Asynchronous digital signal combiner and method of combining asynchronous digital signals in cable television return path
AssigneeFinisar Corporation
InventorGerald F. Sage
Life of this patent
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Abstract
A device for and method of combining asynchronous digital return signals from multiple nodes of a CATV return path is disclosed. The signals are digitally filtered, re-sampled at a common output rate and digitally combined (e.g., summed) without being converted to analog form. The combined signal can be provided to an optical data transmitter for transmission over an optical fiber to the head end. Because the device of the present embodiment does not require analog hardware (e.g., converters, D/A converters and analog summers), it is smaller, costs less and consumes less power than conventional CATV return signal combiners.
Claims27
An asynchronous return path signal combiner, comprising:
- a plurality of signal receivers for receiving a like 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 like 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.
A method for digitally combining asynchronous data streams, comprising:
- receiving a plurality of digital data streams, each digital data stream comprising a sequence of digital data values received asynchronously at a rate that is asynchronous with respect to at least one of the other digital data streams;
- filtering the plurality of digital data streams to generate a like plurality of interpolated sequences of digital output values with a like plurality of FIR filters;
- generating a like plurality of synchronous interpolated sequences of digital output values from the interpolated sequences of digital output values;
- and
- digitally summing the plurality of synchronous interpolated sequences of digital output values to generate a sequence of summed digital signals at a common output sample rate.
An asynchronous dual-rate filter, comprising:
- a FIR filter for receiving a stream of digital values and for generating an interpolated sequence of digital values;
- an output FIFO for retrieving the interpolated sequence of digital values from the FIR filter at an output write sample rate and for outputting the interpolated sequence of digital values at an output read sample rate;
- logic for monitoring a fullness level of the output FIFO;
- logic for adjusting the output write sample rate according to the fullness level of the output FIFO;
- logic for adjusting the FIR filter, coupled to the output FIFO and including logic for computing coefficients for the FIR filter according to at least in part the fullness level of the output FIFO.
An asynchronous return path signal combiner, comprising:
- a plurality of signal receivers for receiving a like 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 clock source for generating a common output clock signal having a common output sample rate;
- a like plurality of asynchronous dual-rate filters, coupled to the plurality of signal receivers and the clock source, 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 at the common output sample rate;
- and
- a digital combiner coupled to the plurality of asynchronous dual-rate filters, the combiner 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 the common output sample rate.
Dependencies are inferred from the claim text.