Physics
Bipolar Junction Transistor
A bipolar junction transistor (BJT) is a three-terminal semiconductor device used for amplification and switching of electronic signals. It consists of three regions of doped semiconductor material: the emitter, base, and collector. By controlling the flow of charge carriers between these regions, the BJT can amplify small signals or act as a switch in electronic circuits.
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11 Key excerpts on "Bipolar Junction Transistor"
eBook - PDF- B. Hart(Author)
- 1996(Publication Date)
- Butterworth-Heinemann(Publisher)
3 The Bipolar Junction Transistor (BJT): d.c.-characterization and biasing Electronics has reached its present state of importance because of the invention of two classes of three-electrode semiconductor control device, known as 'transis-tors', that are capable of amplification in analogue applications, e.g. audio and video amplifiers, and switching in digital logic systems. These devices are the 'unipolar transistor' and the 'bipolar transistor'. Unipolar means that one polarity of charge carrier, either an electron or a hole, dominates device operation. The unipolar device is better known as a Field Effect Transistor (FET). Bipolar means that two polarities of charge carrier play an important role in device operation. Following a long-established custom in the literature the 'transistor', or 'bipolar transistor', unless otherwise qualified, will be referred to by the unambiguous title BJT (Bipolar Junction Transistor). [Note: For the invention of the transistor (circa 1948), the American scientists J. Bardeen, W. Brattain and W. Shockley were jointly awarded the 1956 Nobel Prize for Physics.] It is convenient to consider the BJT before the FET because a discussion of it builds on the treatment of the junction diode in Chapter 1. The FET is introduced in Chapter 5. 3.1 BJT TYPES The BJT is a device with two PN junctions and three electrodes, the collector (C), emitter (E) and base (B). Current flow between C and E into a load connected to one of them is controlled by a signal applied at B. The control signal is usually a current or voltage operating between Band E but other forms of control are possible, e.g. charge, temperature and, dependent on device structure, incident radiation. An essential feature of BJT operation, whether as an amplifier or as a switch, is that the power developed in the load is larger than the control power, by a factor known as the 'power gain'. However, there is no question of getting something for nothing.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- White Word Publications(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 8 Bipolar Junction Transistor A bipolar (junction) transistor ( BJT ) is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices. PNP NPN Schematic symbols for PNP- and NPN-type BJTs. ________________________ WORLD TECHNOLOGIES ________________________ Introduction NPN BJT with forward-biased E–B junction and reverse-biased B–C junction An NPN transistor can be considered as two diodes with a shared anode. In typical operation, the base-emitter junction is forward biased and the base–collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the base–emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or diffuse) through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base.
eBook - ePub- Dale R. Patrick, Stephen W. Fardo, Ray E. Richardson, Vigyan (Vigs) Chandra(Authors)
- 2023(Publication Date)
- River Publishers(Publisher)
6Bipolar Junction Transistors (BJTs)The invention of the transistor in 1947 signaled the start of a new era in electronics. Circuits could be built exceedingly small, operate without heating power, amplify signals with a low-voltage source, and be extremely rugged. Integrated circuits, microprocessors, pocket calculators, personal computers, and communication electronics have all been made possible through the development of the transistor. The impact of this device on the electronics field has still not been fully realized.A transistor is a semiconductor device that is used to control the flow of current. Transistors are used for switching, amplification, and signal generation. There are two major types of transistor: bipolar junction and field effect. In this chapter, you will study the Bipolar Junction Transistor (BJT). You will become familiar with basic transistor principles and BJT operation, test procedures, and lead identification. A person working with these devices must be knowledgeable in these areas. In a later chapter, you will study the field-effect transistor (FET).Objectives
After studying this chapter, you will be able to:- 6.1 describe the physical construction of NPN and PNP Bipolar Junction Transistors;
- 6.2 explain the fundamental operation of a Bipolar Junction Transistor;
- 6.3 predict how a Bipolar Junction Transistor will respond in different regions of operation;
- 6.4 evaluate the condition of a Bipolar Junction Transistor;
- 6.5 analyze and troubleshoot Bipolar Junction Transistors.
Chapter Outline
- 6.1 BJT Construction
- 6.2 BJT Operation
- 6.3 BJT Characteristics
- 6.4 Testing BJTs
- 6.5 Analysis and Troubleshooting – BJTs
Terms
active region base beta bipolar collector cutoff region emitter epitaxial growth gain mesa transistor NPN transistor planar transistor PNP transistor saturation region6.1 BJT Construction
In a previous chapter, you studied the diode − a two-element device with one P–N junction. Diodes are designed to block or pass current according to their biasing and, therefore, are used in switching and rectification applications. A Bipolar Junction Transistor (BJT)
eBook - PDFFundamentals of Electronics
Book 1 Electronic Devices and Circuit Applications
- Thomas F. Schubert, Ernest M. Kim(Authors)
- 2022(Publication Date)
- Springer(Publisher)
133 C H A P T E R 3 Bipolar Junction Transistor Characteristic e Bipolar Junction Transistor (BJT) is perhaps the most basic of three-terminal semiconductor devices. It can be found, for example, as a vital component in digital and analog integrated circuits, audio and other frequency range amplifiers, radio electronics, and electronic control devices with a wide range of applications. e BJT is an active device that is highly non-linear, and, along with applications in non-linear circuitry, plays an important part in many linear electronic applications. e apparent contradiction of a non-linear device being useful in linear applications is placated by a region of BJT operation that is nearly linear. Non-linear BJT operation typically involves a transition between BJT operating regions. BJTs are constructed with two p-n junctions sharing a common region, identified as the base region. is common region, lying between two regions of the complementary doping, causes the two diode-like p-n junctions to become coupled.¹ e base region may be doped as either a p-region or an n-region: the two types of BJT formed are identified as npn or pnp respectively. Before proceeding with technical descriptions of the operation of a BJT, it is necessary to define appropriate descriptive conventions. e two circuit symbols for BJTs are shown in Figure 3.1. I B NUL! #I C "I E I B NUL! #I C "I E OQO QOQ Figure 3.1: BJT circuit symbols. ¹Extensive discussions of the semiconductor physics that lead to coupled p-n junctions forming a Bipolar Junction Transistor are not within the scope of this electronics text. e authors suggest several texts in semiconductor physics and electronic engineering materials at the end of this chapter for those readers interested in these aspects of physical electronics.
eBook - PDFElectronic Concepts
An Introduction
- Jerrold H. Krenz(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
CHAPTER THREE THE Bipolar Junction Transistor: AN ACTIVE ELECTRONIC DEVICE Several types of transistors are used in modern electronic systems, both individ-ually as discrete devices and in conjunction with other transistors in integrated circuits. Transistors have three or more terminals and, as is the case for junction diodes, transistors are nonlinear elements. The Bipolar Junction Transistor (BJT) that will be discussed in this chapter, as well as the field-effect transistor of the next chapter, are active devices. Electronic amplifying circuits in which a small input voltage, current, or both, produces a larger output voltage, current, or both depend on active devices. Amplification is required for nearly all electronic sys-tems. The analysis of transistor circuits is considerably more difficult (a greater challenge) than that of circuits with two-terminal passive elements - resistors, capacitors, and inductors. The history of active electronic circuits dates from the invention of the vac-uum tube (the audion) by Lee De Forest in 1906 (De Forest 1906). From the very beginning the challenge was to develop circuits to utilize this new device. Edwin H. Armstrong was foremost among the early designers of electronic circuits that were initially used to improve wireless communication (Armstrong 1915). The junction transistor, developed in 1950 (following the invention of its predecessor, the point-contact transistor, in 1948), and other transistors, have replaced vac-uum tubes for most (but not all!) applications. These applications, however, tend to rely on electronic circuits similar to those initially used with vacuum tubes {Electronics 1980). A Bipolar Junction Transistor consists of two junction diodes fabricated from a single semiconductor crystal (Figure 3.1). The w-type regions, the emitter and col-lector, are separated by a very thin p-type base region (an NPN-type transistor).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 2 Bipolar Junction Transistor A bipolar (junction) transistor ( BJT ) is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices. PNP NPN Schematic symbols for PNP- and NPN-type BJTs. ________________________ WORLD TECHNOLOGIES ________________________ Introduction NPN BJT with forward-biased E–B junction and reverse-biased B–C junction An NPN transistor can be considered as two diodes with a shared anode. In typical operation, the base-emitter junction is forward biased and the base–collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the base–emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or diffuse) through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base.
eBook - ePub- Wai-Kai Chen(Author)
- 2003(Publication Date)
- CRC Press(Publisher)
1Bipolar Junction Transistor (BJT) Circuits
David J.Comer Donald T.Comer Brigham Young University
1.1 Introduction
The Bipolar Junction Transistor (or BJT) was the workhorse of the electronics industry from the 1950s through the 1990s. This device was responsible for enabling the computer age as well as the modern era of communications. Although early systems that demonstrated the feasibility of electronic computers used the vacuum tube, the element was too unreliable for dependable, long-lasting computers. The invention of the BJT in 19471 and the rapid improvement in this device led to the development of highly reliable electronic computers and modern communication systems.Integrated circuits, based on the BJT, became commercially available in the mid- 1960s and further improved the dependability of the computer and other electronic systems while reducing the size and cost of the overall system. Ultimately, the microprocessor chip was developed in the early 1970s and the age of small, capable, personal computers was ushered in. While the metal-oxide-semiconductor (or MOS) device is now more prominent than the BJT in the personal computer arena, the BJT is still important in larger high-speed computers. This device also continues to be important in communication systems and power control systems.Because of the continued improvement in BJT performance and the development of the heterojunction BJT, this device remains very important in the electronics field, even as the MOS device becomes more significant.1.2 Physical Characteristics and Properties of the BJT
Although present BJT technology is used to make both discrete component devices as well as integrated circuit chips, the basic construction techniques are similar in both cases, with primary differences arising in size and packaging. The following description is provided for the BJT constructed as integrated circuit devices on a silicon substrate. These devices are referred to as “junction-isolated” devices.
- Mike Golio, Janet Golio, Mike Golio, Janet Golio(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
16 Bipolar Junction Transistors (BJTs) John C. Cowles Analog Devices—Northwest Labs 16.1 Introduction .............................................. 16 -1 16.2 A Brief History ........................................... 16 -2 16.3 Basic Operation .......................................... 16 -2 16.4 Parasitics and Refinements .............................. 16 -4 16.5 Models .................................................... 16 -9 16.6 Dynamic Range .......................................... 16 -9 16.7 Complementary pnp .................................... 16 -14 16.8 Topologies ................................................ 16 -15 16.9 Translinear Circuits ...................................... 16 -19 16.10 Biasing Techniques ....................................... 16 -20 16.11 Fabrication Technology ................................. 16 -22 References ....................................................... 16 -24 16.1 Introduction The topic of Bipolar Junction Transistors (BJTs) is obviously quite broad and a full treatment would con-sume volumes. This work focuses on basic principles to develop an intuitive feel for the transistor behavior and its application in contemporary high-speed integrated circuits (ICs). The exponential growth in high bandwidth wired, wireless, and fiber communication systems coupled with advanced IC technologies has created an interesting convergence of two disparate worlds: the microwave and analog domains. The traditional microwave IC consists of a few transistors in discrete form or in low levels of integration sur-rounded by a sea of transmission lines and passive components. The modern high-speed analog IC usually involves tens to thousands of transistors with few passive components. The analog designer finds it a more cost-effective solution to use extra transistors rather than passive components to resolve performance issues.
eBook - ePubElectronics
from Classical to Quantum
- Michael Olorunfunmi Kolawole(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
3 Structure of Bipolar Junction TransistorIn this chapter we present the structure of the bipolar transistor and show how a three-layer structure with alternating n -type and p -type regions can provide current and voltage amplification. We then present the ideal transistor model and derive an expression for the current gain in the forward-active mode of operation, as well as quantifying the operating point stability. We discuss how to model for small and large signals leading to simpler analysis of the circuits.Transistors are the most crucial elements in modern electronics. Transistors are used in a great variety of circuits and remain important devices for ultra-high-speed discrete logic circuits such as emitter coupled logic, power-switching applications (including modern electronic digital computers), and in microwave power amplifiers. Transistors, as amplifiers, are used to amplify an electrical signal by allowing a small current or voltage to control the flow of a much larger current from a direct current (dc) power source. An example of transistor usage is in audio systems. There are two general types of transistors: bipolar and field effect. Very roughly, the difference between these two types is that for bipolar devices an input current controls the large current flow through the device, while for field-effect transistors (FET) an input voltage provides the control. In most practical applications, an operational amplifier (abbreviated as op-amp ) is often used as a source of gain or amplification rather than to build an amplifier from discrete transistors. But there is a compelling case to having a good understanding of transistor fundamentals. For instance, the integrated circuits (ICs or chips) used in most computers are made from transistors (as well as diodes and other passive devices—transistors and capacitors), and so the behavior of logic devices depends upon the behavior of transistors. Also, given that op-amps are built from transistors, a detailed understanding of op-amp behavior, particularly input and output characteristics, must be based on an understanding of transistors. Op-amps are discussed in Chapter 4
eBook - PDFElectronic and Electrical Engineering
Principles and Practice
- Lionel Warnes(Author)
- 2017(Publication Date)
- Red Globe Press(Publisher)
161 Figure 8.1 Transistor types: npn (on left) and pnp (on right), with symbols above 8 Bipolar Junction Transistors A LTHOUGH in principle consisting merely of two p-n junction diodes back to back, in practice the Bipolar Junction Transistor (BJT) is a completely different class of device; whereas the diode is a passive device, the transistor is active it can be used to amplify voltages or signals. The BJT is termed bipolar because its operation unlike the field effect transistor’s depends on both positive (holes) and negative (electrons) charge carriers. Before the transistor was invented, amplifiers used vacuum tubes (‘valves’) and vacuum tubes used a great deal of power, most of which was wasted as heat. Vacuum tubes were also prone to failure by filament burn out, loss of vacuum and just plain breakage; they were also difficult to miniaturise. A ‘large’ computer (by the standards of its day, 1950) such as EDSAC at Cambridge occupied a fair-sized room, required a large amount of power and cooling, and was prone to break down as the tubes failed, though ingenious methods were devised to minimise the stoppages. But it was not only high-technology products like computers which suffered from valve technology; radios for example were large and clumsy, and batteries for ‘portable’ radios were enormous, heavy and costly. Above all, the transistor could be made smaller and smaller, and cheaper and cheaper and more and more reliable. The story of the transistor is far from finished 55 years after its invention. 8.1 Theory of operation Figure 8.1 shows a conceptual diagram of pnp and npn transistors the structures of practical devices are rather different (see Chapter 10) in which a thin layer of semiconductor material, called the base , is sandwiched between two pieces of opposite conductivity type, known as the emitter and the collector .
eBook - PDFBasic Electronics
Principles and Applications
- Chinmoy Saha, Arindam Halder, Debarati Ganguly(Authors)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
Bipolar Junction Transistor 237 In this condition, a large collector current, I I V V R V R C Csat CC CE sat C CC C = = − ≈ , , flows through. Thus, in this case, the transistor behaves as a closed switch with collector effectively shorted with emitter as shown in Figure 4.19(b). How to check whether the transistor is in saturation? First, find I B using KVL in input loop. If transistor is really in saturation, then collector current is given by, I V V R C sat CC CE sat C , ( ) , = − The minimum value of base current required for the transistor to go in saturation region, I I B C sat min ( ) = β Check whether I B > I Bmin If I B > I Bmin , the transistor is in saturation, otherwise it will be in active region. 4.8 Bipolar Junction Transistor AS AN AMPLIFIER An amplifier is a two-port network, which provides an amplified signal at its output port with respect to the input signal applied to the input port of the amplifier. Amplifier v in ( t ) t t t t v 0 ( t ) (a) CE Amplifier v in ( t ) v 0 ( t ) (b) E B E C Figure 4.20 Simplified block diagram of a (a) general amplifier (b) amplifier in CE mode Figure 4.20 shows a very simplified block diagram of an amplifier. When a transistor is operated in its active region, it provides an enhanced output current I C , which is β times its input current I B . Thus, a small change in base current in a transistor can lead to a large change ( β times the input current change) in its output collector current. This property is successfully exploited in designing amplifier circuit. Thus, an amplifier circuit employing BJT normally requires the BJT to be biased in its active region. An amplifier circuit has 238 Basic Electronics both DC (for biasing) and AC quantities associated with it. Before entering into the details of amplification, let us fix signal notation used for DC, AC and DC + AC (combined). This is shown in Table 4.2. DC quantities are represented by c apital letters with capital suffix.
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