Patent ID: 7978799

Claim:
An adaptive digital filter comprising: a filter unit, implemented by at least one processor, that takes a complex signal as an input signal and that generates and outputs an output signal that is a complex signal generated by performing a convolution operation of the input signal and filter coefficients of a real signal; and a coefficient control unit, implemented by the at least one processor, that controls said filter coefficients based on an error between a target signal and an index value derived from said output signal, wherein said coefficient control unit includes: a common unit that generates and outputs a real signal that agrees with the error between said index value and said target signal; and a plurality of separate units provided for each multiplier for said convolution operation in said filter unit, the plurality of separate units calculating real filter coefficients to be used in a next sampling cycle based on: a signal obtained by converting a complex signal to a real number that is applied as an input to a corresponding multiplier, said real signal being received as an input from said common unit, and the current real filter coefficients.