Patent US5745581A successfully refreshed from Google Patents.
US5745581A
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Tracking filter for periodic signals
Assignee: Noise Cancellation Technologies Inc
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Filing: 1996-07-26
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Granted: 1998-04-28
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Expires: 2016-07-26
Abstract
Abstract A method for designing a frequency periodic filter with a frequency response which has a periodic bandwidth including designing a first sampled data filter whose response corresponds to a set period and replacing each unit sampling delay by a second sampled data filter.
Inventors
- 👤 Graham P. Eatwell
- 👤 Yong J. Yan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 13:37
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1291; H03H17/00; H03H17/02; H03H17/0248; H03H17/0251
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
92 words
A method for designing a frequency periodic filter with a frequency response which is substantially periodic in some bandwidths, said filter including filter coefficients and effective delay elements, said method comprising, determining said filter coefficients by designing a first sampled data filter, said first filter including said filter coefficients and unity delay elements, such that the frequency response of said first filter corresponds to one period of the desired frequency response, setting said effective delay elements to have an effective delay proportional to the reciprocal of the period of said frequency response.
Claim 2
Independent Claim
92 words
A method for designing a frequency periodic filter with a frequency response which is substantially periodic in some bandwidths, said filter including filter coefficients and effective delay elements, said method comprising, determining said filter coefficients by designing a first sampled data filter, said first filter including said filter coefficients and unity delay elements, such that the frequency response of said first filter corresponds to one period of the desired frequency response, setting said effective delay elements to have an effective delay proportional to the reciprocal of the period of said frequency response.
Claim 3
Dependent Claim
23 words
A method as in claim 1 in which each frequency periodic filter is a finite impulse response filter with one or more coefficients.
Claim 4
Dependent Claim
23 words
A method as in claim 1 in which each frequency periodic filter is an infinite impulse response filter with one or more coefficients.
Claim 5
Dependent Claim
17 words
A method as in claim 1 in which the first sampled data filter is a high-pass filter.
Claim 6
Dependent Claim
17 words
A method as in claim 1 in which the first sampled data filter is a low-pass filter.
Claim 7
Dependent Claim
17 words
A method as in claim 1 in which the first sampled data filter is a band-pass filter.
Claim 8
Dependent Claim
28 words
A method as in claim 1 in which the sampling frequency of said frequency periodic filter is an integer multiple of the period of said desired frequency response.
Claim 9
Independent Claim
92 words
A method for substantially removing periodic noise or interference from an input signal, said method comprising: passing said input signal through a first sampled data filter to produce a filtered input signal; passing said filtered input signal through a frequency periodic filter, said filter containing weighing coefficients and second sampled data filters, to obtain an output signal; adjusting a delay produced by each second sampled data filter according to the fundamental period of the periodic noise or interference; wherein each second sample data filter contains weighing coefficients and unit sample delay elements.
Claim 10
Independent Claim
92 words
A method for substantially removing periodic noise or interference from an input signal, said method comprising: passing said input signal through a first sampled data filter to produce a filtered input signal; passing said filtered input signal through a frequency periodic filter, said filter containing weighing coefficients and second sampled data filters, to obtain an output signal; adjusting a delay produced by each second sampled data filter according to the fundamental period of the periodic noise or interference; wherein each second sample data filter contains weighing coefficients and unit sample delay elements.
Claim 11
Dependent Claim
32 words
A method as in claim 8 in which said input signal is a communications signal obtained from a microphone, and said output signal is adapted to be provided to a communications system.
Claim 12
Dependent Claim
34 words
A method as in claim 8 including the steps of: determining the period of said periodic noise or interference; and varying the coefficients of the second sampled data filter in relation to said period.
Claim 13
Dependent Claim
16 words
A method as in claim 10 in which said period is determined from said input signal.
Claim 14
Dependent Claim
27 words
A method as in claim 10 in which said period is determined from an additional input signal which is time related to the cause of said interference.
Claim 15
Dependent Claim
30 words
A method as in claim 12 in which two or more frequency periodic filters are arranged in series so as to remove the periodic noise from two or more sources.
Claim 16
Dependent Claim
28 words
A method as in claim 12 in which said input signal is a communications signal obtained from a microphone, said output signal is provided to a communications system.
Claim 17
Dependent Claim
33 words
A method as in claim 8 in which the coefficients of said first sampled data filter are set to predetermined values according to the rate of change of the frequencies of the interference.
Claim 18
Dependent Claim
18 words
A method as in claim 8 and including providing a signal to switch between different frequency periodic filters.
Claim 19
Independent Claim
124 words
A system for removing periodic noise or interference from an input signal, said system comprising: first input means for receiving said input signal; second input means for receiving a reference signal from which the period of said periodic noise or interference can be determined; a frequency periodic filter for filtering said input signal, said frequency periodic filter including fixed filter coefficients and variable effective delays, each effective delay being associated with one or more of the filter coefficients; output means to provide an output signal corresponding to said input signal minus the periodic noise or interference, characterized in that the effective delays in said frequency periodic filter are adjusted to be proportional to the reciprocal of the period of said periodic noise or interference.
Claim 20
Independent Claim
124 words
A system for removing periodic noise or interference from an input signal, said system comprising: first input means for receiving said input signal; second input means for receiving a reference signal from which the period of said periodic noise or interference can be determined; a frequency periodic filter for filtering said input signal, said frequency periodic filter including fixed filter coefficients and variable effective delays, each effective delay being associated with one or more of the filter coefficients; output means to provide an output signal corresponding to said input signal minus the periodic noise or interference, characterized in that the effective delays in said frequency periodic filter are adjusted to be proportional to the reciprocal of the period of said periodic noise or interference.
Claim 21
Dependent Claim
15 words
A system as in claim 17 wherein said frequency periodic filter includes a tachometer means.
Claim 22
Dependent Claim
31 words
A system as in claim 17 wherein said system includes an automatic gain control on the input means which allows for a sampler with a smaller dynamic range to be used.
Claim 23
Dependent Claim
20 words
A system as in claim 17 including a microphone means which provides said input signal to said first input means.
Claim 24
Dependent Claim
18 words
A system as in claim 17 and including a communication system to which said output signal is provided.
Claim 25
Dependent Claim
29 words
A system as in claim 21, wherein said microphone means provides said input signal to said first input means and said output signal is provided to said communication system.
References Cited (Backward Citations)
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