Patent ID: 7096244

Claim:
A reference signal canceling apparatus comprising: a filter for extracting a reference signal; and a subtractor for subtracting an output from said filter from said reference signal, wherein said filter is constructed as a second-order bandpass Infinite Impulse Response (IIR) type digital filter with a transfer function H(Z) expressed by H ⁡ ( Z ) = ( a 0 + a 2 ⁢ Z - 2 ) ( 1 + b 1 ⁢ Z - 1 + b 2 ⁢ Z - 2 ) ; a first-order input feedback coefficient b 1 set at −1+2 −n ; and a second-order input feedback coefficient b 2 set at 1−2 −(n−1) , where n is an odd number of 3 or larger, wherein a zero-order output coefficient a 0 is set at 2 −n (a 0 =2 −n ) and a coefficient a 2 of a second-order output is set at −2 −n (a 2 =−2 −n ), and wherein the first-order input feedback coefficient b 1 and the second-order input feedback coefficient b 2 are set when a sampling pulse, for processing digital signal processing, is set to a frequency six times as large as a central frequency of a passing frequency band of the second-order bandpass IIR digital filter.