Data Converters /《数据转换器》
G.B.Clayton /G.B.克莱顿 著
The current upsurge in the use 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 these 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 self-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 these devices.
USEFULNESS OF CONVERTERS
南瓜加工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 used 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 precisely. [1]However , the accuracy of a purely analog system is often not usable because 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 use of electronic digital techniques into areas where they were formerly not considered practicable because of economic considerations . However ,m digital circuits only operate on digital data –the scientist who
wishes to avail himself of the power of digital techniques must first transform his analog data into digital form . A system called an analog to digital converter , ADC ,is used 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 essential 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 analyses this information . The DAC allows the results of such analyses 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 consequently 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 himself with the latest devices and their capabilities . The material which follo简易升降
平台 ws is intended to serve as a first step in such a familiarisation exercise.
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 yourself-there is no substitute for ‘hands on ’ practical experience in this type of learning exercise . 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氢氧发生器>d1秒
A brief summary is now given in which the main characteristics of devices which use the various conversion techniques that have been discussed will be compared . There are normally there dominant factors which govern the choice of the A/D converter to be used in an application : speed , accuracy and cost . It is convenient to compare the different techniques in relation to these 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 compromise is inherent in all the conversion techniques . Increase accuracy is obtained at the expense 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 .
缘114As far as inherent speed imitations are concerned the techniques discussed in this chapt
er in order of decreasing speed (increase 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 choose a converter which uses 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.
豫公网安备41160202000603
站长QQ:729038198
关于我们
投诉建议