JP2002368633A - Fm noise eliminating device and fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect multipath noise with high accuracy. SOLUTION: A multipath noise detection section 100 of the FM noise eliminating device is provided with a level detection section 110, a level fluctuation detection section 130, and a multipath noise discrimination section 150. The level detection section 110 acquires (a value related to) the magnitude of a component of an FM demodulation signal S20, around 190 kHz and provides the output of the result as a signal S110. The level fluctuation detection section 130 detects fluctuations in the magnitude of the component around 19 kHz from the signal S110 and provides an output of a signal S130. The multipath noise discrimination section 150 discriminates occurrence of a multipath noise from the signal S130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM noise removing apparatus and an FM receiver, and more particularly to a technique for detecting multipath noise with high accuracy and obtaining a good output audio signal.

[0002]

2. Description of the Related Art For example, when an electromagnetic wave is reflected by an electromagnetic wave reflector such as a mountain or a high-rise building, multipath noise is generated due to the reflected wave. Specifically, when a receiving antenna such as a car radio receives a multiplex of a direct wave directly arriving from a transmitting antenna and a reflected wave reflected by a reflector, the direct wave is reflected depending on the phase relationship between the direct wave and the reflected wave. Some may be canceled by reflected waves. It is well known that such interference of the reception by the reflected wave is called multipath noise, and the quality of the output audio signal is reduced by the multipath noise.

In a conventional FM receiver, for example, (a) a stereo separation operation for switching from stereo to monaural or vice versa (that is, changing the degree of separation between left and right channels in stereo sound) or (b) The S / N ratio is improved by the high cut operation for removing high frequency components.

FIG. 15 is a block diagram for explaining a first FM receiver 101P according to the prior art. The FM receiver 101P is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-31316.
No. 1993. In the conventional FM receiver 101P, an FM intermediate frequency signal (IF signal) is applied to an input terminal 1P. When receiving multipath interference during FM reception, F
Since the M carrier (carrier) undergoes amplitude fluctuation due to the multipath wave, the amplitude fluctuation component is extracted by the carrier amplitude detection circuit 3P and smoothed by the DC conversion circuit 16P. Then, the noise suppression circuit 1 uses the smoothed signal as a control signal.
7P controls muting, high-frequency cutoff, and the like. Note that the noise suppression circuit 17P is connected to the output of the FM demodulation circuit 2P. Further, the multiplex demodulation circuit 18P
Reduces noise by reducing the degree of stereo separation. A demodulated output is output from the multiplex demodulation circuit 18P to left and right output terminals 19P and 20P.

[0005] By the way, in a motor vehicle, pulsed electromagnetic wave noise such as ignition noise and electric mirror noise is generated. This pulse noise is mixed into the antenna of the car radio and generates pulse noise in the output audio signal. For this reason, a car radio is generally provided with a pulse noise removing device.

FIG. 16 is a block diagram for explaining a second FM receiver 102P according to the prior art. The FM receiver 102P is described in, for example, Japanese Patent Application Laid-Open No. 63-87026.
No. 1993. In the conventional FM receiver 102P, the FM detection circuit 31P receives the FM intermediate frequency signal and outputs a detection signal. This detection signal is supplied to a delay circuit 32P including an LPF (low-pass filter) to be delayed. The output of the delay circuit 32P is supplied to the stereo demodulation circuit 3 via the gate circuit 33P and the level hold circuit 34P.
5P. Also, the detected signal is HP for noise detection.
F (high-pass filter) 201P and HPF2
The noise component signal that has passed through 10P is
The signal is amplified by P and supplied to the noise detection circuit 203P.

The noise detection circuit 203P includes a noise amplifier 2
The noise detection output is composed of a rectifier circuit for rectifying the output signal of the second circuit 02P and the waveform shaping circuit 204P and the integrating circuit 20P.
5P. The waveform shaping circuit 204P converts the noise detection output into a pulse having a pulse width of a predetermined time width and supplies the pulse to the gate circuit 33P. The gate circuit 33P is turned off by the pulse supplied from the waveform shaping circuit 204P to the gate circuit 33P. In the signal cutoff state, the delayed output level before the signal cutoff held by the level hold circuit 34P is supplied to the stereo demodulation circuit 35P.
This prevents spikes due to sudden changes in potential. When no pulse is supplied from the waveform shaping circuit 204P, the gate circuit 33P and the level hold circuit 3
4P goes through. The integration circuit 205P smoothes the noise detection output to obtain a DC signal corresponding to the noise level, and feeds it back to the noise amplifier 202P. As a result, an AGC loop is formed.

The delay circuit 32P has a pulse noise of H
It is provided to compensate for the time from when the gate circuit 33P is turned off after being supplied to the PF 201P. Also,
The stereo demodulation circuit 35P separates and extracts the Lch and Rch signals included in the level hold circuit 34P.

[0009]

However, in the conventional FM receiver 101P, the carrier amplitude fluctuation component is smoothed and used as a DC control signal in the method for detecting multipath noise interference. Also, there is a problem that the detection voltage changes and a malfunction may occur.

Further, the pulse noise detecting means 200P (consisting of elements 201P to 205P) of the conventional FM receiver 102P also detects multipath noise. Since the generation period of the multipath noise is longer than that of the pulse noise, if the multipath noise is corrected in the same manner as the pulse noise, a correction error increases. That is, the sound quality may be degraded.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an FM noise elimination device capable of detecting multipath noise with high accuracy, and provides an FM noise elimination device having such an FM noise elimination device. An object of the present invention is to provide an FM receiver capable of obtaining an output audio signal.

[0012]

According to a first aspect of the present invention, there is provided an FM noise removing apparatus for acquiring a value relating to the magnitude of a component around 19 kHz of an FM demodulated signal, and outputting the value. A level variation detection unit that detects a variation in the magnitude of the component around 19 kHz from the value related to the magnitude, and a multipath that determines the occurrence of multipath noise from the variation in the magnitude of the component around 19 kHz A noise determination unit.

According to a second aspect of the present invention, there is provided the FM noise elimination apparatus according to the first aspect, wherein the level detection section converts the component around 19 kHz into a first component having a frequency lower than 19 kHz. And a first conversion unit for extracting the first component, and converting the component around 19 kHz into a second component having a frequency lower than 19 kHz and having a phase shift of 90 degrees from the first component. A second conversion unit that converts and extracts the second component, and from the first and second components,
A magnitude detector that generates the value related to the magnitude of the component around 19 kHz.

According to a third aspect of the present invention, there is provided the FM noise elimination apparatus according to the first or second aspect, wherein the level fluctuation detecting section is configured to detect the magnitude of the component around 19 kHz. A first comparing unit that compares a magnitude relationship between the value and a plurality of thresholds and outputs an output signal having a level corresponding to a result of the magnitude relationship comparison;

According to a fourth aspect of the present invention, there is provided the FM noise eliminator according to the third aspect, wherein the plurality of thresholds are an upper threshold and a lower threshold smaller than the upper threshold. And the first comparing section includes the 19 kHz
Outputting a first level of the output signal when the value relating to the magnitude of the nearby component is greater than the upper threshold, wherein the value relating to the magnitude of the component around 19 kHz is greater than the lower threshold; If the value is smaller, the second level output signal is output. If the value related to the magnitude of the component around 19 kHz is between the lower threshold and the upper threshold, the output signal at the third level is output. Output.

According to a fifth aspect of the present invention, there is provided the FM noise elimination apparatus according to any one of the first to fourth aspects, wherein the multipath noise determination unit is configured to detect the level change from the level fluctuation detection unit. A smoothing unit that smoothes the output signal and outputs a smoothed signal, and a second comparing unit that outputs a signal indicating that the multipath noise has occurred when the smoothed signal is equal to or more than a predetermined value. Including.

According to a sixth aspect of the present invention, there is provided the FM noise elimination apparatus according to any one of the first to fifth aspects, wherein the multipath noise determination unit is configured to start the multipath noise. And a predetermined period from the end of the multipath noise are determined as the period of occurrence of the multipath noise.

According to a seventh aspect of the present invention, there is provided an FM noise removing apparatus according to any one of the first to sixth aspects, wherein the noise of the FM demodulated signal is detected, and the detection result and A pulse noise detection unit that detects pulse noise of the FM demodulated signal based on a detection result of the multipath noise by the multipath noise detection unit;
A noise correction unit that corrects the FM demodulated signal in accordance with a result of the detection of the pulse noise by the pulse noise detection unit.

An FM noise eliminator according to claim 8 is the FM noise eliminator according to any one of claims 1 to 6, wherein the multipath noise detection unit detects the multipath noise. A noise detection unit that detects noise of the FM demodulated signal with a detection sensitivity controlled according to the following: a noise correction unit that corrects the FM demodulated signal in accordance with a result of the noise detection by the noise detection unit Further provision.

[0020] The FM receiver according to the ninth aspect provides the FM receiver according to the first aspect.
An FM noise removing apparatus according to any one of claims 8 to 8,
An FM demodulation circuit for generating the FM demodulated signal.

[0021]

<First Embodiment> A. First Embodiment 1. Overall Configuration of FM Receiver FIG. 1 is a block diagram illustrating an FM receiver 10 according to Embodiment 1. The FM receiver 10 includes an FM demodulation circuit 20 and an FM noise elimination device 30. The FM noise elimination device 30 includes a multipath noise detection unit 100, a pulse noise detection unit 200, and a noise correction unit 300. I have.

The FM demodulation circuit 20 outputs the FM intermediate frequency signal (I
(F signal) S0, and generates an FM demodulated signal S20 from the signal S0 and outputs it to the multipath noise detection unit 100, the pulse noise detection unit 200, and the noise correction unit 300.

Further, the multipath noise detecting section 100
Multipath noise of M demodulated signal S20 is detected, and the detection result is output to pulse noise detection section 200 as detection result signal S100.

The pulse noise detecting section 200 is an FM
Based on the demodulated signal S20 and the detection result signal S100 from the multipath noise detector 100, the FM demodulated signal S20
And outputs the detection result to the noise correction unit 300 as a detection result signal S200.

The noise correcting section 300 corrects the noise of the FM demodulated signal S20 based on the detection result signal S200 from the pulse noise detecting section 200, and outputs the corrected FM demodulated signal S20 as a corrected demodulated signal S300. .
Hereinafter, each of the elements 20, 100, 200, and 300 will be described in detail.

B. FM Demodulation Circuit FIG. 2 is a block diagram for explaining the FM demodulation circuit 20. The FM demodulation circuit 20 includes an amplifier 21 and a limiter 22.
And an FM demodulation unit 23. The amplifier 21 receives the intermediate frequency signal S0, amplifies the carrier amplitude of the signal S0, and outputs the amplified signal as a signal S21. The limiter 22 receives the signal S21 from the amplifier 21 and
Is limited and output as a signal S22. The FM demodulation unit 23 receives the signal S22 from the limiter 22,
It demodulates and outputs FM demodulated signal S20. As described above, the FM demodulated signal S20 is output from the multipath noise detector
0, pulse noise detection unit 200 and noise correction unit 30
Output to 0.

The FM demodulated signal S20 has (a) 0
A signal of the sum (L + R) of the left (L) channel and the right (R) channel at 15 kHz, a pilot signal at (b) 19 kHz, and a difference (L-) between the L and R channels at 23 to 53 kHz. R) signal at 38 kHz
M-modulated signal. At this time, the FM demodulated signal S20 has no audio component in the band of 19 kHz ± 4 kHz.

The amplitude of the carrier of the intermediate frequency signal S0 changes according to the received electric field strength. However, even if there is such a fluctuation in the amplitude, the output signal S22 from the limiter 22 becomes a constant level (or amplitude) by the limiter 22. Since the FM noise elimination device 30 uses the FM demodulated signal S20, that is, the signal after the limiter 22, the FM noise removing device 30 can detect multipath noise and the like with little influence of electric field fluctuation.

C. Multipath Noise Detector In the output signal 22 from the limiter 22, the information on the carrier amplitude fluctuation disappears as described above, but the information on the multipath noise remains in the phase fluctuation. The change in the phase of the signal S22 from the limiter 22 is determined by the FM demodulation unit 23.
Is converted to the signal level (amplitude) by FM.
Demodulated signal S20 includes information on multipath noise. Therefore, the multipath noise detection unit 100 detects a phase change in the signal S20 caused by the multipath noise.

First, a method of detecting multipath noise in the multipath noise detection section 100 will be described with reference to the spectrum waveform of FIG. FIG. 3 shows an example of the spectrum of the FM demodulated signal S20 (modulation degree 20%, 100 Hz sine wave) when multipath noise occurs, in which the vertical axis indicates frequency and the horizontal axis indicates time. The darker the color, the higher the signal level.

According to FIG. 3, if no multipath noise occurs, only a pilot signal exists in a band around 19 kHz. On the other hand, when multipath noise occurs, not only the signal level around 19 kHz increases (the color is dark in the figure), but also a multipath noise component occurs near a frequency such as 38 kHz. That is, a multipath noise component is generated in the vicinity of a frequency of m times 19 kHz (m is an integer of 1 or more). Further, according to FIG. 3, it can be seen that the noise component is generated in a wider band as the frequency is higher, that is, as the above-mentioned m is larger.

For this reason, it is considered that multipath noise can be detected from a change in signal level near a frequency of m times 19 kHz. At this time, if the change width of the frequency at which noise occurs is large, a wide band may be set as the detection target. However, the wider the detection target band, the more difficult it is to distinguish multipath noise from other noise.

Therefore, in the multipath noise detection section 100, the band in which the multipath noise is generated is 19 kHz, which is smaller.
By using the level fluctuation of the signal near z, the occurrence of multipath noise is accurately detected.

Next, FIG.
FIG. 2 shows a block diagram for explaining 0. The multipath noise detector 100 includes a level detector 110, a level fluctuation detector 130, and a multipath noise determiner 150.

The level detector 110 receives the FM demodulated signal S20, obtains the magnitude (value relating to) a component around 19 kHz of the signal S20, and outputs it as a level detection signal S110.

The level fluctuation detection section 130 receives the level detection signal S110, detects the fluctuation of the signal S110, in other words, the fluctuation of the magnitude of the component around 19 kHz of the FM demodulated signal S20, and detects the level fluctuation detection signal S130. Output as

The multipath noise determination unit 150 receives the level fluctuation detection signal S130, and from the signal S130,
In other words, it is determined whether or not multipath noise has occurred from the fluctuation in the magnitude of the component around 19 kHz of the FM demodulated signal S20. Then, the multipath noise determination unit 15
0 outputs the determination result as a detection result signal S100.

Hereinafter, the level detecting section 110, the level fluctuation detecting section 130, and the multipath noise determining section 150 will be described in detail.

C-1. Level detection unit As described above, the FM demodulated signal S20 is 19 kHz ± 4 kHz.
There is no audio component in the band z. For this reason, in the level detection unit 110, for example,
By extracting a component around 19 kHz with a bandpass filter capable of sufficiently attenuating a component of 3 kHz or more and smoothing the absolute value of the extracted signal, the level of the component around 19 kHz can be detected.

Alternatively, the level detector 110 can be configured as shown in the block diagram of FIG. In this example, the level detector 110 includes an oscillator 111, a phase shifter 112, first and second converters 113 and 114,
A multiply-accumulate calculator (or a size detector) 119. The first conversion unit 113 includes a multiplier 115 and a low-pass filter (hereinafter, also referred to as “LPF”) 117, and the second conversion unit 114 includes a multiplier 116 and an LPF 118.
It has.

The oscillator 111 generates a sine wave (or sine wave signal) S111 around 19 kHz, and the signal S111
111 is a multiplier 115 and a phase shifter 1 of the first conversion unit 113
12 is output. The phase shifter 112 rotates the phase shift of the signal S111 by 90 degrees, and converts the signal S111 into a sine wave signal S112.
14 to the multiplier 116.

In the first converter 113, a multiplier 115
Receives the sine wave signal S111 and the FM demodulated signal S20, multiplies both signals S111 and S20, and outputs the multiplication result as a signal S115.

The output signal S115 of the multiplier 115 is FM
The sum of the component obtained by shifting the frequency of the demodulated signal S20 by +19 kHz and the component obtained by shifting the frequency of the FM demodulated signal S20 by -19 kHz is obtained. At this time, the FM demodulated signal S20
Is converted to a component near DC (or a first component) when shifted by -19 kHz (therefore, converted to a frequency lower than 19 kHz).
The (LR) component above z is converted to a component above 4 kHz.

Therefore, in the first conversion unit 113, the multiplier 1
The component of 4 kHz or more of the output signal S115 from
A component near the DC component of the signal S115 (or a first component) is extracted by being attenuated by the PF 117. LPF
The component extracted by 117 is output as output signal S113 of first conversion section 113.

Similarly, in the second conversion unit 114, the multiplier 115 receives the sine wave signal S112 and the FM demodulated signal S20 from the phase shifter 112, and receives both signals S112 and S2.
The multiplication result is multiplied by 0, and the multiplication result is output as a signal S116.
Then, the component of 4 kHz or more of the signal S116 is converted to LP
A component near the DC component (or a second component) is extracted by being attenuated by F118. The component extracted by LPF 118 is output as output signal S114 of second conversion section 114.

As described above, according to the level detector 110 of FIG.
After converting the signal around 19 kHz of the M demodulated signal S20 to a signal near DC, the signal is passed near DC and 4 kHz
The above components are attenuated. Therefore, the LPF 117, 1
The performance (specifications) required for 18 can be relaxed,
The above components around 19 kHz can be easily extracted.

Since the frequency of the output signals S113 and S114 from the LPFs 117 and 118 is low, the LPF 11
When the processing of steps 7 and 118 is performed by digital signal processing, the processing amount can be reduced by thinning processing.

Now, the first and second conversion units 113 and 114
Output signals S113 and S114 have a phase difference of 90 degrees. Therefore, by obtaining the square root of the sum of squares of the signals S113 and S114 {(component of signal S113) ² + (component of signal S114) ² }, the FM demodulated signal S2
The magnitude of the component around 0 and 19 kHz can be detected. By the way, since the sum of squares shows the same increasing and decreasing tendency as its square root, it is possible to know the fluctuation of the magnitude of the component around 19 kHz by the square sum (without taking the square root).

Therefore, the level detector 110 shown in FIG.
The first and second conversion units 11 are operated by the square sum operation unit 119.
3, 114 from the output signals S113, S114
The sum of the squares of the components 13 and S114 (or a value related to the magnitude of the component near 19 kHz of the FM demodulated signal S20) is calculated. Then, the calculation result is used as the level detection unit 110
Is output to the level fluctuation detection unit 130 as the level detection signal S110 which is the output signal of As described above, since the square root process is not performed on the sum of squares in the level detection unit 110 in FIG. 5, the level detection unit 110 is simplified as compared with the configuration in which the magnitude of the component around 19 kHz is strictly obtained. be able to.

Here, the square root of the above sum of squares, ie, FM
The magnitude of the component around 19 kHz of the demodulated signal S20 itself may be used as the output signal S110 of the level detection unit 110. The value relating to the magnitude of the component around 19 kHz is
This concept includes the magnitude of the component around 19 kHz.

Here, FIGS. 6 and 7 show examples of waveform diagrams for explaining the operation of the level detector 110 of FIG. 6 and 7, the horizontal axis represents time and the vertical axis represents signal level. In FIGS. 6 and 7,
The upper diagram is a waveform diagram of the FM demodulation signal S20 in which multi-path noise has occurred, for example, while the vehicle is running, and the lower diagram is a waveform diagram of the level detection signal S110 at that time. FIG. 6 illustrates a case where the FM demodulated signal S20 is a signal in which only the pilot signal (19 kHz) is FM-modulated, while FIG. 7 illustrates the FM demodulated signal S20.
Shows a case where a pilot signal and a 1 kHz sine wave having a modulation factor of 90% are FM-modulated signals.

As shown in FIGS. 6 and 7, during a period in which no multipath noise occurs, the level detection signal S11
0 is an almost constant level. Note that this constant level corresponds to the amplitude of the pilot signal. On the other hand, during the period in which multipath noise is occurring, the level detection signal 110 fluctuates from the constant level. Specifically, in the case of FIG. 6, the level detection signal S110 is higher than the level of the pilot signal. This is 19k
This is because the level of the nearby multipath noise is large.
On the other hand, in the case of FIG. 7, the level detection signal S110 is higher or lower than the level of the pilot signal. In particular, unlike the case of FIG. 6, a case where the level becomes lower than the pilot signal level frequently occurs.

C-2. Level Fluctuation Detection Unit As shown in FIGS. 6 and 7, the level detection signal S110 output from the level detection unit 110 in FIG. 5 is not only higher than the level of the pilot signal but also sometimes lower.

For this reason, for example, when the difference between the level detection signal S110 and the average value of the level of the signal S110 is large, the level fluctuation detection unit 130 indicates, for example, a High level indicating that multipath noise is occurring. (H level) signal S130, and if the difference is small, for example, low level (L level) signal S130
Is output.

Alternatively, it is possible to configure the level fluctuation detecting section 130 as shown in the block diagram of FIG. In such an example, the level change detection unit 130 is the first comparison unit 13
1 is provided. The comparing unit 131 includes the level detecting unit 1
10 (see FIG. 4), an upper threshold TH1 and a lower threshold TH2 smaller than the upper threshold TH1, and the signal S110 and the two thresholds T1 are received.
H1 and TH2 are compared in magnitude relation, and a level fluctuation detection signal S130 having a level according to the comparison result of magnitude relation is obtained.
Is output as an output signal of the level change detection unit 130 (see signals S20, S110, and S130 in FIG. 11 described later).

More specifically, the comparing section 131 determines that the level detection signal S110 from the level detecting section 110 is equal to the level of the component of the FM demodulated signal near 19 kHz.
If it is larger than the upper threshold TH1, the level detection signal S
An H level (or first level) signal S130 indicating that the signal 110 has changed is output. Also, the comparison unit 131
Outputs the H-level (or second level) signal S130 even when the level detection signal S110 is smaller than the lower threshold TH2. On the other hand, the comparison unit 130
Outputs an L-level (or third-level) signal S130 indicating that the level detection signal S110 is not fluctuating when the signal S110 is between the upper threshold TH1 and the lower threshold TH2.

At this time, if the level detection signal S110 indicates that the level detection signal S110 has fluctuated, the level detection signal S110 may be larger than the upper limit threshold value TH1 and the lower limit threshold value TH2.
The output level of the level fluctuation detection signal S130 may be different between the case where the level is smaller than the case.

As described above, the level fluctuation detecting section 110 detects whether the fluctuation of the level detection signal 110, in other words, the fluctuation of the component around 19 kHz of the FM demodulated signal S20 becomes larger or smaller than the level of the pilot signal. Since both are detected, it is possible to reliably detect multipath noise whose form changes variously depending on the modulation degree, the audio signal, and the like.

While it is possible to use more thresholds, the first comparator 131 can be simply configured with two thresholds TH1 and TH2.

C-3. Multipath noise determination unit By the way, in an automobile environment, the FM demodulated signal S20
In the vicinity of kHz, noise other than multipath noise, for example, pulse noise due to electromagnetic noise such as electric mirror noise may also be generated. For example, FIG. 9 shows a spectrum waveform diagram for explaining an FM demodulation signal when electric mirror noise occurs. In FIG. 9, the vertical axis represents frequency and the horizontal axis represents time, and the darker the color, the higher the signal level. According to FIG. 9, the frequency at which the electric mirror noise occurs in the FM demodulated signal S20 is random,
It can be seen that electric mirror noise may also occur near Hz.

In general, the period during which pulse noise such as motorized mirror noise occurs is within several hundred μs, whereas the period during which multipath noise occurs is often longer than pulse noise. Further, while multipath noise has a noise component around 19 kHz, pulse noise randomly occurs around 19 kHz. Accordingly, the level change detection signal S1 output from the level change detection unit 130
No. 30 has a higher frequency of being at the H level due to multipath noise than pulse noise.

In view of the above, the multipath noise determination section 150 is configured not to detect pulse noise such as electric mirror noise. For example, the multipath noise determination unit 150 determines that multipath noise has occurred when the level change detection signal S130 has maintained the H level for a predetermined period or more.

FIG. 10 is a block diagram for explaining a specific configuration example of the multipath noise determination section 150, and FIG.
FIG. 1 shows a waveform diagram for explaining the operation of the multipath noise determination section 150.

In FIG. 11, the vertical axis indicates level, and the horizontal axis indicates time. In FIG. 11, multipath noise occurs in the FM demodulated signal S20, and the FM demodulated signal S2
0 shows a case where electric mirror noise is generated around 19 kHz, and a case where spike-shaped noise is continuously generated as a multipath noise for a long period and is generated for a period longer than the electric mirror noise. I have.

At this time, as shown in FIG. 11, the level detection signal S110 has the multipath noise and the above 19 kHz.
During the period in which the nearby electric mirror noise is occurring, the level is higher than the pilot signal level. Further, the level fluctuation detection signal S130 is at the H level when the level detection signal S110 is larger than the upper threshold value TH1 and is smaller than the lower threshold value TH2, and is at the L level otherwise.

Referring back to FIG. 10, the multipath noise determination unit 1
50 is roughly divided into a multipath noise occurrence determination section 151 and a multipath noise occurrence period determination section 152.

The multipath noise occurrence judging section 151 has an LP
An F (or smoothing unit) 153 and a second comparing unit 154 are provided. The multipath noise occurrence period determining unit 152 includes a counter 155 and a third comparing unit 156.

The LPF 153 is connected to the level fluctuation detector 130.
(See FIG. 4) and receives the level variation detection signal S130, smoothes it, and outputs it as a smoothed signal S153. At this time, as shown in FIG. 11, the smoothed signal S153 gradually increases from the time of occurrence of both the multipath noise and the electric mirror noise. However, in the smoothed signal, the amount of change is small for pulse noise having a short generation period, while the amount of change is large for multipath noise having a long generation period.

The second comparing section 154 generates the smoothed signal S15
3 and an occurrence determination threshold value (or a predetermined value) TH3, and when the smoothed signal S153 is equal to or greater than the occurrence determination threshold value TH3 as shown in FIG. 11, an H-level signal indicating that multipath noise has occurred. S154 is output. On the other hand, as shown in FIG. 11, when the smoothed signal S153 is smaller than the occurrence determination threshold TH3, the comparison unit 154 generates an L-level signal S154 indicating that multipath noise has not been generated. Output.

As described above, according to the multipath noise occurrence determination section 151, the level fluctuation detection signal S130 is
Since the smoothing is performed in 153, multipath noise and pulse noise can be distinguished, and erroneous detection of pulse noise such as electric mirror noise can be reliably reduced.

The counter 155 receives the signal S 154 from the second comparing section 154, performs a predetermined counting process based on the signal S 154, and performs a predetermined count process on the counter value (signal relating to) S
155 is output. Specifically, when the signal S154 is at the H level, the counter 155 has a counter value S15.
5 is returned to the initial value, and when the signal S154 is at the L level, the counter value S155 is decremented.
When 5 becomes 0, the subtraction is stopped (see FIG. 11).

The third comparing section 156 receives the counter value S155 and the threshold value TH4 for determining the occurrence period, and outputs an output signal S100 of the multipath noise detecting section 150. Specifically, when the counter value S155 is larger than the occurrence period determination threshold value TH4, the comparison unit 156 outputs the H-level signal S155.
100, and the counter value S155 is equal to the threshold value TH4.
If it is smaller than the threshold value, an L-level signal S100 is output. That is, a period in which the detection result signal S100 is at the H level corresponds to a period in which the multipath noise detected by the multipath noise detection unit 100 occurs.

In particular, the multipath noise occurrence period determination section 1
According to 52, the period from the start to the end of the multipath noise and the counter value S from the end of the multipath noise
The period until 155 becomes smaller than the occurrence period determination threshold TH4 is included in the multipath noise occurrence period. Therefore, as shown in FIG. 11, when the next multipath noise occurs before the counter value S155 becomes smaller than the occurrence period determination threshold value TH4, the signal S100 remains at the H level without interruption. That is, the multipath noise occurrence period determination unit 152 detects these continuous multipath noises as one. As a result, according to the multipath noise occurrence period determination unit 152, and therefore, according to the multipath noise determination unit 150, it is possible to reduce detection omission of continuously occurring multipath noise.

D. (Pulse) Noise Detection Unit and Noise Correction Unit As shown in FIG. 1 described above, in the FM receiver 10, the pulse noise detection unit 200 detects the pulse noise of the FM demodulated signal S20, and the result is Detection result signal S200
Is output to the noise correction unit 300. Then, the noise correction unit 300 corrects the noise of the FM demodulation signal S20 and outputs the result as a corrected demodulation signal S300.

When pulse noise occurs, F
Since the high-frequency component of the M demodulated signal S20 increases, it is basically possible to determine that pulse noise has occurred due to such an increase in the high-frequency component. However, as shown in FIG. 3 described above, the high-frequency component of the FM demodulated signal S20 also becomes large due to the multipath noise. (A level difference before and after the correction) may be increased. This will be described with reference to FIG.

FIG. 12 is a waveform chart for explaining the relationship between the correction period and the correction error. In FIG. 12, the horizontal axis indicates time, and the vertical axis indicates signal level. FIG. 12 illustrates a correction method in which the signal level during the correction period is maintained at the value immediately before the correction period. The signal before correction is indicated by a solid line, and the signal after correction is indicated by a broken line.

As described above, the generation period of the pulse noise is generally within several hundred μs, while the generation period of the multipath noise is often longer than the pulse noise. Therefore, in FIG. 12, the short correction period T1 corresponds to the period for correcting the pulse noise, and the correction period T1
The correction period T2 longer than 1 corresponds to a period for correcting multipath noise. Therefore, according to FIG. 12, it can be seen that the correction error is larger for the multipath noise having a longer correction period.

Therefore, the FM receiver 10 is configured not to correct the FM demodulated signal S20 for multipath noise. Specifically, the multipath noise detection unit 100
Has detected multipath noise, the pulse noise detector 200 outputs a signal S200 indicating that no noise has been detected to the noise corrector 300 even if noise has been detected. Hereinafter, a specific example of the pulse noise detection unit 200 will be described.

FIG. 13 is a block diagram for explaining the pulse noise detector 200. The pulse noise detector 200 is a high-pass filter (hereinafter, also referred to as “HPF”).
201, a noise amplifier 202, and a noise detection circuit 20
3, a waveform shaping circuit 204, an integrating circuit 205, and a switch unit 206. The pulse noise detector 200 has a configuration including the conventional pulse noise detector 200P and the switch 206 in FIG.

In the pulse noise detector 200, H
The PF 201 receives the FM demodulated signal S20, and
The 20 noise component signal S201 is output to the noise amplifier 202. The noise amplifier 202 outputs the noise component signal S20
1 and amplifies the signal as a signal S202.
Output to The noise detection circuit 203 includes the noise amplifier 20
And a rectifying circuit for rectifying the output signal of the second circuit.
Output to 05. The integration circuit 205 outputs the noise detection signal S2
DC signal S20 corresponding to the noise level by smoothing
5 is generated and fed back to the noise amplifier 202. As a result, an AGC loop is formed. On the other hand, the waveform shaping circuit 204 is composed of, for example, a one-shot multivibrator, and converts the noise detection signal S203 into a pulse having a predetermined time width.
Output to

The switch section 206 receives the signal S 204 from the waveform shaping circuit 204 and the multipath noise detection section 100.
(See FIG. 1), and outputs a detection result signal S200 based on these signals S204 and S100. Specifically, when the signal S100 from the multipath noise detection unit 100 indicates that multipath noise is not detected, the switch unit 206 outputs the output signal S204 of the waveform shaping circuit 204 as it is as the detection result signal S200. . Conversely, when the signal S100 from the multipath noise detection unit 100 indicates that multipath noise has been detected, the pulse noise detection unit 200
Is multipath noise, the switch unit 206 outputs a detection result signal S200 indicating that no noise is detected, regardless of the output signal S204 of the waveform shaping circuit 204.

In this way, the pulse noise detector 2
00 detects high frequency noise of the FM demodulated signal S20,
Based on the detection result and the detection result signal S100 from the multipath noise determination unit 100, the pulse noise of the FM demodulated signal S20 is detected. Therefore, according to the pulse noise detection unit 200, erroneous detection of multipath noise can be reduced and pulse noise can be reliably detected from the noise of the FM demodulated signal.

The noise correction section 300 detects the pulse noise detection result signal S20 by the pulse noise detection section 200.
The FM demodulated signal S20 is corrected according to 0. At this time,
The noise correction unit 300 performs FM for multipath noise.
Since the demodulated signal S20 is not corrected, a large correction error caused by multipath noise can be reduced.

As a result, according to the FM receiver 10, a good output audio signal can be obtained.

By the way, the magnitude of the noise is various even if the period during which the multipath noise is generated is the same (generally, the noise generated when the level of the reflected wave is closer to that of the direct wave is larger). At this time, the multipath noise is better than that of FIG.
If it is larger than the correction error by the correction method shown in
The noise of the FM demodulated signal S20 can be reduced by the correction method of FIG. On the other hand, when the multipath noise is smaller than the correction error, the noise increases according to the correction method of FIG. That is, it may be preferable that the small multipath noise is not corrected by the correction method of FIG.

Such a correction method can be realized by applying the noise detecting section 200B shown in the block diagram of FIG. 14 to the FM receiver 10 of FIG. 1 instead of the above-described pulse noise detecting section 200.

The noise detection section 200B includes an HPF 201, a noise amplifier 202, a noise detection circuit 203, a waveform shaping circuit 204, and an integration circuit 205, similarly to the pulse noise detection section 200 of FIG. . In particular,
The noise detection unit 200B includes an adder 207.

The adder 207 outputs the output signal S205 from the integration circuit 205 and the multipath noise detector 100 (FIG. 1).
), A signal S207 is generated based on these signals S205 and S100, and the signal S207 is output to the noise amplifier 202.

In the noise detector 200B, the waveform shaping circuit 2
The signal S204 from S04 corresponds to the detection result signal S200 by the pulse noise detection unit 200 in FIG. 13, and the signal S204 is output to the noise correction unit 300. In addition,
Other configurations are the same as those of the pulse noise detection unit 200 in FIG.

The noise detection sensitivity of the noise detection unit 200B is determined by the detection result signal S1 from the multipath noise detection unit 100.
The noise detection unit 200B detects noise of the FM demodulation signal S20 with such controlled detection sensitivity.

More specifically, in the noise detection section 200B, the gain of the noise amplifier 202 is the signal S from the adder 207.
207, the output signal S2 of the adder 207.
07 is larger, the gain of the noise amplifier 202 is smaller. When the level of the input signal S201 is the same, the level of the output signal S202 of the noise amplifier 202 decreases as the gain decreases. Output signal S2 of noise amplifier 202
02 is small, even if noise of the same magnitude occurs in the FM demodulated signal S20, the signal S2 corresponding to the signal S202
03 does not exceed the threshold of the waveform shaping circuit 204, and the waveform shaping circuit 204 does not determine that noise has occurred.

As described above, the output signal S2 of the adder 2070 is obtained by the signal S100 from the multipath detecting section 100.
Since 07 becomes large, the noise detection unit 200B does not detect small multipath noise (detection sensitivity decreases). Thereby, it is possible to prevent the noise correction unit 300 from correcting small multipath noise,
As a result, it is possible to reduce a correction error caused by correcting a small multipath noise.

On the other hand, in the case of large multipath noise, even if the gain of the noise amplifier 202 is small, the signal S
The signal S203 corresponding to 202 exceeds the threshold of the waveform shaping circuit 204. Therefore, the noise detection unit 200B can detect large multipath noise. Accordingly, large multipath noise can be corrected in the noise correction unit 300.

As a result, a good output audio signal can be obtained even when the pulse noise detecting section 200 is replaced with the noise detecting section 200B in the FM receiver 10.

[0095]

According to the first aspect of the present invention, the FM demodulated signal generally has a limited carrier amplitude.
The multipath noise can be detected accurately with little influence of the fluctuation of the reception electric field. Further, since the multipath noise generated around 19 kHz of the FM demodulated signal has a narrow band, the multipath noise can be easily distinguished from other noises, and the multipath noise can be detected with high accuracy.

According to the second aspect of the present invention, the component around 19 kHz of the FM demodulated signal is extracted at 19 kHz before being extracted.
Are converted to first and second components at lower frequencies. For this reason, the performance (specification) required of the element (for example, a filter) for extracting the first and second components can be relaxed, and the above-described component around 19 kHz can be easily extracted. Further, the sum of the squares of the first and second components whose phases are shifted by 90 degrees is a value relating to the magnitude of the component around 19 kHz, so that the magnitude of the component around 19 kHz is larger than that obtained strictly. The configuration of the detection unit can be simplified.

According to the third aspect of the present invention, since a plurality of thresholds are used, it is possible to reliably detect multi-path noise whose form changes variously depending on the modulation factor and the like.

According to the fourth aspect of the present invention, it is possible to simplify the first comparing section and therefore the level fluctuation detecting section.

According to the fifth aspect of the present invention, in the smoothed signal, the amount of change is small for pulse noise having a short generation period, but is large for multipath noise having a long generation period. . Therefore, the second comparing section can distinguish between the multipath noise and the pulse noise by comparing the smoothed signal with the predetermined value, so that the erroneous detection of the pulse noise can be surely reduced.

According to the invention of claim 6, since the multipath noise determination section includes the predetermined period from the end of the multipath noise in the generation period of the multipath noise, the multipath noise detection section detects the multipath noise that occurs continuously. Leakage can be reduced.

According to the seventh aspect of the present invention, the pulse noise detecting section detects the pulse noise of the FM demodulated signal based on the judgment result of the multipath noise judging section, thereby reducing erroneous detection of the multipath noise. As a result, pulse noise can be reliably detected from the noise of the FM demodulated signal.
Therefore, a large correction error caused by correcting the multipath noise can be reduced.

According to the eighth aspect of the present invention, since the detection sensitivity of the noise detector is controlled according to the determination result of the multipath noise determiner, the noise detector does not detect small multipath noise. In addition, it is possible to prevent the noise correction unit from correcting small multipath noise. Thus, a large correction error caused by correcting a small multipath noise can be reduced.

According to the ninth aspect of the present invention, it is possible to provide an FM receiver capable of obtaining a good output audio signal.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an FM receiver according to a first embodiment.

FIG. 2 is a block diagram for explaining an FM demodulation circuit according to the first embodiment;

FIG. 3 is a spectrum waveform diagram for explaining an FM demodulated signal when multipath noise occurs.

FIG. 4 is a block diagram for explaining a multipath noise detection unit according to the first embodiment.

FIG. 5 is a block diagram for explaining a level detection unit according to the first embodiment.

FIG. 6 is a waveform chart for explaining the operation of the level detection unit according to the first embodiment.

FIG. 7 is a waveform chart for explaining an operation of the level detection unit according to the first embodiment.

FIG. 8 is a block diagram for explaining a level fluctuation detection unit according to the first embodiment.

FIG. 9 is a spectrum waveform diagram for explaining an FM demodulated signal when electric mirror noise (pulse noise) occurs.

FIG. 10 is a block diagram for explaining a multipath noise determination unit according to the first embodiment.

FIG. 11 is a waveform chart for explaining an operation of the multipath noise determination unit according to the first embodiment.

FIG. 12 is a waveform chart for explaining a relationship between a correction period and a correction error.

FIG. 13 is a block diagram for explaining a pulse noise detector according to the first embodiment;

FIG. 14 is a block diagram for explaining a noise detection unit according to the first embodiment.

FIG. 15 is a block diagram illustrating a first FM receiver according to the related art.

FIG. 16 is a block diagram illustrating a second FM receiver according to the related art.

[Explanation of symbols]

10 FM receiver, 20 FM demodulation circuit, 30 FM noise eliminator, 100 multipath noise detector, 110
Level detector, 112 phase shifter, 113 first converter,
114 second conversion unit, 115, 116 multiplier, 11
7, 118 low-pass filter, 119 square-sum calculator (size detector), 130 level fluctuation detector, 131
1st comparison unit, 150 multipath noise determination unit, 15
Reference Signs List 1 multipath noise occurrence determination section, 152 multipath noise occurrence period determination section, 153 low-pass filter (smoothing section), 154 second comparison section, 155 counter, 15
6 third comparing section, 200 pulse noise detecting section, 20
0B noise detector, 206 switch, 207 adder, 300 noise corrector, S20 FM demodulated signal,
S100, S200 detection result signal, S110 level detection signal, S113 signal (first component), S114 signal (second component), S130 level fluctuation detection signal, S1
53 Smoothing signal, S154 signal, S155 count value, TH1 upper limit threshold, TH2 lower limit threshold, TH
3 Occurrence determination threshold (predetermined value), TH4 Occurrence period determination threshold.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Taura 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Masayuki Ishida 2-3-2 Marunouchi, Chiyoda-ku, Tokyo 3 F term in Ryo Denki Co., Ltd. (reference) 5K052 AA01 CC04 DD03 DD21 EE13 FF03 GG20

Claims (9)

[Claims] 1. A level detector for acquiring and outputting a value related to a magnitude of a component around 19 kHz of an FM demodulated signal, and a magnitude of a component around 19 kHz from the value related to the magnitude of the component around 19 kHz. An FM noise eliminator, comprising: a level fluctuation detecting unit that detects a fluctuation of the frequency component; and a multipath noise determining unit that determines the occurrence of multipath noise from the fluctuation of the magnitude of the component around 19 kHz. 2. The FM noise elimination apparatus according to claim 1, wherein the level detector converts the component around 19 kHz into a first component having a frequency lower than 19 kHz, and extracts the first component. A first conversion unit that converts the component around 19 kHz into a second component having a frequency lower than 19 kHz and having a phase shifted by 90 degrees from the first component, and extracting the second component. An FM noise eliminator, comprising: a second conversion unit; and a magnitude detection unit that generates the value related to the magnitude of the component around 19 kHz from the first and second components. 3. The FM noise elimination device according to claim 1, wherein the level fluctuation detecting unit is configured to determine a magnitude relationship between the value related to the magnitude of the component around 19 kHz and a plurality of thresholds. , And a first comparing unit that outputs an output signal of a level according to the comparison result of the magnitude relation. 4. The FM noise elimination device according to claim 3, wherein the plurality of thresholds include an upper threshold and a lower threshold smaller than the upper threshold. Outputting the output signal of the first level when the value of the component around 19 kHz is larger than the upper threshold; and setting the value of the component around 19 kHz to the lower limit. Outputting a second level of the output signal when the value is smaller than a threshold value; and when the value of the magnitude of the component around 19 kHz is between the lower limit threshold value and the upper limit threshold value,
An FM noise eliminator for outputting the output signal of a level. 5. The FM noise elimination apparatus according to claim 1, wherein the multipath noise determination unit smoothes the output signal from the level fluctuation detection unit by smoothing the output signal. An FM noise removing apparatus, comprising: a smoothing unit that outputs a signal; and a second comparing unit that outputs a signal indicating that the multipath noise has occurred when the smoothed signal is equal to or more than a predetermined value. 6. The FM noise elimination apparatus according to claim 1, wherein the multipath noise determination unit includes a period from a start to an end of the multipath noise; A predetermined period from the end of the noise,
FM which is determined as the period of occurrence of the multipath noise
Noise removal device. 7. The FM noise elimination apparatus according to claim 1, wherein noise of the FM demodulated signal is detected, and the detection result and the multipath noise by the multipath noise detection unit are detected. A pulse noise detection unit that detects pulse noise of the FM demodulated signal based on a noise detection result; and a noise that corrects the FM demodulated signal according to the pulse noise detection result of the pulse noise detection unit. An FM noise elimination device further comprising a correction unit. 8. The FM noise elimination apparatus according to claim 1, wherein the detection sensitivity is controlled in accordance with a detection result of the multipath noise by the multipath noise detection unit. And said F
An FM noise eliminator, further comprising: a noise detection unit that detects noise of an M demodulation signal; and a noise correction unit that corrects the FM demodulation signal in accordance with a result of the noise detection by the noise detection unit. 9. An FM noise removing apparatus according to claim 1, comprising: an FM demodulation circuit configured to generate the FM demodulated signal.
FM receiver.