An asynchronous sample-rate converter is presented, which supports rates of up to 192 kHz with a dynamic range of 139 dB. Down-sampling ratios up to 7.75:1 and up-sampling ratio of 1:8 are achieved while maintaining a minimum of 120-dB THD+N within these sampling-rate ratios. A digital servo loop provides excellent jitter rejection and automatic tracking of the sampling ratio. The output samples of the sample-rate converter are obtained by convolving the input samples with the desired antialiasing polyphase filter. To perform the convolution, the upper bits of the output of the digital servo loop are used as the starting pointer to the input samples stored in RAM, while the lower bits are used to select the correct polyphase coefficients from a highly oversampled polyphase filter.
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