JPH1188207A - Noise canceller for fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise canceller for an FM receiver, by which the effect of a phase depending noise produced especially in multi-path disturbance is reduced. SOLUTION: A noise canceller 4 operates when an amplitude pulse noise component included in an IF signal and/or an FM detection output from an FM receiver is a prescribed threshold level or over to eliminate the noise. The noise canceller 4 is provided with a multi-path detection circuit 9 detecting a multi-path disturbance and the sensitivity of the noise canceller 4 is varied with a detection level of the multi-path detection circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an FM noise canceller.

[0002]

2. Description of the Related Art A noise canceller used in a conventional on-vehicle FM tuner is intended to remove amplitude pulse noise mainly generated from an electric system of a vehicle and another vehicle. By the way, in the FM tuner, distortion of the amplitude component and the phase component occurs when receiving multipath interference. Multipath interference occurs because radio waves transmitted from a broadcasting station are reflected on buildings (high-rise buildings, etc.), mountains, and the like, are delayed and received as a plurality of reflected waves, and cause mutual interference with direct waves. For this reason, a plurality of radio waves delayed in time
The distortion of the amplitude component and the phase component occurs in the tuner circuit, resulting in multipath noise. In particular, it is known that when the noise canceller operates when distortion of the amplitude component occurs, the distortion of the signal component deteriorates. However, it is also known that the distortion of the amplitude component is suppressed to some extent by the limiter in the FM tuner and becomes less noticeable.

[0003] Therefore, as one of the prior arts, there is a technique of disabling a noise canceller when multipath interference is received, thereby preventing signal component distortion from deteriorating. (See Japanese Patent Publication No. Sho 62-50007) However, since the distortion of the phase component becomes noise at a high frequency (several kHz or more) after demodulation, in this technique, when the distortion of the phase component is large, the audibility due to the multipath noise is increased. The above-mentioned noise feeling is deteriorated.

Further, as in the noise canceller shown in FIG. 7, when multipath interference is presently caused, measures are taken to reduce multipath noise, such as changing the stereo separation, volume and frequency characteristics. There are many products. The reason for this countermeasure is that, similarly to the above, when multipath interference is caused, multipath noise is generated, and depending on the reception conditions, the noise may be extremely annoying to the sense of hearing.

In FIG. 7, 1 is an IF signal input terminal of an FM receiver, 2 is an IF amplifier, 3 is an FM detector, 4 is a noise canceller, 5 is a stereo demodulation circuit, 6 and 7 are high-pass filters, and 8 is the degree of isolation. And frequency characteristic control circuit, 9
Is a multipath detection circuit, and 10 is a stereo signal output terminal. An IF signal (for example, IF frequency = 10.7 MHz) from an IF input terminal 1 is amplified by an IF amplifier 2 and
The signal is detected by a detector 3, demodulated by a stereo demodulation circuit via a noise canceller 4, and output to a stereo signal output terminal 10.
More L and R stereo signals are obtained.

The noise canceller 4 outputs a high-pass filter 6 (for example, a cutoff frequency Fc = 100 kHz) from an electric field strength detection (S meter) output from the IF amplifier 2.
Noise component detected through the filter and the FM detector 3
(For example, the cutoff frequency Fc = 10
0 kHz) The amplitude noise component detected through the high-pass filter 7 is supplied, and operates at a preset sensitivity, that is, when the level of these amplitude noise components exceeds a predetermined threshold level, and the FM detector 3 A predetermined process is performed on the signal reaching the stereo demodulation circuit 5,
These amplitude noise components are removed.

[0007] The isolation and frequency characteristic control circuit 8 includes an IF
The operation of the stereo demodulation circuit 5 is controlled in accordance with the level of the S-meter output input from the amplifier 2 to vary the degree of separation and frequency characteristics of the L and R stereo signals obtained at the stereo signal output terminal. That is, if the output level of the S meter is low, the stereo separation degree is reduced and the frequency characteristic is narrowed,
If the output level of the S-meter is high, it is varied so as to increase the stereo separation degree and widen the frequency characteristics. On the other hand, the multi-path detection circuit 9 detects, for example, a 19 kHz FM stereo broadcast from the IF output of the IF amplifier 2 by multi-path interference.
An amplitude modulation component generated in the z pilot signal is detected.

Therefore, when the detection level of the multipath detection circuit 9 exceeds a predetermined threshold level, the separation and frequency characteristic control circuit 8 is operated to reduce the stereo separation of the stereo demodulation circuit 5 and reduce the frequency. Control to narrow the characteristics. As a result, when receiving multipath interference, the influence of multipath amplitude noise is reduced.

[0009]

However, in the above-mentioned conventional technique, the influence of the multipath amplitude noise is reduced. However, when the influence of the multipath phase noise is strong, the audibility is extremely low. Had a problem of causing harsh noise.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a noise canceller in an FM receiver which can reduce the influence of phase noise generated due to multipath interference.

[0011]

According to a first aspect of the present invention, there is provided a noise canceller in an FM receiver, wherein an amplitude pulse noise component contained in an IF signal and / or an FM detection output of the FM receiver is included. A noise canceller that operates when the level is equal to or higher than a predetermined threshold level and removes the noise includes a multipath detection circuit that detects multipath interference, and varies the sensitivity of the noise canceller according to the detection level of the multipath detection circuit. It is characterized by doing so.

[0012] The noise canceller in the FM receiver according to the present invention is an I / O of the FM receiver.
A noise canceller that operates when the amplitude pulse noise component included in the F signal and / or the FM detection output is equal to or higher than a predetermined threshold level and removes the noise;
A noise detection circuit for detecting a noise component other than a noise component due to an amplitude pulse noise component and a multipath interference for operating the noise canceller, wherein the noise canceller is provided in accordance with a detection level of the multipath detection circuit and the noise detection circuit. The sensitivity is varied.

[0013]

FIG. 1 is a block diagram showing an embodiment of a noise canceller in an FM receiver according to the present invention. In FIG. 1, the same components as those in FIG. When multipath interference is received, the noise perception deteriorates particularly due to multipath noise due to distortion of the phase component. Therefore, in the present invention, as a configuration different from the conventional configuration of FIG.
By operating the noise canceller 4 in accordance with the level of the multipath interference detected by the multipath detection circuit 9, the noise perception due to multipath noise due to phase component distortion is particularly improved.

More specifically, in FIG. 1, the level of the multipath interference detected by the multipath detection circuit 9 indicates
The sensitivity of the noise canceller 4 is varied. How to change
For example:

The manner of operation of the noise canceller 4 is continuously changed. This method is performed continuously (for example, linearly as shown in FIG. 2) so that the sensitivity of the noise canceller 4 is increased in accordance with the detection level from the multipath detection circuit 9.
Alternatively, as the multipath interference increases, the threshold level of the noise canceller 4 is changed to a lower level, and the amplitude noise component from the high-pass filter 6 and / or the high-pass filter 7 is changed. By making the noise canceller 4 operate at a smaller level and performing predetermined processing on the signal,
Particularly, it is possible to prevent adverse effects on the audibility due to multipath noise due to phase component distortion.

The manner of operation of the noise canceller 4 is changed stepwise. This way is changed so that the sensitivity of the noise canceller 4 increases stepwise according to the detection level from the multipath detection circuit 9.

For example, as shown in FIG. 4, when the detection level of the multi-pass detection circuit 9 becomes L1, the sensitivity of the noise canceller 4 is controlled so as to decrease from the threshold level S1 to S2. Prevents adverse effects on hearing due to path noise.

As shown in FIG. 5, the detection levels of the multipath detection circuit 9 are L1, L2, L3 and L4, respectively.
, The sensitivity of the noise canceller 4 is controlled so as to gradually decrease to the threshold levels S1, S2, S3, and S4, thereby preventing adverse effects on the audibility due to multipath noise due to phase component distortion.

As described above, the sensitivity of the noise canceller 4 is varied according to the detection level of the multipath detection circuit 9 to reduce the influence of the multipath, particularly, the phase component. However,
Regarding the influence of the amplitude component due to the multipath interference, the influence of the overmodulation station, and the like, the noise canceller 4 is operated in the conventional manner so that the distortion and the noise feeling are not deteriorated.

[0020]

FIG. 6 is a block diagram showing another embodiment of the FM noise canceller according to the present invention. 6, the same components as those in FIG. 1 will be described with the same reference numerals. Therefore, FIG. 6 differs from the configuration of FIG. 1 in that the IF output of the IF amplifier 2
And a noise detection circuit 11 for detecting other noise different from the amplitude noise component detected through the high-pass filter 7 from the detection output of the FM detector 3 and the amplitude noise component detected through the FM detector 3. This noise detection circuit 11 detects, for example, adjacent interference from the output of the S meter through a band-pass filter of 100 kHz.

In addition to the above-described adjacent interference, the noise detection circuit 11 may include any other noise component that causes annoying audibility, such as an amplitude pulse noise component for operating the noise canceller 4 and a noise component due to multipath interference, such as an IF amplifier. A noise component due to a weak electric field, a noise component due to a strong electric field, a noise component due to overmodulation, and the like included in the IF output of the second and / or the detection output of the FM detector 3 may be detected.

For example, in a weak electric field, a noise component increases due to deterioration of the S / N ratio, and in overmodulation, distortion occurs due to a ceramic filter or the like in the IF amplifier 2.
The noise canceller 4 may malfunction and the distortion may be deteriorated. Therefore, when the sensitivity of the noise canceller 4 is lowered, the noise canceller 4 does not operate where it is desired to operate, and the noise feeling is deteriorated.

Therefore, in FIG.
In addition to varying the sensitivity of the noise canceller 4 in accordance with the level of the multipath interference detected in step (1), the sensitivity of the noise canceller 4 is also varied in accordance with the detection level of the noise detection circuit 11 (see FIG. 2 to FIG. 5). Similarly, the higher the detection level, the higher the sensitivity.)
In particular, the noise perception due to multipath noise due to phase component distortion and noise components other than the amplitude pulse noise component and the multipath noise component is improved.

As described above, the multipath noise including the distortion of the phase component is smoothed by the operation of the noise canceller 4 to improve the audible noise (particularly in the unpleasant high frequency range). Further, as is currently practiced in many products, if the degree of separation, volume and frequency characteristics are varied, the effect is further enhanced. Here, it has been confirmed that operating the noise canceller does not produce an unpleasant sound when hearing a multipath disturbance having a large phase component distortion. However, unless the sensitivity (especially responsiveness) of the noise canceller is increased, the sense of noise tends to be improved.

[0025]

According to the present invention, it is possible to improve the audible noise particularly due to multipath phase noise.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an FM noise canceller according to the present invention.

FIG. 2 is a graph showing a first example of a multipath detection level-noise canceller sensitivity characteristic in FIG. 1;

FIG. 3 is a graph showing a second example of a multipath detection level versus noise canceller sensitivity characteristic in FIG. 1;

FIG. 4 is a graph showing a third example of a multipath detection level versus noise canceller sensitivity characteristic in FIG. 1;

FIG. 5 is a graph showing a fourth example of the multipath detection level versus noise canceller sensitivity characteristic in FIG. 1;

FIG. 6 is a block diagram showing another embodiment of the FM noise canceller according to the present invention.

FIG. 7 is a block diagram illustrating an example of a conventional FM noise canceller.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 IF input terminal 2 IF amplifier 3 FM detector 4 noise canceller 5 stereo demodulation circuit 6 high-pass filter 7 high-pass filter 8 isolation and frequency characteristic control circuit 9 multi-path detection circuit 10 stereo signal output terminal 11 noise detection circuit

Claims (2)

[Claims] An IF signal and / or FM signal of an FM receiver
A noise canceller that operates when the amplitude pulse noise component included in the detection output is equal to or higher than a predetermined threshold level and removes the noise includes a multipath detection circuit that detects multipath interference, and the detection of the multipath detection circuit A noise canceller in an FM receiver, wherein the sensitivity of the noise canceller is varied according to a level. 2. An IF signal and / or FM signal of an FM receiver.
In a noise canceller that operates when the amplitude pulse noise component included in the detection output is equal to or higher than a predetermined threshold level and removes the noise, a multipath detection circuit that detects multipath interference, and an amplitude pulse that operates the noise canceller A noise detection circuit for detecting a noise component other than a noise component and a noise component due to multipath interference, wherein the sensitivity of the noise canceller is varied according to the detection levels of the multipath detection circuit and the noise detection circuit. A noise canceller in an FM receiver, characterized in that: