Principles of Oversampling A/D Conversion
Growing practical importance of oversampling analog-to-digital converters (OSADCs) reflects a synergism between microelectronic technology trends and signal theory, neither of which alone is sufficient to explain OSADCs fully. This paper reviews the overall problem of performing signal acquisition-antialiasing, sampling, and quantization-with real hardware, and the ways in which oversampling facilitates this task, sometimes counterintuitively. OSADCs can be seen to overlap and redispose these three traditionall separate operations so as to use manufacturable technology efficiently. Various analog topologies in OSADCs-multibit, 1-bit, feedback, and feedforward-can accomplish the critical step of noise shaping. They differ in their detailed behavior and their dependence on fabrication technology. Insight into the roles of oversampling, and its diverse explanations in the literature, arises from surveying the disparate -cultures- of analog-to-digital conversion that have contributed to its development. Finally, in various ways OSADCs can (and cannot) be compared both to more conventional (sample-by-sample) analog-to-digital converters, and to predictive coders, such as delta modulators.
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