JPH01260940A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To prevent a new high level noise due to the elimination of pulse noise by using a gate means so as to interrupt a composite signal supply to a stereo demodulation means at the detection of pulse noise so as not to use a sub signal component for stereo demodulation. CONSTITUTION:When a pulse noise is included in an FM detection signal outputted from an FM detection circuit 4 and detected by a pulse noise detection circuit 9 and a noise detection signal is generated, both gate circuits 6, 15 are interrupted. An output signal level of a delay circuit 5 just before the interruption of the gate circuit is fed from a level holding circuit 7 to adders 19, 20, since no level holding circuit is provided on the output of the gate circuit 15, the level is not fed to multipliers 17, 18. Thus, no sub signal component is extracted and then the signal is not fed to the adders 19, 20. Thus, a main signal component is outputted from the adders 19, 20 as the audio component. Then the sub signal component is not used for stereo demodulation at the detection of pulse noise.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an FM stereo receiver equipped with a pulse noise canceling device.

BACKGROUND ART A conventional example of an FM stereo receiver equipped with a pulse noise removing device is shown in FIG. In this receiver, antenna 1
The FM broadcast radio waves arriving at the front end section 2 are amplified and converted into intermediate frequency signals. After being amplified by an IF (intermediate frequency) amplifier 3 having a limiter function, the signal is applied to an FM detection circuit 4. This detection circuit 4
The signal converted into a composite signal, which is an FM detection signal, is supplied to a delay circuit 5 consisting of an LPF (low pass filter) and delayed, and the delayed output is sent to the left and right channel signals via a gate circuit 6 and a level hold circuit 7. The signal is supplied to a multiplex demodulation circuit 8 which obtains the signal. Further, the composite signal from the FM detection circuit 4 is supplied to a pulse noise detection circuit 9. The pulse noise detection circuit 9 includes, for example, an HPF (bypass filter) that extracts high-frequency components in a composite signal, a rectifier circuit that performs full-wave rectification of the output signal of the HPF, and a rectifier circuit that performs full-wave rectification of the output signal of the HPF. and a comparator circuit that generates a noise detection signal when pulse noise is generated. The gate circuit 6 is cut off by this noise detection signal, and when the gate circuit 6 is cut off, the output signal level of the delay circuit 5 immediately before the cutoff is supplied from the level hold circuit 7 to the multiplex demodulation circuit 8. This eliminates pulse noise.

In such an FM stereo receiver, a circuit consisting of a capacitor 11 and a buffer amplifier 12 is used as the level hold circuit 7, as shown in FIG. In this case, for example, in a composite signal containing pulse noise A as shown in FIG. 6(a), when this pulse noise A is detected and the gate circuit 6 is cut off, the During the period tOFF, the level hold circuit 7 holds the 38 k Ilz subcarrier signal itself and outputs it to the multiplex demodulation circuit 8, as shown in FIG. 6(b). Therefore, when stereo demodulation is performed using sub-signal components as shown in FIG. 6(b), FIG. 6(c)
), the left channel signal waveform is only slightly deformed, but the right channel signal has new large noise due to pulse noise removal, resulting in increased auditory distortion.

In order to prevent such large noise from occurring, there is a receiver that uses a level hold circuit 7 in which a resistor 13 is inserted between the signal line from the gate circuit 6 and the capacitor 11, as shown in FIG. . In this case, Figure 6 (
In the composite signal containing pulse noise A as shown in a), the level hold circuit 7 holds a high frequency signal such as a subcarrier signal during the cutoff period tOFF as shown in FIG. 6(d). The output is approximately at the center level of the subcarrier signal. That is, a time delay occurs between the input voltage Vi from the gate circuit 6 and the terminal voltage Vc of the capacitor 11 as shown in FIG. As shown in FIG. 6B, when the gate circuit 6 is conductive, it follows the input voltage Vi, but during the cutoff period tOFF, the terminal voltage Ve immediately before the gate circuit 6 is cut off is maintained. Therefore, although new noise is generated in the left and right channel signals obtained by stereo demodulation as shown in FIG. 6(e), the level thereof is reduced.

However, capacitor 11 and resistor 13 are a kind of L
Since it acts as a PF, the above-mentioned time delay increases as the frequency is higher among the main signals with a lower frequency than the subcarrier signal in the composite signal, and the high frequency components are not retained at all, and new signals are generated when pulse noise occurs. This had the disadvantage that large noise was generated, resulting in large auditory distortion.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an FM stereo receiver that can reduce perceptual distortion and eliminate pulse noise.

The FM stereo receiver of the present invention includes a noise detection means that generates a noise detection signal when pulse noise is detected in the signal obtained by detecting the received signal, and
FM detection means for detecting M waves, and FM detection means for detecting F waves in response to a noise detection signal.
An FM stereo receiver comprising a suppression means for suppressing the output signal of the M detection means, and a stereo demodulation means for obtaining a sub signal component and a main signal component from the output signal of the suppression means and performing stereo demodulation using these components. The means is FMU
The stereo demodulation means consists of a gate means connected to the output of the wave means and turned off in response to a noise detection signal, and a holding means for holding the signal level output from the gate means. The main signal component is obtained from the output signal of the holding means by obtaining the signal component.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to FIG.

In the FM stereo receiver shown in FIG. 1, which is an embodiment of the present invention, the same parts as those in the receiver shown in FIG. A gate circuit 15 is connected together with 6. The gate circuit 15 has a pulse noise detection circuit 9 similar to the gate circuit 6.
It enters the cut-off state in response to a noise detection signal from. A level hold circuit 7 is connected to the output of the gate circuit 6 as in a conventional receiver. The level hold circuit 7 is the fifth
As shown in the figure (1 is complete), delay circuit 5, gate circuit 1
5 and the outputs of the level hold circuit 7 are connected to a multitiplex demodulation circuit 8.

The multi-tibre demodulation circuit 8 includes a PLL circuit 16, multipliers 17.18, adders 19.20 and de-emphasis circuits 21.22. PLL circuit 16 is delay circuit 5
The pilot signal is obtained from the output signal of the two
38 k Ilz subcarrier signals are generated.

One of these 38 k Ilz subcarrier signals is supplied to a multiplier 17 and the other to a multiplier 18 . The output signal of the gate circuit 15 is separately supplied to multipliers 17 and 18, and the subcarrier signal and the output signal of the gate circuit 15 are multiplied. The output signal of the multiplier 17 is supplied to one adder and added to the output signal of the level hold circuit 7, and the output signal of the multiplier 18 is supplied to the adder 20 and added to the output signal of the level hold circuit 7. Ru. Adder 19
The output signal of the adder 20 is output as a left channel signal via the de-emphasis circuit 21, and the output signal of the adder 20 is output as the right channel signal via the de-emphasis circuit 22. The rest of the configuration is the same as the receiver shown in FIG.

In the FM stereo receiver according to the present invention having such a configuration, let the composite signal output from the delay circuit 5 be L+R+ (L-R) cos (IJs t,
It is assumed that the forward and reverse signals of the subcarrier signal output from the PLL circuit 16 are COSωst. Here, L is the left channel signal, R is the right channel signal, and ωS is the angular frequency of the subcarrier signal.

The output signals VB and V2 of the multipliers 17 and 18 are given tV+ -(
L-R) /2+ (L+R) cos ωs t+
((LR) /21 cos 2ωs tV2 =
-(L-R) /2- (L+R) cos (IJs
t-((LR)/21 cos 2<IJ
It can be expressed as S t. Therefore, as an audio component (low frequency component), from multiplier 17 to adder 1
(LR)/2 is supplied to the multiplier 9, and -(LR)/2 is supplied from the multiplier 18 to the adder 20.

That is, only the sub-signal components are supplied. On the other hand, the composite signal from the level hold circuit 7 is attenuated to 1/2 by an attenuating means such as a resistor (not shown) and supplied to adders 19 and 20. That is, as the audio component, only the main signal component (L+R)/2 is supplied to the adders 19 and 20. Therefore, the adder 19 outputs the left channel signal, and the adder 2
Right channel signal R is output from 0'.

On the other hand, pulse noise is included in the FM detection signal output from the FM detection circuit 4, and the pulse noise detection circuit 9
When detected by the pulse noise detection circuit 9, a noise detection signal is generated.

This noise detection signal causes both gate circuits 6 and 15 to be cut off. For example, when the delay circuit 5 outputs a signal containing pulse noise B as shown in FIG. As shown in FIG. 2(b), the signal is supplied from the level hold circuit 7 to adders 19 and 20.

Since the output of the gate circuit 15 is not provided with a level hold circuit, when the gate circuit 15 is cut off, no signal is supplied to the multipliers 17 and 18 as shown in FIG. 2(c). Therefore, the sub-signal components are not extracted and the adder 19.2
0 is not supplied. However, since the adders 19 and 20 are supplied with the signals held in the level hold circuit 7, the main signal components are output as audio components from the adders 19' and 20, respectively. Therefore, when detecting pulse noise, the sub-signal component is not used for stereo demodulation, and no new large noise is generated due to pulse noise detection 1.

In the above-mentioned embodiment, pulse noise is detected only from the output signal of the FM detection circuit 4, but it is detected from the signal obtained by AM detection of the intermediate frequency signal in the IF amplifier 3, the so-called S (signal) meter signal. Pulse noise may be detected, or moreover, pulse noise may be detected from both the S meter signal and the output signal of the FM detection circuit 4.

Further, in the above embodiment, a muting circuit is inserted between the FM detection circuit 4, the delay circuit 5, and the pulse noise detection circuit 9, and the gate circuit 15 and the multipliers 17 and 18
A separation control circuit is inserted between the level hold circuit 7 and the adder 19.20, and a high frequency attenuation control circuit is inserted between the level hold circuit 7 and the adder 19. It may also be controlled by

Further, in the above embodiment, two gate circuits 6
．． However, as shown in FIG. 3, a buffer amplifier 23 is inserted in the input stage of the level hold circuit 7 so that the input impedance of the level hold circuit 7 does not affect the output signal of the gate circuit 6, and a gate circuit is also provided. 6
If the level hold circuit 7 is configured to perform the holding operation at the timing to control the operation of the gate circuit 6, that is, in response to the noise detection signal, the output signal of the gate circuit 6 can be input to the multipliers 17 and 18 without providing a new gate circuit 15. may be supplied to

As described above, the FM stereo receiver of the present invention has the following effects:
The composite signal of the FMIQ wave output is supplied to the holding means via the gate means which is cut off when pulse noise is detected, the sub signal component is obtained from the output signal of the gate means, and the main signal component is obtained from the output signal of the holding means. Then, stereo demodulation is performed. Therefore, when pulse noise is detected, the supply of the composite signal to the stereo demodulation means is cut off by the gate means, and the sub-signal components are not used for stereo demodulation, making it possible to prevent new large noise due to pulse noise removal. , auditory distortion can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the receiver in FIG. 1, and FIG. 3 is a block diagram showing a part of another embodiment of the present invention. FIG. 4 is a block diagram showing a conventional example of an FM stereo receiver, FIGS. 5 and 7 are circuit diagrams showing specific configurations of a level hold circuit, respectively.
6 is a waveform diagram showing the operation of the receiver shown in FIG. 4, and FIG. 8 is a waveform diagram showing the operation of the level hold circuit shown in FIG. 7. Explanation of symbols of main parts 3... IF amplifier circuit 4... FM detection circuit 6.15... Gate circuit 7... Level hold circuit 8... ...Multiplex demodulation circuit 9...
・Pulse noise detection circuit 17.18... Multiplier 19.20... Adder Applicant Pioneer Corporation

Claims (1)

[Claims] noise detection means for generating a noise detection signal when pulse noise is detected in the signal obtained by detecting the received signal;
FM detection means for performing FM detection on the received signal; suppression means for suppressing the output signal of the FM detection means in response to the noise detection signal; and obtaining a sub signal component and a main signal component from the output signal of the suppression means. and stereo demodulation means for performing stereo demodulation using these components, wherein the suppressing means is connected to the output of the FM detection means and includes gate means that enters a cutoff state in response to the noise detection signal. , holding means for holding the signal level output from the gate means, and the stereo demodulation means obtains the sub signal component from the output signal of the gate means and obtains the main signal component from the output signal of the holding means. An FM stereo receiver characterized by obtaining.