英文文献
Data Converters /《数据转换器》
G.B.Clayton /G.B.克莱顿 守孝三年的规矩著
The current upsurge in the u of digital processing techniques ,brought about by developments in very large scale integration, has forced the role of the interface elements between analog and digital systems to the forefront of attention. Data converters are the interface elements. Although they were once regarded by electronics engineers as expensive, rather specialized pieces of equipment , they are now commonplace . They are available as lf-contained functional units, in both modular and low cost integrated circuit from . No one with an interest in modern electronic instrumentation techniques can afford tube without a sound knowledge and understanding of the operation, capabilities and limitations of the devices.
USEFULNESS OF CONVERTERS
怎么找话题聊天In many of the real world systems studied by scientists and engineers the system parameters are continuously changing quantities (analog variables)and when electronic measurement techniques are ud data is derived in analog form as the electrical output signal of a transducer .It is perfectly possible to process ,manipulate and store analog data using a purely analog electronic system : negative feedback techniques can make analog systems perform very precily. [1]However , the accuracy of a purely analog system is often not usable becau of the difficulty of rending , recording and interpreting analog data with high accuracy . Also , when large amounts of analog data are involved the task of analysis and storage assumes mammoth proportions .
Digital electronic systems can be made to process rapidly and accurately , to manipulate and to store large amounts of data . The advent of low cost digital microprocessor systems has drastically reduced the cost of implementing digital data processing . Microprocessors make it possible to extend the u of electronic digital techniques into areas where they were formerly not considered practicable becau of economic considerations . However ,m digital circuits only operate on digital data –the scientist who
wishes to avail himlf of the power of digital techniques must first transform his analog data into digital form . A system called an analog to digital converter 洗衣机洗鞋,微信打不开怎么回事 ADC ,is ud to perform this function and a system called a digital to analog converter ,DAC ,performs the opposite type of conversion , transforming digital data into analog from . ADCs and DACs provide the esntial interface which is required between analog and digital systems . The ADC allows a digital system to take in information from an outside analog system-the digital system can then rapidly process and analys this information . The DAC allows the results of such analys to be communicated back to the analog system perhaps to modify or control its action .
ADC and DAC systems are not new but until comparatively recently they were expensive to implement and have conquently been regarded as rather specialized pieces of equipment . The advent of low cost monolithic IC converter devices has changed this position: they make awide range of versatile signal processing techniques economically available to the measurement scientist who is prepared to invest some of his time in familiarizing himlf with the latest devices and their capabilities . The material which follo
ws is intended to rve as a first step in such a familiarisation exerci.风景美
Rather than attempt a survey of available converter devices , which , in a fastchanging area such as this ,would be doomed to obsolescence even before it was completed , we concentrate on the principles underlying the most popular conversion techniques . Specific IC devices are mentioned , but only as a means of relating the discussion to practical circuits which you can experimentally evaluate for yourlf-there is no substitute for ‘hands on ’ practical experience in this type of learning exerci . However , it should not be assumed that the devices referred to are he only ones , nor indeed the ‘best’ ones available (from a cost /performance standpoint). The choice of the ‘best’ converter for a specific application can only be made from athorough study of the manufacturers’ latest product guides .
ANALOG TO DIGITAL CONVERSION TECHNIQUS
Comparison Of A/D Conversion Techniques
A brief summary is now given in which the main characteristics of devices which u the various conversion techniques that have been discusd will be compared . There are normally there dominant factors which govern the choice of the A/D converter to be ud in an application : speed , accuracy and cost . It is convenient to compare the different techniques in relation to the three factors .
Speed limitations are inherent in the particular techniques but arrange of speeds can be expected for different converter devices using the same conversion technique . A speed/accuracy design compromi is inherent in all the conversion techniques . Increa accuracy is obtained at the expen of a reduction in conversion speed . In general , cost is directly related to speed and accuracy , but the cost of a converter device(indeed of any device) , is greatly influenced by market factors which might be quit unrelated to the performance of the device . The bigger the market is , the more firms there will be attempting to get a slice of it , and competition brings down the cost .微主题
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As far as inherent speed imitations are concerned the techniques discusd in this chapt
er in order of decreasing speed (increa in conversion time )are : parallel conversion , successive approximation conversion , tracking conversion and integrating conversion .
If sheer conversion speed is a dominating factor in an application , the designer will have to choo a converter which us the parallel conversion technique . At the time of writing there are not many ultra-fast converters on the market and they tend to be expensive , particularly the higher resolution devices . Some firms which make very fast converters are TRW LSI Products , Datel-Intersil, Computer Labs and Motorola . Available parallel converters achieve an 8-bit conversion time of the order of 30ns . Applications in which conversion time must be very short are increasing for example, radar , digital TV and fast transient event recorders . [11,12] No doubt this growing range of applications will interest more manufacturers in very high speed converters and will result in a greater number of less costly devices appearing on the market.
京剧的四大名旦
