JP2004096407A - Noise detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise detecting device for detecting noise included in an electric signal, with higher accuracy. <P>SOLUTION: A noise component Sb included in an input signal Sin is extracted by a noise extracting unit 13. The noise component Sb is smoothed at a pre-cut unit 14 to obtain a signal Sg, and a pre-cut signal Sf is generated by restricting the noise component Sb to a level lower than the signal Sg. The pre-cut signal Sf is supplied to a charging/discharging circuit 16 of a high-speed charging and low-speed discharging type, and a so-called threshold signal Sd of a low level is generated. At a determining unit 19, the noise component Sb is compared with the threshold signal Sd, and a noise component Sb having a level higher than the threshold signal Sd is detected to obtain a noise detected signal Sout. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a noise detection device that detects noise included in an electric signal.
[0002]
[Prior art]
For example, in a receiving device such as a radio receiver, the noise is detected in order to remove noise included in an incoming radio wave, external noise mixed during signal processing in the receiving device, and other noise. Noise removal processing has been performed based on the detection signal.
[0003]
As a noise detecting device for detecting noise mixed in the above-mentioned signal, for example, the one shown in FIG. 1 is known. FIG. 1 shows an example of a noise detection device provided in an on-vehicle radio receiver, and detects an ignition noise generated and mixed when the engine is started.
[0004]
This noise detection device inputs an input signal Sin to a high-pass filter 1 and a rectifier circuit 2, and extracts a noise component Sb0 included in the input signal Sin by high-pass filtering and rectification.
[0005]
Further, by passing the noise component Sb0 through the low-pass filter 3 and the charging / discharging circuit 4, a smoothed threshold signal Sd0 is generated, and by subtracting the threshold signal Sd0 from the noise component Sb0, a level higher than the threshold signal Sd0 is obtained. The noise component Sb0 is obtained and shaped into a rectangular wave pulse by the waveform shaping circuit 6 to obtain the noise detection signal Sout.
[0006]
Here, the charge / discharge circuit 4 is provided in order not to detect high-density multipath noise.
[0007]
That is, the charging / discharging circuit 4 is a high-speed charging / low-speed discharging type circuit, and the time constant of the discharging is set longer than the generation interval of the multipath noise. Therefore, for the high-density multipath noise, the charge of the charge / discharge circuit 4 becomes more dominant than the discharge.
[0008]
Therefore, when high-density multipath noise is mixed, the threshold signal Sd0 generated by the charge / discharge circuit 4 is higher than the level of the extracted noise component Sb0. Has become.
[0009]
[Problems to be solved by the invention]
By the way, in the conventional noise detection device, the charging / discharging circuit 4 is provided in order to prevent high-density multipath noise from being detected. However, the charge / discharge circuit 4 also acts on ignition noise without distinction, and if the ignition noise has a high density, it may be difficult to detect.
[0010]
That is, as the interval between the occurrences of the ignition noise becomes shorter, the threshold signal Sd0 charged by the above-mentioned charge / discharge circuit 4 becomes higher, and the ignition noise having a lower level than the threshold signal Sd0 may not be detected in some cases.
[0011]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a noise detection device having a novel configuration that can accurately detect ignition noise.
[0012]
[Means for Solving the Problems]
The noise detection device according to claim 1, wherein the noise detection device detects noise included in an electric signal, wherein the extraction unit extracts a noise component from the electric signal, and limits a level of the extracted noise component. A precut unit, a charge / discharge circuit that charges and discharges the output of the precut unit, and a determination unit that uses the output of the charge / discharge circuit as a threshold and detects the noise component at a level equal to or higher than the threshold as a noise detection signal. A noise detection device, comprising:
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the present invention will be described with reference to FIGS.
Note that, as the present embodiment, a noise detection device provided in a vehicle-mounted radio receiver will be described.
[0014]
2, the noise detection device 12 is provided in a vehicle-mounted radio receiver including an input unit 7, a signal separation unit 8, a noise removal unit 9, an output unit 10, an output device 11, and the like.
[0015]
Here, the input unit 7 provided in the on-vehicle radio receiver receives a signal transmitted from a broadcast station or other information source and performs processing such as tuning (or tuning) and frequency conversion. .
[0016]
The signal separation unit 8 detects (or demodulates), for example, and outputs a detected signal.
[0017]
The noise removing unit 9 removes a noise component included in the detection signal based on a noise detection signal Sout supplied by a noise detection device 12 described later.
[0018]
That is, the noise removing unit 9 performs processing such as holding the value of the detection signal at the start point of the noise detection signal Sout and releasing the hold of the detection signal at the end point of the noise detection signal Sout in accordance with the noise detection signal Sout. Thus, noise included in the detection signal is removed.
[0019]
The output unit 10 reproduces an audio signal that sounds the output device 11 such as a speaker from the detected signal from which noise has been removed.
[0020]
The noise detection device 12 uses a detection signal as an input signal Sin and detects noise included in the input signal Sin. Then, when noise is detected, a noise detection signal Sout is output and supplied to the above-described noise removing unit 9 and the like.
[0021]
Next, the configuration of the noise detection device 12 will be described in detail with reference to FIG.
The noise detection device 12 includes a noise extraction unit 13, a precut unit 14, a charge / discharge circuit 16, and a determination unit 19.
[0022]
The noise extracting unit 13 extracts high-frequency noise components Sb included in the input signal Sin by performing processes such as high-pass filtering and rectification on the input signal Sin such as the above-described detection signal.
[0023]
The precut unit 14 smoothes the noise component Sb with a low-pass filter, and cuts (removes) only the noise component Sb higher in level than the smoothed signal component, thereby reducing the level of the noise component Sb. A limited precut signal Sf is generated.
[0024]
The time constants of the charge / discharge circuit 16 are set so as to charge at high speed and discharge at low speed.
Here, the time constant of the discharge of the charge / discharge circuit 16 is set to a value experimentally predetermined so as to be longer than the interval of occurrence of high-density multipath noise and shorter than the interval of occurrence of ignition noise. I have.
[0025]
Then, the charging / discharging circuit 16 charges within the generation period of the precut signal Sf and discharges according to the above time constant, thereby generating a threshold signal Sd having a waveform corresponding to the charging / discharging.
[0026]
The determination unit 19 is, for example, a high-gain comparator, detects the noise component Sb having a higher level than the threshold signal Sd by comparing the threshold signal Sd with the noise component Sb, and outputs a noise detection signal Sout.
[0027]
Next, the operation of the above-described noise detection device 12 will be described.
According to the present noise detection device, when the input signal Sin is input to the noise extraction unit 13, the rectified high-frequency noise component Sb is extracted.
Then, the precut section 14 generates a precut signal Sf in which the level of the noise component Sb is limited, and supplies the precut signal Sf to the charge / discharge circuit 16.
[0028]
The charge / discharge circuit 16 charges the precut signal Sf subjected to the above-described level limitation at a high speed. Therefore, a threshold signal Sd having a lower level is generated as compared to a case where the noise component Sb of the ignition noise is charged by the charge / discharge circuit 16.
[0029]
Further, the time constant of the discharge of the charge / discharge circuit 16 is set to be shorter than the interval at which the ignition noise occurs. Therefore, in the charging / discharging circuit 16, the electric charge charged by the precut signal Sf is discharged during the generation of the ignition noise.
[0030]
That is, even if ignition noise occurs in the input signal Sin, the threshold signal Sd output from the charge / discharge circuit 16 attenuates and approaches zero level.
[0031]
The determination unit 19 compares the threshold signal Sd with the noise component Sb, detects a noise component Sb having a higher level than the threshold signal Sd, and outputs a noise detection signal Sout.
That is, since the threshold signal Sd is close to the zero level, the low-level noise component Sb can be reliably detected.
[0032]
The time constant of the discharge of the charge / discharge circuit 16 is set shorter than the interval at which high-density multipath noise occurs.
[0033]
Therefore, when multipath noise occurs in the input signal Sin, charging becomes dominant as compared with discharging in the charging / discharging circuit 16, and the threshold signal Sd is held at a high level without attenuation.
[0034]
Therefore, while multipath noise is occurring, the threshold signal Sd is higher than the level of the noise component Sb, and the detection of multipath noise can be eliminated.
[0035]
That is, according to the present noise detection device 12, it is possible to exclude the detection of high-density multipath noise and accurately detect the ignition noise.
[0036]
In the embodiment of the present invention shown in FIGS. 2 and 3, the case where noise included in the detection signal generated by the radio receiver is detected has been described. However, the present invention is not limited to this. The present noise detection device 12 can be widely applied to the detection of noise contained in a signal whose main component is a high frequency band or a low frequency band, or a signal modulated on a carrier wave.
[0037]
【Example】
Next, a more specific embodiment will be described with reference to FIGS.
FIG. 4 is a block diagram for explaining the configuration of the noise detection device according to the present embodiment.
In FIG. 4, the same or corresponding components as those shown in FIGS. 2 and 3 are denoted by the same reference numerals.
[0038]
4, the noise detection device 12 of the present embodiment includes a noise extraction unit 13, a precut unit 14, a low-pass filter 15, a charge / discharge circuit 16, and a determination unit 19.
[0039]
The noise extraction unit 13 includes a high-pass filter 131 and a rectifier circuit 132.
The high-pass filter 131 performs high-pass filtering on the input signal Sin to extract a high-frequency noise component Sa.
The rectifier circuit 132 rectifies the noise component Sa and generates a noise component Sb.
[0040]
The precut unit 14 includes a low-pass filter 141, a subtraction circuit 142, a switching signal generation circuit 143, and a switch circuit 144.
The low-pass filter 141 smoothes the noise component Sb and generates a signal Sg.
[0041]
The subtraction circuit 142 subtracts the signal Sg input to the addition input terminal (+) from the noise component Sb input to the subtraction input terminal (-) to generate a difference signal Sh.
[0042]
The switching signal generation circuit 143 is, for example, a high gain comparator, and inverts and amplifies the negative component of the difference signal Sh. Then, a switching signal Si is generated to drive the switch circuit 144 in the subsequent stage.
[0043]
The switch circuit 144 selects the noise component Sb or the signal Sg output from the low-pass filter 141 according to the switching signal Si, and outputs a precut signal Sf.
[0044]
That is, when the switching signal Si is in the ON state (high-voltage output), the switch circuit 144 selects the output Sg of the low-pass filter 141 and outputs it as the precut signal Sf, and the switching signal Si is in the OFF state (low-voltage output). In some cases, the noise component Sb is selected and output as the precut signal Sf.
[0045]
The low-pass filter 15 removes unnecessary high-frequency noise components that are not targets of noise removal from the precut signal Sf, and supplies the same to the charge / discharge circuit 16 as a signal Sc.
[0046]
The time constants of the charge / discharge circuit 16 are set so as to charge at high speed and discharge at low speed.
Here, the time constant of the discharge of the charge / discharge circuit 16 is set to a value experimentally determined in advance so as to be longer than the interval of occurrence of high-density multipath noise and shorter than the interval of occurrence of ignition noise. I have.
[0047]
The charging / discharging circuit 16 receives the signal Sc obtained through the low-pass filter, and generates a threshold signal Sd by charging / discharging.
[0048]
The determination unit 19 includes a subtraction circuit 191 and a waveform shaping circuit 192.
The subtraction circuit 191 receives the threshold signal Sd at the addition input terminal (+), and subtracts the noise component Sb input to the subtraction input terminal (-) from the above-described threshold signal Sd to generate the difference signal Se. Generate.
[0049]
The waveform shaping circuit 192 is formed of, for example, a high gain comparator. Then, it inverts and amplifies the negative component of the difference signal Se and outputs a detection signal Sout shaped into a rectangular pulse.
[0050]
That is, the noise component Sb having a higher level than the threshold signal Sd is detected by the subtraction circuit 191 and the waveform shaping circuit 192, and the detection result is output as the noise detection signal Sout.
[0051]
Next, the operation of the noise detection device 12 having such a configuration will be described.
In the detection device, when a signal Sin including ignition noise as shown in FIG. 5 is input to the noise extraction unit 13, a high-pass noise component is extracted by the high-pass filter 131. Then, the noise component Sb as shown in FIG. 6 is supplied to the precut unit 14 by being rectified by the rectification circuit 132.
[0052]
In the precut unit 14, the noise component Sb is smoothed by the low-pass filter 141 as shown in FIG. 7, and a smoothed signal Sg shown in FIG. 7 is obtained.
[0053]
In the subtraction circuit 142, the noise component Sb is subtracted from the signal Sg, and a difference signal Sh as shown in FIG. 8 is generated.
[0054]
The switching signal generation circuit 143 inverts and amplifies the difference signal Sh to generate a switching signal Si as shown in FIG. Here, the switching signal Si is in an ON state (high-voltage output) only for a period corresponding to the pulse width thereof in synchronization with a rise of the noise component Sb, and is in an OFF state (low-voltage output) in other cases.
[0055]
The switching circuit 144 performs a switching operation in accordance with the switching signal Si. When the switching signal Si is ON, the output Sg of the low-pass filter 141 is selected. When the switching signal Si is OFF, the noise component Sb is selected and the pre-cut signal Sf is selected. Is output as
[0056]
Therefore, as shown in FIG. 10, the precut signal Sf is synchronized with the noise component Sb, and has a waveform in which the output of the low-pass filter 141 is selected during a period in which noise occurs.
[0057]
Next, the low-pass filter 15 removes unnecessary high-frequency noise components from the precut signal Sf, and the signal Sc shown in FIG. 11 is generated.
When the signal Sc thus generated is supplied to the charging / discharging circuit 16, high-speed charging and low-speed discharging are performed. That is, immediately after the ignition noise occurs, the output signal Sc of the low-pass filter is charged at high speed.
[0058]
Therefore, a threshold signal Sd having a lower level is generated as compared to a case where the noise component Sb of the ignition noise is charged by the charge / discharge circuit 16.
[0059]
At the same time, as described above, the discharge time constant of the charge / discharge circuit 16 is set to be shorter than the ignition noise generation interval. Therefore, in the charge / discharge circuit 16, the charge charged by the output signal Sc of the low-pass filter is discharged during the time when the ignition noise occurs.
[0060]
That is, even if ignition noise occurs in the input signal Sin, the threshold signal Sd generated by the charge / discharge circuit 16 attenuates and approaches zero level as shown in FIG.
[0061]
Then, the noise component Sb is subtracted from the threshold signal Sd in the subtraction circuit 191 provided in the determination unit, and the negative component of the difference signal Se is inverted and amplified in the waveform shaping circuit 192, so that the noise shown in FIG. The detection signal Sout is output from the waveform shaping circuit 192.
[0062]
As described above, according to the noise detection device of the present embodiment, as shown in FIG. 12, since the threshold signal Sd having a sufficiently lower level than the noise component Sb is generated, the low-level ignition noise component is generated. Sb can also be reliably detected.
[0063]
Further, even when high-density ignition noise generated at a short interval is mixed in the input signal Sin, the time constant of the discharge of the charge / discharge circuit 16 is set shorter than the interval of the generation of the ignition noise. Discharge becomes more dominant than charge retention.
[0064]
Therefore, the threshold signal Sd is attenuated and approaches zero level, so that high-density ignition noise can be reliably detected.
[0065]
When high-density multipath noise is generated in the input signal Sin, the discharge time constant of the charge / discharge circuit 16 is set shorter than the multipath noise generation interval. , Charging becomes dominant compared to discharging, and the threshold signal Sd is held at a high level.
[0066]
Therefore, while multipath noise is occurring, the threshold signal Sd is higher than the level of the noise component Sb, and the detection of multipath noise can be eliminated.
That is, according to the present noise detection device, it is possible to accurately detect the ignition noise without detecting the high-density multipath noise.
[0067]
FIG. 14 is a diagram corresponding to FIG. 12, and shows a noise component Sb0 extracted from the input signal Sin shown in FIG. 5 and a threshold signal Sd0 generated by the conventional noise detection device. FIG. 15 is a diagram corresponding to FIG. 13 and shows a noise detection signal Sout obtained by a conventional noise detection device.
[0068]
According to the conventional noise detection device, the threshold signal Sd0 shown in FIG. 14 is subtracted and compared with the noise component Sb0 to obtain the noise detection signal Sout shown in FIG. 15, but the noise detection device obtains the noise detection signal Sout. Comparing with the noise detection signal Sout shown in FIG. 13, it is clear that the present noise detection device can detect lower-level ignition noise.
[0069]
As described above, according to the noise detection device of the present embodiment and the present embodiment, the level of the so-called threshold signal is set to a value close to zero level with respect to the ignition noise included in the input signal. However, it can be reliably detected.
[0070]
In addition, the discharge time constant of the charge / discharge circuit is set to be longer than the interval of occurrence of multipath noise and shorter than the interval of occurrence of ignition noise, so that the detection of multipath noise is eliminated and the ignition noise is detected with high accuracy. be able to.
[0071]
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a conventional noise detection device.
FIG. 2 is a diagram showing a configuration of a noise detection device according to an embodiment of the present invention.
FIG. 3 is a diagram further illustrating a configuration of a noise detection device according to the present embodiment.
FIG. 4 is a diagram illustrating a configuration of an embodiment of a noise detection device.
FIG. 5 is a waveform diagram for explaining the operation of the noise detection device shown in FIG.
FIG. 6 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 7 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 8 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 9 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 10 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
11 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 12 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 13 is a waveform chart for further explaining the operation of the noise detection device shown in FIG.
FIG. 14 is a waveform chart for explaining the operation of the conventional noise detection device shown in FIG.
FIG. 15 is a waveform chart for explaining a comparison between a conventional noise detection device and the noise detection device of the present embodiment.
[Explanation of symbols]
12 noise detection device 13 noise extraction unit 14 precut unit 15 low-pass filter 16 charge / discharge circuit 19 determination unit 131 high-pass filter 132 rectifier circuit 141 low-pass filter 142 subtraction circuit 143 switching signal generation circuit 144 ... Switch circuit 191 ... Subtraction circuit 192 ... Waveform shaping circuit

Claims (9)

A noise detection device that detects noise included in an electric signal,
Extracting means for extracting a noise component from the electric signal,
A precut unit for limiting the level of the extracted noise component,
A charging and discharging circuit for charging and discharging the output of the precut unit,
A determination unit that detects an output of the charge / discharge circuit as a threshold and detects the noise component at a level equal to or higher than the threshold as a noise detection signal,
A noise detection device comprising: The noise detection device,
The noise detection device according to claim 1, wherein an ignition noise is detected as a noise component included in the electric signal. The precut portion,
The noise detection device according to claim 1, wherein the noise component is smoothed, and the noise component is limited to a noise component having a lower level than the smoothed level. The precut portion,
A first filter for smoothing the noise component;
An arithmetic circuit for calculating the difference between the output of the first filter and the noise component;
A switching signal generation circuit that amplifies an output of the subtraction circuit;
A switch circuit that selects and exclusively outputs the noise component or the output of the first filter according to an output of the switching signal generation circuit;
The noise detection device according to claim 1, further comprising: The charge and discharge circuit,
5. The noise detection device according to claim 1, wherein a time constant of discharging is longer than a time constant of charging. The discharge time constant of the charge / discharge circuit is
6. The noise detection device according to claim 5, wherein the interval is shorter than an ignition noise generation interval. The discharge time constant of the charge / discharge circuit is
6. The noise detection device according to claim 5, wherein the interval is shorter than the interval between occurrences of ignition noise and longer than the interval between occurrences of multipath noise. The extracting means,
A second filter that passes a noise component included in the electric signal,
Rectifying means for rectifying the output of the second filter;
The noise detection device according to claim 1, further comprising: A noise detection method for detecting noise included in an electric signal,
A first step of generating a first generation signal by performing extraction and rectification of a high-frequency component on the electric signal;
A second step of generating a second generated signal by smoothing the first generated signal;
A third step of generating a third generation signal by limiting the first generation signal to a lower level than the second generation signal;
A fourth step of charging and discharging the third generation signal to generate a threshold signal;
A noise detection method comprising: comparing the first generation signal with the threshold signal; and detecting the first generation signal having a higher level than the threshold signal as a noise detection signal. .

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