Digital signal processing apparatus

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;
• an edge-detection circuit for detecting an edge of a sign signal output by said digital filter and for generating a set pulse;
• a period measuring circuit for generating a measurement of period changes in the sign signal which is output by said digital filter;
• a threshold holding circuit for setting a threshold equal to a period of an intermediate frequency between a normal frequency band and an 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 reset pulse when the period is not larger than the threshold;
• and
• a detection register outputting a first signal when said set pulse is received as input thereby placing said detection register in a set state and outputting a second signal when said reset pulse is input thereby placing said detector register in said reset state.

A digital signal processing apparatus comprising:

• a digital filter performing half-band processing on a digital signal to output a processed signal and a sign signal;
• and
• an anti-aliasing circuit coupled to said digital filter to suppress or remove an aliasing noise from said processed signal by use of said sign signal a period measuring circuit for measuring a changing period of the sign signal outputted by said digital filter;
• a threshold holding circuit for holding a period of an intermediate frequency between the normal band and the aliasing band;
• a comparator for comparing and determining whether or not the period measured by said period measuring circuit is larger than the threshold which is set to said threshold holding circuit and for outputting a shift control signal when it is determined that the period measured by said period measuring circuit is not larger than the threshold;
• and a shift register for shifting a signal which is inputted from said digital filter and is stored, based on said shift control signal, and for suppressing an amplitude of the aliasing noise.