bjt-1 - Chapter II Bipolar Junction Transistors(BJTs...

This preview shows page 1 - 3 out of 11 pages.

Chapter II Bipolar Junction Transistors (BJTs) Introduction In Chapter 1, we saw that the current voltage characteristics of the diode are useful in electronic switching and wave shaping circuits. However, diodes are not capable of amplifying currents or voltages. As we know that, the electronic device that is capable of current and voltage amplification, or gain, in conjunction with other circuit elements, is the transistor. The development of the transistor by Bardeen, Brattain, and Schockley at Bell Telephone Laboratories in the late 1940s started the first electronics revolution of the 1950s and 1960s. This invention led to the development of the first integrated circuit in 1958 and to the transistor operational amplifier (op-amp), which is one of the most widely used electronic circuits. The bipolar transistor, which is introduced in this chapter, is one of the two major types of transistors. The second type of transistor, the field-effect transistor (FET), was introduced in Chapter 3. These two device types are the basis of modern microelectronics. Each device type is equally important and each has particular advantages for specific applications. 2.1 Bipolar Junction Transistor The bipolar junction transistor (BJT) has three separately doped regions and contains two pn junctions. A single pn junction has two modes of operation forward bias and reverse bias. The bipolar transistor, with two pn junctions, therefore has four possible modes of operation, depending on the bias condition of each pn junction, which is one reason for the versatility of the device. With three separately doped regions, the bipolar transistor is a three- terminal device. The basic transistor principle is that the voltage between two terminals controls the current through the third terminal . Our discussion of the bipolar transistor starts with a description of the basic transistor structure and a qualitative description of its operation. To describe its operation, we use the pn junction concepts presented in Chapter 1. However, the two pn junctions are sufficiently close together to be called interacting pn junctions. The operation of the transistor is therefore totally different from that of two back-to-back diodes. Current in the transistor is due to the flow of both electrons and holes, hence the name bipolar. Our discussion covers the relationship between the three terminal currents. In addition, we present the circuit symbols and conventions used in bipolar circuits, the bipolar transistor current voltage characteristics, and finally, some non ideal current voltage characteristics.
Image of page 1

Subscribe to view the full document.

2.1.1 Transistor Structures Figure 2.1 shows simplified block diagrams of the basic structure of the two types of bipolar transistor: npn and pnp. The npn bipolar transistor contains a thin p-region between two n-regions. In contrast, the pnp bipolar transistor contains a thin n region sandwiched between two p-regions. The three regions and their terminal connections are called the emitter, base, and collector.
Image of page 2
Image of page 3
  • Spring '16
  • Transistor, Volt, Bipolar junction transistor, bipolar transistor, transistor operation

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern