JPH07203492A - In-band signal detection circuit - Google Patents

Abstract

PURPOSE:To obtain the in-band signal detection circuit capable of distinguishing signals from external noise, comparing and collating, signals even with the same frequency component from the signal frequency in terms of potential and time and distinguishing the noise from the other signal. CONSTITUTION:A detection circuit is provided with a band pass filter 21 passing a signal band in use, a low pass filter 2 separating a low frequency and a high frequency, and a high pass filter 3. Signals of f..-f4 are extracted by circuits 6, 7 extracting only the signals. Signal block circuits 4, 5 obtain the voltage other than the signals f1-f4. Comparator circuits 8, 9 obtain the potential at the signal extraction side and the potential at the block circuit side. The signals 5, 6 extracted by the comparison control circuit are outputted via comparison control circuits 2, 10, 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for transmitting an in-band signal used as a control signal in a communication switching network or the like, and more particularly to a signal detection circuit capable of distinguishing a signal from an external noise or a pseudo signal.

2. Description of the Related Art A conventional in-band signal detection circuit has a structure as shown in FIG. When a signal is input,
It is extracted by the pass filter 108 for f1. The extracted signal is rectified by the rectification circuit 104 and becomes a DC signal, which is input to the comparison circuit 106. f1 blocking filter 101
The signal that has been amplified by the amplifier 103 and has been rectified by the rectifying circuit 105 to become a DC signal is compared by the comparison circuit 106. The compared signal is input to the delay circuit 107 at the next stage. The comparison circuit 106 compares the signal E with the signal F, and outputs the signal to the next stage only when the signal E is larger than the signal F. The delay circuit 107 sends out a signal having a constant width only when the signal E is obtained. FIG. 3 shows a case where a signal (two frequencies) is used. The input signal f1 is passed through the pass filter 2
Only f1 is extracted by 01. The extracted f1 is amplified by the amplifier 203 to a required level in the next stage. The amplified f1 is rectified by the rectifier circuit 205 and becomes a DC signal, which is input to the AND circuit 207 in the next stage. On the other hand, the signal f2 is extracted by the pass filter 202 only as f2.
The extracted f2 is amplified to the level required by the amplifier 204 in the next stage.
Is amplified by. The amplified f2 is rectified by the rectifier circuit 206 and becomes a DC signal, and the AND circuit 207 of the next stage is used.
Is input to. The AND circuit 207 sends the output signal to the delay circuit 208 at the next stage only when the signals G and H arrive.
The delay circuit 202 corrects the waveform of the signal and sends out a signal waveform having a constant width.

The above-mentioned conventional circuit of FIG. 2 has the following problems because it is of the one-frequency type. (A) When f1, a pseudo signal, or a sudden signal is input, it is treated as a signal frequency and is sent to the next stage, so it is impossible to distinguish between signals and other signals. (B) As a malfunction prevention, since the delay circuit is included, the signals f1 to the other party and signals other than the true signal are also adjusted in time. On the other hand, in the circuit shown in FIG. 3, (a) since there is no protection circuit (temporal check circuit), it cannot be distinguished from the signal when the same frequency component as the signal frequency component comes. There is a problem in that the signal detection malfunctions in the generated frequency components (operations due to the 2nd wave and 3rd wave). It is an object of the present invention to provide an in-band signal detection circuit which eliminates the above-mentioned drawbacks.

In order to achieve the above object, the detection circuit of the present invention uses four frequencies as a signal frequency and has a protection circuit and a comparison control circuit. Specifically, a dedicated bandpass filter 1 (f1 to f4) is provided so as not to be disturbed by external noise. Moreover, even if the same frequency as the signal frequency (three frequencies) is received, a protection circuit for checking the potential and time is provided.

Next, the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the detection circuit of the present invention includes a bandpass filter 1 that passes a band of a signal to be used and a filter that divides a low band and a high band (a low pass filter 2 and a high pass filter 3). F1 through the circuits 6 and 7 for extracting only signals
The signal of f4 is extracted. The signal blocking circuits 4 and 5 determine potential values other than the signals (f1 to f4). Comparison circuit 8,
9, the potential on the signal extraction side and the potential on the blocking circuit side are obtained.
The signals (arrows 5 and 6) extracted by the comparison control circuit are output via the comparison control circuit 2 (10 and 11). next,
The operation of the circuit of FIG. 1 will be described. With bandpass filter 1,
Secure a band to use and block frequencies outside the band. The secured frequency band is further divided into two (low pass filter 2 and high pass filter 3). Low pass filter 2
Is the relationship between the signal frequencies f1 and f2, and the high pass filter 3
Are related to the signal frequencies f3 and f4. The following is a description of how the output signal of the comparison circuit 8 is obtained after passing through the low pass filter 2 (the same applies to the circuits 5 and 7). The signal frequency f1 is obtained by the band-pass filter 601 dedicated to f1, amplified by the amplifier circuit 603, and becomes a DC signal by the rectifier circuit 605. The same applies to the signal frequency f2, and the rectifier circuit 606 produces a DC signal. The signal stop circuit 4 includes a band stop filter 40 for stopping the signal frequencies f1 and f2.
1 amplifies frequency bands other than f1 and f2. The amplified band becomes a DC signal by the rectifier 403 and is guided to the comparison circuit 8 of the comparison control circuit. (Fig. 5 (a)
Relationship between band-pass filter 1, low-pass filter 2, band-pass filters 601, 602, (b) relationship between low-pass filter 2 and band-stop filter 401) f1 DC signal and f2 DC obtained above The signal is
The control circuit 607 of the comparison control circuit controls A in three ways. Only the signal of f1 is used for the above three ways. Only the signal of f2 is used. The combined value of the f1 signal and the f2 signal is used. The resulting signal is
The comparison circuit in the comparison control circuit 1 compares with a threshold circuit,
Signals within G = n ± 1 are sent to the next stage (Fig. 4
(A)). The obtained signal is used as a comparison control circuit 2 (10, 1).
Guided to 1). The selection control circuit 10 of the comparison control circuit 2 allows three types of selection (the same function as 607), and B control is performed. The obtained signal is compared by the threshold circuit in the comparator 11, and the signal within (H = n ± 1) is transmitted. (Fig. 4 (b))

The present invention described above has the following effects. (1) Since the band pass filters 1 to 3 to be used are provided, the interference wave from the band not used can be reduced. (2) Since the signal detection circuit (6, 7) and the blocking circuit (4, 5) are provided, (a) It is not affected by an interfering wave generated instantaneously. (B) f1 to f4 separated from the pseudo signal component are obtained. (C) Since the blocking circuits (4, 5) are provided, the state value of the band can be obtained in real time and can be used for comparison. (D) Since the bandpass filters (601, 602) are used, highly accurate and high-speed signal reception can be performed. (3) Comparison control circuit 607 (in the case of detection circuit 6), 10
Since it is equipped with, it can be used according to the situation of the transmission line, purpose of use, and competing manufacturers. (4) Since the protection circuit (threshold circuits 8 and 11) is provided, it is possible to accurately distinguish between a true signal and an erroneous signal. (5) The common block and circuit configuration makes it easy to perform a cut test. (6) Filter circuit (1, 2, 3), blocking circuit (4,
5), the signal detection circuit (6, 7) and the comparison control circuit (8,
Since 9, 10, 11) are subjected to digital signal processing (DSP), the assembly and manufacturing time can be shortened (one integrated circuit compared with the conventional one). (7) The comparison control circuit enables the following. (A) It is possible to make settings that match the transmission path. (B) Settings that match the line quality can be made. (C) It is possible to connect (opposite) the device of another company.

[Brief description of drawings]

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

FIG. 2 is a conventional detection circuit diagram.

FIG. 3 is a conventional detection circuit diagram.

4A and 4B are views for explaining the operation of the present invention.

5A and 5B are diagrams for explaining the operation of the present invention.

[Explanation of symbols]

 1 band pass filter 2 low pass filter 3 high pass filter 4, 5 signal blocking circuit 6, 7 signal detection circuit 8, 9 comparison control circuit 1 10, 11 comparison control circuit 2 101 band rejection filter 102, 103 amplification circuit 104 , 105 rectifier circuit 106 comparator circuit 107 delay circuit 108 band pass filter 201 f1 pass filter 202 f2 pass filter 203, 204 amplifier circuit 205, 206 rectifier circuit 207 AND logic circuit 208 delay / waveform correction circuit

Claims (1)

[Claims] 1. A band pass filter for passing a band of a signal to be used, a low pass filter and a high pass filter for dividing an output of the band filter into a low pass signal and a high pass signal,
First to extract only signals from the low-pass and high-pass signals
And a second signal extraction circuit, first and second blocking circuits for blocking signals other than the signals to be passed in the low-frequency and high-frequency signals, and the first and second signal extraction circuits It is composed of first and second comparison circuits for comparing an output with the outputs of the first and second blocking circuits, and a third comparison circuit for comparing the outputs of the first and second comparison circuits. An in-band signal detection circuit characterized by the above.