Table 22 shows these various conditions for the

This preview shows page 5 - 9 out of 10 pages.

Table 2.2 shows these various conditions for the circuit in Figure 2.21(b). In a positive logic system, meaning that the larger voltage is a logic 1 and the lower voltage is a logic 0, this circuit performs the NOR logic function. The circuit of Figure 2.21(b) is then a two-input bipolar NOR logic circuit. Table 2.2 The bipolar NOR logic circuit response
Image of page 5

Subscribe to view the full document.

EXAMPLE Determine the currents and voltages in the circuit shown in Figure 2.21(b). Assume the transistor parameters are: β =50, V BE (on) = 0 . 7V, and V CE (sat) = 0.2V. Let R C = 1k and R B = 20k . Determine the currents and output voltage for various input conditions. Solution: The following table indicates the equations and results for this example. Comment: In this example, we see that whenever a transistor is conducting, the ratio of collector current to base current is always less than β . This shows that the transistor is in saturation, which occurs when either V 1 or V 2 is 5V. Amplifier The bipolar inverter circuit can also be used to amplify a time-varying signal. Figure 2.22(a) shows an inverter circuit including a time-varying voltage source v I in the base circuit. The voltage transfer characteristics are shown in Figure 2.22(b). The dc voltage source V BB is used to bias the transistor in the forward-active region. The Q -point is shown on the transfer characteristics. The voltage source v I introduces a time-varying signal on the input. A change in the input voltage then produces a change in the output voltage. These time-varying input and output signals are shown in Figure 2.22(b). If the magnitude of the slope of the transfer characteristics is greater than unity, then the time-varying output signal will be larger than the time-varying input signal thus an amplifier.
Image of page 6
Figure 2.22 (a) A bipolar inverter circuit to be used as a time-varying amplifier; (b) the voltage transfer characteristics 2.1.8. BJT Circuits at DC We’ve considered the basic transistor characteristics and properties. We can now start analyzing and designing the dc biasing of bipolar transistor circuits. A primary purpose of the rest of the chapter is to become familiar and comfortable with the bipolar transistor and transistor circuits. The dc biasing of transistors, the focus of this concept, is an important part of designing bipolar amplifiers. The piecewise linear model of a pn junction can be used for the dc analysis of bipolar transistor circuits. We will first analyze the common-emitter circuit and introduce the load line for that circuit. We will then look at the dc analysis of other bipolar transistor circuit configurations. Since a transistor in a linear amplifier must be biased in the forward-active mode, we emphasize, in this section, the analysis and design of circuits in which the transistor is biased in this mode. Common-Emitter Circuit One of the basic transistor circuit configurations is called the common- emitter circuit. Figure 2.23(a) shows one example of a common-emitter circuit. The emitter terminal is obviously at ground potential.
Image of page 7

Subscribe to view the full document.

Figure 2.23 (a) Common-emitter circuit with npn transistor and (b) dc equivalent circuit.
Image of page 8
Image of page 9

{[ 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