【正文】 stream of binary numbers whose values represent the input electrical voltages at each sampling instant.3. Signal processingSignals monly need to be processed in a variety of ways. For example, the output signal from a transducer may well be contaminated with unwanted electrical noise. The electrodes attached to a patient’s chest when an ECG is taken measure tiny electrical voltage changes due to the activity of the heart and other muscles. The signal is often strongly affected by mains pickup due to electrical interference from the mains supply. Processing the signal using a filtercircuit can remove or at least reduce the unwanted part of the signal. Increasingly nowadays, the filtering of signals to improve signal quality or to extract important information is done by DSP techniques rather than by analog electronics.4. Development and Applications of DSPThe development of digital signal processing dates from the 1960’s with the use of mainframe digital puters for numbercrunching applications such as the Fast Fourier Transform (FFT), which allows the frequency spectrum of a signal to be puted rapidly. These techniques were not widely used at that time, because suitable puting equipment was generally available only in universities and other scientific research institutions.Because puters were expensive during this time, DSP was limited to only a few critical applications. Pioneering efforts were made in four key areas: radar amp。 sonar, where national security was at risk。 oil exploration, where large amounts of money could be made。 space exploration, where data are irreplaceable。 and medical imaging, where lives could be saved.The personal puter revolution of the 1980s and 1990s caused DSP to explode with new applications. Rather than being motivated by military and government needs, DSP was suddenly driven by the mercial marketplace. Anyone who thought they could make money in the rapidly expanding field was suddenly a DSP vendor. DSP reached the public in such products as: mobile telephones, pact disc players, and electronic voice mail.This technological revolution occurred from the topdown. In the early 1980s, DSP was taught as a graduate level course in electrical engineering. A decade later, DSP had bee a standard part of the undergraduate curriculum. Today, DSP is a basic skill needed by scientists and engineers in many fields. As an analogy, DSP can be pared to a previous technological revolution: electronics. While still the realm of electrical engineering, nearly every scientist and engineer has some background in basic circuit design. Without it, they would be lost in the technological world. DSP has the same future. DSP has revolutionized many areas in science and engineering. A few of these diverse applications are shown in Figure 1.5. Digital Signal Processors (DSPs)The introduction of the microprocessor in the late 1970’s and early 1980’s made it possible for DSP techniques to be used in a much wider range of applications. However, generalpurpose microprocessors such as the Intel x86 family are not ideally suited to the numericallyintensive requirements of DSP, and during the 1980’s the increasing importance of DSP led several majorelectronics manufacturers (such as Texas Instruments, Analog Devices and Motorola) to develop Digital Signal Processor chips specialized microprocessors with architectures designed specifically for the types of operations required in digital signal processing. (Note that the acronym DSP can variously mean Digital Signal Processing, the term used for a wide range of techniques for processing signals digitally, or Digital Signal Processor, a specialized type of microprocessor chip). Like a generalpurpose microprocessor, a DSP is a programmable device, with its own native instruction code. DSP chips are capable of carrying out millions of floating point operations per second, and like their betterknown generalpurpose cousins, faster and more powerful versions are continually being introduced. DSPs can also be embedded within plexsystemonchip devices, often containing both analog and digital circuitry.Although some of the mathematical theory underlying DSP techniques, such as Fourier and Hilbert Transforms, digital filter design and signal pression, can be fairly plex, the numerical operations required actually to implement these techniques are very simple, consisting mainly of operations that could be done on a cheap fourfunction calculator. The architecture of a DSP chip is designed to carry out such operations incredibly fast, processing hundreds of millions of samples every second, to provide realtime performance: that is, the ability to process a signal live as it is sampled and then output the processed signal, for example to a loudspeaker or video display. All ofSpace :Space photograph enhancement 。 Data pression 。Intelligent sensory analysis by remote space probesMedical :Diagnostic imaging (CT, MRI, ultrasound, and others)。 Electrocardiogram analysis。 Medical image storage/retrieval Commercial: Image and sound pression for multimedia presentation。 Movie special effects。 Video conference callingDSP Telephone: Voice and data pression。 Echo reduction。 Signal multiplexing。 Filtering Military: Radar。 Sonar。 Ordnance guidance。 Secure munication Industrial: Oil and mineral prospecting。 Process monitoring amp。 control。 Nondestructive testing。 CAD and design tools Scientific: Earthquake recording amp。 analysis。 Data acquisition。 Spectral analysis。 Simulation and modelingFig. 1 The application area of DSPthe practical examples of DSP applications mentioned earlier, such as hard disc drives and mobile phones, demand real