Tunable bandpass filter system and filtering method

A bandpass filter system for operating on an input signal having a fundamental frequency, said system comprising:

• (a) a tunable bandpass filter whose bandwidth is controllable, said bandpass filter comprising a constant quality factor filter whose quality factor and center frequency are adjustable, said bandwidth being controlled by adjusting said center frequency;
• (b) bandwidth tuning means for controlling said bandwidth as a function of said fundamental frequency;
• and
• (c) harmonic number tuning means for adjusting said quality factor in inverse proportion to the number of a selected harmonic of said fundamental frequency and adjusting said center frequency in direct proportion to said harmonic number.

A bandpass filter system for operating on an input signal having a fundamental frequency, said system comprising:

• (a) a tunable constant bandwidth bandpass filter whose center frequency is adjustable, whose bandwidth is controllable and which produces a filtered output signal;
• (b) bandwidth tuning means for controlling said bandwidth as a function of said fundamental frequency, said bandwidth tuning means including means for computing the quotient of said fundamental frequency divided by a selected bandpass filter quality factor and adjusting said filter bandwidth to be proportional to said quotient, and center frequency tuning means for adjusting said center frequency to be proportional to the product of said fundamental frequency and the number of a selected harmonic of said fundamental frequency;
• and
• (c) means for measuring the amplitude of said output signal to determine the amount of distortion in said input signal.

A bandpass filter system for operating on an input signal having a fundamental frequency, said system comprising:

• (a) a tunable constant quality factor bandpass filter whose center frequency is adjustable, whose bandwidth is controllable and which produces a filtered output signal;
• (b) bandwidth tuning means for controlling said bandwidth as a function of said fundamental frequency;
• (c) harmonic number tuning means for adjusting said quality factor in inverse proportion to the number of a selected harmonic of said fundamental frequency;
• (d) center frequency tuning means for adjusting said center frequency to be proportional to the product of said fundamental frequency and said harmonic number;
• and
• (e) means for measuring the amplitude of said output signal to determine the amount of distortion in said input signal.

A method for filtering a signal having a fundamental frequency, comprising the steps of:

• (a) applying said signal as an input signal to a constant quality factor tunable bandpass filter whose center frequency is adjustable, whose quality factor is adjustable and whose bandwidth is controllable;
• (b) controlling said bandwidth by adjusting said center frequency as a function of said fundamental frequency;
• and
• (c) adjusting said quality factor in inverse proportion to the number of a selected harmonic of said fundamental frequency;
• and
• (d) adjusting said center frequency in direct proportion to said harmonic number.

A method for filtering a signal having a fundamental frequency, comprising the steps of:

• (a) applying said signal as an input to a constant bandwidth tunable bandpass filter whose center frequency is adjustable, whose bandwidth is controllable and which produces a filtered output signal;
• (b) controlling said bandwidth as a function of said fundamental frequency by computing the quotient of said fundamental frequency divided by selected bandpass filter quality factor, adjusting said filter bandwidth to be proportional to said quotient, and adjusting said center frequency to be proportional to the product of said fundamental frequency and the number of a selected harmonic of said fundamental frequency;
• and
• (c) measuring the amplitude of said output signal to determine the amount of distortion in said input signal.

A method for filtering a signal having a fundamental frequency, comprising the steps of:

• (a) applying said signal as an input signal to a constant quality factor tunable bandpass filter whose center frequency is adjustable, whose bandwidth is controllable and which produces a filtered output signal;
• (b) controlling said bandwidth as a function of said fundamental frequency by adjusting said quality factor in inverse proportion to said harmonic number and adjusting said center frequency to be proportional to the product of said fundamental frequency and the number of a selected harmonic of said fundamental frequency;
• and
• (c) measuring the amplitude of said output signal to determine the amount of distortion in said input signal.