Patent EP0253902A1 successfully refreshed from Google Patents.
EP0253902A1
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EP
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Noise reduction apparatus and method
Assignee: Denso Ten Ltd
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Filing: 1987-01-24
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Granted: —
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Expires: 2007-01-24
Abstract
Abstract Input signals are guided into a first signal path which includes a variable low-pass filter, and into a second signal path. A control circuit so controls that the cut-off frequency of the variable low-pass filter changes with the frequency of the input signals. When the noise is being generated, the output signals are obtained through the first signal path. When no noise is being generated, the output signals are obtained through the second signals path.
Inventors
- 👤 Kazuo Takayama
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 20:07
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
128 words
A noise reduction apparatus for removing noise superimposed on an input signal, comprising: a noise detecting circuit for detecting the noise from the input signal; a first signal path including a variable low-pass filter capable of varying a cut-off frequency, for outputting the input signal through said variable filter; a second signal path through which the input signal is passed; a control circuit for controlling the cut-off frequency of said variable low-pass filter such that said frequency is varied in accordance with a frequency of the input signal; and a selecting circuit for selecting an output signal from said first signal path when the noise is detected by said noise detecting circuit and selecting an output signal from said second signal path when the noise is not detected.
Claim 2
Dependent Claim
128 words
A noise reduction apparatus for removing noise superimposed on an input signal, comprising: a noise detecting circuit for detecting the noise from the input signal; a first signal path including a variable low-pass filter capable of varying a cut-off frequency, for outputting the input signal through said variable filter; a second signal path through which the input signal is passed; a control circuit for controlling the cut-off frequency of said variable low-pass filter such that said frequency is varied in accordance with a frequency of the input signal; and a selecting circuit for selecting an output signal from said first signal path when the noise is detected by said noise detecting circuit and selecting an output signal from said second signal path when the noise is not detected.
Claim 3
Dependent Claim
30 words
An apparatus according to claim 1, wherein said control circuit control is such that the cut-off frequency substantially coincides with a frequency of a major component of the input signal.
Claim 4
Dependent Claim
46 words
An apparatus according to claim 1, wherein said control circuit compares an output signal level of said first signal path with an output signal level of said second signal path and feedback-controls the cut-off frequency of said variable low-pass filter in accordance with the comparison result.
Claim 5
Dependent Claim
28 words
An apparatus according to claim 3, wherein the output signals of said first and second signal paths are made to substantially coincide with each other by the comparison.
Claim 6
Dependent Claim
25 words
An apparatus according to claim 3, wherein a predetermined difference is generated between the output signals of said first and second signal paths by,the comparison.
Claim 7
Dependent Claim
42 words
An apparatus according to claim 1, wherein said control circuit has a holding circuit for fixing an output signal of said control circuit to a value just before the noise is generated when the noise is detected by said noise detecting circuit.
Claim 8
Dependent Claim
37 words
An apparatus according to claim 1, wherein said second signal path includes a phase shifter for supplying a fixed shifted phase for compensating for a phase delay of an input signal generated in said first signal path.
Claim 9
Independent Claim
59 words
An apparatus according to any one of claims 1 to 6, wherein said second signal path includes a variable phase shifter capable of varying a shifted phase, and the shifted phase is controlled by an output signal of said control circuit so that said variable phase shifter has the same phase-frequency characteristic as that of said variable low-pass filter.
Claim 10
Dependent Claim
106 words
An apparatus according to claim 3, wherein said control circuit comprises a first detector for detecting an output signal of said variable phase shifter, a second detector for detecting an output signal of said variable low-pass filter, a differential voltage supply circuit for supplying a differential voltage to an output signal of said first or second detector, a differential amplifier for differentially amplifying a difference between output signals of said second or first detector and said differential voltage supplying circuit, and a holding circuit for holding an output signal of said differential amplifier to be constant when the noise is detected by said noise detection circuit.
Claim 11
Dependent Claim
41 words
An apparatus according to claim 1, wherein noise detection sensitivity of said noise detecting circuit is decreased as a 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
34 words
An apparatus according to claim 10, wherein a comparison reference voltage for determining a noise detecting level of said noise detecting circuit is varied in accordance with an output signal of said control circuit.
Claim 13
Dependent Claim
48 words
An apparatus according to claim 1, wherein a cut-off frequency of said variable low-pass filter set in accordance with the frequency of the input signal is set at a frequency that is higher when an input signal level is high than when the input signal level is low.
Claim 14
Dependent Claim
59 words
An apparatus according to claim 1, further comprising a circuit for detecting the noise level, and wherein the cut-off frequency of said variable low-pass filter set in accordance with a frequency of the input signal is set at a lower frequency that is lower when a detected noise level is high than when the detected noise level is low.
Claim 15
Dependent Claim
45 words
An apparatus according to claim 1, wherein said control circuit compares signal levels at input and output sides of said variable low-pass filter and feedback-controls such that the both signals substantially coincide with each other, thereby regulating the cut-off frequency of said variable low-pass filter.
Claim 16
Dependent Claim
17 words
15 . An apparatus according to claim 1, wherein said apparatus is constituted by an analog circuit.
Claim 17
Dependent Claim
15 words
An apparatus according to claim 1, wherein said apparatus is constituted by a digital circuit.
References Cited (Backward Citations)
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