JPH01227529A - Eliminating device for impulsive noise in fm receiver - Google Patents

Abstract

PURPOSE:To prevent misdetecting noise except impulsive noise for the impulsive noise and to improve a detecting accuracy by setting impulsive noise detecting sensitivity according to the peak value of the high band component of a received detecting signal. CONSTITUTION:The high band component of the output signal of an FM detecting circuit 1 is extracted by an HPF 6, full-wave-rectified by a rectifying circuit 8, and supplied to a comparator 10 and a control signal generating circuit 16 in containing the noise except the impulsive noise. The control signal generating circuit 16 generates a voltage to follow the peak value of the output voltage of the rectifying circuit 8 in making it into a control signal, and an AGC error amplifier 13 fed back a direct current signal according to a level difference between the control signal and a second reference signal to a noise amplifier 7. Consequently, since a control signal level is raised and the gain of the noise amplifier 7 is lowered as the peak value of an input noise signal is made large, the detecting sensitivity of the impulsive noise is lowered. Since the detecting sensitivity is changed according to the control signal level, the impulsive noise can be surely detected.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an apparatus for removing pulsed noise in an FM receiver.

BACKGROUND ART A conventional example of a pulse noise removing device in an FM receiver is shown in FIG. In this device, a detection signal output from an FM detection circuit 1 of an FM receiver is supplied to a delay circuit 2 consisting of an LPF (low pass filter) and delayed.
This delayed output is supplied to a stereo demodulation circuit 5 via a gate circuit 3 and a level hold circuit 4. In addition, the detection signal is an HPF (bypass filter) 6 for noise detection.
The noise component signal passed through the HPF 6 is amplified by the noise amplifier 7 and supplied to the full-wave rectifier circuit 8.9. The output signal of the rectifier circuit 8 is compared with the first reference signal output from the voltage source 14 by a noise detection comparator 10. The output signal of the comparator 10 is supplied to the waveform shaping circuit 11, and the waveform shaping circuit 11, for example,
It consists of a one-shot multivibrator, converts a high level signal representing noise detection output from the comparator 10 into a pulse with a predetermined wave height and time width, and supplies the pulse to the gate circuit 3. The gate circuit 3 is driven by the pulses supplied to the gate circuit 3 from the waveform shaping circuit 11 and enters the 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 the stereo demodulation circuit is activated. 5. This prevents the occurrence of spikes due to sudden changes in potential. The output signal of the rectifier circuit 9 is supplied to the HPF 12 , and the HPF 12 smoothes the noise component output from the rectifier circuit 9 and supplies it to the AGC error amplifier 13 . The AGC error amplifier 13 forms an AGC loop by obtaining a DC signal corresponding to the level difference between the output signal of the rectifier circuit 9 and the second reference signal and feeding it back to the noise amplifier 7. Therefore, HPF12
Since the output signal level of rectifier circuit 8.9 is controlled to be equal to the second reference signal level output from voltage source 15, the average value of each output signal level of rectifier circuit 8.9 is constant.

For example, even when pulse noise with a steep rise is input, the pulse noise is smoothed by the HPF 12, so the signal level output from the HPF 12 to the AGCX difference amplifier 13 hardly changes. 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 for example, uses the delay characteristics of an active low-pass filter. .

In such a conventional pulse noise removal device, noise other than pulse noise (for example, background noise)
A blunt noise A with a wave height E as shown in Fig. 7(a).
Comparing the case where noise A is input with the case where sharp noise B with the same wave height E as shown in FIG. 7(b) is input, the average value e1 of noise A is equal to that of noise B. The average value e
It will be higher than 2. However, when inputting noise, the output signal of HPF 12 and the second
Since the level difference from the reference signal increases, the gain of the noise amplifier 7 decreases, and the pulse noise detection sensitivity decreases. Therefore, there are problems in that noises other than pulse noise may be erroneously detected, or pulse noise may not be detected. On the other hand, in the case of a noise that is more acute than the noise B, the level difference between the output signal of the HPF 12 and the second reference signal becomes small, so the gain of the noise amplifier 7 becomes large.
Pulse noise detection sensitivity increases. However, it is easy to mistakenly detect noise other than pulse noise.

In particular, in the case of in-vehicle FM receivers that require a pulse noise removal device, sharp noises such as noise B rapidly increase when the received signal level decreases, and distortion increases due to erroneous detection of pulse noise. Is there a problem with making the listener feel uncomfortable? Ta.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pulse noise removal device for an FM receiver that can reliably detect pulse noise and prevent an increase in distortion so that FM broadcasts can be listened to without discomfort. That's true.

The pulse noise removing device of the present invention includes an extraction means for extracting a high frequency component of a signal obtained by detecting a received signal of an FM receiver, and a cutoff signal when the output level of the extraction means exceeds a reference level. and a gate means that responds to the cutoff signal to cut off the supply of the output signal of the FM detection circuit in the FM receiver to the subsequent stage, and detects the peak value of the output signal of the extraction means. It is characterized in that it includes $IJ8 signal generation means for generating a control signal of a tracked level, and is configured to change the detection sensitivity of the noise detection means in accordance with the control signal level.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

In the pulse noise removing device for an FM receiver that is an embodiment of the present invention shown in FIG. 1, the same parts as those in the conventional device shown in FIG. A noise detection comparator 10 and a control signal generation circuit 16 are connected to the output. The control signal generation circuit 16 generates a voltage that follows the peak value of the output voltage of the rectifier circuit 8 as a control signal. An AGC error amplifier 13 and an adder 17 are connected to the output of the control signal generation circuit 16. AGC error amplifier 13
obtains a DC signal corresponding to the level difference between the control signal and the second reference signal and feeds it back to the noise amplifier 7. The adder 17 adds the control signal and the offset signal output from the offset signal generation circuit 18, and supplies the signal obtained by the addition to the comparator 10 as a first reference signal.

The rest of the configuration is the same as the pulse noise removing device shown in FIG.

FIG. 2 shows a specific configuration of the control signal generation circuit 16. This control signal generation circuit 16 includes a current mirror circuit 41, transistors 42 and 43, and a current source 44.
A differential amplifier circuit consisting of the following is provided. The output signal of the rectifier circuit 8 is supplied to the base of the transistor 42 with a voltage v8 of the bias power supply 45 superimposed thereon. The collector of transistor 42 is connected to the base of PNP transistor 46. A voltage Vcc is supplied to the emitter of the transistor 46 through a diode 47 in the forward direction.
The collector is the base of the transistor 43 and the capacitor 4
8 and is connected to the bias power supply 4 via a resistor 49.
5. The base of the transistor 46 has P
NP) transistor 50 and a gate circuit consisting of resistors 51 and 52 are connected. The collector of the transistor 50 is connected to the base of the transistor 46, the emitter is supplied with the voltage Vcc, and the base is connected to a resistor 51 . 52
A divided voltage is applied.

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 C) as shown in FIG. The high frequency component of the output signal of the FM detection circuit 1 is extracted, and the output signal of the HPF 6 is amplified by the noise amplifier 7 to obtain the waveform shown in FIG. 3(b). Then, it is full-wave rectified by the rectifier circuit 8 as shown in Fig. 3 (
It is output as shown in C). The output signal of the rectifier circuit 8 is a rectified signal containing noise other than pulse noise, and this rectified signal is sent to the comparator 10 and the control signal generation circuit 1.
6.

In the control signal generation circuit 16, the level of the input rectified signal to the base of the transistor 42 causes the transistor 42 to
When the base voltage of the transistor 43 becomes higher than the base voltage of the transistor 43, the transistor 46 turns on, and the capacitor 48
is charged to increase the base voltage of the transistor 43. The charging continues until the base voltage of transistor 43 reaches the base voltage of transistor 42. When charging of the capacitor 48 is completed, the voltage Vc across the capacitor 48 becomes approximately equal to the peak value of the input noise signal (background noise) N, as shown in FIG.

When the base voltage of transistor 42 is lower than the base voltage of transistor 43, transistor 46 is cut off and charging of capacitor 48 is stopped, so that the charge in capacitor 48 is discharged via resistor 49. During normal operation when pulse noise is not occurring, transistor 4
As mentioned above, the transistors 42 and 4 are repeatedly turned on and off according to the base voltages of the transistors 42 and 43.
The voltages across the capacitor 48, ie, the control signal, are maintained at the peak value of the input rectified signal. This control signal controls the gain of the noise amplifier 7. Therefore, as the peak value of the input noise signal increases, the control signal level increases and the noise amplifier 7
Since the gain of is reduced, the detection sensitivity of pulsed noise is reduced.

Further, the control signal is added by the adder 17 to the offset signal VOF output from the offset signal generating circuit 18, and the resultant signal is supplied to the comparator 10 as the first reference signal Vr1. Therefore, when the peak value of the input noise signal increases, the control signal level increases and the first reference signal level increases. Due to the increase in the first reference signal level, only a large level of pulsed noise is detected by the comparator 10, and the detection sensitivity of the pulsed noise is reduced. On the other hand, when the peak value of the input noise signal becomes smaller, the control signal level decreases and the first reference signal level decreases. As the first reference signal level decreases, even a small level of pulse noise is detected by the comparator 10, and the detection sensitivity of pulse noise increases.

When the output signal level of the rectifier circuit 8 exceeds the first reference signal level output from the adder 17, the comparator 10 generates a high level signal as a noise detection signal as shown in FIG. 3(d). In response to the rise of this high level output, the waveform shaping circuit 11 generates a pulse with a predetermined wave height and time width as a cutoff signal, as shown in FIG. 3(e). This cutoff signal causes the gate circuit 3 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. Since the delay circuit 2 is provided to compensate for the detection time of pulse noise, when the gate circuit 3 is cut off, the supply of the detection signal containing the pulse noise from the delay circuit 2 to the level hold circuit 4 is cut off. The level hold circuit 4 outputs the signal immediately before the cutoff.

Further, the transistor 50 is turned on in accordance with the output signal of the waveform shaping circuit 11. This turns off transistor 46 and stops tracking the peak value of the input rectified signal. Since there is a delay in the detection of pulse noise from when the pulse noise actually occurs until the transistor 50 turns on, the generation of the pulse noise causes the transistor 40 to
The base voltage of capacitor 48 rises and the capacitor 48 increases by the detection delay.
is charged.

In such a pulse noise removing device according to the present invention,
When the received signal is weakly input, the peak value of the noise in the waveform shown in FIG. 7(b) increases, so the first reference signal level increases, and the gain of the noise amplifier 7 decreases, causing pulse noise Detection sensitivity decreases. Note that in the case of this weak input, the pulsed noise is masked by other noises, so the influence of a decrease in the detection sensitivity of the pulsed noise is small. Even if noise with the waveform shown in Figure 7(a) occurs when the received signal is input to the lieutenant, the peak value of the noise decreases as the electric field becomes stronger, so the first reference signal level decreases, and the noise The gain of the amplifier 7 increases, and the detection sensitivity of pulsed noise increases.

Note that since the control signal level output from the control signal generation circuit 16 is a value slightly lower than the peak value of the input noise signal, it is possible to add an offset signal to the control signal to compensate for this and supply it to the comparator 10. It is done. Further, by changing the offset signal level, the offset of the comparator 10 and the pulse noise detection sensitivity can be adjusted.

Further, in the embodiment of the present invention described above, the transistor 46 responds to the high level signal from the waveform shaping circuit 11.
is turned off, and the on/off operation of the transistors 42 and 43 is stopped according to the output signal of the rectifier circuit 8, but the rectifier circuit 8 and the control signal generation circuit 16 are used instead of the transistor 50 and the resistors 51 and 52. In response to a high level signal from the waveform shaping circuit 11, the input signal is cut off between
Alternatively, a gate circuit may be provided to suppress the input signal level.

In addition, in the embodiment of the present invention described above, pulse noise is detected from the output signal of the FM detection circuit 1 of the FM receiver, but the IF multiplied signal A in the IF (intermediate frequency) amplification circuit is
Pulse noise may be detected from the signal obtained by M detection, that is, the S (signal) meter signal, or from both the signal and the output signal of the FM detection circuit 1. Further, although both the gain of the noise amplifier 7 and the first reference signal level are changed in response to the control signal level, only one of them may be changed.

Furthermore, as shown in FIG. 5, the control signal generating circuit 16 connects a series circuit of a discharging resistor 53 and a normally closed switch element 54 to a capacitor 48 in parallel, and generates a high level signal from the waveform shaping circuit 11. In response to this, the switch element 54 may be turned off to stop the discharge of the capacitor 48.

Effects of the Invention As described above, the pulse noise removing device in the FM receiver of the present invention generates a control signal whose level changes in accordance with the peak value of the high frequency component of the received detection signal, and The noise detecting means is configured to change the detection sensitivity of the noise detecting means. Therefore, no matter what waveform the noise other than pulse noise has, the pulse noise detection sensitivity is set according to its peak value, which prevents noise other than pulse noise from being mistakenly detected as pulse noise. This makes it possible to improve the detection accuracy of pulse noise. This makes it possible to reliably remove pulse noise from the FM detection signal, thereby preventing an increase in distortion and making it possible to listen to FM broadcasts in good condition.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram specifically showing the control signal generation circuit in the device shown in FIG. 1, and FIGS. 3 and 4 are the devices shown in FIG. 1. 5 is a circuit diagram showing another circuit example of the control signal generation circuit, FIG. 6 is a block diagram showing a conventional example of a pulse noise removing device, and FIG. It is a figure which shows the operation|movement in this apparatus. Explanation of symbols of main parts 1...FM detection circuit 2...Delay circuit 3...Gate circuit 10...Comparator 13...Error Amplifier 16... Control signal generation circuit

Claims (4)

[Claims] (1) Extraction means for extracting high-frequency components of the signal obtained by detecting the received signal of the FM receiver; and noise detection means for generating a cutoff signal when the output level of the extraction means exceeds a reference level. , gate means for cutting off the supply of the output signal of the FM detection circuit in the FM receiver to a subsequent stage in response to the cutoff signal, the pulse noise removing device comprising: What is claimed is: 1. A pulse noise removing device comprising control signal generating means for generating a control signal whose level changes in accordance with a value of the noise detecting means, the detection sensitivity of said noise detecting means being changed in accordance with said control signal level. (2) The control signal generating means includes a rectifying means for rectifying the output signal of the extracting means, a charging means that uses the output voltage of the rectifying means as an input voltage and is provided with a current discharge path, and a charging means that responds to the cutoff signal. 2. The pulse noise removing device according to claim 1, further comprising suppressing means for suppressing the output voltage level of said rectifying means. (3) The pulse noise removing device according to claim 1, wherein the extraction means includes an amplification means that amplifies the high frequency component with a gain corresponding to the control signal level and supplies the amplified high-frequency component to the noise detection means. . (4) The pulse noise removing device according to claim 1, wherein the noise detection means has a setting means for setting the reference level by superimposing a predetermined offset signal level on the control signal level.