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.
8 Key excerpts on "Bipolar Junction Transistor"
eBook - ePub- Jerry C. Whitaker, Jerry C. Whitaker, Jerry C. Whitaker(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
...9 Bipolar Junction and Junction Field-Effect Transistors Sidney Soclof California State University, Los Angeles 9.1 Bipolar Junction Transistors 9.2 Amplifier Configurations 9.3 Junction Field-Effect Transistors JFET as an Amplifier: Small-Signal AC Voltage Gain JFET as a Constant Current Source Operation of a JFET as a Voltage-Variable Resistor Voltage-Variable Resistor Applications 9.1 Bipolar Junction Transistors A basic diagram of the Bipolar Junction Transistor (BJT) is shown in Fig. 9.1. Whereas the diode has one PN junction, the BJT has two PN junctions. The three regions of the BJT are the emitter, base, and collector. The middle, or base region, is very thin, generally less than 1 μm wide. This middle electrode, or base, can be considered to be the control electrode that controls the current flow through the device between emitter and collector. A small voltage applied to the base (i.e., between base and emitter) can produce a large change in the current flow through the BJT. BJTs are often used for the amplification of electrical signals. In these applications the emitter-base PN junction is turned on (forward biased) and the collector-base PN junction is off (reverse biased). For the NPN BJT as shown in Fig. 9.1, the emitter will emit electrons into the base region. Since the P-type base region is so thin, most of these electrons will survive the trip across the base and reach the collector-base junction. When the electrons reach the collector-base junction they will roll downhill into the collector, and thus be collected by the collector to become the collector current I C. The emitter and collector currents will be approximately equal, so I C ≅ I E. There will be a small base current, I B, resulting from the emission of holes from the base across the emitter-base junction into the emitter. There will also be a small component of the base current due to the recombination of electrons and holes in the base...
eBook - ePubCompact Models for Integrated Circuit Design
Conventional Transistors and Beyond
- Samar K. Saha(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...11 Bipolar Junction Transistor Compact Models 11.1 Introduction As described in Chapters 4 and 5, the pn -junctions are integral part of a MOSFET (metal-oxide-semiconductor field-effect transistor) device structure as the source and drain regions. Under the appropriate biasing condition of a MOSFET device, the source of the source-substrate pn -junction provides a steady supply of mobile carriers to form a conducting channel from the source to drain and the drain of the drain-substrate pn -junction collects the mobile carriers generating drain current. Two back-to-back pn -junctions form a Bipolar Junction Transistor (BJT). BJTs are very often used in VLSI (very-large-scale-integrated) circuits. Therefore, a basic understanding of BJT modeling is necessary for engineers and researchers involved in device modeling. In this chapter, we present the basic but widely used BJT compact models for circuit CAD. BJTs are active three-terminal devices and were the main active elements for ICs (integrated circuits) in the 1960s [ 1, 2 ]. The areas of applications of BJTs include amplifiers, switches, high-power circuits, and high-speed logic circuits for high-speed computers. After the invention of bipolar transistors in 1947 [ 3 ], discrete BJTs were used to design circuits on printed circuit boards. In order to analyze the performance of BJTs, Ebers and Moll in 1954 reported a physics-based large signal BJT model, referred to as the Ebers–Moll or EM model [ 4 ]. The level 1 EM model, known as the EM1 model, is valid for the entire operating regime of BJTs from cutoff to active region. However, the application and accuracy of EM1 model are limited to evaluating the DC performance of the devices only due to several simplifying assumptions...
eBook - ePub- Wai-Kai Chen, Wai-Kai Chen(Authors)
- 2003(Publication Date)
- CRC Press(Publisher)
...1 Bipolar 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 1947 1 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...
eBook - ePubElectronics
Basic, Analog, and Digital with PSpice
- Nassir H. Sabah(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...6 Bipolar Junction Transistor The chapter explains the operation of the Bipolar Junction Transistor (BJT). It is shown, to begin with, that the BJT is an amplifying device that basically amplifies power and voltage, albeit in a manner that is quite different from that of FETs. An important difference between BJTs and FETs is that the input current in the BJT is not negligible. In fact, in one of the BJT configurations, the common-base (CB) configuration, the output current is slightly less than the input current. However, considerable current amplification occurs in other BJT configurations. The general approach in analyzing the behavior of the BJT is the same as that applied to the MOSFET, namely, to consider first the behavior of an idealized device based on physical principles, and derive its voltage–current relations and small-signal equivalent circuit. Effects that significantly influence device behavior are then considered, including secondary effects that become important under certain operating conditions. Mathematical treatment is kept to a minimum; derivations of transistor equations and other mathematical relations are left to Supplementary Examples and Topics on the website. Analogous to channel-length modulation in FETs, base-width modulation in BJTs makes the incremental output resistance finite, rather than ideally infinite. Moreover, because of base-width modulation, the output of a BJT has a small effect on the input, even under dc conditions–an example of reverse transmission. High-frequency performance is limited by the effects of stored charges, which are modeled by incremental capacitances, and by physical considerations, such as the time it takes current carriers to move through the base of the BJT. An interesting, recent variation on the conventional BJT is the heterojunction bipolar transistor (HBT), which affords additional design flexibility and improved performance...
eBook - ePubElectronics
from Classical to Quantum
- Michael Olorunfunmi Kolawole(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...3 Structure of Bipolar Junction Transistor In 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...
eBook - ePubSemiconductor Basics
A Qualitative, Non-mathematical Explanation of How Semiconductors Work and How They are Used
- George Domingo(Author)
- 2020(Publication Date)
- Wiley(Publisher)
...The arrows show the direction of the positive current in the emitter. Figure 8.8 Transistor performance is graphically given by the collector current versus the collector to emitter voltage as a function of the base current. The slope of the lines is due to the leakage current, I CEO. If I keep increasing V CB (see Figure 8.3), at some point the slope of the transition region between the base and the collector will reach the emitter, connecting both n‐type materials, and the current will increase drastically. We call this the breakdown condition. One important and final point is that both the current I CE0 and the transistor gain, β, are not stable. They change with temperature and voltage. This change is quite important if we want a very accurate gain. Have this in mind when I show how to bias a transistor in Chapter 9. 8.3 The Junction Field‐effect Transistor Another transistor device is the JFET, sometimes called the Schottky transistor. It works quite differently from the standard transistor, but its operation depends on two pn‐junctions. I show a graphical simplistic representation of a JFET in Figure 8.9. The JFET is like an Oreo cookie, where the sweet cream filling, the n‐type semiconductor, is sandwiched between two chocolate biscuits, the two p‐type semiconductors. That's it. To bias it properly, the left side of the n‐type semiconductor is grounded and the right side has a positive voltage, V D. The two p‐type semiconductors are connected together and right now they are grounded, that is, voltage V G = 0. This structure results in two pn‐junctions, one at the top and one at the bottom of the channel. The difference is that now the current does not go through the junctions, as in the BJT. The current goes only between the junctions through the n‐type material from right to left. This transistor is called a unipolar transistor because only electrons in the n‐type material are moving (or only holes in a p‐type channel)...
- Earl Boysen, Harry Kybett(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
...This condition is important in AC electronics and is covered in Chapter 8. The Junction Field Effect Transistor (JFET) 28 Up to now, the only transistor described has been the BJT. Another common transistor type is the JFET. Like the BJT, the JFET is used in many switching and amplification applications. The JFET is preferred when a high input impedance circuit is needed. The BJT has a relatively low input impedance as compared to the JFET. Like the BJT, the JFET is a three-terminal device. The terminals are called the source, drain, and gate. They are similar in function to the emitter, collector, and base, respectively. Questions A. How many terminals does a JFET have, and what are these terminals called? _____ B. Which terminal has a function similar to the base of a BJT? _____ Answers A. Three, called the source, drain, and gate. B. The gate has a control function similar to that of the base of a BJT. 29 The basic design of a JFET consists of one type of semiconductor material with a channel made of the opposite type of semiconductor material running through it. If the channel is N material, it is called an N-channel JFET; if it is P material, it is called a P-channel. Figure 3.28 shows the basic layout of N and P materials, along with their circuit symbols. Voltage on the gate controls the current flow through the drain and source by controlling the effective width of the channel, allowing more or less current to flow. Thus, the voltage on the gate acts to control the drain current, just as the voltage on the base of a BJT acts to control the collector current. Questions A. Which JFET would use electrons as the primary charge carrier for the drain current? _____ B. What effect does changing the voltage on the gate have on the operation of the JFET? _____ Figure 3.28 Answers A. N-channel because N material uses electrons as the majority carrier. B. It changes the current in the drain...
eBook - ePub- Wai Kai Chen(Author)
- 2004(Publication Date)
- Academic Press(Publisher)
...The collector substrate junction is not shown here The basic operation principle can be derived already for the 1-D structure under the emitter. Classical transistor theory is discussed first; however, it becomes invalid at medium to high current densities because in all practical transistors, N C N B, so that more general equations are also presented. To allow a generic representation of the typical characteristics and a comparison of technologies, a collector current density J C = I C / A E is used in the following considerations, where A E is the (effective) emitter area that is larger than the emitter window area A E 0. The controlling terminal voltages of the 1-D transistor are denoted as V B ′ E ′ and V B ′ C ′. 5.2.1 Basic Equations Based on the 1-D structure, the basic BJT action can be explained as follows. For normal forward operation (V B′E′ > 0 and V B′C′ < 0), electrons are injected from the emitter across the BE SCR into the neutral base. The carriers traverse the base by a combination of drift and diffusion, the partition of which depends on the electric field in the base, and then enter the BC SCR, where they are pulled toward the collector with high velocity. Since in today’s processes, recombination of minorities (electrons in this case) in the base can be neglected, the (1-D) current I C at the collector (x = x c) equals the current injected into the base and, for useful bias conditions V B′E′, even the current entering the BE SCR at the emitter side; this current component is often called forward transfer current I Tf. Similarly, holes are injected from the base across the BE SCR into the neutral emitter, constituting the base current I B ; a portion of the associated holes recombine in the emitter (Auger recombination), while the remaining portion arrives at the emitter contact. Under practically useful bias conditions V B′E′, recombination in the BE SCR is negligible...
