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Patent US4910799A successfully refreshed from Google Patents.
US4910799A
Expired / Lapsed
US
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Noise reduction apparatus
Assignee: Denso Ten Ltd
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Filing: 1989-09-12
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Granted: 1990-03-20
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Expires: 2009-09-12
Abstract
Abstract A noise reduction apparatus in which an input signal is supplied to a first signal path (2) including a variable low-pass filter (2) and a second signal path (1), a control circuit (4) control is such that a cut-off frequency of the variable low-pass filter (2) is varied in accordance with a frequency of the input signal S(1), and an output signal is obtained from the first signal path when noise is generated and from the second signal path when noise is not generated.
Inventors
- 👤 Kazuo Takayama
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 13:36
CPC Classifications
H; H03; H03G; H03G5/00; H03G3/00; H03G3/20; H03G3/30; H03G3/34; H04; H04B; H04B1/00; H04B1/06; H04B1/10; H04B1/1027; H04B1/1081
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
176 words
A noise reduction apparatus for removing noise superimposed on an input signal having a phase and a frequency including a major component, comprising: noise detecting circuit means for detecting the noise in the input signal; first signal path means including a variable low-pass filter having a variable cut-off frequency that varies in response to a control signal, for receiving the input signal and for providing an output responsive the input signal and said variable cut-off frequency so that the output includes all frequencies below the cut-off frequency; second signal path means for receiving and providing as an output the input signal; control circuit means for providing the control signal for controlling the cut-off frequency of said low-pass filter such that said cut-off frequency is varied in accordance with the frequency of the input signal; and selecting circuit means for selecting the output signal from said first signal path means when noise is detected by said noise detecting circuit means and for selecting the output signal from said second signal path when the noise is not detected.
Claim 2
Dependent Claim
176 words
A noise reduction apparatus for removing noise superimposed on an input signal having a phase and a frequency including a major component, comprising: noise detecting circuit means for detecting the noise in the input signal; first signal path means including a variable low-pass filter having a variable cut-off frequency that varies in response to a control signal, for receiving the input signal and for providing an output responsive the input signal and said variable cut-off frequency so that the output includes all frequencies below the cut-off frequency; second signal path means for receiving and providing as an output the input signal; control circuit means for providing the control signal for controlling the cut-off frequency of said low-pass filter such that said cut-off frequency is varied in accordance with the frequency of the input signal; and selecting circuit means for selecting the output signal from said first signal path means when noise is detected by said noise detecting circuit means and for selecting the output signal from said second signal path when the noise is not detected.
Claim 3
Dependent Claim
32 words
An apparatus according to claim 1, wherein said control circuit control means includes: means for controlling the cut-off frequency so that it substantially coincides with the major component of the input signal.
Claim 4
Dependent Claim
51 words
An apparatus according to claim 1, wherein said control circuit means includes: means for comparing the output signal of said first signal path means with the output signal of said second signal path means and for controlling the cut-off frequency of said variable low-pass filter in accordance with the comparison result.
Claim 5
Dependent Claim
40 words
An apparatus according to claim 3, wherein said control circuit means further includes: means for controlling the output signals of said first and second signal path means so as to substantially coincide with each other, based on the comparison result.
Claim 6
Dependent Claim
42 words
An apparatus according to claim 3, wherein said control circuit means further includes: means for controlling the output signals of said first and second signal path means so as to generate a predetermined difference between these signals, based on the comparison result.
Claim 7
Dependent Claim
43 words
An apparatus according to claim 1, wherein said control circuit means includes: holding circuit means for fixing an output signal of said control circuit means to a level that was outputted just before the noise was detected by said noise detecting circuit means.
Claim 8
Dependent Claim
22 words
An apparatus according to claim 1, wherein said second signal path means includes: phase shifter means for phase shifting the input signal.
Claim 9
Independent Claim
88 words
An apparatus according to any one of claims 1 to 6, wherein said low pass filter has a phase-frequency characteristic and said second signal path means includes: variable phase shifter means, having a phase-frequency characteristic, for shifting the phase of the input signal by an amount based on an output signal of said control circuit means; and means for controlling the amount of phase shift by said variable phase shifter means so that said variable phase shifter has the same phase-frequency characteristic as that of said low-pass filter.
Claim 10
Dependent Claim
129 words
An apparatus according to claim 3, wherein said control circuit means further comprises: first detector means for detecting the output signal of said second signal path means and for providing an output responsive to said detection; second detector means for detecting an output signal of said variable low-pass filter and for providing an output responsive to said detection; differential voltage supply circuit means for varying the output of one of said first and second detector means; differential amplifier means for differentially amplifying the output of the other one of said second and first detector means and said differential voltage supply circuit means; and holding circuit means for holding an output signal of said differential amplifier to be constant when the noise is detected by said noise detection circuit means.
Claim 11
Dependent Claim
53 words
An apparatus according to claim 1, wherein said noise detecting circuit means has a variable sensitivity, and includes: means for varying the sensitivity so that the sensitivity is decreased as the frequency of the input signal is increased, so that noise reduction processing is suppressed as the frequency of the input signal increases.
Claim 12
Dependent Claim
28 words
An apparatus according to claim 10, wherein said noise detecting circuit means includes means for varying the sensitivity in accordance with an output signal of said control circuit.
Claim 13
Dependent Claim
60 words
An apparatus according to claim 1, wherein the input signal has a level, and said control circuit means includes: means for controlling the cut-off frequency of said low-pass filter in accordance with the frequency of the input signal so that the cut-off frequency is higher when the input signal level is high than when the input signal level is low.
Claim 14
Dependent Claim
65 words
An apparatus according to claim 1, wherein the noise has a level and said apparatus further comprises: means for detecting the noise level; and means for controlling the cut-off frequency of said low-pass filter in accordance with the frequency of the input signal so that the cut-off frequency is lower when a detected noise level is high than when the detected noise level is low.
Claim 15
Dependent Claim
60 words
An apparatus according to claim 1, wherein said control circuit means includes: means for comparing the signal received by said first signal path means and the signal outputted by said first signal path means; and means for providing feedback-control such that both signals substantially coincide with each other so as to regulate the cut-off frequency of said variable low-pass filter.
Claim 16
Dependent Claim
13 words
An apparatus according to claim 1, wherein said apparatus comprises an analog circuit.
Claim 17
Dependent Claim
13 words
An apparatus according to claim 1, wherein said apparatus comprises a digital circuit.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-03-19 | 1993-09-18 | 1994-03-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-03-19 | 1997-09-18 | 1998-03-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-03-19 | 2001-09-18 | 2002-03-20 | $7700.00 | Window Closed / Lapsed |