JPH0557775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a pulse noise removal device in an FM receiver.

BACKGROUND ART A conventional example of a pulse noise removing device for an FM receiver is shown in FIG. In this device, FM
The detection signal output from the FM detection circuit 1 of the receiver passes through a delay circuit 2 consisting of an LPF (low pass filter).
This delayed output is supplied to a stereo demodulation circuit 5 via a gate circuit 3 and a level hold circuit 4. The detected signal is also supplied to a HPF (high pass filter) 6 for noise detection, and the nozzle component signal that has passed through the HPF 6 is amplified by a noise amplifier 7 and supplied to a noise detection circuit 8. Noise detection circuit 8 is noise amplifier 7
It consists of a rectifier circuit that rectifies the output signal of the rectifier circuit, and a level determination circuit that determines the output level of the rectifier circuit, and this noise detection output is supplied to the waveform shaping circuit 9. The waveform shaping circuit 9 is composed of, for example, a one-shot multipibrator, and converts the noise detection output into a pulse having a predetermined wave height and time width, and supplies the pulse to the gate circuit 3. The gate circuit 3 is controlled by the pulses supplied from the waveform shaping circuit 9 to the gate circuit 3.
is driven to a signal cutoff state, and in the signal cutoff state, the delayed output level immediately before the signal cutoff is held by the level hold circuit 4 and supplied to the stereo demodulation circuit 5. This prevents the occurrence of spikes due to sudden changes in potential. Also noise amplifier 7
The output signal of is rectified by the rectifier circuit 10.
The signal is supplied to an LPF (low pass filter) 11.
The LPF 10 smoothes the rectified output to obtain a DC signal corresponding to the noise level and feeds it back to the noise amplifier 7, thereby forming an AGC loop.

For example, when receiving a weak electric field, the white noise characteristic of FM tends to increase, and in this case, the HPF
The noise level of the output signal of No. 6 increases. Due to the increase in the noise level, the level of the DC signal output from the LPF 10 increases, and this decreases the gain of the noise amplifier 7 as an AGC signal. Therefore, the noise level supplied from the noise amplifier 7 to the noise detection circuit 8 is kept constant. This action prevents each circuit such as the noise amplifier 7 and the noise detection circuit 8 from becoming saturated.

Note that the delay circuit 2 is provided to compensate for the time required from when the pulse noise is supplied to the HPF 6 to when the gate circuit 3 is cut off, and uses, for example, the delay characteristics of an active low-pass filter. .

In such a conventional pulse noise removal device, the DC signal obtained by rectifying and smoothing the high frequency component of the FM detection output is taken as the average level of the high frequency component of the FM detection output, and a signal higher than the average level is The pulse noise is removed by detecting it as a pulse noise and controlling the gate circuit to cut it off.
However, when continuous noise is received by multipath, the gate circuit remains cut off for a long period of time, resulting in problems such as increased distortion and generation of new noise due to hold errors in the level hold circuit.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pulse noise removal device that can prevent an increase in the feeling of distortion and the generation of noise due to a hold error of a level hold circuit when continuous noise occurs.

The pulse noise removing device of the present invention includes an amplifying means for amplifying the high-frequency component of the signal obtained by detecting a received signal of an FM receiver, and an output signal level of the supplied amplifying means exceeds a reference level. noise detection means that generates a cutoff signal upon detecting noise;
a first gate means for cutting off the supply of the output signal of the FM detection circuit to the subsequent stage in response to the cutoff signal; It is characterized by comprising a DC signal generating means for controlling the gain, and a suppressing means for suppressing the generation of the cutoff signal when the cutoff state of the first gate means continues for a predetermined time or more.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 7.

In the pulse noise removing device for an FM receiver which is an embodiment of the present invention shown in FIG.
The same parts as in the conventional device shown in the figure are indicated by the same reference numerals, and a noise detection circuit 8 and a rectifier circuit 12 are connected to the output of the noise amplifier 7. The rectifier circuit 12 has a full-wave rectification function and is provided to make the polarity of the output signal of the noise amplifier 7 unidirectional. An LPF 11 is connected to the output of the rectifier circuit 12 via a second gate circuit 13 . Like the first gate circuit 3, the gate circuit 13 enters a cut-off state in response to the output signal of the first waveform shaping circuit 9. However, there is a normally closed switch element 1 between the gate circuit 13 and the waveform shaping circuit 9.
6 is provided. It is turned off according to the output signals of the switch element 16 and the timer 17. timer 17
measures the high level output duration time of the waveform shaping circuit 9, and turns off the switch element 16 when the measured time reaches a predetermined time. LPF11 is resistor 14
and a capacitor 15. The output signal of the LPF 11 is supplied to the noise amplifier 7 as in the conventional case.

In the pulse noise removing device according to the present invention having such a configuration, if the output signal of the FM detection circuit 1 is a signal containing pulse noise (symbol A) as shown in FIG. The high-frequency component of the output signal of FM detection circuit 1 is extracted, and the HPF
The output signal of 6 is amplified by the noise amplifier 7 to obtain the waveform shown in FIG. 2b. The signal is then full-wave rectified by the rectifier circuit 12 and output as shown in FIG. 2c. The output signal of the rectifier circuit 12 is a rectified signal containing noise other than pulse noise,
This rectified signal passes through the gate circuit 13 and passes through the LPF 11.
supplied to The LPF 11 obtains a DC signal by smoothing the rectified signal. This DC signal controls the gain of the noise amplifier 7. That is, the gain of the noise amplifier 7 decreases as the DC signal level increases.

On the other hand, the noise detection circuit 8 includes a rectifier circuit (not shown) that performs full-wave rectification of the output signal of the noise amplifier 7;
A comparison circuit (not shown) is provided to compare the rectified output level with a reference level. When the rectified output level exceeds the reference level, the noise detection circuit 8 generates a high level signal as shown in FIG. 2d. In response to the rise of this high level output, the waveform shaping circuit 9 generates a pulse with a predetermined wave height and time width as a cutoff signal, as shown in FIG. 2e. This cutoff signal causes the gate circuits 3 and 13 to be cut off (OFF state). Therefore, the detection signal output from the FM detection circuit 1 and passed through the delay circuit 2 is blocked by the gate circuit 3. Delay circuit 2
is provided to compensate for the detection time of pulse noise, so when the gate circuit 3 is cut off, the supply of the detection signal containing pulse noise from the delay circuit 2 to the level hold circuit 4 is cut off, and the level hold circuit 4 outputs the signal immediately before the cutoff. Furthermore, even if a rectified signal containing pulse noise is output from the rectifier circuit 12 due to shutoff of the gate circuit 13, the rectified signal is output from the gate circuit 13 to the LPF.
11 is not supplied. The rising portion of the pulse noise component is due to the delay in the generation of the cutoff signal.
In this cutoff state, the DC voltage level held in the capacitor 15 of the LPF 11 is supplied to the noise amplifier 7.

On the other hand, the timer 17 starts measuring a predetermined time when the output level of the waveform shaping circuit 9 is reversed from a low level to a high level. When pulse noise occurs, the output level of the waveform shaping circuit 9 returns to a low level until the end of measuring the predetermined time, so the timer 17 is reset without turning off the switch element 16.

Next, when the received signal level decreases as shown in FIG. 3a due to the occurrence of multipath, the output signal of the FM detection circuit 1 becomes a signal containing burst-like continuous noise as shown in FIG. 3b. In this case, similar to the pulse noise described above, the output level of the waveform shaping circuit 9 is reversed from a low level to a high level, and the gate circuits 3 and 13 are cut off. At the same time, the timer 17 starts measuring a predetermined time. When the high level output state of the waveform shaping circuit 9 continues for a predetermined time and the timer 17 finishes measuring the predetermined time, the timer 17 generates a cutoff stop signal and switches the switch element 1
6 is turned off. As a result, the supply of the high level signal, that is, the cutoff signal, from the waveform shaping circuit 9 to the gate circuit 13 is cut off. Therefore, rectifier circuit 1
The output signal from 2 passes through the gate circuit 13.
The level of the DC signal supplied to and output from the LPF 11 increases. As the gain of the noise amplifier 7 decreases due to the increase in the DC signal level, the noise detection sensitivity of the noise detection circuit 8 decreases, and the input level becomes below the reference level, and the noise detection circuit 8 stops generating a high level signal. Therefore, the generation of the cutoff signal from the waveform shaping circuit 9 is stopped, the timer 17 is reset, and the gate circuit 3 is turned on, so that the FM detection signal is transmitted to the delay circuit 2, the gate circuit 3, and the level hold circuit 4. The signal is supplied to the stereo demodulation circuit 5 via.

FIG. 4 shows another embodiment of the invention. In this pulse noise removing device, a constant current source 1
8 is connected to the output of the LPF 11 via a switch element 19. Switch element 19 is timer 1
It is turned on in response to the output signal of 7. That is, when the high level output state of the waveform shaping circuit 9 continues for a predetermined time and the timer 17 finishes measuring the predetermined time, the timer 17 generates a cutoff stop signal and turns on the switch element 19. When the switch element 19 is turned on, a current flows from the constant current source 18 to the capacitor 15 via the switch element 19 to charge the capacitor 15. As a result, the voltage across the capacitor 15, that is, the DC signal level increases, the noise detection circuit 8 stops generating a high-level signal, and the waveform shaping circuit 9 stops generating a cutoff signal, similar to the device shown in FIG. The operation is stopped and the gate circuit 3 is turned on.

FIG. 5 also shows another embodiment of the invention. In this pulse noise removing device, a gate circuit 20 is connected in parallel to the gate circuit 13.
The gate circuit 20 is turned on in response to the output signal of the timer 17. That is, when the high level output state of the waveform shaping circuit 9 continues for a predetermined time and the timer 17 finishes measuring the predetermined time, the timer 17 generates a cutoff stop signal and turns on the gate circuit 20. When the gate circuit 20 is turned on, the output signal of the rectifier circuit 12 is supplied to the LPF 11 via the gate circuit 20, and the capacitor 15 is charged. As a result, the voltage across the capacitor 15, that is, the DC signal level increases, and the noise detection circuit 8 stops generating a high-level signal, similar to the device shown in FIG.
The generation of the cutoff signal from the waveform shaping circuit 9 is stopped and the gate circuit 3 is turned on.

In addition, in each embodiment of the present invention described above,
Although the timer 17 is used to actually measure the elapse of a predetermined time, it is also possible to utilize the voltage change due to charging of the capacitor 15 of the LPF 11 without using the timer 17, as shown in FIGS. 6a and 6b. 6th
In the pulse noise removal device shown in Figure a,
A constant current source 21 with a current I ₁ is provided between the output of the rectifier circuit 12 and the ground, and a constant current source 22 with a current I ₂ is provided between the output of the LPF 11 and the power supply (voltage Vc.c.). ing. Current I ₁ and current I ₂ are equal, or current I ₁ is slightly larger. When the gate circuit 13 is on, the current I ₁ and the current I ₂ cancel each other out. On the other hand, when the gate circuit 13 is off, the current I ₂ flows into the capacitor 15 of the LPF 11, the voltage across the capacitor 15 gradually increases, and the gain of the noise amplifier 7 gradually decreases. After approximately a predetermined period of time has elapsed, the input level in the noise detection circuit 8 becomes lower than the reference level, and the gate circuits 3 and 13 are turned on.

In the pulse noise eliminating device shown in FIG. 6b, a constant current source 22 of current I ₂ is provided between the output of the LPF 11 and the power supply (voltage Vc.
A series circuit including a constant current source 21 of current I ₁ and a switch element 23 is provided between the output of the current I 1 and the ground. The switch element 23 is turned off by the high level output of the waveform shaping circuit 9. As a result, Figure 6a
It performs the same operation as the device.

Further, in the pulse noise removing device shown in FIG. 6c, a changeover switch 2 is used as the second gate means.
4 is used. The changeover switch 24 switches the rectifier circuit 12 when the waveform shaping circuit 9 outputs a low level.
When the waveform shaping circuit 9 outputs a high level, the relay of the output signal of the rectifier circuit 12 is stopped, and the output current _I2 of the constant current source 22 is relayed and supplied to the LPF 11, and the capacitor 15 is relayed. charge.

Furthermore, in each of the embodiments of the present invention described above,
Although the gain of the noise amplifier 7 is reduced when the gate circuits 3 and 13 remain off for a predetermined period of time or more, the reference level of the comparison circuit in the noise detection circuit 8 may be increased.

In addition, in the above-described embodiments of the present invention,
Pulse noise is detected from the output signal of the FM detection circuit 1 of the FM receiver, but the signal obtained by AM detection of the IF signal in the IF (intermediate frequency) amplifier circuit, that is, the signal for the S (signal) meter. , or the pulse noise may be detected from both the signal and the output signal of the FM detection circuit 1.

Further, in the embodiment of the present invention described above, the gate circuit 13 is completely cut off according to the output signal of the waveform shaping circuit 9, but the signal from the rectifier circuit 12 is attenuated and supplied to the LPF 11,
Alternatively, the signal from the rectifier circuit 12 may be bypassed. Further, the gate circuit 13 may be provided on the input side of the rectifier circuit 12, or the operation of the rectifier circuit 12 may be stopped in accordance with the output signal of the waveform shaping circuit 9.

Furthermore, in the embodiment of the present invention described above, the capacitor 15 is charged to the positive side with respect to the predetermined reference potential, but the capacitor 15 may be charged to the negative side with respect to the predetermined reference potential. .

Effects of the Invention As described above, in the pulse noise removing device for an FM receiver of the present invention, the first gate means prevents the output signal of the FM detection circuit from being supplied to the subsequent stage for a predetermined period of time or more due to continuous noise generation. If it continues, the generation of the cutoff signal that cuts off the first gate means is suppressed, which prevents the first gate means from being cut off for a long period of time, resulting in an increase in the sense of distortion and a hold error in the level hold circuit. It is possible to prevent the generation of noise due to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the operation of each part of the apparatus shown in FIG. 1, and FIGS. 4, 5, and 6 a, b, 7c is a block diagram showing a part of another embodiment of the present invention, and FIG. 7 is a block diagram showing a conventional example of a pulse noise removing device. Explanation of symbols of main parts, 1...FM detection circuit,
2...Delay circuit, 3, 13...Gate circuit, 9...
...Waveform shaping circuit, 11...LPF, 16, 19...
...Switch element.

[Claims]

1. In order to remove noise that enters the main input terminal, an adaptive filter removes the noise based on the reference signal obtained from the reference input terminal, which is placed near the source of the noise to be removed and receives only the noise as input. A replica is generated, and the noise is extracted from a mixed signal in which the received signal obtained at the main input terminal and noise having a correlation with the reference signal are mixed.
When removing noise by reducing the difference signal obtained by subtracting the replica, the difference signal power is obtained by squaring the difference signal, and after subtracting the averaged difference signal power from the difference signal power, the average A method of noise removal using an adaptive filter, characterized in that the coefficient correction amount of the adaptive filter is adaptively changed using the product of the difference signal and a value proportional to the value obtained by the conversion. 2. An adaptive filter that is placed near the source of the noise to be removed and that receives reference noise from a reference input terminal that receives only the noise as input and generates a noise replica;

Claims (1)

3. The DC signal generating means includes a rectifying means for rectifying the output signal of the amplifying means, a smoothing means for smoothing the output signal of the rectifying means to generate the DC signal, and a smoothing means for generating the DC signal according to the supplied cutoff signal. a second gate means for suppressing the output signal level of the rectifying means, the suppressing means detecting that the cutoff signal has been generated continuously for a predetermined period of time or more, and a time measuring means for generating a cutoff stop signal; 2. The pulse noise removing device according to claim 1, further comprising current supply means for supplying a charging current to a capacitor of said smoothing means in response to a cutoff stop signal. 4. The DC signal generating means includes a rectifying means for rectifying the output signal of the amplifying means, a smoothing means for smoothing the output signal of the rectifying means to generate the DC signal, and a smoothing means for generating the DC signal according to the supplied cutoff signal. a second gate means for suppressing the output signal level of the rectifying means, the suppressing means detecting that the cutoff signal has been generated continuously for a predetermined period of time or more, and a time measuring means for generating a cutoff stop signal; 2. The pulse noise removing device according to claim 1, further comprising a third gate means provided in parallel with the second gate means and rendered conductive in response to the cutoff stop signal. 5. The pulse noise removing device according to claim 1, wherein the suppressing means raises the reference level when detecting that the cutoff signal continues to occur for a predetermined period of time or more.