Digital signal processing

Chapter Digital signal processing

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • You might ask, “Why convert a signal to digital form in the first place, if it’s going tobe changed back to analog form at the receiver anyway?” The reason is that a digital sig-nal is inherently simpler than an analog signal, in the sense that is less random. Thus,a digital signal resembles noise less than an analog signal.It’s good to make a signal as different from noise as possible, in as many ways (orsenses) as possible. This is because the more different a signal is from unwanted noise,the easier it is to separate the data from the noise, and the better is the realizable S/Nratio.You might think of signal/noise separation in terms of apples, oranges, and a water-melon. It takes awhile to find an orange in a tub of apples. (You’ll probably have to dumpthe tub). Think of the orange as an analog signal and the apples as noise. But supposethere’s a watermelon in a bushel basket with apples. You’ll have no trouble at all findingthe watermelon. Think of the melon as a digital signal and the apples as noise.Another, more interesting feature of digital communications arises when you thinkof a watermelon in a tub of oranges. It’s as easy to separate a digital signal from a jum-ble of analog signals as it is to extract a digital signal from noise. In a band occupied bythousands of analog signals, a lone digital signal can be picked out easily—far more eas-ily than any of the analog signals.In recent years, digitization has become commonplace not only in data communica-tions, but in music recording and even in video recording. The main advantage of digi-tal recording is that a selection can be recorded, re-recorded, re-re-recorded, etc., andthe quality does not diminish.Digital signal processingA new and rapidly advancing communications technique, digital signal processing(DSP), promises to revolutionize voice, digital, and image communications.In analog modes, DSP works by converting the received voice or video signal inputinto digital data by means of an analog-to-digital (A/D) converter. The digital signal isprocessed and is reconverted back to the original voice or video via a D/A converter(Fig. 27-9).510 Data reception27-9Digital signal processing.In digital modes, A/D and D/A conversion is not necessary, but DSP can still be usedto “clean up” the signal. This reduces the number of errors.It is in the digital part of the DSP circuit that the signal enhancement takes place.Digital signals have a finite number of discrete, well-defined states. It is easier to processa signal of this kind than to process an analog signal, which has a theoretically infinite