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1752 results in Circuits and systems

Page 27 of 88

  • Chapter 15 - Introduction to Digital Logic Circuits

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 751-810

  • Summary

    15.1 INTRODUCTION

    In previous chapters, we dealt with various electronic devices (diode, BJT, FET, etc.) that have been used to design various electronic circuits like rectifier, various kind of amplifiers, oscillators, etc. For all these electronic circuits, the input and or output signals can take any value within a practical range; such signals are known as ‘analog’ signal. Electronic circuits and systems dealing with such analog signals are commonly known as analog circuits. Even though all practical signals are analog in nature, various practical applications and processing of these analog signal require certain sort of quantization and discretization. For instance, while measuring voltage/current using an analog meter, we rely on the deflection of the needle on a properly calibrated scale. Using such analog meter, we can measure any practical voltage/current. On the other hand, while measuring same voltage or current using a digits meter we can get only certain discrete values based on the number of digits in the display panel. However, if adequate numbers of display digits are used, it will provide very accurate result!

    In this chapter, we will introduce the basic concepts and circuits dealing with digital signal, a signal that can take only a finite number of values.

    Figure 15.1(a) and (b) show an analog and digital signal plotted against time(t). As discussed previously, analog signal can take any value within a range, while for a digital signal only a few restricted ranges of amplitudes are allowed. The most common digital signals are binary signal that takes amplitude either high (represented as ‘1’) or low (represented as ‘0’). The circuit that deals with digital signals is commonly known as digital circuit. Most of the modern electronic systems like computer, memory circuits, microprocessors and various electronic gadgets like cell phone, iPad, laptop, etc. are high-end examples of digital circuits.

    The objective of this chapter is to learn the features and operations of fundamental digital logic circuits, which are the backbone of the modern digital computers.

    15.2 DIFFERENT NUMBER SYSTEMS

    To have a clear idea on how arithmetic and logical operations are executed in digital systems, we need to be familiar with various schemes of representation of number in digital systems. From our childhood and school days, we have been familiar with decimal number system, which consists of 10 digits, ranging from 0 to 9.

  • Chapter 5 - Transistor Biasing and Stabilization

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 262-321

  • Summary

    5.1 INTRODUCTION

    In the previous chapter, we studied about the fundamental operation of the BJT and got acquainted with various configurations and characteristics of a transistor. We have seen that a transistor can be operated in three regions, namely active region, saturation region and cut-off region. We learned that transistor is to be operated in its active region for amplifying action. The saturation and cut-off regions, on the other hand, are mainly used for switching applications. Each of these applications requires the DC operating point (Q point) of the transistor to be fixed in a desired location of the output characteristics before the application of the alternating signal. The entire process of selecting proper voltage sources and external resistors to bias the transistor junctions (EBJ and CBJ) with suitable amplitude and polarity of voltage and ensuring stability of the DC operating point (without any applied signal) is known as transistor biasing. It ensures suitable positioning of the Q point, i.e. choosing proper set of input current, output current and output voltage. Once the transistor is properly biased, we can apply the alternating voltage in the transistor circuit for various applications. This normally causes symmetrical swing of the input and output voltage and currents about their DC level, fixed previously by biasing.

    Figure 5.1 shows a block diagram demonstrating the influence of biasing in a transistor amplifier, indicated by symbol A. Let the amplifier is a CE amplifier with a 180° phase difference between input and output. Figure 5.1(a) corresponds to a biasing scheme where the Q point is positioned in active region and its entire swing due to the application of AC signal is confined to the active region. This yields a perfect amplification, i.e. entire input signal is amplified. On the other hand, if the Q point enters into cut-off or saturation region due to the applied AC signal, we get a distorted output signal, as indicated in Figure 5.1(b) and (c). Here, a portion of the desired output signal is clipped off as the Q point enters into cut-off or saturation region for some portion of the input signal. This produces distorted output signal. This particular example tells us the profound impact of transistor biasing on the operation of the device and its desired application.

  • 8 - Feedback Amplifiers

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 476-519

  • Summary

    INTRODUCTION

    The term feedback is the basic backbone for all amplifier systems. An electronics engineer named Harold Black working with the Western Electric Company back in 1928 had been searching for various means of gain stabilization in amplifiers used in telephone repeaters. It was then that he intuitively conceived and invented the feedback amplifier. The process or technique by which a fraction of the output voltage or current is combined back/fed back to the input, to produce a desired output of a system is called feedback. But the question is – why does an amplifier circuit need feedback for gain stabilization!

    As discussed in Chapters 4 and 5, in a BJT, parameters like DC common-emitter current gain β, base-emitter voltage VBE and collector current IC may vary with temperature. In the manufacturer's data sheet, a range of values for these parameters are specified for a given type of transistor group because of material property tolerance. As a result of this, voltage and current gain, quiescent point and input/output impedances usually tend to differ from one circuit to another and also become temperature dependant. By applying the feedback mechanism, transistor circuit characteristics are made independent of the aforesaid parameters of transistors. Although feedback is being formally introduced to the reader in the present chapter, the concept of feedback was utilized in Chapter 5 in connection with biasing of transistor. For example, in the emitter feedback bias and voltage-divider bias circuits, an emitter resistor (RE) was introduced in common-emitter circuits to stabilize the Q-point. In these circuits, when the collector current increases, the drop across the emitter resistor (RE) increases which decreases the base-emitter voltage and that, in turn, further opposes any change in the collector current. This opposition is actually referred to as negative feedback. Thus, the readers encountered the technique of feedback even before they were introduced to it formally.

    The feedback technique is generally known by its two types: positive or regenerative feedback, used in designing oscillators, and negative or degenerative feedback, used in designing amplifiers. When the feedback voltage (current) is in phase with the input signal, i.e.

  • Chapter 14 - Analog Communication

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 710-750

  • Summary

    14.1 INTRODUCTION

    Message or information in any and every form such as words, codes, symbols, sound or picture needs to be propagated from a source to a destination. This communication by all general means can be defined as the process of establishing a link of information exchange between two points: the transmitter (source) and the receiver (destination). Ever since the term communication received its technical significance, typical examples of modern communication systems like line telephony, line telegraphy, ratio-broadcasting, point-to-point communication, radar communication, satellite communication, optical fibre communication and many more have come into existence. Modern communication uses different frequency bands of the entire electromagnetic spectrum from 30Hz to 300GHz, as shown in Table 14.1. These bands are popularly known as Extremely Low Frequency (ELF), Very Low Frequency(VLF), Low Frequency (LF),Medium Frequency (MF), Very High Frequency (VHF), Ultra High Frequency (UHF) and Super High frequency (SHF), indicated sequentially in Table 14.1, along with applications of various bands.

    Apart from the radio frequency bands extending up to 300GHz, the electromagnetic spectrum comprise of millimeter wave bands too with wavelengths varying from 10-3–10-4m, followed by Infrared signals (∼ 0.7μm–100μm) used for astronomy for detection of heavenly bodies, weapon guidance and TV remote control. In between the microwaves (3GHz– 300GHz) and infrared waves (3THz–380THz) lies the Terahertz radiation (300GHz–3THz) having wavelengths from 1mm to 100μm. Thus, the entire electromagnetic spectrum can be classified as shown in Figure 14.1.

    14.2 ELEMENTS OF COMMUNICATION SYSTEM

    Any communication system designed to operate over a particular band of frequency, as shown in Figure 14.1, for a specialized purpose either military or civilian or commercial, needs a certain set of electronic stages assembled together, as shown in Figure 14.2. These stages collectively form a communication link between the transmitter end and the receiver end.

    The information source provides the desired message which may or may not be electrical in nature. The input transducer converts the given message into electrical signal; e.g., for radio broadcasting a microphone converts incoming sound waves into electrical signals, making it suitable for transmission.

  • Chapter 8 - Feedback Amplifiers

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 476-519

  • Summary

    8.1 INTRODUCTION

    The term feedback is the basic backbone for all amplifier systems. An electronics engineer named Harold Black working with the Western Electric Company back in 1928 had been searching for various means of gain stabilization in amplifiers used in telephone repeaters. It was then that he intuitively conceived and invented the feedback amplifier. The process or technique by which a fraction of the output voltage or current is combined back/fed back to the input, to produce a desired output of a system is called feedback. But the question is – why does an amplifier circuit need feedback for gain stabilization!

    As discussed in Chapters 4 and 5, in a BJT, parameters like DC common-emitter current gain β, base-emitter voltage VBE and collector current IC may vary with temperature. In the manufacturer's data sheet, a range of values for these parameters are specified for a given type of transistor group because of material property tolerance. As a result of this, voltage and current gain, quiescent point and input/output impedances usually tend to differ from one circuit to another and also become temperature dependant. By applying the feedback mechanism, transistor circuit characteristics are made independent of the aforesaid parameters of transistors. Although feedback is being formally introduced to the reader in the present chapter, the concept of feedback was utilized in Chapter 5 in connection with biasing of transistor. For example, in the emitter feedback bias and voltage-divider bias circuits, an emitter resistor (RE) was introduced in common-emitter circuits to stabilize the Q-point. In these circuits, when the collector current increases, the drop across the emitter resistor (RE) increases which decreases the base-emitter voltage and that, in turn, further opposes any change in the collector current. This opposition is actually referred to as negative feedback. Thus, the readers encountered the technique of feedback even before they were introduced to it formally.

    The feedback technique is generally known by its two types: positive or regenerative feedback, used in designing oscillators, and negative or degenerative feedback, used in designing amplifiers.

  • Chapter 1 - Introduction to Electronics: Basic Ideas

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 1-18

  • Summary

    1.1 INTRODUCTION

    Electronics, evolved from the word ‘electron’ (a sub-atomic particle carrying negative charge), is the branch of science and engineering dealing with the study, design and use of devices that depend on the conduction of electricity through vacuum, gas or semiconductor, contributed by the transport phenomenon of the electrons. Earlier, electronics or electronics engineering used to be considered as an integral part of electrical engineering. However, due to the tremendous growth of electronics and its unprecedented applications in various fields over the last few decades, it has evolved as a separate branch of engineering. In addition, due to its widespread application in almost all possible branches of engineering and science, acquiring basic understanding of electronics and fundamentals of electronic devices has become a common requirement for students of all engineering disciplines.

    Before we discuss the details of the preliminary concepts required to understand the basic ideas of electronics, let us have a look at the chronological growth of modern electronics:

    1850: Geissler, a German scientist, demonstrated the flow of electric current through a vacuum glass tube.

    1878: Sir William Crookes, a British scientist, showed how current in vacuum tubes appears to consist of particles.

    1890: Perrin, a French physicist, demonstrated that current in vacuum tube is due to the movement of negatively charged particles.

    1897: Sir J. J. Thomson, a British physicist, measured some of the properties of the “negatively charged particle” (cathode ray) contributing to current in vacuum tube (named as cathode ray tube). He concluded that these particles are much smaller than atoms possessing high specific charge (charge to mass ratio). Thus, he is credited with the discovery of the first sub-atomic particle (later named as electron).

    1904: John Ambrose Fleming, a British physicist, invented vacuum tube that allows current only in one direction. This was named as Fleming valve- the primitive version of a diode- and was also known as vacuum tube or vacuum diode.

    1907: Lee de Forest, an American scientist, invented a tube which could amplify weak electrical AC signal. This tube, a primitive version of the transistor, was named as vacuum triode.

    1909: Robert Millikan, an American physicist, measured the charge of an electron.

  • Preface

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp xiii-xvi

  • Summary

    Almost every undergraduate engineering discipline starting from electronics, electrical, computer science, instrumentation engineering, information technology, mechanical engineering, biotechnology etc. requires a solid foundation in basic electronics which comprises a study of fundamental devices like diodes, transistors and their applications in designing amplifiers, switching/logic circuits etc. While for some disciplines, a basic understanding might be sufficient, for other disciplines like electronics, electrical etc., this course acts as an important building block in the curriculum. Moreover, for various advanced courses like analog electronics, digital circuits and VLSI, in-depth understanding of basic electronics is a prerequisite. This book is written keeping both these aspects in mind and as a result it will serve undergraduate students of various engineering disciplines. In addition, it can also cater to the needs of college and university students belonging to disciplines like physics, electronics, and also in electronics courses in polytechnics. A competent electronics engineer, even in the modern era of integrated-circuit based design, needs a thorough and solid understanding of the basic concepts of semiconductors and a firm grasp of fundamental devices like diodes and various kind of transistors. This book attempts a perfect balance between housing all the basic concepts in accordance with the syllabi of leading institutes and universities and a thorough understanding required for future courses. In solid state electronics and analog electronics, which normally appears at a later stage of the undergraduate electronics curriculum, the approach is significantly different: while solid state electronics provides more emphasis on device physics and detailed understanding, analog electronics concentrates more on the applications, where the device is generally treated as a black box. Even though these two advanced courses are mutually dependent on each other, there exists a significant gap between the two approaches and undergraduate students face real difficulties in making a correlation and correspondence between them. This book attempts to minimize this gap between the different approaches to solid state devices and analog circuits. Special care has been taken to explain all the semiconductor devices in this book from both, physical and circuit approaches. To facilitate this, extra stress is given in chapters 2 and 3 while discussing crystal structures and the p-n junctions. As all modern semiconductor devices are based on clusters of p-n junctions, a detailed explanation about the various aspects of p-n junctions will provide readers a strong foundation for future courses.

  • Chapter 2 - Introduction to Semiconductor

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 19-73

  • Summary

    2.1 INTRODUCTION TO SOLIDS AND CRYSTALS

    As the atoms or molecules in solids are attached to one another with strong attracting forces, the solid maintains a definite volume and shape. A separate subject named solid-state physics has been evolved for the study of the electrical, thermal and electronic properties as well as behaviour of solids. Solid-state physics can be defined as the branch of physics which deals with physical properties of solids, particularly crystals, and the behaviour of electrons in these solids. A subset of solid-state physics is solid-state electronics, which mainly focuses on the electrical and electronic behaviour of solids, especially semiconductors and the movement/transport of electrons in semiconductor materials and different semiconductor devices, basic and advanced, which have evolved over the last century.

    Solids may be broadly classified into two categories depending upon the arrangement of the atoms and molecules:

    i) Crystalline Solid: It consists of regular or periodic arrangement of atoms or molecules. Most of the solids are crystalline in nature. This is due to the fact that crystalline state is the low energy state and is, therefore, preferred by most solids.

    ii) Amorphous/Non-Crystalline Solid: It consists of completely random arrangement of atoms or molecules. Such type of materials are formed when the atoms do not get sufficient time to undergo a periodic arrangement.

    Example: Glass, plastic, rubber, etc.

    Crystalline solids may be further subdivided into Single Crystal Solid and Polycrystalline Solid. In single crystal solids, the periodicity of the atoms extends throughout the material, as in the case of diamond, quartz, mica, etc. A polycrystalline material is an aggregate of a number of small crystallites with random orientations separated by well-defined boundaries. Most of the metals and ceramics exhibit polycrystalline structure. Silicon (Si), the most widely used semiconductor material, is also a polycrystalline in its natural form.

    2.2 CRYSTALLINE SOLID

    Before describing the arrangement of atoms in a crystalline solid, it is always convenient to describe the arrangement of the imaginary points in space which have a definite positional/spatial relationship with the atoms of the crystal. This set of imaginary three-dimensional points forms a framework on which the actual crystal structure is based.

  • Chapter 7 - Field-Effect Transistors

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 407-475

  • Summary

    7.1 INTRODUCTION

    The field-effect transistor, customarily known as FET, like bipolar junction transistor (BJT), is a three-terminal semiconductor device extensively used in numerous electronic circuits and systems ranging from digital logic circuits to amplifier design. The term ‘field effect’ arises due to the fact that applied external electric field creates a conduction path called channel and controls the output current of the device. Even though FET has various structural and operational similarities with BJT, they have some fundamental differences, which are as follows:

    • In BJT, the current is contributed by two types of carriers: electrons and holes (hence the term ‘bi’, meaning two, which justifies its name bipolar). In case of FET, based on its structure, only one type of carrier, i.e. either electron or hole, contributes to the current. Hence, it is known as a unipolar device. Due to this, FETs do not suffer from minority carrier storage effects and consequently have higher switching speeds and higher cut-off frequencies.

    • BJT is a current-control device, where output current IC is solely controlled by the input current IB with a relation IC ≈ βIB. On the other hand, FET is a voltage-controlled device, where the voltage between two terminals VGS controls the output current ID. This is indicated in the schematic block diagram of Figure 7.1. Thus, FET is termed as a voltage-controlled device.

    One of the most important features of FET is its very high input impedance, typically much higher than that of BJT. This makes FETs a very good choice for designing linear amplifiers. Another advantageous feature of FETs is their better temperature stability compared to BJT. At high current level, FET offers negative temperature coefficient of current (meaning that current decreases due to increase in temperature). Due to this phenomenon, FETs can prevent thermal runaway. In addition, FETs are much compact in size. All these features make FET a very good candidate for integrated-circuit (IC) chips.

    FETs can be broadly classified into two types: a) Junction Field-Effect Transistor (JFET) and b) Metal Oxide Semiconductor Field-Effect Transistor (MOSFET). The latter can be further divided into depletion and enhancement types. JFET and both types of MOSFETs, based on the structures, can be further divided into n-channel and p-channel types. Figure 7.2 shows various types of MOSFET.

  • 2 - Introduction to Semiconductor

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 19-73

  • Summary

    INTRODUCTION TO SOLIDS AND CRYSTALS

    As the atoms or molecules in solids are attached to one another with strong attracting forces, the solid maintains a definite volume and shape. A separate subject named solid-state physics has been evolved for the study of the electrical, thermal and electronic properties as well as behaviour of solids. Solid-state physics can be defined as the branch of physics which deals with physical properties of solids, particularly crystals, and the behaviour of electrons in these solids. A subset of solid-state physics is solid-state electronics, which mainly focuses on the electrical and electronic behaviour of solids, especially semiconductors and the movement/transport of electrons in semiconductor materials and different semiconductor devices, basic and advanced, which have evolved over the last century.

    Solids may be broadly classified into two categories depending upon the arrangement of the atoms and molecules:

  • i) Crystalline Solid: It consists of regular or periodic arrangement of atoms or molecules. Most of the solids are crystalline in nature. This is due to the fact that crystalline state is the low energy state and is, therefore, preferred by most solids.

  • ii) Amorphous/Non-Crystalline Solid: It consists of completely random arrangement of atoms or molecules. Such type of materials are formed when the atoms do not get sufficient time to undergo a periodic arrangement.

    • Example: Glass, plastic, rubber, etc.

    Crystalline solids may be further subdivided into Single Crystal Solid and Polycrystalline Solid. In single crystal solids, the periodicity of the atoms extends throughout the material, as in the case of diamond, quartz, mica, etc. A polycrystalline material is an aggregate of a number of small crystallites with random orientations separated by well-defined boundaries. Most of the metals and ceramics exhibit polycrystalline structure. Silicon (Si), the most widely used semiconductor material, is also a polycrystalline in its natural form.

    CRYSTALLINE SOLID

    Before describing the arrangement of atoms in a crystalline solid, it is always convenient to describe the arrangement of the imaginary points in space which have a definite positional/spatial relationship with the atoms of the crystal. This set of imaginary three-dimensional points forms a framework on which the actual crystal structure is based. Such a three-dimensional network is called a space lattice, and it can be described as an infinite three-dimensional array of points. Each point in the space lattice has identical surroundings and is named as a lattice point.

  • Chapter 6 - Modelling of BJT and Design of Amplifiers

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 322-406

  • Summary

    6.1 INTRODUCTION

    In Chapter 4, we discussed the basic construction, characteristics, various modes and principle of operation of bipolar junction transistor (BJT) in detail. Subsequently, in Chapter 5, we dealt with biasing techniques of the transistor in an elaborate manner. In addition, we understood the fundamental concept of BJT acting as an amplifier in a qualitative manner. While biasing a transistor our main goal is to fix a proper operating point, also known as Q point, based on the specific applications. This is achieved by proper choice of the bias resistor and DC voltages. Once this Q-point is finalized, we apply the AC signal in the input side of the biased transistor circuit. Thus, complete analysis of an amplifier consists of DC analysis followed by an AC analysis. In this chapter, we will focus on the AC analysis of the BJT circuits in an elaborate manner with special emphasis on design of the BJT-based linear amplifiers. One important ingredient in the AC analysis and design of linear amplifiers is to replace the BJT with proper equivalent circuits. Such replacement of BJTs with equivalent circuits, known as ‘modeling’ of the BJT, is applicable under small signal approximations. This assumes the amplitude of the applied AC signal is small enough to consider that BJT is essentially operated in active region and its characteristics can be approximated by linear relations. Such linear relations between input and output signals of the BJT allow superposition theorem applicable in BJT circuits and we can obtain the total response of the BJT circuit by separately determining the response due to i) DC sources alone (called biasing), and ii) AC sources. Figure 6.1 shows a schematic diagram of an electronic circuit driven by both DC and AC input. While the purpose of the DC input is to ensure that the device operates in the desired region of operation, i.e. bias the device properly, AC input provides the required functionality like amplification, switching, etc. By applying the small-signal models of the device, thereby linearizing their performance, we apply the superposition theorem to obtain the overall response of the circuit by separately obtaining the individual responses due to DC input and AC input, as shown in Figure 6.1.

Page 27 of 88