Patent ID: 7359447

Claim:
An asynchronous return path signal combiner, comprising: a plurality of signal receivers for receiving a plurality of digital data streams, each digital data stream comprising a sequence of digital data values received asynchronously at a rate and phase that is asynchronous with respect to at least one of the other digital data streams; a plurality of asynchronous dual-rate filters, coupled to the plurality of signal receivers, each asynchronous dual-rate filter receiving a respective digital data stream of the plurality of digital data streams at a respective input sample clock rate and generating a respective interpolated sequence of digital output samples; and a digital summer coupled to the plurality of asynchronous dual-rate filters, the digital summer summing the respective interpolated sequences of digital output samples from the plurality of asynchronous dual-rate filters so as to generate a sequence of summed digital signals at a common output sample rate; wherein at least one of the asynchronous dual-rate filters includes: an input FIFO buffer storing digital data values according to an input write clock and outputting stored digital values to a respective one of the asynchronous dual-rate filters according to a respective input sample clock rate; logic for generating a first fullness signal representing fullness of the input FIFO buffer; an output FIFO buffer storing interpolated digital values according to an output write clock and outputting the stored interpolated digital values at the common output sample rate; logic for generating a second fullness signal representing fullness of the output FIFO buffer; logic for adjusting the input read clock according to the first fullness signal; and logic for adjusting the output write clock according to the second fullness signal a coefficient sets memory for storing a plurality of distinct sets of interpolation coefficients, each said set of interpolation coefficients for generating an output digital signal with a respective distinct phase relative to the sequence of digital data values in a respective digital data stream of the plurality of digital data streams; an FIR filter for generating each digital output sample of the respective interpolated sequence of digital output samples, each digital output sample being generated in accordance with a coefficient index identifying a set of interpolation coefficients from among the plurality of sets of interpolation coefficients in the coefficient sets memory; and coefficient selection logic for generating a sequence of coefficient indices, for identifying a sequence of coefficient sets to be used by the FIR filter to generate a corresponding sequence of digital output samples.