Adaptive tracking notch filter system

A tracking notch filter system comprising:

• a notch filter for filtering an input signal to produce an output signal;
• a dither signal applied to the notch filter to dither a notch center frequency of the filter;
• and
• a feedback circuit comprising:
• a first band pass filter coupled to receive the output signal of the notch filter and pass a select frequency band of the output signal;
• a rectifier receiving and rectifying a signal from the first band pass filter;
• a second band pass filter receiving a signal from the rectifier and passing a dither frequency component of the received signal;
• a synchronous demodulator receiving a signal from the second band pass filter and synchronously demodulating the received signal with the dither signal;
• and
• an integrator circuit receiving and integrating a signal from the synchronous demodulator, an output of the integrator circuit being applied to the notch filter in combination with the dither signal.

A tracking notch filter system for tracking and suppressing a large-magnitude, narrow band portion of a notch filter input signal comprising:

• a bridged-T notch filter for filtering the input signal to produce an output signal;
• a dither signal generator applying a dither signal to the notch filter such that the notch center frequency fluctuates at the frequency of the dither signal;
• a feed-forward circuit generating a DC scaling signal having a magnitude proportional to the magnitude of said narrow band input signal portion;
• and
• a feedback circuit coupled to receive the filter output signal, the feedback circuit comprising:
• a first band pass filter passing the frequency band of the narrow band, large-magnitude input signal portion;
• a rectifier receiving and rectifying a signal input from the first band pass filter;
• a second band pass filter passing a dither frequency component of a signal received from the rectifier;
• a scaler dividing the output of the second band pass filter by said scaling signal;
• a synchronous demodulator multiplying the output of the scaler by the dither signal;
• and
• an integrator circuit integrating the output of the synchronous demodulator, the output of the integrator being applied to the control input of the notch filter in combination with the dither signal.

Method of tracking and attenuating select frequencies of an input signal, comprising:

• providing an attenuation filter for filtering the input signal to produce an output signal;
• applying an alternating dither signal to the filter to dither a center frequency of the filter;
• feeding back a signal from the output of the attenuation filter, the feedback signal containing a component of the output signal resulting from the dither of the attenuation filter center frequency;
• and
• applying the feedback signal to the attenuation filter in combination with the dither signal to vary the center frequency of the filter for increased attenuation of said select frequencies.

A method of tracking and attenuating a narrow band, large-magnitude portion of an input signal, the method comprising:

• providing a notch filter for filtering the input signal to produce an output signal;
• applying a dither signal to the notch filter to dither a center frequency of the notch filter;
• filtering with a first band pass filter an output of the notch filter to pass a frequency band containing frequencies of said narrow band;
• rectifying an output of the first band pass filter;
• filtering with a second band pass filter an output of the rectifier to pass a band of frequencies containing the dither frequency;
• synchronously demodulating an output of the second band pass filter signal with the dither signal;
• integrating the synchronously demodulated signal with an integrator circuit;
• and
• applying the output of the integrator circuit to the notch filter tn combination with the dither signal to vary the notch center frequency of the notch filter to better attenuate the narrow band input signal portion.