DIGITAL-TO-DIGITAL CONVERSION USING NONUNIFORM SAMPLE RATES

摘要

A method and apparatus for digital-to-digital conversion using sigma-delta modulation of the temporal spacing between digital samples. The method and apparatus of the present invention provides for sigma-delta modulation of the time base such that noise produced by nonuniform sampling are frequency-shaped to a region (i.e., shifted to higher frequencies) where it can be removed by conventional filtering techniques. In one embodiment, the digital data is interpolated (16) by fixed ratio and then decimated (21) under control of a first sigma-delta modulated frequency selection signal (26) that represents, on average, the data rate of the incoming digital data stream. Thereafter, the digital data is interpolated (30) under control of a second sigma-delta modulated frequency selection signal (46) that represents, on average, the data rate of the digital data to be output by the converter and then decimated (40) by a fixed ratio. In another embodiment, the digital data is interpolated under control of a first sigma-delta modulated frequency selection signal that represents, on average, the data rate of the incoming digital data stream and then decimated by a fixed ratio. Thereafter, the digital data is interpolated by a fixed ratio and then decimated under control of a second sigma-delta modulated frequency selection signal that represents, on average, the data rate of the digital data to be output by the converter. The first and second frequency signal selection numbers are modulated using n-th order m-bit sigma-delta modulators. The method and apparatus converts the data rate of the incoming digital data stream to the data rate of the first n-th m-bit sigma-delta modulator and then converts the digital data stream from the first sigma-delta modulator (20) to an output data rate determined by the second n-th order m-bit sigma-delta modulator (32).