate the students.
The first introductory chapter outlines briefly the evolution, significance and widespread applications of electronics. Since semiconductors take major part in the fabrication of electronic devices, the subject learning starts with the basic properties and types of semiconductors, electrons and holes, concepts of energy band and effective mass and current transport phenomena (Chapter 2).
A fundamental structure in electronics is p–n junction. Chapter 3 explains its rectification property, forward and reverse biasing and the corresponding energy band diagrams. It also elucidates how the same p–n junction with constructional changes can give rise to different devices, such as rectifier diode, Zener diode and light-emitting diode. The important applications of diode as half-wave, full-wave and bridge rectifier, clipper and clamper are presented in Chapter 4.
The bipolar junction transistor (BJT) is a very remarkable device in electronics. It is the basic building block for many analog and digital circuits. So the book dedicates four chapters on different aspects of transistor. Chapter 5 contains the construction and working principle of n–p–n and p–n–p transistors, the amplifying action of transistor and detailed explanations of common-emitter, common-base and common-collector configurations.
Bibliography
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Chapter 15 - Sequential Logic Circuits
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Summary
The previous chapter has dealt with digital circuits having output states dependent only on the instantaneous combination of the inputs. There exist yet another set of digital circuits, known as sequential logic circuits, which are presented in this chapter. A sequential digital circuit is almost always associated with a clock or a timer. This chapter illustrates the properties of a clock and explains several popular sequential digital circuits, namely flip-flop, register and counter that are the building blocks for many complicated digital systems including computer hardware.
Clock and Timer
First let us understand the meaning of the word ‘sequential’ sticking to some digital circuits. It is named so because:
• the output is affected by the positional and temporal sequence of the input states,
• the sequence of the change of output states is different from that of the inputs, and
• a memory property is sometimes exhibited by holding one or more bits in terms of voltage levels.
Table 14.1 may be revisited in this occasion. Now the question arises, who makes this sequence to occur? That is the job of the clock and the timer. As explained in the previous chapters, digital circuits need two fixed and discrete voltage states as inputs. It is a very common phenomenon in a digital system, such as a computer that a number of circuits have to change the logic states in synchronism. That synchronizing is initiated by a timer and a clock.
The timer is an electronic circuit that generates a voltage waveform, generally square or rectangular, of well-defined amplitude and precise frequency. That voltage waveform of fixed amplitude and frequency generated by the timer is referred to as clock signal, clock pulse or simply clock. It defines a timing interval during which the circuit operations must be performed. Thus the timer is the ‘heart’ and the clock is the ‘heartbeat’ of a digital system. The clock has the following properties.
• It may be symmetric or asymmetric voltage waveform but should have fixed and pre-determined amplitude and frequency.
• The prime requirement for a clock is the perfection of its frequency and its stability.
• The high and low voltage levels of the clock should be distinct enough for denoting logical 1 and 0.
The absolute voltage values should comply with the circuit requirements.
Chapter 2 - Semiconductor Fundamentals
- Barun Raychaudhuri, Presidency University, Kolkata
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Summary
This chapter introduces the types of semiconductors and their electrical properties. The origin of two types of charge carriers, namely electrons and holes in semiconductors are explained. The related theoretical concepts of energy band, Fermi energy and effective mass are introduced. The carrier transport in semiconductors causing drift and diffusion currents are discussed. Two important experimental techniques, namely Hall Effect and four-probe resistivity measurement are deliberated.
Crystalline Solids
A broad field of studies, known as condensed matter physics encompasses the macroscopic and microscopic physical properties of matter, mainly in the solid and liquid phases, being ‘condensed’ due to the electromagnetic forces between atoms. A part of this is solid state physics that studies the atomic level and bulk level properties of matter in its solid state. A solid is distinguished from liquid or gas by its definite shape and rigidity. This is because of the atoms or the molecules of a solid being closely packed and strongly bound. However, the atoms in a solid may or may not be in regular arrangement, which determines whether or not the solid is crystalline.
A semiconductor is generally a solid material having electrical conductivity level somewhere between that of conductors (e.g. metals) and insulators (e.g. ceramics). The conducting properties of semiconductors can be altered by application of external electrical fields, light and heat and by a process of incorporating impurities, known as doping. Devices made from semiconductors, such as diode, transistor and logic gates are the basic building blocks for modern electronic circuits. Before going through the properties of semiconductors, it is reasonable to get a brief idea on the fundamental properties of a crystalline solid.
A solid is called crystalline, if the atoms and the molecules in it are organized in symmetric arrays in three dimensions. A definite grouping of atoms is repeated periodically in three dimensions. If the crystal structure is perfect and the same regular arrangement is extended throughout the entire solid, it is called single crystal and if the periodicity is found to be intermittent and confined within a small region, it is called polycrystalline material. Solids not having such regular atomic arrangement are termed as amorphous.
Frontmatter
- Barun Raychaudhuri, Presidency University, Kolkata
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Contents
- Barun Raychaudhuri, Presidency University, Kolkata
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