JPH0722297B2 - Office line termination circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention relates to a station line terminating circuit having a polarity reversal detection function applied to a key telephone device or the like.

(Prior art) In the subscriber telephone line, the polarity of the call current is reversed when the call is answered by the other party and when the call ends, and the billing starts on the exchange side (station side). ， Because the end time is also done at that timing,
By detecting the polarity reversal of the call current on the subscriber telephone terminal side (terminal side), the terminal side can know the call time, call charge, and the like.

Conventionally, the polarity reversal detection of the above-mentioned call current is performed by a circuit called a polarity reversal detection circuit, and the polarity reversal detection circuit has been additionally connected in series or in parallel to the office line termination circuit. .

FIGS. 2 (a) and 3 (a) show how the polarity reversal detection circuit is connected in the related art. FIG. 2 (a) shows the station lines L ₁ and L _{2 with} respect to the station line. When the terminating circuit 1 and the polarity reversal detecting circuit 2 are connected in series, the station line terminating circuit 1 and the polarity reversing detecting circuit 2 for the station lines L ₁ and L ₂ are shown in FIG.
It shows the case where and are connected in parallel.

2 (b) and 2 (c) show a concrete configuration example of the polarity inversion detection circuit 2 in FIG. 2 (a),
(B) is an example using a photo coupler, and (C) is an example using a relay. Then, in the case of FIG. 2B, since the light emitting diodes which are the input circuits of the photocouplers PC ₁ and PC ₂ are connected in parallel in the opposite directions, the station lines L ₁ and L ₂ are connected to the station termination circuit. One of the light emitting diodes is driven according to the direction of the current flowing into 1, and an output is obtained from the phototransistor which is the output circuit of the corresponding photocoupler, and the polarity can be determined by this output. On the other hand, in the case of Fig. 2 (c), the relay coils of the relays Ry ₁ and Ry ₂ are diodes with opposite directions.
They are connected in parallel via D ₁ and D _2, and one relay coil is excited by the direction of the current flowing from the station lines L ₁ and L ₂ to the station line termination circuit 1, and the corresponding contact turns on and the output is output. can get.

FIG. 3B shows a specific configuration example of the polarity reversal detection circuit 2 in FIG. 3A, which is an example using a photocoupler. Thus, parallel connected light-emitting diodes, which is the input circuit of the photocoupler PC _1, PC ₂ in opposite directions, office line L ₁ through the resistor R, Yes connected between L _2, the office line L _1, One of the light emitting diodes is driven according to the polarity of the voltage across L _2, and the output is obtained from the phototransistor which is the output circuit of the corresponding photocoupler.

Further, FIG. 4 shows a circuit example of the station line terminating circuit 1. After passing through the diode bridge DB, a DC current is made to flow in the current sink circuit 3 so as to meet the DC resistance standard, and is an AC component. The call voice signal is transmitted to the terminal side through the capacitor C and the transformer T.

(Problems to be Solved by the Invention) Although the conventional polarity reversal detection circuit is connected in series or in parallel with the station line termination circuit as described above, it has the following drawbacks.

In other words, when connected in series as shown in FIG.
It has a disadvantage of causing an increase in DC resistance to L _1, L _2. Specifically, in the case of Fig. 2 (b), the forward voltage drop (about 2V) of the light emitting diodes of the photocouplers PC ₁ and PC ₂ acts in either direction of the call current, so the direct current at the demarcation point The resistance increases by about 100 Ω at a call current of 20 mA, and in the case of Fig. 2 (C), the DC resistance is about 30 Ω even if the relays Ry ₁ and Ry ₂ are highly sensitive reed relays (about 35 Ω).
This is an increase of 70Ω. In either case, the design of the terminal line termination circuit side is subject to severe conditions for the DC resistance standard (300Ω or less) of the terminal, and in some cases, the distance limitation between the station and the terminal is necessary. .

On the other hand, when connected in parallel as shown in FIG. 3, there is a drawback that the call quality is deteriorated. That is, in the circuit of FIG. 3B, when the photocouplers PC ₁ and PC ₂ do not have a sufficient input / output transfer ratio, that is, when the sensitivity is not so high, the resistance value of the resistor R inserted in series is changed. Inevitably, the impedance of the polarity reversal detection circuit 2 cannot be made sufficiently higher than the impedance of the station line termination circuit 1, so the impedance for the voice signal between the station lines L ₁ and L ₂ should be lowered. Because it will be. Therefore, it is useful for the purpose of detecting only the other party's response such as an automatic notification device with a predetermined call time, but it is not suitable for detecting the end of a call.

The present invention has been proposed in view of the above points, and an object of the present invention is to provide a station line termination circuit with a polarity reversal detection function, and to provide a circuit that does not cause an increase in DC resistance and deterioration in call quality. .

(Means for Solving Problems) Hereinafter, the present invention will be described in detail with reference to the drawings illustrating an embodiment.

FIG. 1 shows an embodiment of a station line terminating circuit of the present invention. Explaining the configuration in the figure, the transistor
The series circuit of Q ₁ and resistance R _{1 and} the series circuit of transistor Q ₂ and resistance R ₂ are symmetrically connected in series in opposite directions, and
Is connected between L _1, L _2, transistor Q _1, the series circuit and the transistor Q ₂ of the resistor R _1, each diode D _1, D ₂ to a series circuit of resistors R ₂ are connected in parallel to the current direction opposite to the direction ing. The base of the transistor Q ₁ is the photocoupler PC _1
Is connected to the office line L ₁ via the light emitting diode which is the input circuit of the resistor and the resistor R _b1, and is also connected to the resistor via the capacitor C _1.
It is connected to the connection point of R ₁ and R ₂ . Similarly transistor
The base of Q ₂ is connected to the office line L ₂ via the light emitting diode which is the input circuit of the photocoupler PC ₂ and the resistor R _b2, and is also connected to the connection point of the resistors R ₁ and R ₂ via the capacitor C _2. Has been done. Further, in the phototransistor which is the output circuit of the photocouplers PC ₁ and PC ₂ , the collector is connected to the positive power source + V, and the emitter is grounded through the resistors R ₃ and R ₄ , respectively.
The output is obtained from each emitter. On the other hand, a series circuit of a capacitor C and a primary winding of a transformer T is connected between the office lines L ₁ and L _2, and a secondary winding of the transformer T is connected to the terminal side.

Then, transistor Q ₁ , resistance R ₁ , R _b1 , capacitor C
₁ constitutes the first current sink circuit, the transistor Q ₂ , the resistors R ₂ , R _b2 and the capacitor C ₂ constitute the second current sink circuit, and the diodes D ₁ and D ₂ are the local line L ₁ , It bypasses the reverse-biased current sink circuit depending on the polarity of L ₂ , and also functions to prevent an excessive voltage from being applied to the current sink circuit.

In the operation, when the office line L ₁ is positive from the office line L ₁ resistor R
Base current is supplied to the transistor Q ₁ through the light emitting diode of _b1 and photocoupler PC ₁ , the current sink circuit on the transistor Q ₁ side operates, and the station line L ₁ → transistor Q ₁ → resistance
Current flows in the route of R ₁ → diode D ₂ → office line L ₂ . When the station line L ₂ is positive, the base current is supplied from the station line L ₂ to the transistor Q ₂ via the resistor R _b2 and the light emitting diode of the photocoupler PC ₂ , and the current sink circuit on the transistor Q ₂ side operates. Then, a current flows through the route of the station line L ₂ → transistor Q ₂ → resistance R ₂ → diode D ₁ → station line L ₁ . It should be noted that the base of each of the transistors Q ₁ and Q _{2 has} a resistor R _b1 ,
Since the signal is given through the smoothing means by the capacitor C _{1, the} resistor R _b2 and the capacitor C ₂ , the base current does not change with respect to the voice signal.

On the other hand, _one of the light emitting diodes of the photocouplers PC ₁ and PC ₂ inserted in the base circuit of each transistor Q ₁ and Q ₂ is connected to the local line.
It is driven according to the polarities of L ₁ and L ₂ , and the output is obtained from the emitter of the phototransistor, which is the output circuit. For example,
If the station line L ₁ side is positive when making a call, the resistance from the station line L ₁
The base current is supplied to the transistor Q ₁ via the light emitting diode of R _b1 and the photocoupler PC ₁ , the current sink circuit on the transistor Q ₁ side operates, and the photocoupler PC ₁ operates to connect the resistor R ₃ to both ends. A high level voltage signal is obtained. When the polarity is reversed by the response from the other party,
The L ₂ side becomes positive, and the resistance R _b2 from the station line L ₂ to the photocoupler PC ₂
The base current is supplied to the transistor Q ₂ via the light emitting diode of, the current sink circuit on the transistor Q ₂ side operates, and the photocoupler PC ₂ operates to obtain a high-level voltage signal across the resistor R _4. To be Then, when the call ends and polarity inversion occurs again, the photocoupler PC ₁ operates and a high-level voltage signal is obtained across the resistor R ₃ . Therefore, by monitoring the outputs of the photocouplers PC ₁ and PC ₂ , it is possible to detect the polarity reversal of the station lines L ₁ and L ₂ .

In the circuit shown in FIG. ₁ , the light emitting diodes, which are the input circuits of the photocouplers PC ₁ and PC ₂ , are inserted in the base circuits of the transistors Q ₁ and Q ₂ , but the photocouplers PC ₁ and P 2 are connected.
If C ₂ does not have a sufficient input / output transfer ratio, that is, if the sensitivity is poor and it is difficult to increase the resistances R _b1 and R _b2 , insert a light emitting diode into the emitter circuit of transistors Q ₁ and Q _2. You may do it. In this case, the DC resistance will be slightly increased, but it is possible to adopt a configuration that does not affect the call quality. Also, if the polarities of the office lines L ₁ and L _{2 in} the disconnected state are known, and if no instantaneous interruption occurs during a call on the office line, one photo coupler is deleted and the remaining one photo The desired function can be achieved by monitoring only the output signal of the coupler circuit.

(Effects of the Invention) As described above, according to the present invention, the voltage is applied to the collector in the station line terminating circuit which is connected between the station lines and acts as a predetermined impedance and which transmits the call voice signal to the terminal side. The current sink circuit is configured such that two current sink circuits, each of which has the collector and the emitter of the transistor whose input and output terminals are applied to the base through the smoothing means as input and output terminals, are connected in series in the reverse direction and are connected between the station lines. A diode is connected in parallel to each of the transistors in the direction opposite to the current direction, the input circuit of the photocoupler is inserted in at least one of the base circuit and the emitter circuit of the transistor, and the polarity reversal of the call current is detected from the output circuit of the photocoupler. Therefore, (a) the polarity inversion detection circuit can be integrated without impairing the function of the office line termination circuit.

(B) Since the light emitting diode which is the input circuit of the photocoupler is inserted in the base circuit of the transistor which forms the current sink circuit, the DC resistance is increased as in the case where the polarity inversion detection circuit is inserted in the conventional series. Never.

(C) Since the light emitting diode, which is the input circuit of the photocoupler, is connected through the smoothing circuit, there is no deterioration in speech quality as in the case where the polarity inversion detection circuit is inserted in parallel as in the related art.

(D) Compared with the conventional station line termination circuit shown in FIG. 4, the DC voltage drop for the station line can be reduced by one diode, and the voltage drop of the transistor of the current sink circuit must be increased by that amount. Thus, the dynamic range of the office line termination circuit can be expanded.

And so on.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a station line termination circuit of the present invention, and FIGS. 2 to 4 are circuit configuration diagrams of a conventional polarity inversion detection circuit and a station line termination circuit. L ₁ , L ₂ …… Station line, Q ₁ , Q ₂ …… Transistor, D ₁ , D ₂ ……
Diode, PC ₁ , PC ₂ ... Photo coupler, R _{1 to} R ₄ ,
R _b1 , R _b2 ...... Resistance, C ₁ , C ₂ ,, ... Capacitor, T ...... Transformer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Teruyuki Kubo Inventor Teruyuki, Yokosuka City, Kanagawa Prefecture 2356, NTT Corporation (72) Inventor Masatsugu Muranaka 1-2356 Takeshi, Yokosuka City, Kanagawa Prefecture Nippon Telegraph and Telephone Corporation, Complex Communication Laboratory

Claims (1)

[Claims] 1. In a station line terminating circuit which is connected between station lines and acts as a predetermined impedance and which transmits a call voice signal to a terminal side, a voltage applied to a collector is applied to a base of its own through a smoothing means. The two current sink circuits each having the collector and emitter of the transistor applied to the input and output terminals as input / output terminals are reversely connected in series and connected between the station lines, and a diode is provided in each of the current sink circuits in the direction opposite to the current direction. A local line terminating circuit characterized by being connected in parallel, inserting an input circuit of a photocoupler into at least one of a base circuit and an emitter circuit of the transistor, and detecting a polarity reversal of a speech current from an output circuit of the photocoupler.