JPH0436617B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] A ring trip voltage detection circuit used in a subscriber circuit in a time-division switching system, which detects two voltages with almost the same absolute value, which have different reference polarities and are shifted by the switching power supply voltage. It becomes possible to give an equivalent comparison voltage to a single comparator for the input signal.

[Industrial application field]

The present invention relates to a ring trip voltage detection circuit for stopping a ringing signal when a subscriber answers a call in a subscriber circuit of a time division switching system. This invention relates to a ring trip voltage detection circuit that can detect a subscriber's response with a single comparator without changing the circuit, even if a ringing signal oscillator (hereinafter referred to as an oscillator) is inserted on either side (referred to as a power supply).

The ringing signal is a commonly used 16 Hz to 20 Hz AC signal, and a DC voltage is superimposed to monitor the subscriber's response. A ring trip voltage detection circuit is used to detect the change in the DC voltage that occurs when the subscriber answers and thereby to stop sending out the ringing signal and establish a communication path. This circuit includes a low pass filter for blocking the ringing signal and extracting the DC signal, and a comparator for detecting changes in the DC signal. The output of the comparator is used to restore the relay that controls the sending of the ringing signal and the formation of the communication path. Typically, the oscillator is inserted into a series circuit consisting of a resistor, the subscriber's telephone and a DC power supply. Further, the oscillator is inserted into either the ground side or the -power supply side depending on the device. Generally, the operating power supply voltage of the comparator is lower than the voltage of the DC power supply connected to the calling signal circuit, so it is necessary to prepare different power supply systems depending on the insertion position of the oscillator.

Therefore, it is desired to provide a circuit that can detect a ring trip using the same circuit configuration and a low voltage comparator regardless of the insertion position of the oscillator.

[Conventional technology]

To send a ringing signal to a subscriber circuit in a time-sharing switching system, a telephone connected to a general circuit that supplies power, etc. is connected to a series circuit consisting of a DC power supply, an oscillator, and a series resistor by switching it with a relay. A circuit system is used. FIG. 5 is a block circuit diagram of a ring trip circuit used in such a system, and shows an oscillator 26, a resistor 4, contact 2 of the relay 14, a telephone 1, and a contact 3 of the relay 14 between the earth and the VBB power supply. and resistor 5 are shown formed. Note that the contacts 2 and 3 of the relay 14 are normally energized to connect the telephone 1 to the general circuit 8. If the subscriber responds when the calling signal is sent and a direct current short circuit is formed within the telephone set 1, a direct current voltage indicated by VB in the figure is applied to the input terminal of the low pass filter 6. The low-pass filter 6 is provided to take out only the DC potential from the connection point between the contact 2 and the resistor 4, and the output of the low-pass filter 6 is supplied to the + side input terminal of the comparator 12. Note that the input terminal of the low-pass filter 6 may be connected to the resistor 5 side as shown by the broken line in the figure. The output of comparator 12 is signal line 15
A signal determining the connection period of the calling signal is supplied to the relay driver 13, and the relay 14 is restored based on the subscriber's response, and its contacts 2 and 3 are supplied to the relay driver 13.
is switched to the general circuit 8 side. Since the rated power supply voltage of the comparator 12 shown in FIG. 5 is generally lower than the VBB power supply voltage of the exchange, a separate power supply system indicated by VC in the figure is used for power supply.

FIG. 6 is a block circuit diagram of another conventional example, in which an oscillator 26 is inserted between the VBB power supply and the resistor 5. In this circuit, a voltage indicated by VA is applied to the input terminal of the low-pass filter 7. The output of low pass filter 7 is VBB power supply and VC
+ of the comparator 13 connected between the power supplies indicated by
It is supplied to the side input terminal, detects the DC change due to the subscriber's response, and the relay driver 13 controls the energization to restore the relay 14. Note that the circuit shown in FIG. 6 can also be constructed so that the input to the low-pass filter 7 is obtained from the connection point between the contact 2 and the resistor 4, as shown by the broken line.

[Problem that the invention seeks to solve]

In this conventional method, the comparator that operates on the voltage between the ground air and the VBB power supply is expensive, so if a comparator with a lower rated power supply voltage is used, a different power supply system is required depending on the insertion position of the oscillator. It's not economical at all. Also, when the low-pass filter is composed of active elements,
A separate power supply lower than the system power supply voltage is required.

The present invention was created in view of these points, and it is possible to detect ring trip voltage using a single comparator with a relatively low rated operating voltage, regardless of the insertion position of the oscillator or the reference voltage at the voltage extraction point. The purpose of this invention is to obtain a ring trip voltage detection circuit.

[Means for solving problems]

FIG. 1 shows a principle block diagram of the present invention. As shown in FIG. 1A, the first invention provides a first input signal applied to a first input terminal 10 and a second
is applied to the input terminal 9 of the first input signal, and has a voltage polarity opposite to that of the first input signal, and is shifted by the exchange power supply voltage from the reference potential with respect to the first input signal. A first transistor 101 whose base is connected to the first input terminal 10, whose collector is connected to a first power supply, and whose emitter is connected to a constant current source 100, which is detected by a comparator.
a second transistor 103 whose base is connected to the emitter of the first transistor 101 and whose emitter is connected to the first power supply via a first resistor 25; , a second resistor 21 and a third resistor 22 are connected in series, one end of which is connected to the second power supply, and the other end connected to the second input terminal 9 and the second transistor 103. Connect to the collector of
and a compared voltage circuit that outputs a voltage proportionally divided by the resistance values of the second resistor 21 and the third resistor 22 to a connection point 104 between the second resistor 21 and the third resistor 22; 105, and the resistance value of the first resistor 25 is such that the voltage that appears at the connection point 104 when the first transistor 101 is conductive is equal to the voltage that appears at the connection point 104 when the first transistor 101 is not conductive. Said second
When an input signal of
It is configured such that the value is selected to be equal to the voltage appearing at .

The second invention, as shown in FIG.
a first input signal applied to the input terminal 10 of the , and a second input signal applied to the second input terminal 9 of the first input signal, the voltage polarity being opposite to the voltage polarity of the first input signal and from the reference potential with respect to the first input signal. The circuit detects a voltage change of a second input signal shifted by the exchanger power supply voltage using a single comparator, and the base is connected to the first input terminal 10 and the collector is connected to the first power supply. And Emitsuta is the first
First transistor 1 connected to constant current source 100
01, and a second transistor 1 whose base is connected to the emitter of the first transistor 101 and whose emitter is connected to the first power supply via the first resistor 25.
03, and a third transistor 1 whose base is connected to the second input terminal 9, whose collector is connected to the second power supply, and whose emitter is connected to the second constant current source 108.
09; a fourth transistor 113 whose base is connected to the emitter of the third transistor 109 and whose collector is connected to a predetermined voltage source; a second resistor 21 and a third transistor 110; Resistors 22 are connected in series, one end of which is connected to the second power supply, and the other end connected to the emitter of the fourth transistor 113 and the collector of the second transistor 103, and the second A compared voltage circuit 105 that outputs a voltage proportionally divided by the resistance values of the second resistor 21 and the third resistor 22 is provided at a connection point 104 between the resistor 21 and the third resistor 22, The resistance value of the first resistor 25 is such that the voltage that appears at the connection point 104 when the first transistor 101 is conductive is equal to the voltage that appears at the connection point 104 when the first transistor 101 is not conductive.
The voltage is selected to be equal to the voltage appearing at the connection point 104 when the transistor 109 becomes conductive.

[Effect]

The first detected voltage is shifted from the reference potential to the negative potential by the exchange power supply voltage. The first detected voltage input to the first transistor circuit 102 is at a potential higher than the potential shifted negatively from the reference potential by the exchange power supply voltage by a predetermined value. Comparative voltage generation circuit 1 via transistor 103 of
05. A comparison voltage determined by a proportional division ratio between the resistance value of the second resistor 21 and the resistance value of the third resistor 22 is generated from the connection point 104 of the comparison voltage generation circuit 105 .

Further, when the second detected voltage is supplied to the second input terminal 9, the first detected voltage is not supplied to the first input terminal 10, and therefore the transistor 1
03 is not conductive. The second detected voltage is based on the reference voltage, has the same absolute value as the first detected voltage, and has an opposite polarity. By the second detected voltage supplied to the second input terminal 9, the connection point 1
The detected voltage generated at 04 is the first input terminal 1
0 is made equal to the voltage generated at the connection point 104 when the first detected voltage is supplied to the node 104.

Therefore, the two voltages to be detected, which have the same absolute value but opposite polarities, can be generated as a single voltage to be compared.

〔Example〕

FIG. 2 shows the overall configuration of the ring trip voltage detection circuit of the present invention.

In the figure, 6 and 7 are low pass filters (LPF) provided at each voltage extraction point, and the outputs of these low pass filters 6 and 7 are connected to the interface circuit via connection points 9 and 10. 11. The output of the interface circuit 11 is supplied to a comparator 12 which receives power from the earth and the negative power supply VC, and the output of the comparator 12 is
It is supplied to a control terminal of a relay driver 13 that operates a relay 14. Further, the interface circuit 11 includes a transistor whose collector is connected to ground, a constant current source, and a resistor for dividing voltage.

FIG. 3 is a circuit diagram of an embodiment of the present invention, which includes resistors 16, 21, 22, 25, a PNP transistor 19, an NPN transistor 20, a constant current source 18, a Zener diode 17, and a circuit for limiting the output voltage. It consists of a diode 23. In the same figure, the potential indicated by VA supplied to connection point 10 is
6 to the base of a PNP type transistor 19 (corresponding to the first transistor 101 in claims 1 and 2) whose collector is connected to ground. V _A is a potential that is V _A higher than a potential that is lower than the reference potential source (earth potential) by the exchange power supply voltage V _BB . In this embodiment, the exchange power source or the reference potential source is the first power source as claimed, whereas the reference potential source or the exchange power source is the second power source as claimed. .
A constant current source 1 is connected to the emitter of this transistor 19.
8 (corresponding to the constant current source of claim 1 and the first constant current source 100 of claim 2). When the voltage V _A is input from the input terminal 10, the transistor 19 becomes conductive and the constant current source 1
A constant current flows from the transistor 19, but at this time, the input impedance seen from the base of the transistor 19 becomes extremely high because the amplification amount of the transistor 19 is added to the original high impedance characteristic of the constant current source 18. This is input terminal 10
provides an advantage in matching with the LPF connected to the
Furthermore, when the transistor 19 is turned on, its emitter voltage is smaller than the voltage V _A.
The voltage will be higher by the base-emitter drop _VBE . This voltage is applied to the NPN transistor 20 (the second transistor 103 of claims 1 and 2).
corresponds to ), the voltage drop between the base and emitter of transistor 20 causes the emitter of transistor 20 to have approximately VA
A voltage equal to appears. Here, if the resistance value Rc of the resistor 25 is selected to be equal to the sum of the resistance value Ra of the resistor 21 and the resistance value Rb of the resistor 22, the current flowing through the resistor 25 becomes VA/Rc. Also, VB≒
When a voltage VA appears at input terminal 9, resistor 2
The current flowing through 1 and 22 is VB/(Ra+Rb). That is, the output terminal 24 to the comparator 12 is connected to the connection point between the resistor 21 and the resistor 22.
The same voltage appears with either input at connection point 9 or connection point 10.

FIG. 4 shows another embodiment of the present invention, in which an NPN transistor 28 (corresponding to the third transistor 109 in claim 2) is used to increase the input impedance on the connection point 9 side.
and an NPN transistor 30 (corresponding to claim 2 and the fourth transistor 113), a transistor circuit with a collector connected to ground is provided. In this circuit, a constant current source 29 (corresponding to the second constant current source 108 in claim 2).
The input voltage at the connection point 9 is applied to the base circuit of the NPN transistor 28 driven by the resistor 2.
A voltage equal to the voltage indicated by VB appears at the connection point between the resistor 22 and the collector of the transistor 20 due to the common-collector PNP transistor 30 supplied through the transistor 6 and connected to the emitter of this transistor. The relationship between the exchange power supply and the reference potential source in this embodiment and the first and second power supplies recited in the claims is the same as in the embodiment shown in FIG. 3 above. Further, the constant current source 29 also produces the same function as the current source 18. The Zener diode 27, like the Zener diode 17, is inserted to protect the base of the transistor, but by setting the Zener voltage to an appropriate value, it is possible to respond to a wide range of changes in input voltage. . Also, diode 23
is for limiting the output voltage of the output terminal 24 and protecting the comparator connected next.

〔Effect of the invention〕

As described above, according to the present invention, ring trip voltage detection allows ring trip voltage to be detected by a single comparator with a relatively low rated operating voltage, regardless of the insertion position of the oscillator or the reference voltage at the voltage extraction point. A circuit is obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a diagram showing the overall configuration of the invention, Fig. 3 is a circuit diagram of an embodiment of the invention, and Fig. 4 is another embodiment of the invention. 5 and 6 are block circuit diagrams of conventional examples. 1 and 2, 100 is a comparator, 101, 102, 104, and 105 are first, second, third, and fourth transistor circuits, 103 is a compared voltage generating circuit, 1 is a telephone, 2, 3 is a relay contact, 4, 5, 16, 21, 22, 25 is a resistor, 6, 7 is a low-pass filter, 8 is a general circuit such as power supply, 11 is an interface circuit, 12 is a comparator, 13 is a Relay driver, 14 is a relay, 17, 27 is a Zener diode, 18, 2
9 is a constant current source, 19 is a PNP type transistor, 2
0 is an NPN type transistor.

Claims (1)

[Claims] 1. A first input signal applied to a first input terminal 10, and a voltage applied to a second input terminal 9, with a voltage polarity opposite to that of the first input signal. 1
The circuit detects, with a single comparator, a voltage change of a second input signal shifted by the exchange power supply voltage from the reference potential with respect to the input signal of a first transistor 101 whose emitter is connected to a first power source and whose emitter is connected to a constant current source 100;
a second transistor 103 whose base is connected to the emitter of the first transistor 101 and whose emitter is connected to the first power supply via a first resistor 25; , a second resistor 21 and a third resistor 22 are connected in series, one end of which is connected to the second power supply, and the other end connected to the second input terminal 9 and the second transistor 103. Connect to the collector of
and a compared voltage circuit that outputs a voltage proportionally divided by the resistance values of the second resistor 21 and the third resistor 22 to a connection point 104 between the second resistor 21 and the third resistor 22; 105, and the resistance value of the first resistor 25 is such that the voltage that appears at the connection point 104 when the first transistor 101 is conductive is equal to the voltage that appears at the connection point 104 when the first transistor 101 is not conductive. Said second
When an input signal of
A ring trip voltage detection circuit characterized in that the ring trip voltage detection circuit is selected to have a value equal to the voltage appearing in the ring trip voltage detection circuit. 2 A first input signal applied to the first input terminal 10 and a first input signal applied to the second input terminal 9 with a voltage polarity opposite to that of the first input signal.
The circuit detects, with a single comparator, a voltage change of a second input signal shifted by the exchange power supply voltage from the reference potential with respect to the input signal of is connected to the first power supply and the emitter is connected to the first power supply.
a first transistor circuit 102 including a first transistor 101 connected to a constant current source 100; a base connected to the emitter of the first transistor 101; the second transistor 1 connected to the power supply of
03, and a third transistor 1 whose base is connected to the second input terminal 9, whose collector is connected to the second power supply, and whose emitter is connected to the second constant current source 108.
09; a fourth transistor 113 whose base is connected to the emitter of the third transistor 109 and whose collector is connected to a predetermined voltage source; a second resistor 21 and a third transistor 110; Resistors 22 are connected in series, one end of which is connected to the second power supply, and the other end connected to the emitter of the fourth transistor 113 and the collector of the second transistor 103, and the second A compared voltage circuit 105 that outputs a voltage proportionally divided by the resistance values of the second resistor 21 and the third resistor 22 is provided at a connection point 104 between the resistor 21 and the third resistor 22, The resistance value of the first resistor 25 is such that the voltage that appears at the connection point 104 when the first transistor 101 is conductive is equal to the voltage that appears at the connection point 104 when the first transistor 101 is not conductive.
A ring trip voltage detection circuit characterized in that the voltage is selected to be equal to the voltage appearing at the connection point 104 when the transistor 109 of the ring trip is conductive.