Patent ID: 7031412

Claim:
A digital signal processing apparatus comprising: an A/D converter for converting an analog input signal into a digital signal; a digital filter performing half-band processing to a sample output of said digital signal, and attenuating a frequency component other than a predetermined normal frequency band included in the sample output; and an anti-aliasing circuit for suppressing or removing aliasing noise having an aliasing frequency band caused by the half-band processing in said digital filter, said noise is suppressed or removed using a sign signal output from said digital filter a period measuring circuit for generating measurement of period changes in the sign signal output by said digital filter; a threshold holding circuit for setting a threshold equal to a period of an intermediate frequency between the normal frequency band and the aliasing frequency band; a comparator for comparing and determining whether or not the period measured by said period measuring circuit is larger than the threshold, and for outputting a shift control signal when it is determined that the measurement of said period measuring circuit is not larger than the threshold; and a shift register for shifting a signal which is input from said digital filter and stored, based on said shift control signal, and for suppressing an amplitude of the aliasing noise.