MODIFIED TIME DOMAIN COMB FILTERS

• US 3,691,486 A
• Filed: 09/02/1970
• Issued: 09/12/1972
• Est. Priority Date: 09/02/1970
• Status: Expired due to Term

• Current Assignee: Michael Howard Borsuk, Paul Nolan Browne
• Original Assignee: Michael Howard Borsuk, Paul Nolan Browne
• Inventors: Borsuk, Michael Howard, Browne, Paul Nolan
• Primary Examiner(s): Gensler, Paul L.
• Application Number:
  US05/068,905
• Time in Patent Office: 741 Days
• Field of Search: 333/70,29,28,18,7T 328/167
• US Class Current: 333/166
• CPC Class Codes: H03H 15/00 Transversal filters electromechanical filters H03H9/46, H03H9/70
• CPC Class Codes: H03H 17/0251 Comb filters

Abstract

A delay line type comb filter is adapted to produce a response in which a selected portion of the comb characteristic is modified. This is accomplished by attenuating the signal through the delay line in a predetermined manner over a selected frequency range and inversely modifying the nondelayed transmission in that range. These two functions are provided by applying the input signal to a filter element having a transfer function appropriate to the desired modification and combining the filtered output with the input signal in two combiners (one additive and one subtractive). The differential resultant signal is applied to the delay line to produce the prescribed attenuation and the additive resultant signal (enhanced inversely to the differential resultant) is added to the output of the delay line producing the desired modified comb transmission characteristic.

Claims

1. A modified comb characteristic filter responsive to an input signal comprising:

means for filtering the input signal to produce a filtered output having a selected transmission characteristic, a first means for combining the input signal with the filtered output to produce an inverse signal having the inverse transmission characteristic of the filtered signal, a second means for combining the input signal and the filtered output to produce an enhanced signal having the filtered transmission characteristic superposed upon the input signal, means for delaying the inverse signal and a third means for combining the delayed inverse signal with the enhanced signal to produce a modified comb characteristic output.

2. A modified comb characteristic filter of claim 1 wherein the selected transmission characteristic of said filtering means is normalized to one in its passbands.

3. A modified comb characteristic filter of claim 1 wherein the selected transmission characteristic of said filtering means provides unity transmission in a selected passband whereby the output of said comb characteristic filter has an unattenuated transmission response through out the selected passband.

4. A modified comb characteristic filter of claim 1 wherein the selecteD transmission characteristic of said filtering means provides zero transmission in a selected rejection band whereby the output of said comb characteristic filter has a comb characteristic response exclusively within the rejection band.

5. A modified comb characteristic filter of claim 1 wherein said delaying means provides a fixed delay of time T and said third means for combining is additive, whereby the frequencies of the nulls of the output comb response are odd multiples of 1/2T.

6. A modified comb characteristic filter of claim 1 wherein said delaying means provides a fixed delay of time T and said third means for combining is differential and subtracts the delayed inverse signal from the enhanced signal, whereby the frequencies of the nulls of the output comb response are 0 and multiples of 1/T.

7. A modified comb characteristic filter of claim 1 wherein said third means for combining includes means for attenuating the output signal by one-half.

8. A comb filter responsive to an input signal comprising:

a first path for said input signal, a second path for said input signal including a delay different from said first path, means for combining signals from said first and second paths to produce a comb characteristic output, means for modifying said characteristic such that its magnitude exists in inverse proportion to a preselected transmission characteristic, said last means including filter means having said preselected transmission characteristic for filtering a portion of the frequency spectrum of said input signal, and means for combining the output of said filter means with the signals in each of said paths, wherein said last combining means combines the output of said filter means in respectively different signs in each of said paths.

9. A comb filter of claim 8 wherein said filter means has a bandpass characteristic of unity transmission between a first and a second frequency and said modified comb filter produces unity transmission between said first and second frequencies.

10. A comb filter of claim 8 wherein said filter means has a rejection characteristic and unity transmission below and above a first and a second frequency, respectively, and wherein said modified comb filter provides a comb response exclusively between said first and second frequencies.

11. A time domain configuration responsive to an input signal including a first path for said input signal, a second path for said input signal including a delay different from said first path and means for combining signals from said first and second paths to produce a comb characteristic output, characterized in that said configuration further includes:

means for modifying said characteristic such that its magnitude exists in inverse proportion to a preselected transmission characteristic, said last means including filter means having said preselected transmission characteristic for filtering a portion of the frequency spectrum of said input signal, and means for combining the output of said filter means with the signals in each of said paths, wherein said last combining means combines the output of said filter means in respectively different signs in each of said paths.