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1808 results in Circuits and systems

Page 29 of 91

  • Chapter 3 - P-N Junction and P-N Junction Diode

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 74-210

  • Summary

    3.1 P-N JUNCTION

    All modern semiconductor devices and integrated circuits (IC), which are the backbone of modern day electronics, contain at least one junction between p-type and n-type semiconductor, commonly known as p-n junction. This p-n junction is the most fundamental semiconductor device as all other devices like various types of transistors (Bipolar Junction Transistor, Field Effect Transistor, Metal Oxide Semiconductor Field Effect Transistor, etc.) require p-n junctions of various configurations, which will be discussed in subsequent chapters. Various analog and digital operations and performance like rectification, amplification, switching, logic operations require this fundamental semiconductor device. In this chapter, we will discuss various issues related to the p-n junction followed by application of such junction diodes, called p-n junction diodes, for various operations.

    In chapter 2, we have been familiar with different types of semiconductors, classified in different aspects. We recall p- and n-type semiconductor, which are realized by doping an intrinsic semiconductor with different type of impurities to obtain large number of free carriers in the form of holes in p-type semiconductor and electrons in n-type semiconductor, respectively. However, these n-type and p-type semiconductors having electrons and holes in abundance are electrically neutral, as they are neutralized by the impurity ions which have created them. To be more specific, electrons are neutralized by associated donor ions, each of which has equal (opposite in sign) amount of charge as that of each electron, and holes are neutralized by acceptors ions, each of which has equal (opposite in sign) amount of charge as that of a hole, ensuring a charge neutrality. This is clearly shown in Figure 3.1. However, if we consider a semiconductor whose two sides are differently doped with acceptor and donor impurities, their effect is not like two isolated pieces of p- and n- type semiconductor due to the transport phenomena of the mobile charge carriers. Such a device is known as p-n junction and needs to be discussed in detail. It is the most fundamental semiconductor device and is the backbone of modern day electronics.

  • Chapter 12 - Integrated Circuits

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 610-619

  • Summary

    12.1 INTRODUCTION

    In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that is manufactured on the surface of a thin substrate of semiconductor material. A hybrid Integrated Circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board. Integrated circuits are used in almost all electronic equipment and have revolutionized the world of electronics.

    To a large extent, the demand for miniaturization was driven by the demands of the American Space Program. For some time, people had been thinking that it would be a good idea to be able to fabricate an entire circuit on a single piece of semiconductor. The first public discussion of this idea is credited to a British radar expert, Geoffrey William Arnold Dummer (1909–2002), in a paper presented in 1952. Jack Kilby's first prototype was a phase-shift oscillator comprising of five components on a piece of germanium, half an inch long and thinner than a toothpick. Although manufacturing techniques subsequently took different paths from those used by Kilby, yet he is considered as the pioneer in the area of IC fabrication.

    ICs are polarized and every pin is unique in terms of both location and function. Most ICs use either a notch or a dot to indicate the pin numbers and its counting sequence. This is depicted in Figure 12.1.

    12.2 IC: ADVANTAGES AND DISADVANTAGES

    The main advantages of ICs over those made by interconnecting discrete components are as follows:

    • 1. Extremely small size, i.e. thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements on a single chip of semiconductor material.

    • 2. Very small weight owing to miniaturized circuit.

    • 3. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production, IC costs as much as an individual transistor.

    • 4. More reliable because of elimination of soldered joints and need for fewer interconnections.

    • 5. Lower power consumption because of their smaller size.

    • 6. Easy replacement as it is more economical to replace them than to repair them.

    • 7. Increased operating speed because of absence of parasitic capacitance effect.

    • 8. Close matching of components and temperature coefficients because of bulk production in batches.

  • Chapter 10 - Power Amplifiers

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 554-589

  • Summary

    10.1 INTRODUCTION

    In Chapter 6, we derived various small-signal models of BJT, followed by detailed analysis of the BJT amplifiers for CE, CB and CC configurations. In designing such small-signal amplifier the main focus is on amplification linearity and magnitude of gain. Since signal voltage and current in the small-signal amplifier is restricted to small amplitude for maintaining linearity, their power handing capability or the power efficiency with which it delivers AC power to the load at the expense of DC power are of secondary concern. A voltage (current) amplifier provides voltage (current) amplification primarily to increase the applied input voltage (current). Thus, in general, these small-signal amplifiers are not capable of delivering large amount of power to a passive load. But most of the practical electronic amplifiers (starting from audio amplifier to switching power supply) require a final output stage capable of delivering large power to the load. Such amplifier/amplifying stage at the output stage of a practical amplifier circuit is known as power amplifier. It can be designed using BJTs, MOSFETs and various special semiconductor devices like thyristors. However, we will consider only BJTs while discussing the design of such amplifiers.

    10.2 PERFORMANCE CHARACTERISTICS OF POWER AMPLIFIERS

    The quality of power amplifiers is characterized by the following parameters:

    • • Power handling capability: The amplifier must be capable of delivering the required amount of power to the load in an efficient manner. This demands that the power dissipation in the transistors be as low as possible.

    • • High power conversion efficiency: Power conversion efficiency is another important figure of merit of a power amplifier defined as the ratio of AC power delivered to the load to the DC input power. It is expressed as,

    We will calculate the power conversion efficiency η of different types of power amplifiers. A high value of η is desired as it utilizes less DC power to deliver same output AC power to the load.

    • • Low total harmonic distortion: Since a power amplifier deals with relatively large signals, the small-signal approximations and resultant linear equivalent circuit models are not applicable here due to the nonlinearities of the transistors while dealing with large signals. Even though power handling capability and high conversion efficiency are major design criteria in power amplifiers, linearity still remains an important criterion.

  • Chapter 13 - Operational Amplifier

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 620-709

  • Summary

    13.1 INTRODUCTION

    Operational amplifier or OPAMP is one of the most important building blocks in all aspects of analog circuitry. It becomes the universal analog IC because of its wide range of application in analog signals processing. It can function as a line drive, comparator (one bit A/D), amplifier, level shifter, oscillator, filter, signal conditioner, actuator driver, current source, voltage source, and many other applications.

    The OPAMP is a multistage two-input differential amplifier that is designed to be an almost ideal control device, specifically a voltage-controlled voltage source. Basically, it is an abstraction of ideal voltage amplifier with very high gain. We will employ the OPAMP to construct more complex circuits using its simple, abstract model. The equivalent circuit of OPAMP is shown in Figure 13.1.

    The integrated circuit OPAMP usually consists of a cascade of three stages:

    • a) Input stage: May contain one or two differential amplifier stages

    • b) Intermediate stage: Emitter follower and DC level shifter.

    • c) Output stage: Driver stage (Class B amplifier)

    Internally, the OPAMP itself is a moderately complicated circuit and its design is beyond the scope of this book. The heart of the OPAMP is its input stage acting as differential amplifier using BJT/MOSFET. This differential input stage gives the OPAMP its high input resistance and a high gain with very little noise. It also converts the differential input voltage to a single-ended output. A typical OPAMP also has a second stage similar to the first stage, which provides additional amplification and level shifts the output voltage to zero when both inputs are equal. OPAMPs may also have an output stage similar to the buffer, due to which OPAMP exhibits low output impedance.

    Symbolic representation of the operational amplifier shown in Figure 13.2, suggests that it as a two-port device. The two ports are an input and an output port. A + V voltage (for example, 15 V) is applied at the ‘plus’ power port and a –V voltage (for example, −15 V) is applied at the ‘minus’ power port. An input voltage (the control) applied across the non-inverting and inverting input terminals of the OPAMP is amplified by a large amount and appears at the output port.

  • 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

    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.

  • 1947: Walter Brattain, John Bardeen and William Shockley of Bell Laboratory, USA invented the transistor. This is considered as the beginning of a new era of electronics in the form of solid-state electronics.

  • 4 - Bipolar Junction Transistor

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 211-261

  • Summary

    INTRODUCTION

    The invention of various semiconductor devices and the chronological growth in the field of microelectronics in electronics industry is the backbone of most of the modern electrical/electronic and communication gadgets that have dramatically changed human life, leading to a new technology-driven society. One of the most remarkable breakthroughs to drive technology in the last few decades is the invention of transistor, a three terminal device that is extremely useful and almost an integral part of any analog or digital circuit. The first version of transistor was invented by Dr William Shockley and his co-workers Walter H Brattain and John Bardeen in Bell Lab, USA in 1947. Owing to various operational advantages like low power requirements, high efficiency, etc., coupled with its ultra-compact size, the transistor became very popular since its invention and replaced the previously used vacuum tube-based systems. Over time, the first transistor invented by Shockley et al (point-contact transistor) went through several rounds of modification, resulting in various new variants of the transistor, which include Bipolar Junction Transistor (BJT), Field Effect Transistor (FET), Metal Oxide Semiconductor Field Effect Transistor (MOSFET), etc.

    In this chapter, we will discuss the construction of a transistor, basic principle of operation and its two most important applications, namely amplification and switching, in detail. Advanced concept regarding transistor operation and various other functionalities will be discussed in subsequent chapters.

    BJT: CONSTRUCTION AND TERMINALS

    A Bipolar Junction Transistor, popularly known as BJT, is a three-terminal semiconductor device with two junctions between them. As shown in Figure 4.1(a), the structure of a transistor resembles a sandwich in which a very narrow and lightly doped p-region is sandwiched between two n-regions. Such a transistor is named as n-p-n transistor. A complementary structure of Figure 4.1(a), as shown in Figure 4.1(b), consists of an n-region sandwiched between two p-regions, resulting in a p-n-p transistor. The term ‘bipolar’ in BJT signifies the presence of two different types of carriers, electron and hole, and the resultant current is the combined contribution of both the carriers. As indicated in Figure 4.1, the three regions of the transistor are named as emitter (E), base (B) and collector (C).

  • Chapter 4 - Bipolar Junction Transistor

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 211-261

  • Summary

    4.1 INTRODUCTION

    The invention of various semiconductor devices and the chronological growth in the field of microelectronics in electronics industry is the backbone of most of the modern electrical/electronic and communication gadgets that have dramatically changed human life, leading to a new technology-driven society. One of the most remarkable breakthroughs to drive technology in the last few decades is the invention of transistor, a three terminal device that is extremely useful and almost an integral part of any analog or digital circuit. The first version of transistor was invented by Dr William Shockley and his co-workers Walter H Brattain and John Bardeen in Bell Lab, USA in 1947. Owing to various operational advantages like low power requirements, high efficiency, etc., coupled with its ultra-compact size, the transistor became very popular since its invention and replaced the previously used vacuum tube-based systems. Over time, the first transistor invented by Shockley et al (point-contact transistor) went through several rounds of modification, resulting in various new variants of the transistor, which include Bipolar Junction Transistor (BJT), Field Effect Transistor (FET), Metal Oxide Semiconductor Field Effect Transistor (MOSFET), etc.

    In this chapter, we will discuss the construction of a transistor, basic principle of operation and its two most important applications, namely amplification and switching, in detail. Advanced concept regarding transistor operation and various other functionalities will be discussed in subsequent chapters.

    4.2 BJT: CONSTRUCTION AND TERMINALS

    A Bipolar Junction Transistor, popularly known as BJT, is a three-terminal semiconductor device with two junctions between them. As shown in Figure 4.1(a), the structure of a transistor resembles a sandwich in which a very narrow and lightly doped p-region is sandwiched between two n-regions. Such a transistor is named as n-p-n transistor. A complementary structure of Figure 4.1(a), as shown in Figure 4.1(b), consists of an n-region sandwiched between two p-regions, resulting in a p-n-p transistor. The term ‘bipolar’ in BJT signifies the presence of two different types of carriers, electron and hole, and the resultant current is the combined contribution of both the carriers. As indicated in Figure 4.1, the three regions of the transistor are named as emitter (E), base (B) and collector (C). They form two junctions: i) emitter-base junction (EBJ), and ii) collector-base junction (CBJ). In a transistor, emitter is heavily doped, whereas base is lightly doped.

  • 3 - P-N Junction and P-N Junction Diode

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 74-210

  • Summary

    P-N JUNCTION

    All modern semiconductor devices and integrated circuits (IC), which are the backbone of modern day electronics, contain at least one junction between p-type and n-type semiconductor, commonly known as p-n junction. This p-n junction is the most fundamental semiconductor device as all other devices like various types of transistors (Bipolar Junction Transistor, Field Effect Transistor, Metal Oxide Semiconductor Field Effect Transistor, etc.) require p-n junctions of various configurations, which will be discussed in subsequent chapters. Various analog and digital operations and performance like rectification, amplification, switching, logic operations require this fundamental semiconductor device. In this chapter, we will discuss various issues related to the p-n junction followed by application of such junction diodes, called p-n junction diodes, for various operations.

    In chapter 2, we have been familiar with different types of semiconductors, classified in different aspects. We recall p- and n-type semiconductor, which are realized by doping an intrinsic semiconductor with different type of impurities to obtain large number of free carriers in the form of holes in p-type semiconductor and electrons in n-type semiconductor, respectively. However, these n-type and p-type semiconductors having electrons and holes in abundance are electrically neutral, as they are neutralized by the impurity ions which have created them. To be more specific, electrons are neutralized by associated donor ions, each of which has equal (opposite in sign) amount of charge as that of each electron, and holes are neutralized by acceptors ions, each of which has equal (opposite in sign) amount of charge as that of a hole, ensuring a charge neutrality. This is clearly shown in Figure 3.1. However, if we consider a semiconductor whose two sides are differently doped with acceptor and donor impurities, their effect is not like two isolated pieces of p- and n- type semiconductor due to the transport phenomena of the mobile charge carriers. Such a device is known as p-n junction and needs to be discussed in detail. It is the most fundamental semiconductor device and is the backbone of modern day electronics.

    A p-n junction is formed from a single crystal intrinsic semiconductor in which one side is doped with acceptor impurity, i.e. trivalent atoms (p-region), and the other side is doped with donor impurity, i.e. pentavalent atoms (n-region).

  • 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

    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.

  • 12 - Integrated Circuits

  • Chinmoy Saha, Arindam Halder, Debarati Ganguly
  • Book:
    Basic Electronics
    Published online:
    03 June 2025
    Print publication:
    01 March 2018, pp 610-619

  • Summary

    INTRODUCTION

    In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that is manufactured on the surface of a thin substrate of semiconductor material. A hybrid Integrated Circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board. Integrated circuits are used in almost all electronic equipment and have revolutionized the world of electronics.

    To a large extent, the demand for miniaturization was driven by the demands of the American Space Program. For some time, people had been thinking that it would be a good idea to be able to fabricate an entire circuit on a single piece of semiconductor. The first public discussion of this idea is credited to a British radar expert, Geoffrey William Arnold Dummer (1909–2002), in a paper presented in 1952. Jack Kilby's first prototype was a phase-shift oscillator comprising of five components on a piece of germanium, half an inch long and thinner than a toothpick. Although manufacturing techniques subsequently took different paths from those used by Kilby, yet he is considered as the pioneer in the area of IC fabrication.

    ICs are polarized and every pin is unique in terms of both location and function. Most ICs use either a notch or a dot to indicate the pin numbers and its counting sequence. This is depicted in Figure 12.1.

    IC: ADVANTAGES AND DISADVANTAGES

    The main advantages of ICs over those made by interconnecting discrete components are as follows:

  • Extremely small size, i.e. thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements on a single chip of semiconductor material.

  • Very small weight owing to miniaturized circuit.

  • Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production, IC costs as much as an individual transistor.

  • More reliable because of elimination of soldered joints and need for fewer interconnections.

  • Lower power consumption because of their smaller size.

  • Easy replacement as it is more economical to replace them than to repair them.

  • Increased operating speed because of absence of parasitic capacitance effect.

  • 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.

Page 29 of 91