Digital filter and reference signal cancelling device and method using the same

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
• ⁡
• (
• 1
• -
• Z
• -
• 2
• )
• (
• 1
• +
• b
• 1
• ⁢
• Z
• -
• 1
• +
• b
• 2
• ⁢
• Z
• -
• 2
• )
• ,
• a first-order input feedback coefficient b1 set at −1+2−n;
• and
• a second-order input feedback coefficient b2 set at 1−2−(n−1), where n is an odd number of 3 or larger,
• wherein a second-order output is subtracted from a zero-order output and the subtraction result is multiplied by a (a=2−n), and
• wherein the first-order input feedback coefficient b1 and the second-order input feedback coefficient b2 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.

A reference signal canceling apparatus comprising:

• a filter for extracting a reference signal contained in a frequency modulation (FM) detected signal;
• and
• a subtracter for subtracting an output from the filter from said FM detected 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
• 1
• ⁢
• Z
• -
• 1
• +
• a
• 2
• ⁢
• Z
• -
• 2
• )
• (
• 1
• +
• b
• 1
• ⁢
• Z
• -
• 1
• +
• b
• 2
• ⁢
• Z
• -
• 2
• )
• ,
• and when a sampling pulse for processing digital signal processing is set to a frequency is six times as large as a central frequency of a passing frequency band of the second-order bandpass IIR digital filter, a first-order input feedback coefficient b1 is set at −1+2−n and a second-order input feedback coefficient b2 is set at 1−2−(n−1), where n is an odd number of 3 or larger, and a0, a1, and a2 are output coefficients having real values.

A method of canceling a reference signal in a reference signal canceling apparatus having a filter for extracting a reference signal contained in a frequency modulation (FM) detected signal and a subtracter for subtracting an output from the filter from said FM detected signal, said method comprising:

• constructing said filter as a second-order bandpass Infinite Impulse Response (IIR) type digital filter with a transfer function
• H
• ⁡
• (
• Z
• )
• =
• (
• a
• 0
• +
• a
• 1
• ⁢
• Z
• -
• 1
• +
• a
• 2
• ⁢
• Z
• -
• 2
• )
• (
• 1
• +
• b
• 1
• ⁢
• Z
• -
• 1
• +
• b
• 2
• ⁢
• Z
• -
• 2
• )
• ;
• setting a first-order input feedback coefficient b1 at −1+2−n;
• and
• setting a second-order input feedback coefficient b2 at 1−2−(n−1), where n is an odd number of 3 or larger, and a0, a1, and a2 are output coefficients having real values,
• wherein the first-order input feedback coefficient and the second-order input feedback coefficient 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.