| OCR Text |
Show 2 of ir uit ornponents is r quired. The sensitivity of th omp n nts an also b relaxed du to the single-bit nature of the quantizer in th sigma-d Ita unit. The SNR of a sigrna-delta (one-bit oversampl -and-d cimat ) A/D onv rt r 1 ' not limited by component matching in the analog circuitry, unlike conventional A/D designs and other Oversampling converters based on a multibit initial conversion. Also because of its simplicity and robustness against circuit imperfections, oversampled sigma-delta modulation has been proposed as a practical implementation for most high speed A/D conversions. The rnain disadvantage of a sigma-delta A/D converter is the need to oversample the input signal by a large factor. This requirement can lead to very high sampling rates in cases where sigma-delta A/D conversion is intended for use in a high-speed system. High-speed sampling with precise timing accuracy can be difficult and expensive to realize in a practical system. Under such circumstances, there is a tradeoff between rate of oversampling and the performance required. Considering this and the accuracy needed for the spread spectrum receiver system, and oversampling rate of 20 was chosen for the sigma-delta modulator, which is much lesser than the conventional modulators used for low speed audio purposes. |
