JPS5894242A - Suppressing device of impulsive noise - Google Patents

Abstract

PURPOSE:To eliminate the impulsive noise out of the audible signal without producing noises, by eliminating also the pilot signal when the impulsive noise is eliminated through an arithmetic circuit. CONSTITUTION:The signal having a delayed FM wave detection output which is applied to the input emerges at an output point A of an LPF1. The output of the LPF1 is applied to the minus input terminal of one side of a subtractor circuit 7. The pilot cancel signal is applied to the other minus input terminal of the circuit 7. The pilot signal in the composite signal is cancelled at the circuit 7. In such a constitution, a mono-multi 6 turns off a switch circuit 10 when the impulsive noise occurs in the composite signal. When the circuit 10 is turned off, the waveforms at points A and B are transmitted to a point C via the level holding circuits 8 and 9. Therefore the impulsive noise emerges at the point C, and a waveform obtained by eliminating the pilot signal and the impulsive noise from the waveform emerging at the point A emerges at the output point D of the circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse noise suppression device for effectively removing pulse noise in a vehicle-mounted FM receiver.

Such a conventional device is constructed as shown in FIG. In the figure, l is a low-pass filter (hereinafter referred to as P, F, and II) that functions as a signal delaying means, and delays the signal by the time necessary to perform noise processing. gate 2
works to momentarily cut off the signal only when pulse noise is input, and the level hold circuit 3 works to hold its output level at the signal level immediately before the cutoff while the signal is cut off by the gate 2.

Reference numeral 4 denotes a bypass filter (hereinafter abbreviated as H, P, and F) having a cutoff frequency of about 100 KHz, which functions to extract only noise components from the detection output from the FM detector (not shown). The noise amplifier 5 with AGC amplifies the outputs of H, P, and F4, and when the noise energy exceeds a certain level, the AGC operates to lower the gain. This is to prevent the gate 2 from being operated frequently and the signal being interrupted when the white noise component increases due to a weak electric field or the like. A monostable multivibrator (hereinafter abbreviated as monostable multi) 6 generates a pulse signal of a constant width for driving the gate 2 when the output of the noise amplifier 5 exceeds a constant value.

In the above-mentioned noise suppression device, when the signal from the FM detector is of a relatively low frequency as shown in FIG. At the output, a signal is generated that maintains the level when the gate 2 is closed, as shown in the second opening.

In this case, the level hold circuit 3 functions without any problem and no noise is generated.

However, when the stereo pilot signal as shown in FIG. 3 1a) is interrupted during the period indicated by the broken line - instantaneous gate 2,
As shown in FIG. 3(b), the signal held at the DC level during the period when the gate 2 is cut off is transferred to the level hold circuit 3.
Since the waveform is discontinuous, noise is generated. This is because the frequency of the pilot signal is high, so the time the gate 2 is cut off extends to half a wavelength or one wavelength, and the level hold circuit 3, which simply corrects with DC potential, cannot correct it well. It is.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to suppress pulse noise by removing pulse noise from an audible signal including a stereo pilot signal without generating noise. The goal is to provide equipment.

The present invention will be explained below with reference to FIG. 4 and subsequent figures.

FIG. 4 is a block diagram showing an embodiment of the pulse noise suppressing device according to the present invention.

H, P, F4, noise amplifier with AGC 5, and monostable multi-function device 6 may be the same as those in the conventional device shown in FIG.

At the output point A of L, P, and Ft, a signal as shown in Figure 5 (al) appears, which is the delayed FM detection output applied to the input. This signal is a composite signal consisting of a pilot signal and an audible signal. The outputs of L, P, and Fl are the result of superimposed pulse noise.
) signal is bypassed and supplied to the circuit requiring the pilot signal, and is applied to one input terminal of the subtraction circuit 7. The other input terminal of the subtraction circuit 7 (this is referred to as point B) receives a pilot cancellation signal (hereinafter referred to as a pie-can signal) as shown in FIG. 5(b).
has been added. This pie-can signal is in opposite phase to the pilot signal in the composite signal, so
In the subtraction circuit 7, the pyro 7) signal in the composite signal is canceled.

Level hold circuits 8 and 9 are connected between both input terminals and the ten input terminal (point C) of the subtraction circuit 7, and are normally turned on between the ten input terminal and the ground. A switch circuit IO is connected. Therefore, the point C is normally grounded in an alternating current manner. Note that the switch circuit 10 is turned off by a pulse signal generated by the monostable multi 6, and when the switch circuit 10 is turned off, the impedance at point C increases.

With the above-described configuration, when pulse noise as shown in FIG. The OFF operation of the circuit 1O is performed at the time t1 shown by the broken line, before the pulse noise rises, for the composite signal at point A that has been passed through L, P, and Fl and delayed. When the circuit 10 is turned off, the impedance at the point C increases as described above, so the waveform at the point A is transmitted to the point C via the level hold circuit 8, and the waveform at the point B is transmitted to the point C via the level hold circuit 9.

The waveform at point C starts from the DC potential at point C just before the switch circuit 10 turns off, and the pilot signal in the signal transmitted through the level hold circuit 8 is transmitted through the level hold circuit 9. 5 (pulse nature as shown in C1) appears at point C. This waveform is then applied to the negative phase input terminal of the subtraction circuit 7. Therefore, at the output point of the subtraction circuit 7, a waveform as shown in FIG. holds the level immediately before the switch circuit 10 turns off until time t2 when the switch circuit IO turns on.

As mentioned above, in the pulse noise suppression system according to the present invention, when removing pulse noise, the pilot signal is also removed at the same time, so a signal in which the pilot signal is cut off may appear in the output. do not have. Therefore, waveform distortion caused by the pilot signal being cut off midway and generation of noise associated with it are eliminated.

Furthermore, the device according to the present invention cancels both the pilot signal and the noise by using a general arithmetic circuit, which may be a subtraction circuit or an addition circuit. Since this is done by using means, a practically effective effect of simplifying the circuit configuration can also be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a conventional device, and Figure 2 (
al and (b) and FIG. 3(a) and crest) are waveform diagrams for explaining the operation of the device in FIG. 1, FIG. 4 is a block diagram showing one embodiment of the device according to the present invention, and FIG. Figures (al to (di) are waveform diagrams showing waveforms at each point of the device in Figure 4. ■...Low pass filter (delay means), 4...Bypass filter, 5...Noise amplifier with AGC , 6...
・Monostable multivibrator, 7... Subtraction circuit (arithmetic circuit), 8.9... Level hold circuit, 10...
Switch circuit (switch means) Patent applicant Pioneer Corporation (a) (C) Har1ruzu11 noise (b) ↑+ t2 Tohi1 High A in Ai Shigo (d)

Claims (1)

[Claims] a delay means for delaying a human signal; an arithmetic circuit to which an output signal of the delay means and a pilot cancellation signal for canceling a pilot signal in the output signal are respectively input; and a pulse characteristic in the input signal. A noise detection section that detects noise and generates a pulse signal of a constant width, and an input terminal of the arithmetic circuit having a phase opposite to the input terminal to which the output signal and the pilot cancellation signal are applied are connected in an alternating current manner between the ground and the input terminal of the arithmetic circuit. , switch means which is normally on and turned off in response to a pulse signal from the noise detection section; and while the switch means is off, the output signal of the delay means and the pilot cancellation signal are transmitted to the output signal of the arithmetic circuit. A pulse noise suppression device characterized by comprising a level hold circuit that transmits data to each negative phase input terminal.