JPH0661876A - Noise detection circuit - Google Patents

Abstract

PURPOSE:To enhance the accuracy of noise detection by using a simple malfunction prevention circuit so as not to output a noise detection signal against an impulsive noise and to set a detection time width optionally. CONSTITUTION:When a malfunction prevention circuit 5 receives a detection signal S1 and outputs an impulsive noise whose time width is T1, an output signal S2 of an integration circuit 51 integrates it, a monostable multivibrator 52 uses the integrated signal as a trigger to output a pulse whose time width is T2 after a rising time T3. An output signal S4 of an OR circuit 53 is not outputted because the integration circuit 51 absorbs a rising time T3 of the monostable multivibrator 52 and keeps the non-detection state with an output pulse from the monostable multivibrator 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise detection circuit,
In particular, it relates to a noise detection circuit for detecting noise on a communication line.

[0002]

2. Description of the Related Art Conventionally, a noise detecting circuit of this type generally has a structure shown in FIG. FIG. 4 is a block diagram of a conventional example.

A noise signal in the input signal is selected by a band pass filter 41 having a pass characteristic for selecting noise in the transmission band of the input signal, the noise signal is amplified by an amplifier 42, and rectified by a rectifying circuit 43. Then use a DC signal. Detection circuit 4
In step 4, the DC signal is compared with a predetermined reference voltage, and when the DC signal exceeds the reference signal, a noise detection signal is output.

[0004]

As described above, in the conventional example, there is no standard for the noise detection time, and there is a case where even momentary noise is detected. If one wants to detect noise that persists to some extent, this has the problem of false detection. In addition, this detection time may be fixedly set, but in this case, there is a problem that the required accurate detection time cannot be obtained.

[0005]

SUMMARY OF THE INVENTION A noise detection circuit according to the present invention includes a bandpass filter having a pass characteristic for selecting noise in a transmission band of an input signal, and an output signal of the bandpass filter is amplified. A noise detection circuit comprising: an amplifier; a rectifier circuit that converts the output signal of the amplifier into a direct current; and a detection circuit that compares the output signal of the rectifier circuit with a predetermined reference voltage and outputs a detection signal. An integrating circuit for integrating, a monostable multivibrator for inputting the detection signal, an OR circuit for ORing an output signal of the integrating circuit and an output signal of the monostable multivibrator, and outputting as a noise detection signal. A malfunction prevention circuit equipped with is added.

Further, the monostable multivibrator is
The output pulse width may be variable.

[0007]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of this embodiment.

In FIG. 1, the present noise detection circuit includes a bandpass filter 1 having a pass characteristic for selecting noise in the transmission band of an input signal, and an amplifier 2 for amplifying an output signal of the bandpass filter 1. A rectifier circuit 3 for converting the output signal of the amplifier 2 into a direct current, a detection circuit 4 for comparing the output signal of the rectifier circuit 3 with a predetermined reference voltage and outputting a detection signal S1, and an integration circuit for integrating the detection signal S1. 51, a monostable multivibrator 52 for inputting the detection signal S1, and an integrating circuit 5
The malfunction prevention circuit 5 is provided with a logical sum circuit 53 which takes the logical sum of the output signal S2 of 1 and the output signal S3 of the monostable multivibrator 52 and outputs it as a noise detection signal S4.

Next, the operation will be described. The operation is the same as that described with reference to FIG. 4 until the detection signal S1 is output. The operation of the malfunction prevention circuit 5 will be described below with reference to FIGS.
2 is a circuit diagram of the malfunction prevention circuit 5 in FIG. 1, and FIG. 3 is a timing chart in FIG.

In FIG. 2, the integrating circuit 51 is a resistor R1.
The monostable multivibrator 52 comprises an IC1 and a resistor R2 for setting an output pulse width.
And a capacitor C2. Further, in FIG. 3, when the detection signal S1 outputs a momentary noise of the time width T1, the integrating circuit 51 integrates it and outputs the output signal S2, and the monostable multivibrator 52 rises by using this as a trigger. After time T3, a pulse having a time width T2 is output. Since the output of the OR circuit 53 absorbs the rising time T3 of the monostable multivibrator 52 in the integrating circuit 51 and holds the non-detection state by the output pulse of the monostable multivibrator 52, the noise detection signal S4 is output. Not done.

That is, the detection signal S1 has a detection time width T
If 1 is within the time width T2 of the pulse generated by the substantially monostable multivibrator 52, it is not output as the noise detection signal S4.

In the monostable multivibrator 52, if the values of the resistor R2 and the capacitor C2 that determine the pulse time width T2 are made variable, an arbitrary noise detection time width T1 is obtained.
Can correspond to.

[0013]

As described above, according to the present invention, by using the simple malfunction prevention circuit, the noise detection signal is not output for the momentary noise, and the detection time width is also set arbitrarily. Therefore, there is an effect of improving the accuracy of noise detection.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a malfunction prevention circuit in FIG.

FIG. 3 is a timing chart in FIG.

FIG. 4 is a block diagram of a conventional example.

[Explanation of symbols]

 1 band pass filter (BPF) 2 amplifier 3 rectifier circuit 4 detection circuit 5 malfunction prevention circuit 51 integration circuit 52 monostable multivibrator

Front page continuation (72) Inventor Tomiyuki Onoda 2 Raijin, Yoshioka, Yamato-cho, Kurokawa-gun, Miyagi Miyagi NEC Corporation (72) Hiroshi Tachibana, 2 Raijin, Yoshioka, Yamato-cho, Kurokawa-gun, Miyagi Miyagi NEC Within the corporation

Claims (2)

[Claims] 1. A bandpass filter having a pass characteristic for selecting noise in a transmission band of an input signal, an amplifier for amplifying an output signal of the bandpass filter, and an output signal of the amplifier converted to direct current. In a noise detection circuit including a rectifier circuit that outputs a detection signal by comparing an output signal of the rectification circuit with a predetermined reference voltage, an integration circuit that integrates the detection signal and the detection signal are input. A monostable multivibrator, and a malfunction prevention circuit provided with a logical sum circuit that takes the logical sum of the output signal of the integrating circuit and the output signal of the monostable multivibrator and outputs it as a noise detection signal. Noise detection circuit. 2. The noise detection circuit according to claim 1, wherein the monostable multivibrator has a variable output pulse width.