Removing low frequency interference in a digital FM receiver

In a digital FM receiver, a demodulator apparatus comprising:

• input means for receiving a radio signal;
• means for converting the radio signal into a phase sample;
• means for removing a low-frequency interference signal from the phase sample, comprising:
• first means for converting the phase sample into a frequency sample;
• high-pass filter means for removing, from the frequency sample, energy associated with frequencies below a predetermined frequency, the high-pass filter means supplying a filtered frequency sample at a filter output;
• and
• second means for converting the filtered frequency sample into a filtered phase sample;
• detection means for detecting the presence of the low-frequency interference signal in the radio signal;
• selection means, operatively coupled to the detection means, for alternatively selecting, as an output from the selection means, the phase sample when the low-frequency interference signal is not detected in the radio signal, or the filtered phase sample when the low-frequency interference signal is detected in the radio signal;
• and
• demodulation means for generating a demodulated signal on the basis of the output from the selection means.

In a digital FM receiver, a demodulator apparatus comprising:

• input means for receiving a radio signal;
• means for converting the radio signal into an original phase sample;
• means for removing a low-frequency interference signal from the original phase sample, comprising:
• first means for converting the original phase sample into a frequency sample;
• high-pass filter means for removing, from the frequency sample, energy associated with frequencies below a predetermined frequency, the high-pass filter means supplying a filtered frequency sample at a filter output;
• and
• second means for converting the filtered frequency sample into a filtered phase sample;
• first demodulation means for generating a corrected demodulated signal from the filtered phase sample;
• second demodulation means for generating a non-corrected demodulated signal from the original phase sample;
• first error detection means for detecting a first quantity of errors contained in the corrected demodulated signal;
• second error detection means for detecting a second quantity of errors contained in the non-corrected demodulated signal;
• selection means, operatively coupled to the first and second demodulation means and to the first and second error detection means, for alternatively selecting, as an output from the selection means, either the corrected demodulated signal or the non-corrected demodulated signal on the basis of a comparison of the first quantity of errors with the second quantity of errors.

In a digital FM receiver having a demodulator that receives a radio signal and generates therefrom a phase sample whose behavior determines an output of the demodulator, a method of removing a low-frequency interference signal from the phase sample, comprising the steps of:

• receiving the phase sample;
• converting the phase sample into a frequency sample;
• removing, from the frequency sample, energy associated with frequencies below a predetermined frequency to produce a filtered frequency sample;
• and
• converting the filtered frequency sample into a filtered phase sample.

In a digital FM receiver, a method of demodulating a radio signal, comprising the steps of:

• receiving the radio signal;
• converting the radio signal into a phase sample;
• performing a procedure to remove a low-frequency interference signal from the phase sample, the procedure comprising the steps of:
• converting the phase sample into a frequency sample;
• removing, from the frequency sample, energy associated with frequencies below a predetermined frequency to produce a filtered frequency sample;
• and
• converting the filtered frequency sample into a filtered phase sample;
• detecting the presence of the low-frequency interference signal in the radio signal;
• alternatively selecting, for use as a selected phase sample, the phase sample when the low-frequency interference signal is not detected in the radio signal, or the filtered phase sample when the low-frequency interference signal is detected in the radio signal;
• and
• generating a demodulated signal on the basis of the selected phase sample.

In a digital FM receiver, a method of demodulating a radio signal, comprising the steps of:

• receiving the radio signal;
• converting the radio signal into an original phase sample;
• performing a procedure for removing a low-frequency interference signal from the original phase sample, the procedure comprising the steps of:
• converting the original phase sample into a frequency sample;
• removing, from the frequency sample, energy associated with frequencies below a predetermined frequency to produce a filtered frequency sample;
• and
• converting the filtered frequency sample into a filtered phase sample;
• generating a corrected demodulated signal from the filtered phase sample;
• generating a non-corrected demodulated signal from the original phase sample;
• detecting a first quantity of errors contained in the corrected demodulated signal;
• detecting a second quantity of errors contained in the non-corrected demodulated signal;
• alternatively selecting either the corrected demodulated signal or the non-corrected demodulated signal on the basis of a comparison of the first quantity of errors with the second quantity of errors.