JP2786064B2 - Noise detection circuit - Google Patents

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, the present invention relates to a noise detection circuit for detecting noise in a communication line.

[0002]

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

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

[0004]

As described above, in the conventional example, there is no reference to the detection time of the noise, and there is a case where the noise is detected even for an instantaneous noise. If there is a need to detect noise that persists to some extent, this poses a problem of false detection. In some cases, the detection time is fixedly set, but in this case, there is a problem that a required accurate detection time cannot be obtained.

[0005]

A noise detection circuit according to the present invention includes a band-pass filter having a pass characteristic for selecting noise in a transmission band of an input signal, and amplifies an output signal of the band-pass filter. An amplifier, a rectifier circuit that converts an output signal of the amplifier into a direct current, and a noise detection circuit including a detection circuit that compares the output signal of the rectification circuit with a predetermined reference voltage and outputs a detection signal, wherein the detection signal And a monostable multivibrator for inputting the detection signal, and an OR circuit for performing a logical sum of an output signal of the integration circuit and an output signal of the monostable multivibrator and outputting the result as a noise detection signal. A malfunction prevention circuit having the following is added.

[0006] The monostable multivibrator includes:
The output pulse width may be variable.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the present embodiment.

In FIG. 1, the present noise detection circuit includes a band-pass filter 1 having a pass characteristic for selecting noise in a transmission band of an input signal, an amplifier 2 for amplifying an output signal of the band-pass filter 1, and A rectifier circuit 3 for converting an 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
A malfunction prevention circuit 5 comprising a logical sum circuit 53 for performing a logical sum of the output signal S2 of the output signal S1 and the output signal S3 of the monostable multivibrator 52 and outputting the result as a noise detection signal S4.

Next, the operation will be described. The operation until the detection signal S1 is output is the same as the operation described with reference to FIG. Hereinafter, the operation of the malfunction prevention circuit 5 will be described with reference to FIGS.
FIG. 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, an integrating circuit 51 includes a resistor R1.
And a capacitor C1. A monostable multivibrator 52 includes an IC1 and a resistor R2 for setting an output pulse width.
And a capacitor C2. In FIG. 3, when the detection signal S1 outputs an instantaneous noise having a time width T1, the integrating circuit 51 integrates the output and outputs an output signal S2, and the monostable multivibrator 52 starts using the output as a trigger. After the time T3, a pulse having a time width T2 is output. Since the output of the OR circuit 53 absorbs the rise time T3 of the monostable multivibrator 52 by the integration circuit 51 and maintains 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 monostable multivibrator 52, it is not output as the noise detection signal S4.

In the monostable multivibrator 52, when the values of the resistor R2 and the capacitor C2 for determining the pulse time width T2 are made variable, an arbitrary noise detection time width T1 is obtained.
Can be handled.

[0013]

As described above, according to the present invention, a noise detection signal is not output for instantaneous noise by using a simple malfunction prevention circuit, and the detection time width is set arbitrarily. This has the effect of increasing the accuracy of noise detection.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a malfunction prevention circuit in FIG. 1;

FIG. 3 is a timing chart in FIG. 2;

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

[Explanation of symbols]

 DESCRIPTION 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

Continuation of front page (72) Inventor Tomiyuki Onoda, Miyagi Prefecture, Kurokawa-gun, Yamato-cho, Yoshioka-ji, Raijin, 2nd Miyamiya Inside NEC Corporation (72) Inventor, Hiroshi Tachibana, Miyagi-ken, Kurokawa-gun, Yamato-cho, Yoshioka, Raikajin, 2nd Miyagino NEC Corporation (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 1/10

Claims (2)

(57) [Claims] 1. A band-pass filter having pass characteristics for selecting noise in a transmission band of an input signal, an amplifier for amplifying an output signal of the band-pass filter, and converting an output signal of the amplifier into a direct current. And a detection circuit that compares an output signal of the rectification circuit with a predetermined reference voltage and outputs a detection signal. An integration circuit that integrates the detection signal, and an input of the detection signal. A malfunction prevention circuit including a monostable multivibrator that performs a logical sum of an output signal of the integration circuit and an output signal of the monostable multivibrator and outputs the result as a noise detection signal. Noise detection circuit. 2. The noise detection circuit according to claim 1, wherein said monostable multivibrator has a variable output pulse width.