Adaptive digital filter including low-pass filter

An adaptive digital filter for estimating a response characteristic of a signal path by monitoring a sampled output signal of said signal path, estimating a predetermined number of filter coefficients which represent the response characteristic of the signal path, and generating an estimated output signal of said signal path using a plurality of successive sampled input signals of the signal path and estimated filter coefficients, wherein an estimation is carried out so that a difference between said output signal and said estimated output signal is reduced, the filter comprising:

• an input signal register for holding a plurality of sampled input signals which have been sampled since a predetermined number of cycles before the current time;
• a filter coefficient register for holding said predetermined number of filter coefficients which respectively correspond to the plurality of sampled input signals;
• a convolution calculating means for calculating a convolution between said input signal and said estimated response characteristic using a plurality of successive sampled input signals which are held in said input signal register, and said estimated filter coefficients which are held in said filter coefficient register;
• an error obtaining means for obtaining a difference between said sampled output signal of said signal path and said convolution as an error in said estimation;
• and
• a filter coefficient estimating means for estimating said predetermined number of filter coefficients so that said error is reduced;
• said filter coefficient estimating means comprising a filter coefficient renewing means for each of said predetermined number of filter coefficients, for renewing the corresponding filter coefficient in each cycle of sampling, and wherein
• said filter coefficient renewing means comprises
• a multiplier for obtaining a product of one of said sampled output signals corresponding to the filter coefficient renewing means, and said sampled input signal,
• an accumulating means for accumulating an output of the multiplier,
• a power calculating means for calculating a power of said one of said sampled output signals corresponding to the filter coefficient renewing means,
• a divider for dividing an output of the accumulating by an output of the power calculating means, and
• an integrating means for integrating the output of said divider to extract a component of said filter coefficient corresponding to the filter coefficient renewing means.

An adaptive digital filter for estimating a response characteristic of a signal path by monitoring a sampled output signal of said signal path, estimating a predetermined number of filter coefficients which represent the response characteristic of the signal path, and generating an estimated output signal of said signal path using a plurality of successive sampled input signals of the signal path and estimated filter coefficients, wherein an estimation is carried out so that a difference between said output signal and said estimated output signal is reduced, the filter comprising:

• an input signal register for holding a plurality of sampled input signals which have been sampled since a predetermined number of cycles before the current time;
• a filter coefficient register for holding said predetermined number of filter coefficients which respectively correspond to the plurality of sampled input signals;
• a convolution calculating means for calculating a convolution between said input signal and said estimated response characteristic using a plurality of successive sampled input signals which are held in said input signal register, and said estimated filter coefficients which are held in said filter coefficient register;
• an error obtaining means for obtaining a difference between said sampled output signal of said signal path and said convolution as an error in said estimation;
• and
• a filter coefficient estimating means for estimating said predetermined number of filter coefficients so that said error is reduced;
• said filter coefficient estimating means comprising a filter coefficient renewing means for each of said predetermined number of filter coefficients, for renewing the corresponding filter coefficient in each cycle of sampling, and wherein
• said filter coefficient renewing means comprises a dividing means for dividing said sampled input signal by one of said sampled output signals corresponding to the filter coefficient renewing means,
• a zero detecting means for determining that said one of said sampled output signals corresponding to the filter coefficient renewing means is below a predetermined level,
• an integrating means for integrating the output of the said dividing means so that a component of said filter coefficient corresponding to the filter coefficient renewing means is extracted in an output thereof, and
• a stop control means for stopping the operation of said integrating means when said zero detecting means determines that said one of said sampled output signals corresponding to the filter coefficient renewing means is below the predetermined level.

An adaptive digital filter for estimating a response characteristic of a signal path by monitoring a sampled output signal of said signal path, estimating a predetermined number of filter coefficients which represent the response characteristic of the signal path, and generating an estimated output signal of said signal path using a plurality of successive sampled input signals of the signal path and estimated filter coefficients, wherein an estimation is carried out so that a difference between said output signal and said estimated output signal is reduced, the filter comprising:

• an input signal register for holding a plurality of sampled input signals which have been sampled since a predetermined number of cycles before the current time;
• a filter coefficient register for holding said predetermined number of filter coefficients which respectively correspond to the plurality of sampled input signals;
• a convolution calculating means for calculating a convolution between said input signal and said estimated response characteristic using a plurality of successive sampled input signals which are held in said input signal register, and said estimated filter coefficients which are held in said filter coefficient register;
• an error obtaining means for obtaining a difference between said sampled output signal of said signal path and said convolution as an error in said estimation;
• and
• a filter coefficient estimating means for estimating said predetermined number of filter coefficients so that said error is reduced;
• said filter coefficient estimating means comprising a filter coefficient renewing means for each of said predetermined number of filter coefficients, for renewing the corresponding filter coefficient in each cycle of sampling, and wherein
• m-th filter coefficient renewing means corresponding to m-th filter coefficient, where m is an integer satisfying 1.ltoreq.i.ltoreq.I where I is equal to said number of filter coefficients, comprises
• a low-pass filter for integrating said sampled input signals so that a component of said filter coefficient corresponding to the filter coefficient renewing means is extracted in the output thereof, and
• said low-pass filter comprises
• a first multiplier for multiplying each of said sampled input signals by a first factor which is equal to K.X.sub.j (m)/r, where K is a coefficient correction constant, X.sub.j (m) is the sampled input signal which have been sampled (m-1) cycles before the current time j, j denotes a number indicating a current time, and r denotes a value for normalizing the first factor,
• an adder,
• a delay means for delaying an output of said adder, and
• a second multiplier for multiplying an output of the delay means by a second factor which is equal to 1-K.X.sub.j (m).sup.2 /r,
• said adder adding outputs of the first and second multipliers, and the output of the adder becoming the output of said filter coefficient renewing means.

An adaptive digital filter for estimating a response characteristic of a signal path by monitoring a sampled output signal of said signal path, estimating a predetermined number of filter coefficients which represent the response characteristic of the signal path, and generating an estimated output signal of said signal path using a plurality of successive sampled input signals of the signal path and estimated filter coefficients, wherein an estimation is carried out so that a difference between said output signal and said estimated output signal is reduced, the filter comprising:

• an input signal register for holding a plurality of sampled input signals which have been sampled since a predetermined number of cycles before the current time;
• a filter coefficient register for holding said predetermined number of filter coefficients which respectively correspond to the plurality of sampled input signals;
• a convolution calculating means for calculating a convolution between said input signal and said estimated response characteristic using a plurality of successive sampled input signals which are held in said input signal register, and said estimated filter coefficients which are held in said filter coefficient register;
• an error obtaining means for obtaining a difference between said sampled output signal of said signal path and said convolution as an error in said estimation;
• and
• a filter coefficient estimating means for estimating said predetermined number of filter coefficients so that said error is reduced;
• said filter coefficient estimating means comprising a filter coefficient renewing means for each of said predetermined number of filter coefficients, for renewing the corresponding filter coefficient in each cycle of said sampling, and
• said filter coefficient renewing means comprising
• a first multiplier for multiplying each of said sampled output signals by a coefficient correction constant (K),
• a divider for dividing an output of the first multiplier by a value (r) for normalizing the first factor,
• a second multiplier for multiplying an output of the divider by one of the sampled output signals, and
• an adder for adding a previously estimated filter coefficient corresponding to the filter coefficient renewing means, to the output of the second multiplier.