JPH05344231A - Polarity inversion detection circuit - Google Patents

Abstract

PURPOSE:To provide a polarity inversion detection circuit where an integration is possible, a detection operation is sure, the resistance to noise is provided, cost is reduced and a high stable operation is possible. CONSTITUTION:The current flowing to telephone lines L1, L2 is rectified in a rectifying circuit 10. First and second charge storage circuits 30a, 30b store the states of the L1, L2 through first and second charging circuits 20a, 20b from the L1, L2. Based on the outputs of the circuits 30a, 30b, the respective transmission thresholds are set by first and second threshold setting circuits 40a, 40b, and AND is determined in an AND gate circuit 50 by the outputs of the circuits 40a, 40b. As for the output of the circuit 50, it is held in a holding circuit 70 after a waveform shaping and an amplification are performed. The circuit 70 and a discharge driving circuit 80 are simultaneously operated, the storage charge of the circuits 30a, 30b is discharged by first and second discharge circuits 90a, 90b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a no-ringing terminal which is a driving terminal for bell signals such as a telemeter terminal.
The present invention relates to a polarity reversal detection circuit for receiving a start signal and a restoration signal sent from a telephone office via a telephone line.

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field,
For example, JP-A 61-49543 and JP-A 63-
There are those described in Japanese Patent No. 52553 and Japanese Patent Laid-Open No. 3-124154. FIG. 2 is a circuit diagram showing a configuration example of the conventional polarity inversion detection circuit described in the above document. This polarity inversion detection circuit is an isolator (isolat
or) an input side element (for example, a light emitting diode of a photocoupler, hereinafter referred to as an LED) 1, a resistor 2, and a capacitor 3
, Which are connected in series between the telephone lines L1 and L2. In this type of polarity reversal detection circuit, when the polarity reversal of the telephone lines L1 and L2 is performed from a telephone station (not shown) by the polarity reversal control of the telephone lines L1 and L2, electric charge is discharged from one electrode of the capacitor 3. The other electrode is simultaneously charged with the opposite polarity. When the charge is discharged from the capacitor 3, the isolator input side element 1 is driven through the resistor 2 with a constant time constant. The output of the driven isolator input side element 1 is guided to an output side element (not shown), and the polarity is determined to be inverted by the output.

[0003]

However, the polarity inversion detection circuit having the above configuration has the following problems and it is difficult to solve them. (1) In order to drive the isolator input side element (eg, photocoupler LED) 1, a large-capacity μF capacitor 3 and a high withstand voltage capacitor 3 of 250 V or more are required, so integration is performed from the viewpoint of capacitance value. Is impossible. (2) In principle, the polarity reversal detection is performed by using the charge / discharge current of the capacitor 3, so that the output duration of the isolator input side element 1 is short and the output detection is difficult. (3) In particular, in a system in which a large number of polarity inversion detection circuits of FIG. 2 are connected in parallel, the total capacitor per line must be 3 μF or less in the case of Nippon Telegraph and Telephone Corporation (NTT), for example. There is a standard. Therefore, for example, when 10 units of the polarity reversal detection circuit of FIG. 2 are connected in parallel, the drive current of the isolator input side element 1 must be extremely small because the unit must be 0.3 μF or less. The polarity reversal detection function may not be obtained. (4) Furthermore, since the operating principle is a detection circuit that uses charging / discharging of the capacitor 3, not only is it liable to malfunction due to potential changes at the no-ringing trunk connection at the central office side, but also malfunction due to noise on the transmission line. There was a problem that there is a risk of causing. The present invention, as a problem that the above-mentioned conventional technology has,
(1) The circuit cannot be integrated, (2) It is difficult to detect the output because the output duration time of the isolator input side element 1 is short, and (3) In the parallel connection system of n units, the capacitor component alone is specified according to the terminal installation standard. Since it has to be 1 / n as compared with the case of the system, the drive current of the isolator input side element 1 is small, and there is a possibility that the polarity inversion detection function may not be obtained. Furthermore, (4) Malfunction due to noise when connecting a no-ringing trunk at the central office side, (5)
The present invention provides a polarity reversal detection circuit which has solved problems such as malfunction due to noise in a transmission line.

[0004]

To solve the above problems, the present invention provides a polarity inversion detection circuit for a no-ringing terminal for receiving a start signal and a recovery signal from a pair of telephone lines, wherein the pair of phones are A rectifier circuit connected to the line and rectifying a current flowing through the telephone line to output a voltage of a constant polarity from the positive output terminal and the negative output terminal;
Of the first and second charge storage circuits for storing charges from the pair of telephone lines to the negative output terminals of the rectifier circuit through the first and second charge circuits respectively, and the first and second charge storage circuits. First and second threshold value setting circuits that receive outputs and set respective transmission threshold values, and an AND gate circuit that is configured by voltage-driven elements and that obtains a logical product of outputs of the first and second threshold value setting circuits, I have it.

Further, a detection output circuit that shapes and amplifies the waveform of the output of the AND gate circuit, a holding circuit that has an isolator, and holds the polarity inversion detection result by the output of the detection output circuit, and the holding circuit. Discharge driving circuits that are driven at the same time, and first and second discharging circuits that are driven by the discharge driving circuits and discharge the accumulated charges of the first and second charge accumulating circuits, respectively, are provided.
Then, the AND gate circuit, the detection output circuit, the holding circuit, the discharge drive circuit, and the first and second discharge circuits are configured to operate within the rectifier circuit output potential.

[0006]

According to the present invention, since the polarity reversal detection circuit is constructed as described above, the current flowing through the telephone line is rectified by the rectifier circuit, and the AND gate circuit, the detection output circuit, and the discharge are generated within the rectifier circuit output potential. The drive circuit and the first and second discharge circuits operate. The first and second charge storage circuits store the state of the telephone line through the first and second charging circuits from the telephone line, respectively. A transmission threshold is set by the first and second threshold setting circuits based on the outputs of the first and second charge storage circuits, and a logical product is obtained by the AND gate circuit from the outputs of the first and second threshold setting circuits. Be done.

The detection output circuit performs waveform shaping and amplification on the output of the AND gate circuit. The output of the detection output circuit is held by the holding circuit, at the same time, the discharge drive circuit is driven, and the accumulated charge of the first and second charge accumulation circuits is
It is discharged by the second discharge circuit. This enables integration, reliable detection operation, noise immunity, low cost, and highly stable operation. Therefore, the above problem can be solved.

[0008]

1 is a circuit diagram of a polarity inversion detection circuit showing an embodiment of the present invention. This polarity reversal detection circuit is a rectification circuit 10 composed of diodes 11, 12, 13, and 14.
And its input terminal is connected between the pair of telephone lines L1 and L2. The first charging circuit 20 is provided between the telephone lines L1 and L2 and the negative output terminal N10b of the rectifier circuit 10.
a, first charge storage circuit 30a, second charge storage circuit 30
b and the second charging circuit 20b are connected in series.
The first charging circuit 20a includes a resistor 21a and a diode 22.
b, which are connected in series to the telephone line L1. Similarly, the second charging circuit 20b has a resistor 21b and a diode 22b, which are connected in series to the telephone line L2. First and second charge storage circuits 30a, 3
Reference numeral 0b is a circuit for storing the states of the telephone lines L1 and L2 from the telephone lines L1 and L2 through the first and second charging circuits 20a and 20b.
Is composed of a series circuit of capacitors 31a and 32a, and the second charge storage circuit 30b is composed of capacitors 31b and 3a.
It is composed of a series circuit of 2b.

The first threshold value setting circuit 40a is connected to the connection point N30a between the capacitors 31a and 32a, which is the output point of the first charge storage circuit 30a, and the second charge storage circuit 3 is connected.
The second threshold value setting circuit 40b is connected to the connection point N30b between the capacitors 31b and 32b, which is the output point of 0b.
The first and second threshold value setting circuits 40a and 40b are
It is a circuit that receives outputs of the charge storage circuits 30a and 30b and sets transmission thresholds (detection thresholds), and is configured by Zener diodes 41a and 41b, respectively. The output terminals of the first and second threshold value setting circuits 40a and 40b are connected to the input terminal of the AND gate circuit 50.

The AND gate circuit 50 is a circuit for obtaining a logical product of the output of the first threshold value setting circuit 40a and the output of the second threshold value setting circuit 40b, and is voltage driven by the output of the first threshold value setting circuit 40a. Mold element (eg, MOS
Transistor 51 and a voltage drive type element (for example, MOS transistor) 52 driven by the output of the second threshold value setting circuit 40b, and the drain / source of these MOS transistors 51 and 52 form an AND gate. Are connected as. Each MOS transistor 5
Protective elements (for example, Zener diodes) 53 and 54 for preventing gate breakdown at the time of inputting an overvoltage are connected between the gate and the source of 1, 52, respectively. The output terminal of the AND gate circuit 50 is connected to a detection output circuit 60 that shapes and amplifies the waveform of the output of the AND gate circuit. The detection output circuit 60 includes a current limiting resistor 61, an emitter resistor 62, an operation stabilizing resistor 63, a surge protection resistor 64, a PNP transistor 65, and a diode 6.
It has 6,67. One end of the current limiting resistor 61 is
It is connected to the drain of the MOS transistor 52 in the AND gate circuit 50, the other end is connected to the base of the PNP transistor 65, and is connected to the positive output terminal N10a of the rectifier circuit 10 via the operation stabilizing resistor 63. And diodes 67, 6 connected in series in the opposite direction
It is connected to the positive output terminal N10a of the rectifier circuit 10 via 6.

The PNP transistor 65 constitutes a constant current circuit by the emitter resistor 62 and the diodes 66 and 67, and the power source side thereof is the positive output terminal N10 of the rectifier circuit 10.
It is connected to a. One end of the surge protection resistor 64 is connected to the collector of the PNP transistor 65, and the other end is connected to the input terminal of the holding circuit 70. The holding circuit 70 is a circuit that holds the polarity reversal detection result by the output of the detection output circuit 60, and includes an isolator input side element (for example, a photocoupler LED) 71, an NPN transistor 72, a PNP transistor 73, an emitter resistor 74, and an operation. Stabilizing resistor 75, surge protection resistor 76,
An emitter resistor 77, an operation stabilizing resistor 78, and diodes 79a, 79b, 79c, 79d are provided. N
The base of the PN transistor 72 is connected to the surge protection resistor 64 in the detection output circuit 60, and the negative output terminal N of the rectifier circuit 10 is connected via the operation stabilizing resistor 75.
A diode 79 connected in series and connected in series with 10b.
It is connected to the negative output terminal N10b via a and 79b. The NPN transistor 72 has an emitter resistor 7
4 and the diodes 79a and 79b constitute a constant current circuit, the ground side of which is the negative output terminal N10 of the rectifier circuit 10.
connected to b.

At the collector of the NPN transistor 72,
One end of the surge protection resistor 76 is connected and the other end is
It is connected to the base of the PNP transistor 73, is further connected to the positive output terminal N10a of the rectifier circuit 10 via the operation stabilizing resistor 78, and is connected to the positive electrode via the diodes 79d and 79c connected in series in the reverse direction. Sex output terminal N10a. PNP transistor 73
Is a constant current circuit composed of the emitter resistor 77 and the diodes 79c and 79d, the power source side of which is connected to the positive output terminal N10a of the rectifier circuit 10. The anode of the LED 71 is connected to the collector of the PNP transistor 73, and the cathode thereof is connected to the base of the NPN transistor 72 to form a positive feedback loop. A discharge drive circuit 80 is connected to the base of the PNP transistor 73. The discharge drive circuit 80 has PNP transistors 81 and 82 and resistors 83 and 84. The bases of the PNP transistors 81 and 82 are P in the holding circuit 70.
The bases of the NP transistors 73 are commonly connected, and their respective emitters are respectively connected to the positive output terminal N10a of the rectifier circuit 10 via resistors 83 and 84. PNP
Each of the collectors of the transistors 81 and 82 has a first discharge circuit 90a and a second discharge circuit 90 driven by it.
b are connected to each other.

The first and second discharging circuits 90a and 90b are circuits for discharging the respective accumulated charges of the first and second charge accumulating circuits 30a and 30b. The first discharge circuit 90a is
It has diodes 91a, 92a, 93a, an operation stabilizing resistor 94a, an NPN transistor 95a, and a PNP transistor 96a. The anode of the diode 91a is connected to the collector of the PNP transistor 81 in the discharge driving circuit 80, and the cathode thereof is the operation stabilizing resistor 9
It is connected to the negative output terminal N10b of the rectifying circuit 10 via 4a and to the base of the NPN transistor 95a. The NPN transistor 95a is a PN
A complementary Darlington transistor is formed together with the P-transistor 96a, and the output of the complementary Darlington-transistor PNP transistor 96a has an emitter connected to the first charge storage circuit 3.
Diodes 92a and 93a are connected in a direction in which charges are extracted from the high potential side of the capacitors 31a and 32a in 0a. Similarly, the second discharge circuit 90b includes a diode 9
1b, 92b, 93b, operation stabilizing resistor 94b, NP
N transistor 95b and PNP transistor 96b
have. The anode of the diode 91b is connected to the collector of the PNP transistor 82 in the discharge drive circuit 80, and the cathode thereof is connected to the negative output terminal N10b of the rectifier circuit 10 via the operation stabilizing resistor 94b and also the NPN. It is connected to the base of the transistor 95b. The NPN transistor 95b forms a complementary Darlington transistor together with the PNP transistor 96b, and the output of the NPN transistor 96b is in the direction of extracting charges from the high potential side of the capacitors 31b and 32b in the second charge storage circuit 30b. To the diodes 92b and 93b.

Next, referring to FIGS. 3 (a) to 3 (g),
The operation of the polarity inversion detection circuit of FIG. 1 will be described. Figure 3 (a)
1 to (g) are time charts showing the operation of FIG.
The figure (a) shows the communication state of the no ringing terminal, the figure (b) shows the waveform showing the polarities of the telephone lines L1 and L2, and the figure (c) shows the charge state waveform of the first charge storage circuit 30a. FIG. 6D shows the waveform of the charge state of the second charge storage circuit 30b,
The figure (e) shows the waveform of the output of the AND gate circuit 50 and the output current of the detection output circuit 60, and the figure (f) shows the holding circuit 70.
The waveform of the current (holding current) flowing through the polarity reversal detection output LED 71 in the figure, and (g) of the figure show the output current waveform of the discharge drive circuit 80, respectively.

The operation of the polarity inversion detection circuit of FIG. 1 is as shown in FIG.
As shown in (a), the communication state of the no-ringing terminal can be classified into a standby state T1 → detection state T2 → communication T3 → recovery state T4 → standby state T5. Hereinafter, (1) an operation when the telephone line L1 is earth and L2 is a battery, and (2) an operation when the telephone line L1 is a battery and L2 is earth is described.

(1) Operation when Telephone Line L1 is Ground and L2 is Battery First, the operation from the standby state T1 of normal power supply in which the telephone line L1 is ground and L2 is a battery will be described. In the standby state during normal power feeding (S1 in FIG. 3B), the charges stored in the capacitors 31a and 32a of the first charge storage circuit 30a pass through the resistor 21a and the diode 22b of the first charging circuit 20a to the earth- It is charged at the potential between the batteries (S2 in FIG. 3C). Capacitors 31a and 32a
Is set appropriately, and the potential of the capacitor 32a is set to the threshold value of the first threshold value setting circuit 40a and the MOS transistor 51a.
Be sure to exceed the sum of the rising voltage between the gate and source of. In this state, the MOS transistor 5
1 is on, but the MOS transistor 52 is off, and the AND gate circuit 50 is not operating.
No output is made from the drain of the MOS transistor 52. Here, the capacitor of the first charge storage circuit 30a is set to 3
The purpose of dividing into 1a and 32a is to configure the above voltage dividing circuit and at the same time to divide the voltage to alleviate the required maximum value (for example, 250 V) of the withstand voltage of the capacitor film at the time of integration. If no, first
From the charging circuit 20a to the first threshold setting circuit 40a and the MOS
A current path is formed through the Zener diode 53, which is a protection element connected between the gate and the source of the transistor 51, and the input impedance of the first threshold value setting circuit 40a during standby is significantly reduced. This is to reduce the power consumption during standby to zero.

Next, the polarity reversal of the telephone lines L1 and L2 is started under the control of the central office side (S in FIG. 3B).
3) When the reverse power supply state is entered from the break state (S4 in FIG. 3B), the potential of L2 becomes higher than that of the telephone line L1. Therefore, the charge of the first charge storage circuit 30a is stopped and the charge is held, and the capacitors 31b and 32b of the second charge storage circuit 30b are charged through the resistor 21b and the diode 22b of the second charge circuit 20b. (S5 in FIG. 3D). Here, the capacitors 31b and 32b of the second charge storage circuit 30b are configured similarly to the capacitors 31a and 32a.

The reverse power feeding state is the second threshold setting circuit 40.
When the second detection threshold value of b (S6 of FIG. 3B) is reached,
The MOS transistor 52 of the AND gate circuit 50 is also turned on. As a result, the drain of the MOS transistor 52 drives the detection output circuit 60 through the resistor 61, and the output current of the detection output circuit 60 flows from the collector of the PNP transistor 65 through the resistor 64 (FIG. 3).
(E) S7). This output current is equal to N in the holding circuit 70.
The base of the PN transistor 72 is driven, and the base of the PNP transistor 73 is driven from its collector through the resistor 76. As a result, the current output from the collector of the PNP transistor 73 drives the LED 71 (S8 of FIG. 3 (f)), and the drive current is fed back to the base of the NPN transistor 72, thereby the polarity inversion detection result is output. It can be held by the holding circuit 70.
The driven LED 71 is transmitted to an output side element (not shown), and its output is guided to an external circuit. For example, when the isolator is composed of a photocoupler as shown in FIG.
Since the input side element is an LED, the output side element becomes a phototransistor.

The PNP transistors 81 and 82 in the discharge driving circuit 80 are the PNP transistors 7 in the holding circuit 70.
3 is connected in common with the base to form a current source circuit,
From the collectors of the NP transistors 81 and 82, the PNP
The output current of the discharge drive circuit 80 is obtained at the same timing as the collector output current of the transistor 73 (S in FIG. 3 (g)).
9). The discharge drive circuit output current from the collector of the PNP transistor 81 passes through the diode 91a and forms the complementary Darlington transistor NP.
It drives the base of the N-transistor 95a, and the capacitor 3
Charges accumulated in 1a and 32a are transferred to diodes 92a and 93a.
Through the collector of the PNP transistor 96a through the collector path (S10 in FIG. 3C). Similarly, the discharge drive circuit output current from the collector of the PNP transistor 82 passes through the diode 91b and forms the complementary Darlington transistor NPN.
It drives the base of the transistor 95b, and the capacitor 31
The accumulated charges in b and 32b are discharged through the diodes 92b and 93b through the path from the emitter to the collector of the PNP transistor 96b (S11 in FIG. 3D). First and second
Capacitors 31a, 3 in the charge storage circuits 30a, 30b
The accumulated charge of 2a, 31b, 32b starts discharging, and the potential of the capacitor 32a or 32b becomes the first detection threshold of the first threshold setting circuit 40a + the gate-source rising voltage of the MOS transistor 51 or the second threshold setting circuit 40b.
The second detection threshold value + the gate-source rising voltage of the MOS transistor 52 becomes lower, the MOS transistors 51 and 52 are turned off. Therefore, the AND gate circuit 5
The output of 0 is turned off, and the output current of the detection output circuit 60 is also turned off (S12 in FIG. 3E). With the above operation, the polarity reversal detection of the telephone lines L1 and L2 is completed, and the communication T3 keeps this state.

Next, the operation of completing the communication and going from the recovery state T4 to the standby state T5 will be described. The communication line T3 and the telephone lines L1 and L2 under the reverse power feeding state start the restoration state T4 under the control of the central office (S1 in FIG. 3B).
3). Then, when the potential difference between the telephone lines L1 and L2 becomes small and the holding circuit 70 cannot keep the holding current flowing and is in the OFF state (S1 in FIG. 3F).
4), since the PNP transistors 81 and 82 are also turned off, the output current of the discharge drive circuit 80 is also turned off (S15 in FIG. 3G). As a result, the LED 71 is not driven, and the output of the output side element (not shown) is also turned off. Further, when the break state shifts to the normal power feeding state (S16 in FIG. 3B), the first charge storage circuit 30a starts charging through the resistor 21a and the diode 21b of the first charging circuit 20a (FIG. 3C). ) S17). When the normal power feeding is completed, the standby state T5 is set (S18 in FIG. 3B).

(2) Operation when telephone line L1 is battery and L2 is ground In the above (1), the polarity is reversed from the power supply state when telephone line L1 is ground and L2 is battery. Although the operation has been described, the same operation as described above is performed when the telephone line L1 is a battery and L2 is ground. That is,
In this case, in the standby state T1, the second charging circuit 20
The capacitors 31b and 32b of the second charge storage circuit 30b are charged through the resistor 21b of b and the diode 22b, and the gate of the MOS transistor 52 is turned on.
The difference from (1) is that the gate of the MOS transistor 51 is off. However, with respect to the telephone lines L1 and L2, the first charging circuit 20a, the first charge storage circuit 30a and the first discharge circuit 90a are different from the second charge circuit 20b, the second charge storage circuit 30b and the second discharge circuit 90b. The circuit structure and the circuit structure are electrically symmetrical, and the AND gate circuit 50, the detection output circuit 60, the holding circuit 70, and the discharge drive circuit 80 have the telephone lines L1 and L2 as input sides. Since it is connected to the output side of the rectifier circuit 10 to operate, the polarity reversal detection and restoration can be performed regardless of the polarities of the telephone lines L1 and L2, and therefore the operation is substantially the same as in (1) above.

As described above, this embodiment has the following advantages. (I) Except for the LED 71 which is the isolator input side element, the element can be integrated so that the circuit scale can be reduced and a low cost integrated circuit can be realized. (Ii) The result of polarity reversal detection is displayed during no ringing communication,
Since it can be held by the holding circuit 70, a sufficient polarity inversion detection output time can be obtained. (iii) Since the polarity inversion detection circuit has a small number of capacitor components, it is possible to very easily realize the configuration of a parallel connection system in which a large number of the polarity inversion detection circuits are connected in parallel. (Iv) First and second threshold value setting circuit 40 for polarity inversion detection
Since a and 40b are provided, it is possible to prevent malfunctions due to noise at the time of connection of the no ringing trunk on the telephone office side and malfunctions due to noise on the transmission line. (V) Since the AND gate circuit 50 is composed of the MOS transistors 51 and 52 which are voltage drive type elements,
The standby power consumption becomes zero, and the power consumption can be reduced.

The present invention is not limited to the above embodiment,
Various modifications are possible. Examples of such modifications include the following. (A) Although the isolator is composed of a photocoupler in FIG. 1, it may be composed of an isolator using other means such as electromagnetic waves. (B) If the AND gate circuit 50 of FIG. 1 is configured by a NAND gate circuit with its output inverted and the circuit configuration of the detection output circuit 60 on the output side is changed accordingly, the same operation as in the above embodiment, The effect is obtained. (C) The circuit of each block in FIG. 1 can be changed to another circuit configuration by using transistors or elements other than those illustrated.

[0024]

As described in detail above, according to the present invention, the rectifier circuit, the first and second charge storage circuits, and the first and second charge storage circuits.
Since it is composed of a threshold value setting circuit, an AND gate circuit, a detection output circuit, a holding circuit, and the first and second discharge circuits, the integration becomes easy, the circuit scale becomes small, the cost becomes low, and the operation is highly stable. Is possible. In addition, the polarity inversion detection result can be held by the holding circuit during no ringing communication, so that a sufficient polarity inversion detection output time can be obtained. Since the polarity inversion detection circuit can be configured with a circuit having a small capacitor component, the configuration of the parallel connection system can be realized very easily. Furthermore, since the first and second threshold value setting circuits for polarity reversal detection are provided, it is possible to prevent malfunctions due to noise at the time of connection of the no ringing trunk at the central office side and malfunctions due to noise on the transmission line, and to detect the detection operation. It can be done reliably. Moreover, since the AND gate circuit is composed of voltage-driven elements, the power consumption during standby becomes zero, and the power consumption can be reduced.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a conventional polarity inversion detection circuit.

FIG. 3 is a time chart showing the operation of FIG.

[Explanation of symbols]

 10 Rectifier circuit 20a, 20b 1st, 2nd charging circuit 30a, 30b 1st, 2nd charge storage circuit 40a, 40b 1st, 2nd threshold value setting circuit 50 AND gate circuit 60 Detection output circuit 70 Holding circuit 80 Discharge drive circuit 90a, 90b First and second discharge circuits L1, L2 Telephone line

Claims (1)

[Claims] 1. A polarity reversal detection circuit for a no-ringing terminal for receiving a start signal and a recovery signal from a pair of telephone lines, wherein the current connected to the pair of telephone lines is rectified to positive polarity. A rectifier circuit that outputs a voltage of a certain polarity from the output terminal and the negative output terminal, and stores charges from the pair of telephone lines to the negative output terminals of the rectifier circuits through the first and second charging circuits, respectively. First and second charge storage circuits, first and second threshold value setting circuits that receive the outputs of the first and second charge storage circuits and set respective transmission threshold values, and a voltage-driven element An AND gate circuit that obtains a logical product of the outputs of the first and second threshold value setting circuits, a detection output circuit that performs waveform shaping and amplification of the output of the AND gate circuit, and an isolator. A holding circuit that holds the polarity inversion detection result by the output of the output circuit, a discharge driving circuit that is driven at the same time as the holding circuit, and a discharge driving circuit that is driven by the discharge driving circuit to store the accumulated charges of the first and second charge accumulating circuits First and second to discharge respectively
And a discharge circuit, wherein the AND gate circuit, the detection output circuit, the holding circuit, the discharge drive circuit, and the first and second discharge circuits are configured to operate within the rectifier circuit output potential. Detection circuit.