Author: workhouse123
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Metal-Oxide Semiconductor Field-Effect Transistors
Another family of transistors is known as metal-oxide semiconductor field-effect transistors (MOSFETs) of which there are two basic types called n-channel and p-channel; once again these names relate to the way in which the silicon is doped (Figure 10.7). Figure 10.7 Metal-oxide semiconductor field-effect transistors (MOSFETs) (a) NMOS field-effect transistor; (b) PMOS field-effect transistor In the case of these devices, the drain and source form…
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Bipolar Junction Transistors
More complex components called transistors can be created by forming a sandwich out of three regions of doped silicon. One family of transistors is known as bipolar junction transistors (BJTs) of which there are two basic types called NPN and PNP; these names relate to the way in which the silicon is doped (Figure 10.5). Figure 10.5 Bipolar junction transistors (BJTs); (a) NPN…
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Semiconductors
Most materials are conductors, insulators, or something in-between, but a special class of materials known as semiconductors can be persuaded to exhibit both conducting and insulating properties. The first semiconductor to undergo evaluation was the element germanium (chemical symbol Ge). However, for a variety of reasons, silicon (chemical symbol Si) replaced germanium as the semiconductor of choice.…
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Information Theory
Information theory involves communication in general—on wires, fibers, or over the air—and it’s applied to widely varied applications such as information storage on optical disks, radar target identification, and the search for extraterrestrial intelligence. In general, the goal of a communication system is to pass “information” from one place to another through a medium contaminated by…
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Digital Modulation Techniques
In the last few sections methods of transmitting analog information using analog signals were explained. This section will consider methods of transmitting digital data using analog signals. The most familiar use of these methods is in data communications, where modems and telephone networks are used; because integrated circuits are generally used a block diagram approach…
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FM Modulators
The most frequently used modulator in FM systems is the reactance modulator, which incorporates some method of varying the reactance across the oscillator circuit. This can be done by incorporating a device which changes either its inductive or capacitive reactance, depending on the oscillator involved. With a Colpitts oscillator some type of capacitive modulator would…
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Frequency Modulation and Demodulation
With frequency modulation the frequency (rather than the amplitude) of a constant-amplitude, constant-frequency sinusoidal carrier is made to vary in proportion to the amplitude of the applied modulating signal. This is shown in Figure 19.10, where a constant-amplitude carrier is frequency-modulated by a single tone. Note how the frequency of the carrier changes. Figure 19.10 Constant-amplitude carrier…
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The Balanced Modulator/Demodulator
The function of a modulator, as has been shown, is to superimpose the baseband signals on to a carrier while the demodulator provides the reverse role by extracting a carrier, known as the intermediate frequency, and leaving the baseband. There are many modulators and demodulators commercially sold on the market as integrated chips or as part…
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Analog Modulation Techniques
Amplitude Modulation When the amplitude of a carrier signal is varied in accordance with the information signal, amplitude modulation is produced. This method is mainly used where large power outputs are required for long-distance communications. Figure 19.3 shows a constant-amplitude, constant-frequency carrier being modulated by a single tone. In practice, many modulating signals may be used.…
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Introduction
shows a simplified block diagram of a color television receiver. We will refer to it throughout this chapter. It shows that any receiver must be capable of extracting information from the incoming channels to which it is tuned. The shaded blocks show examples of where demodulation or detection occur for the video and audio signals.…