Ch 4a 2006

Ch 4a 2006 - CH 4.0 BASIC BJT AMPLIFIERS In the last...

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CH. 4.0 BASIC BJT AMPLIFIERS In the last chapter, we described the operation of the bipolar junction transistor, and analyzed and designed the dc response of circuits containing these devices. In this chapter, we emphasize the use of the bipolar transistor in linear amplifier applications. Linear amplifiers imply that we are dealing with analog signals. A linear amplifier then means that the output signal is equal to the input signal multiplied by a constant, where the magnitude of the constant of proportionality is in general, greater than unity. A linear amplifier is capable of producing signal power gain: that is the power in the output signal is greater than the power in the input signal. We will investigate the source of this "extra" power. We examine the properties of three basic single-stage, or single-transistor, amplifier circuits. These circuits are the common-emitter, emitter-follower, and common-base configurations. These configurations form the building blocks for more complex amplifiers, so gaining a good understanding of these three amplifier circuits is an important goal of this chapter. We introduce a few of the many possible multistage configurations in which multiple amplifiers are connected in series, or cascade, to increase the overall small-signal voltage gain or to provide a particular combination of voltage gain and output resistance. Our discussion includes the method of analysis required for these types of circuits and a synopsis of their properties. 4.1 ANALOG SIGNALS AND LINEAR AMPLIFIERS In this chapter, we will be considering signals, analog circuits, and amplifiers. A signal contains some type of information. For example, sound waves produced by a human contain the information the person is conveying to another person. Our physical senses, such as hearing, vision, and touch, are naturally analog. Analog signals can represent parameters such as temperature, pressure, and wind velocity. Here, we are interested in electrical signals, such as the output signal from a compact disc, a signal from a microphone, or a signal from a heart rate monitor. The electrical signals are in the form of time-varying currents and voltages. Time-varying signals from a particular source very often need to be amplified before the signal is capable of being "useful." For example. Figure 4.1 shows a signal source that is the output of a compact disc system. . That signal consists of a small time-varying voltage and current, which means the signal power is relatively small. The power required to drive the speakers is larger than the output signal from the compact disc, so the compact disc signal must be amplified before it is capable of driving the speakers in order that sound can be heard. Other examples of signals that must be amplified before they are capable of driving loads include the output of a microphone, voice signals EE 329 Introduction to Electronics 147
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received on earth from an orbiting manned shuttle, and video signals from an orbiting weather satellite. Also shown in Figure 4.1 is a dc voltage source connected to the amplifier.
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Ch 4a 2006 - CH 4.0 BASIC BJT AMPLIFIERS In the last...

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