JP2917667B2 - Ring tone signal 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 ring tone detecting circuit, and more particularly to a ring tone detecting circuit used in an echo canceller type digital subscriber line transmission system using a pair of metallic cables.

[0002]

2. Description of the Related Art In a digital subscriber line system, a calling signal called a tone signal is transmitted in order to call a terminal device on the other side. In the terminal, the ring tone signal detection circuit receives the tone signal from the subscriber line.

Conventionally, this kind of calling tone signal detection circuit (hereinafter simply referred to as tone detection circuit) has a configuration shown in FIG. FIG. 4 is a block diagram of a tone detection circuit of a conventional terminal device. The tone detection circuit 15 includes a band-pass filter 16, a folding circuit 17, and a low-pass filter 1.
8. It is composed of a comparison / determination unit 19.

[0004] A received signal propagating through the subscriber line 11 and passing through the hybrid transformer 12 is input to a band-pass filter 16. In the digital subscriber transmission system, 10 kHz
The signal of z is defined as a tone signal. The 10 kHz signal component detected by the low-pass filter 16 is
The full-wave rectified by the folding circuit 17 and the signal subjected to the full-wave rectification are converted by the low-pass filter 18 into a DC signal component. The DC signal component detected by the low-pass filter 18 is input to the comparator 19. The comparison determiner 19
The DC component is compared with a predetermined threshold voltage to determine whether the signal is a tone signal. This conventional tone detection system is a power detection system that determines the presence or absence of a tone signal based on the power of the signal.

[0005]

In the conventional tone signal detection circuit 15, since the detection frequency is extracted only by the band-pass filter 16, surge noise including the same frequency component as that of the tone signal or normal transmission is used. In some cases, the signal was erroneously detected as a tone signal. Further, since the band-pass filter 16, the folding circuit 17, and the low-pass filter 18 are constituted by analog circuits, aging, temperature change,
There is a problem that the influence of a change in characteristics due to a manufacturing deviation or the like is large. Furthermore, the conventional example uses a power detection method,
Particularly, when the transmission distance is long, the power of the tone signal becomes small, and there is a problem that near-end crosstalk is erroneously detected as a tone signal.

[0006]

A calling tone signal detecting circuit according to the present invention is provided with a sampler for sampling a calling tone signal of an AC waveform inputted from a transmission line, and an output signal of the sampler as input and output. pattern over signal to detect a comparator for converting into a digital signal of "0" to "1" a negative voltage if a positive voltage, the path <br/> Turn-down of the tone signal from an output signal of the comparator a down detection circuit, a timer for counting a predetermined time an output signal of the pattern detection circuit as a trigger, the outside-tone signal when a predetermined number of counts the output signal of the patterns detecting circuit by an output signal of the timer A counter for outputting a detection signal. For example, the patterns detecting circuit, when the output signal of the comparator was the tone signal, i.e., a "0" consecutive represents a "1" and the negative cycles continuously represents the positive cycle of the tone signal A shift register having a plurality of registers for storing the same for a predetermined number of cycles when it is repeated alternately regularly; and a continuous "1" or a continuous "0" of the tone signal stored in each of the registers.
The may be configured which respectively refer except "1" or "0" of the tail end is provided with a plurality of AND circuits and NAND for outputting an output signal of the patterns detected when was predetermined patterns.

[0007]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the present embodiment. The tone signal detection circuit includes a sampler 1 that samples a received tone signal 101 and a comparator 2 and a comparator 2 that convert a signal sampled by the sampler 1 into a digital output signal 103 of 1 or 0 according to a positive or negative voltage. Output signal 1
03 from detecting the tone signal unique patterns patterns detection circuit 3, a timer 5 for defining the detection time, and a counter 4 for counting the pattern detection frequency within a detection time determined by the timer 5.

[0008] Figure 2 shows a circuit diagram of patterns detection circuit 3 shown in FIG. Patterns detection circuit 3 includes a shift register 36 for storing the output of the comparator 2, the shift register 36
Input AND circuits 31 and 3 for detecting a pattern from
3 and 3 input NAND circuits 32, 34, 4 input AND
It is constituted by a circuit 35. FIG. 3 is a time chart showing a process of detecting a tone signal in FIG.

In FIG. 1 and FIG. 2, the sampler 1 is 80 k
Operates in Hz, the shift register 3 of the patterns detecting circuit 3
6 is 2T of the tone signal 101 (10 KHz) (period T =
1 to 10 KHz), and includes 0 to 14th registers for storing the output signals 103 of the comparator 2 for 1/10 KHz).
Is a 2-bit counter, and timer 5 is 32T (T = 1/8)
0 kHz). FIG. 3A shows the waveform of the tone signal 101 received from the subscriber line. The waveform of the tone signal 101 is a short AC wave having a positive / negative cycle on the transmission side, but is distorted on the transmission line, and thus becomes as shown in the figure, for example. FIG.
When the waveform (a) is input, the comparator 2 outputs 1 when the input is positive, and outputs 0 when the input is negative. FIG.
3A shows an output signal 103 of the comparator 2 corresponding to FIG.

The AND circuits 31, 33, 35, and NA of FIG.
Only 1 of the patterns detected signal when the output signal 103 circuit is stored in the shift register 36 composed of ND circuit 32, 34 that matches the detection pattern of FIG. 3 (c) 104
Is output. Here, the data whose data is D in FIG. 3C is not referred to. This is because when the sampler point of sampler 1 is in the vicinity where the tone signal switches between positive and negative,
This is because the signal level at this point is very small, and is susceptible to harmful noise such as near-end crosstalk, so that the output of the comparator 2 differs from the expected value. In this case, if pattern detection is performed using all data stored in the shift register 36, a tone signal cannot be detected. For this reason, data that is not referred to is provided for each half cycle of a tone to protect against harmful noise such as near-end crosstalk.

[0011] patterns compared is input to the detection circuit 3 unit 2
The output signal 103 of the time matching the patterns of FIG. 3 (c), that is, the output signal 103 is first first pattern detection signal 104 to the second cycle from the input time is output. As a result, the timer 5 starts counting time, and the counter 4 increments the count by one. Timer 5 counts 3
Patterns detection circuit 3 before the time-out elapsed 2T
When 1 is output four times, the received signal is determined as a tone signal, and a tone signal detection signal 102 is output.
Patterns detection circuit 3 detects the signal 102 for each cycle of the first when an output signal 103 following the output signal 103
Is output. When the timer 5 times out, the timer 5 initializes the counter 4 and stops.

[0012]

As described above, the tone signal detection circuit according to the present invention includes a circuit which quantizes an input signal into 1, 0 digital signals using a comparator and detects a pattern unique to the tone signal. , A tone signal can be detected without malfunction due to noise such as surge noise, near-end crosstalk and the like, and without erroneous transmission signals. Therefore, there is an effect of improving detection accuracy. Further, by detecting the input signal by digital processing, there is an effect that the integration is facilitated, the size is reduced, the manufacturing deviation and the secular change are reduced.

[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 pattern detection circuit in FIG.

FIG. 3 is a timing chart showing a process of detecting a tone signal in FIG. 1;

FIG. 4 is a block diagram showing a conventional circuit.

[Explanation of symbols]

1 sampler second comparator 3 patterns detection circuit 4 counter 5 Timer 3,6 shift register 31 and 33 3-input AND circuit 32, 34 3-input NAND circuit 35 4-input AND circuit

Claims (2)

(57) [Claims] 1. A sampler for sampling a tone signal for calling an AC waveform input from a transmission line, and an output signal of the sampler is input. If the output signal is a positive voltage, "1" is negative and "0" is a negative voltage. a comparator for converting into a digital signal of "predetermined and patterns detection circuit for detecting a pattern over <br/> down of the tone signal from an output signal of said comparator, an output signal of the pattern detection circuit as a trigger a timer for counting time, a call, characterized in that it comprises a counter for outputting a detection signal of the tone signal to the outside when a predetermined number of counts the output signal of the patterns detecting circuit by an output signal of the timer Tone signal detection circuit. Wherein said patterns detection circuit, an output signal of said comparator when said was tone signal, i.e., successive represents a "1" and the negative cycles continuously represents the positive cycle of the tone signal " And a shift register having a plurality of registers for storing a predetermined number of cycles when the "0" is alternately repeated, and a continuous "1" or a continuous "0" of the tone signal stored in each of the registers. "the reference each except" 1 "or" 0 "of the tail end, characterized in that it comprises a plurality of aND circuits and NAND for outputting an output signal of the patterns detected when was predetermined patterns 2. The calling tone signal detecting circuit according to claim 1, wherein