JP3276684B2 - Multipath noise removal circuit for FM receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipath noise elimination circuit for an FM receiver, and more particularly to an improved multipath noise elimination circuit capable of securing an optimum sound quality according to the state of a broadcast wave while deteriorating channel separation. Circuit.

[0002]

2. Description of the Related Art In an FM receiver, various kinds of noises are mixed depending on a radio wave propagation state, and a good receiving operation is impaired. In particular,
In the on-vehicle FM receiver, there is a problem that a received electric field fluctuates greatly as a vehicle travels, and that multipath noise is easily picked up by reflection of a building or the like. A stereo noise control circuit for temporarily degrading the separation is provided.

FIG. 3 shows a schematic configuration of a conventional general FM receiver. The FM reception signal received by the antenna 10 is subjected to processing such as desired high-frequency amplification by the front-end processor 11, and then intermediate frequency amplification is performed by the IF circuit 12. The intermediate-amplified received signal is detected by a detector 13,
Channel and L channel signals, which are respectively separated into R speakers 17 and L via low frequency amplifiers 15 and 16 respectively.
It is sent to the speaker 18.

[0004] In such an FM receiver, when multipath noise occurs, noise removal is performed to degrade the separation of the R and L channels and switch to monaural reception, thereby making the multipath noise apparently inconspicuous. The deterioration of the channel separation is performed by a stereo noise control circuit. In FIG.
The FET 21 is operated by this signal,
The channel separation is deteriorated by mixing the signals of the R and L channels.

[0005]

However, in the conventional apparatus described above, the stereo noise control circuit deteriorates the channel separation over the entire frequency band of the detected audio signal, usually in the range of 50 to 15 KHz. Therefore, there is a disadvantage that the sound quality of the FM receiver is unnecessarily deteriorated. For example, when multipath noise occurs, the channel separation must be reduced to about 4 dB in order to improve the S / N by 10 dB. As a result, in the conventional apparatus, the sound quality significantly decreases, and the multipath noise removal and the sound quality are reduced. It was not possible to balance maintenance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an improved FM receiver capable of achieving both optimal removal of multipath noise and maintenance of sound quality. It is in.

[0007]

In order to achieve the above object, the present invention provides an FM receiver having a stereo noise control circuit for deteriorating channel separation when multipath noise is generated. A variable band-pass filter or a variable band elimination filter for greatly deteriorating the low- and high-frequency channel separation with respect to the middle band, and filtering the band-pass filter or the band elimination filter according to the state of the broadcast radio wave. Wave characteristics can be changed.

[0008]

Therefore, according to the present invention, the filtering characteristics of the variable band-pass filter or the variable band elimination filter provided in the stereo noise control circuit are changed in accordance with the state of the broadcast radio wave, whereby the channel separation is performed. Is mainly performed for both the high frequency range and the low frequency range, and the sound quality is ensured by the middle frequency component.

[0009] The state of the broadcast radio wave can be varied by changing the Q, frequency band, cut-off frequency and the like of the band-pass filter or band elimination filter according to the type of news broadcast or music broadcast, for example. Alternatively, the characteristics of the band elimination filter can be changed according to the received electric field strength.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first preferred embodiment of an FM receiver having a built-in multipath noise elimination circuit according to the present invention. The same members as those in FIG. I do.

In this embodiment, the R-channel and L-channel signals separated by the multiplexer 14 are converted into L + R and L-R signals by an adder 30 and a subtractor 31, respectively. The output of the subtractor 31 (L−
R) is sent to a variable band-pass filter 32 which is characteristic of the present invention, and only the middle band component is extracted. The signal is added to the (L + R) signal in the detector 34 to generate an L channel signal. On the other hand, the mid-range component output from the amplifier 33 is subtracted from the (L + R) signal output from the adder 30, and as a result, an R channel signal is obtained.

According to the first embodiment, the bandpass filter 3
2 extracts the middle band component of the (LR) signal, so that when multipath noise occurs, the low band and high band components of the received signal are reduced, and the output L and R channel signals have low channel separation from each other. And a signal deteriorated in the high frequency range, and as a result, the multipath noise is controlled to be apparently inconspicuous. Then, even with such channel separation, the L and R signals of both channels remain in the middle band component, so that the deterioration of sound quality can be suppressed to a minimum.

[0014] In the first embodiment, the variable bandpass filter 32 to ride wave characteristic is selected by the control signal from the input terminal 32a, filtering characteristics in the examples sharpness Q, the frequency band f ₀ and cut configured alone or in combination from off frequency f _c. And terminal 32
The control signal supplied to a is switched according to the type of broadcast wave, for example, a news broadcast having narrow-band characteristics, a music broadcast having wide-band characteristics, and the like. Alternatively, the frequency may be automatically switched from the frequency spectrum of the received signal detected from the IF circuit 12. In addition, a change in the received electric field strength can be used as the control signal. In this case, as the received electric field strength decreases, the channel separation of only the initial low band and the high band is sequentially changed from the channel separation deterioration of the entire band to the channel separation deterioration of the entire band. It is also preferable to shift.

FIG. 2 shows a second preferred embodiment of the FM receiver according to the present invention.

In the second embodiment, the detected L and R
The signal is subtracted by a subtractor 40, and the difference output is supplied to a variable band elimination filter 41. The variable band elimination filter 41 in the second embodiment is different from the subtractor 4
Only the low-frequency component and the high-frequency component of the L / R difference, which is the output of 0, are extracted, amplified to a predetermined level by a variable amplifier 42, and both L signals and R
Subtract the signal. Also in the second embodiment, a control signal similar to that described in the first embodiment is supplied to the input terminal 41a of the variable band elimination filter 41. It is possible to output L and R signals in which predetermined low band and high band components are mainly subjected to channel separation deterioration.

Therefore, also in the second embodiment, the frequency characteristic of the band elimination filter is varied in accordance with the state of the broadcast radio wave, thereby achieving both optimal channel separation deterioration and sound quality assurance depending on the type of noise or the type of broadcast program. be able to.

Although not shown in detail in each of the above-described embodiments, it is preferable that the variable amplifier 33 or 42 also changes its amplification or attenuation in accordance with the state of the broadcast radio wave or the received electric field strength. , The level of channel separation in the present invention can be selected.

As described above, according to the present invention, when multipath noise is generated, the bandpass filter of the stereo noise control circuit is generally a narrow band filter having a large Q, and the middle band component has a small amount. The region is left, the channel separation is degraded over a wide band of the low band and the high band, and reliable multipath noise is removed.

On the other hand, when weak electric field noise is generated, in the present invention, the band of the variable band-pass filter or the band elimination filter is changed in accordance with the reception electric field level as described above. By doing so, a large amount of the extracted components are left, and only a part of the low band and the high band is used for deterioration of the channel separation.

[0021] As a result, it is possible to obtain a receiving operation that places importance on ensuring sound quality.

Further, as described above, in a reception state having a narrow band such as news, importance is attached to the elimination of multipath noise by using a narrow band characteristic having a large Q according to the type of a broadcast program. When the receiving band is wide like a program, a wide band filter with a small Q is used. As a result, it is possible to maintain the reception function that ensures sound quality, although there is a disadvantage that some multipath noise remains.

Further, in a drama broadcast program or the like, by selecting an intermediate band between the bands used for the news and music, it is possible to always achieve both the removal of multipath noise and the securing of sound quality.

[0024]

As described above, according to the present invention,
While removing multipath noise due to channel separation degradation, it performs band control that leaves the mid-range component of the received signal in accordance with the state of the broadcast wave, thereby enabling optimal compatibility between multipath noise removal and sound quality. Becomes

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a first preferred embodiment of an FM receiver according to the present invention.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a block circuit diagram of a conventional FM receiver.

[Explanation of symbols]

 32 Variable band pass filter 33, 42 Variable amplifier 41 Variable band elimination filter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/10

Claims (3)

(57) [Claims] [Claim 1] noise stereo broadcasting radio waves received at the time of occurrence
The right and left signals obtained by
An FM receiver comprising a stereo noise control circuit for deteriorating channel separation, wherein the stereo noise control circuit includes the right signal and the right signal in a middle band with respect to a low frequency band and a high frequency band.
Variable band-pass filter for reducing the degree of mixing with the left signal, or the variable band elimination filter is provided, the filtering characteristics of the variable band-pass filter or the variable band elimination filter according to the state of the airwaves Stereo noise control for FM receiver characterized by variable
Lumpur circuit. 2. Receiving a stereo broadcast wave when noise occurs.
By mixing the right and left signals obtained by
Stereo that degrades the separation of both right channels
Stereo FM receiver with noise control circuit
Oite, the stereo noise control circuit is low among the difference signal representing the difference between the left signal and the right signal
Extract the middle frequency component from the high and low frequency components.
A variable band-pass filter, and a sum signal representing a sum of the left signal and the right signal;
Based on the output signal from the variable bandpass filter
A stereo signal that generates stereo signals for both left and right channels
Signal generation means, and the variable band-pass filter according to the state of the broadcast radio wave.
FM receiver characterized by changing the filtering characteristics
Rheo noise control circuit. 3. Receiving a stereo broadcast wave when noise occurs.
By mixing the right and left signals obtained by
Stereo that degrades the separation of both right channels
Stereo FM receiver with noise control circuit
Oite, the stereo noise control circuit, in ones of the difference signal representing the difference between the left signal and the right signal
Low frequency and high frequency components
A variable band elimination filter for outputting the left signal and an output signal from the variable band elimination filter.
It generates a stereo signal of the left channel on the basis of the item,
The right signal and the output signal from the variable band elimination filter.
And generate a right channel stereo signal based on the
It comprises a stereo signal generation means, a of the variable band elimination filter according to the state of the airwaves
FM receiver characterized by changing the filtering characteristics
Rheo noise control circuit.