Transversal filter useable in echo canceler, decision feedback equalizer applications for minimizing non-linear distortion in signals conveyed over full duplex two-wire communication link

For use with a full duplex communication network having a transmitter path coupled by way of a digital-to-analog converter resistor network and a transmitter path filter network to a hybrid circuit which is operative to couple a two-wire communication link to said transmitter path and a receiver path, said receiver path including a receiver path filter network and an analog-to-digital converter, the output of said analog-to-digital converter containing a received signal from said two-wire communication link and a transmission signal leakage component from said hybrid circuit as an echo signal, an echo canceler for effectively canceling said echo signal from said receiver path comprising:

• a multistage delay line, through which successive symbols of said multi-symbol data modulation system, conveyed over said transmitter path to said hybrid circuit for transmission by way of said two-wire communication link, are sequentially introduced;
• a plurality of partial sum generators, respective ones of which are associated with respective ones of symbols employed by said multi-symbol data modulation system, a respective one of said plurality of partial sum generators, which is associated with a respective one of said symbols, being coupled to receive first coefficients associated with each of the stages of said multistage delay line which store said respective one of said symbols, and producing a summation of the products of said first coefficients and said respective one of said symbols;
• a plurality of multiplier stages respectively coupled to a selected number of said partial sum generators, said selected number being less than said plurality of said partial sum generators, each multiplier stage being operative to multiply a respective partial sum by a respective second coefficient;
• a coefficient generator operative to generate said first and second coefficients;
• and
• a summation stage for summing together outputs of said plurality of multiplier stages and the output of at least one partial sum generator whose output is not coupled to a multiplier stage, so as to produce a summation signal as an echo estimate signal, said echo estimate signal being differentially combined with the output of said analog-to-digital converter to produce an output signal which is coupled to said coefficient generator for adjusting said first and second coefficients.

For use with a full duplex communication network having a communication link coupled to a far end transmitter site and a near end receive signal path, a decision feedback equalizer comprising:

• a linear transversal filter section to which a signal received by way of said near end receive signal path from said communication link is applied;
• and
• a decision feedback transversal filter section which is operative to generate a postcursor output, said postcursor output being differentially combined with the output of said linear transversal filter section and the resulting differential signal is applied to a symbol decision operator, and wherein said differential signal is subtracted from received symbol value estimates derived by said symbol decision operator to produce a residual error signal for updating a first coefficient generator which supplies first coefficients of said linear transversal filter section, said decision feedback transversal filter section including
• a multistage delay line through which successive symbols from said symbol decision operator are sequentially introduced, a plurality of partial sum generators, respectively associated with respective ones of symbols from said symbol decision generator, a respective one of said plurality of partial sum generators, which is associated with a respective one of said symbols, being coupled to receive, from said first coefficient generator, first coefficients associated with each of the stages of said multistage delay line which store said respective one of said symbols, and producing a summation of the products of said first coefficients and the symbol values stored in the delay line stages with which said first coefficients are associated,
• a plurality of multiplier stages respectively coupled to a selected number of said partial sum generators, said selected number being less than said plurality of said partial sum generators, each multiplier stage being operative to multiply a respective partial sum by a respective second coefficient,
• a second coefficient generator operative to generate said second coefficients, and
• a summation stage for summing together outputs of said plurality of multiplier stages and the output of at least one partial sum generator whose output is not coupled to a multiplier stage, so as to produce a summation signal, said summation signal being differentially combined with a signal representative of a noise containing signal carried by said communication path, to produce said postcursor output signal.

A method of filtering a multi-symbol data signal sequence transmitted over a communication path comprising the steps of:

• (a) sequentially clocking said multi-symbol data signal sequence through a multistage delay line;
• (b) for each of the respective symbols of said multi-symbol data signal sequence, summing first coefficients associated with each of the stages of said multistage delay line which store said each respective symbol and producing a partial sum of products of said first coefficients and said each respective symbol;
• (c) for a selected number of partial products produced in step (b), multiplying a respective partial sum by a respective second coefficient to obtain a set of scaled partial products;
• and
• (d) summing together the scaled partial products obtained in step (c) and a partial sum or partial sums not scaled in step (c), so as to produce a summation signal, said summation signal being differentially combined with a signal representative of a noise containing signal carried by said communication path, to produce an output signal through which said first and second coefficients are adjusted.