Demodulator for a multi-pair gigabit transceiver

A feedforward equalizer for equalizing a sequence of signal samples received from a remote transmitter, the feedforward equalizer having a gain and being included in a receiver, the receiver having a timing recovery module for setting a sampling phase and a decoder, the feedforward equalizer comprising:

• (a) a non-adaptive filter receiving the signal samples and producing a filtered signal;
• (b) a gain stage coupled to the non-adaptive filter, the gain stage allowing adjustment of the gain of the feedforward equalizer by adjusting the amplitude of the filtered signal, the amplitude of the filtered signal being adjusted so as to fit in an operational range of the decoder;
• wherein the feedforward equalizer does not affect the sampling phase setting of the timing recovery module of the receiver;
• further comprising a noise cancellation stage, the noise cancellation stage subtracting from the filtered signal a noise signal received from a noise computing module of the receiver and producing a noise-reduced filtered signal, and
• wherein the noise cancellation stage is disposed between the non-adaptive filter and the gain stage and provides the noise-reduced filtered signal to the gain stage, the location of the noise cancellation stage allowing the noise signal to be substantially unaffected by the gain of the feedforward equalizer.

A method for equalizing a sequence of input samples received at a receiver from a remote transmitter, the receiver having a timing recovery module for setting a sampling phase and a decoder, the method comprising:

• (a) filtering the input samples using a non-adaptive filter to produce a filtered signal;
• (b) adjusting the amplitude of the filtered signal so that the amplitude of the filtered signal fits in an operational range of the decoder;
• wherein filtering the input samples and adjusting the amplitude of the filtered signal do not affect the sampling phase setting of the timing recovery module of the reciever;
• wherein filtering the input samples comprises providing a precursor in the filtered signal, the precursor being an indicatior preceding each of the signal samples in the filtered signal to facilitate timing recovery;
• and
• wherein the non-adaptive filter is a finite impulse response filter having a transfer function of the form g+z−1, where g is programmable constant, and where z−1 is a delayed signal sample.

A method for equalizing a sequence of input samples received at a receiver from a remote transmitter, the receiver having a timing recovery module for setting a sampling phase and a decoder, the method comprising:

• (a) filtering the input samples using a non-adaptive filter to produce a filtered signal;
• (b) adjusting the amplitude of the filtered signal so that the amplitude of the filtered signal fits in an operational range of the decoder;
• wherein filtering the input samples and adjusting the amplitude of the filtered signal do not affect the sampling phase setting of the timing recovery module of the receiver;
• wherein filtering the input samples comprises substantially eliminating from the received signal samples intersymbol interference introduced by pulse shaping at the remote transmitter, and
• wherein the non-adaptive filter is an infinite impulse response filter having a transfer function of the form 1/(1+z−1K), where K is a programmable constant, and where z−1 is a delayed signal sample.

A system for demodulating a sequence of input samples received from a remote transmitter, the system being included in a receiver, the receiver having a timing recovery module for setting a sampling phase, the system comprising:

• (a) a feedforward equalizer having a gain, receiving and equalizing the input samples;
• (b) a decoder system coupled to the feed-forward equalizer to receive and decode the equalized input samples;
• wherein the feedforward equalizer does not affect the sampling phase setting of the timing recovery module of the receiver;
• and
• wherein the feedforward equalizer comprises:
• (a) a first filter receiving the input samples and generating a first signal, the first signal including a precursor, the precursor being an indicator preceding each of the input samples to facilitate timing recovery,
• (b) a second filter coupled to the first filter, the second filter compensating intersymbol interference included in the first signal and producing a second signal;
• (c) a noise cancellation stage coupled to the second filter, the noise cancellation stage receiving the second signal from the second filter and a noise signal from a noise computing module of the receiver, the noise cancellation stage subtracting the noise signal from the second signal and producing a third signal;
• and
• (d) a gain stage coupled to the noise cancellation stage the gain stage providing adjustment of the gain of the feedforward equalizer by adjusting the amplitude of the third signal, the amplitude of the third signal being adjusted so as to fit in operational range of the decoder.