Oversampled, linear predictive and noise-shaping coders of order N > 1

First-order predictive coders (e.g., DPCM) and first-order noise shaping coders (e.g, interpolative coders) are familiar A/D conversion techniques. Using a feedback network containing an A/D and a first-order (single-pole) analog filter, they reduce the number of A/D output levels, for a given SNR requirement, at the expense of the additional analog filter complexity. Oversampling (i.e., sampling at higher than the Nyquist rate) provides excess bandwidth in the feedback loop, allowing further reductions in the number of A/D output levels at the expense of faster circuitry. This paper extends such first-order oversampled coders to include higher order analog filters under the constraint that the filters be independent of the statistical properties of the input analog signal. The resulting robust Nth-order predictive and noise-shaping coders allow
N+1/2
bits to be eliminated from the coder's A/D for each doubling of the sample rate. The design of such Nth-order oversampled coders and an experimental third-order predictive coder are described.