JPS60226295A - Detection circuit of in-band signal - Google Patents

Abstract

PURPOSE:To obtain an impulse detection circuit which will not execute malfunction with respect to the overlapping of impulsive noises by providing a delay circuit for an output of a noise detection circuit and controlling the inserting and separating of the provided delay circuit. CONSTITUTION:When an in-band signal is nil, an output of a comparator 3 is switched to the solid line side of a switching circuit 5. When the in-band signal exists, said output is switched to the dotted line side. The in-band signal passes through an in-band signal detector 1 and becomes a positive DC voltage. On the other hand, noise components except the in-band signal pass through a detector 2 for noise components and become positive DC voltages. If there are impulsive sounds, they are eliminated by a delay circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an in-band signal detection circuit in a system that uses the voice band of a telephone line to transmit a dial signal or a supervisory signal depending on the presence or absence of a single-frequency in-band signal.

(Prior Art) It is necessary that such a signal detection circuit does not malfunction due to voice, musical tone, noise, etc. passing through the line.

As shown in FIG. 1, a conventional signal detection circuit selects an inband signal frequency, monitors a noise component, and compares the levels of both to determine the presence or absence of an inband signal. That is, even if there is an in-band frequency component, if the difference in level between other components is small, it is determined to be noise. This is because detecting only the in-band signal frequency may cause the detection circuit to malfunction due to voice or musical tones, so the detection circuit is designed to operate only with a pure single frequency signal. In addition, in FIG. 1, 1 is an in-band signal detector;
2 is a noise component detector, and 3 is a level comparator. The input side is connected to the receiving side of the telephone line, and the output side is connected to the exchange side.

However, in such a circuit, if noise is superimposed while receiving an in-band signal, the detection operation may be stopped, resulting in a malfunction.

(Object of the Invention) An object of the present invention is to provide an in-band signal detection circuit that does not malfunction due to superposition of impulsive noise.

(Structure of the Invention) As shown in FIG. 2, the in-band signal detection circuit of the present invention has a delay circuit added to the output of the noise detection circuit of the conventional circuit, and the output of the level comparison circuit is insert,
Control disconnection.

(Principle and operation) In Fig. 2, when there is no in-band signal, the comparator circuit 3
The output is controlled so that the switching circuit 5 is connected to the solid line side.

In this case, if the circuit is equivalent to the conventional circuit, the output of circuit 3 is controlled so that circuit 5 is connected to the dotted line side. In this case, a delay circuit 4 is inserted at the output of the noise detection circuit. Here, the circuit 4 acts on the output signal of the impulse noise short-time noise detection circuit to eliminate this impulse noise. As a result, if it is determined that there is an in-band signal, the output of the circuit 3 will not be disturbed even if there is impulse noise.

(Embodiment of the invention) FIG. 3 shows an embodiment of the invention. The in-band signal is selected by a filter 11 and rectified by a rectifier 12 to become a positive DC voltage. Further, the noise signal components other than the in-band signal components pass through the filter 21 and are rectified by the rectifier 22 to become a positive DC voltage. When impulse noise occurs, the output of the rectifier 22 becomes a positive pulse, but it is suppressed by the action of the integrating circuit and voltage comparator circuit 44, which are composed of a resistor 41, a capacitor 42, and a diode 43 in the delay circuit 4. It cannot occur at the output of circuit 4. The switching device 5 performs the same operation as in the case of FIG. In addition, 51 is a relay, and 52 is its contact.

(Effects of the Invention) As described above, according to the present invention, even if impulse noise generated in a telephone line, an in-band signal generator, etc. is superimposed on an in-band signal, a dial signal can be reproduced without being affected by this. I can do it.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a block diagram showing the configuration of the present invention, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 1... In-band signal detector, 2...
Noise component detector, 3...Level comparator, 4.
...delay circuit, 5...switcher, 11...filter, 21...filter, 12.22...
... Rectifier, 41 ... Resistor, 42 ...
... Capacitor, 43 ... Diode, 51.
... Relay, 52 ... Relay RL contact, 3.44 ... Voltage comparison circuit. Wow / Figure h? figure

Claims (1)

[Claims] a first means for detecting the level of the in-band signal, a second means for detecting the level of the noise signal, and a third means for eliminating the pulsed noise signal output from the second means;
fourth means for outputting the output of the second means when there is no in-band signal and outputting the output of the third means when there is the in-band signal; and the output of the first means. and fifth means for comparing and outputting the output of the third means to control switching of the fourth means.