JPS62269542A - Trunk line termination circuit - Google Patents

Abstract

PURPOSE:To integrate a polarity inversion detection circuit without spoiling the function of a trunk line termination circuit by inserting a photocoupler to at least one circuit of transistors (TRs) constituting a current suction circuit to detect the polarity inversion of a talking current. CONSTITUTION:When the trunk line L1 is positive at the time of dialing, a base current is fed to a TR Q1 via a resistor Rb1 and a light emitting diode of a photocoupler PC1 from the trunk line L1 and a high-level voltage signal is obtained across a resistor R3. When the polarity is inverted by the answer of an opposite party, the voltage of the trunk line L2 is positive, a base currentis fed to a TR Q2 from the trunk line L2 via a resistor Rb2 and a light emitting diode if a photocoupler PC2 and a high-level voltage signal is obtained across the resistor R4. When the talking is finished and the polarity inversion is caused again, the photocoupler PC1 is operated and a high-level voltage is obtained across the resistor R3. Thus, the polarity inversion of the trunk lines L1, L2 is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a central office line terminating circuit with a polarity reversal detection function applied to telephone necks and the like.

(Prior Art) In subscriber telephone lines, the polarity of the communication current is reversed when the other party answers a call and when the call ends. I! , machine side (station side)
Since billing starts and ends at the same timing, by detecting the polarity reversal of the call current on the subscriber telephone terminal side (terminal side), the terminal side can also calculate the call time 2.
It is possible to know call charges, etc.

Conventionally, the above-mentioned polarity reversal detection of the communication current has been performed by a circuit called a polarity reversal detection circuit.The polarity reversal detection circuit has been designed to be additionally connected in series or parallel to the central office line termination circuit. Ta.

Figure 2 (A) and Figure 3 (A) show the connection of a conventional polarity reversal detection circuit.
Figure 3 (A) shows the case where the station line termination circuit 1 and the reversal detection circuit $82 are connected in series to the station line L2.
1 and 2 respectively show the case where the station line termination circuit 1 and the polarity reversal detection port 182 are connected in parallel to the station line L2.

FIGS. 2(B) and 2(C) show specific configuration examples of the polarity reversal detection circuit 2 in FIG. 2(A), and (B) shows an example using a photocoupler; C) is an example using a relay. In the case of Fig. 2 (b), since the light emitting diodes that are the input circuits of the photocouplers PC, PC2 are connected in parallel in opposite directions, the central line
One of the light emitting diodes is driven by the direction of the current flowing into the central line termination port Ml, and an output is obtained from the phototransistor which is the output circuit of the corresponding photocoupler, and the polarity can be determined from this output.

On the other hand, in the case of FIG. 2(c), relay Ry1. The relay coils of Ry2 are connected in parallel through oppositely directed diodes D, D2, and one relay coil is excited depending on the direction of the current flowing from the station line L2 to the station line termination circuit 1, and the corresponding The contact turns on and output is obtained.

FIG. 3(B) shows a specific configuration example of the polarity reversal detection circuit 2 in FIG. 3(A), and is an example using a photocoupler. However, photocoupler PC, ,
The light emitting diodes, which are the input circuit of PC2, are connected in parallel in opposite directions to each other, and are connected through a resistor R between the central line and the central line.

One of the light emitting diodes is driven according to the polarity of the voltage across L2, and an output is obtained from the phototransistor that is the output circuit of the corresponding photocoupler.

FIG. 4 shows a circuit example of the station line termination circuit 1. After passing through the diode bridge DB, a DC current is passed through the current sink circuit 3 so as to meet the DC resistance standard.
The communication voice signal, which is AC, is connected to capacitor C,) lance T.
The information is transmitted to the terminal side via .

(Problems to be Solved by the Invention) Conventional polarity reversal detection circuits were connected in series or parallel with the station line termination circuit as described above, but they had the following drawbacks.

That is, when they are connected in series as shown in FIG. 2, there is a drawback that the direct current resistance for the central line and L2 increases. Specifically, in the case of FIG. 2(b), photocouplers pc1. Due to the forward voltage drop (approximately 2 V) of the light emitting diode of PC2, the DC resistance at the demarcation point increases by approximately 100 Ω at a communication current of 20 mA, and in the case of Fig. 2 (c), Relay RV.

Even if Ry2 is a highly sensitive reed relay (approximately 35Ω), the DC resistance increases by 70Ω. In either case, strict restrictions will be imposed on the design of the station line termination circuit side with respect to the terminal DC resistance standard (300 Ω), and if it is necessary to limit the distance between the station and the terminal. There was also.

On the other hand, if they are connected in parallel as shown in FIG. 3, there is a drawback that the quality of the call will deteriorate. That is,
In the circuit of Figure 3 (b), when the photocouplers PC, PC2 do not have a sufficient input/output transfer ratio, that is, when the sensitivity is not very high, the resistance value of the resistor R inserted in series must be lowered. polarity reversal detection circuit 2.
Since the impedance of the central line cannot be made sufficiently high compared to the impedance of the central line termination port ll51, the central line is closed.

This is because it reduces the impedance to the voice (No. 3) between L2. Therefore, it is useful for applications such as automatic notification devices (such as those with a predetermined call time and only detecting the other party's response). However, it was not suitable for detecting the end of a call.

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

(Means for solving problems) Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 1 shows an embodiment of the station line termination circuit of the present invention. To explain the configuration in the figure, the transistor Q
Series circuit of lj resistor R, and transistor Q2z resistor R2
series circuits are symmetrically connected in series in opposite directions and connected between the central lines 1, , and R2, and the transistors 1, , and R2 are connected in series in opposite directions. Diodes D, D2 are connected in parallel to the series circuit of resistor R, and the series circuit of transistor Q2j and resistor R2, respectively, in a direction opposite to the current direction. In addition, the base of the transistor Q is connected to the light emitting diode that is the input circuit of the photocoupler PC, and to the central line via the resistor Rb1, and is also connected to the connection point of the resistors R, and R2 via the capacitor C1. has been done. Similarly, the base of the transistor Q2 is connected to the station RL2 via the light emitting diode and the resistor R2, which is the input circuit of the photocoupler PC2, and is also connected to the connection point of the resistors R, , R2 via the capacitor C2. There is. In addition, the collectors of the phototransistors that are the output circuits of the photocouplers PC, PC2 are connected to the positive power supply +V, and the emitters are connected to a resistor R, respectively.

It is grounded via R4, and output is obtained from each emitter. On the other hand, a series circuit of a primary winding of a capacitor C, l and a lance T is connected between the central office wires and R2, and a secondary winding of the transformer T is connected to the terminal side.

Therefore, the transistor Qlj resistance R,,Rb,.

Capacitor C constitutes a first current sink circuit, transistor Q2p resistor R2, Rb2 . Capacitor C constitutes a second current sink circuit, and diodes D, D, bypass the current sink circuit on the side that is reverse biased depending on the polarity of the central line and R2, and also It functions to prevent excessive voltage from being applied to the circuit.

In operation, when the station line L1 is positive, the base current is supplied from the station line to the transistor Q via the resistor Rb, the light emitting diode of the photocoupler PC2, and the current sink circuit on the transistor line 1 side. operates, station ML, -1-
Transistor Q1 → resistor R, -e diode D2 - station line L
Current flows through the second path.

Also, if station %91L2 is positive, resistor R from station RL2
b2゜Base current is supplied to transistor Q2 via the light emitting diode of photocoupler PC2, the current sink circuit on the transistor side 2 operates, and the path of station line L2 → transistor Q - resistor R → diode D → station line L1 Let the current flow. Note that the base of each transistor Q, , Q2 is connected from its own collector to a resistor RbI, a capacitor CI, and a resistor Rb2 . Since the signal is fed through the smoothing means by the capacitor 02, the base current does not fluctuate with respect to the speech signal.

On the other hand, one of the light emitting diodes of the photocouplers PC, PC2 inserted into the base circuit of each transistor Q, Q2 is driven according to the polarity of the station ML, R2, and the output is output from the emitter of the phototransistor which is the output circuit. is obtained. For example, when making a call, the station, IJL, 67! If I is positive, from station ML to resistor Rb, photocoupler P
A base current is supplied to the transistor Q1 through the light emitting diode C, and the current sink circuit on the transistor Q side operates, and the photocoupler PC2 operates to obtain a high-level voltage signal across the resistor R3. reactor. Then, when the other party's response indicates that the i-type inversion is to be performed, the station line R2 side becomes positive, and the base current is supplied from the station IIIL2 to the transistor Q2 via the resistor R02 and the light emitting diode of the photocoupler PC2, and the current on the transistor Q2 side When the suction circuit operates, the photocoupler PC2 operates, and a high-level voltage signal is obtained across the resistor R4. Then, when the call ends and polarity reversal occurs again, the photocoupler PC operates and a high-level voltage signal is obtained across the resistor R3. Therefore, photocouplers PC,, PC2
It is possible to detect the polarity reversal of stations #L and R2 by monitoring the outputs of the stations #L and R2.

In addition, in the circuit of Fig. 1, the light emitting diodes which are the input circuits of the photocouplers PC, , PC2 are replaced by transistors Q, , Q.
However, if the photocouplers PC, PC2 do not have a sufficient input/output transfer ratio, the sensitivity is poor and it is difficult to increase the resistor Rb, R,2. In such a case, a light emitting diode may be inserted into the emitter circuit of the transistors Q, Q2.

In this case, the direct current resistance may have to be increased slightly, but it is possible to create a configuration that does not affect the quality of the call. In addition, if the polarity of the central office lines L1 and L2 is known when the call is over, and no instantaneous interruption occurs during a call on the central office line, one photocoupler is deleted and the remaining photocoupler is Even if only the output signal of the coupler circuit is monitored, the desired function can be performed.

(Effects of the Invention) As described above, in the present invention, in the office line terminating circuit that is connected between office lines and acts as a predetermined impedance, and also transmits the call voice signal to the terminal side, the voltage applied to the collector is A current sinking circuit in which the collector and emitter of a transistor, in which the voltage applied to its base through a smoothing means is used as input/output terminals, is connected in series in the reverse direction of 2aI and connected between the station lines, and the current sinking circuit is connected between the station lines. A diode is connected in parallel to each in a direction opposite to the current direction, a photocoupler input circuit is inserted into the base circuit or emitter circuit of at least one of the transistors, and polarity reversal of the communication current is detected from the output circuit of the photocoupler. (a) The polarity reversal detection circuit can be integrated without impairing the function of the central line termination circuit.

(b) Since the light emitting diode, which is the input circuit of the photocoupler, is inserted into the base circuit of the transistor that constitutes the current sink circuit, the DC resistance must be increased as in the conventional case of inserting a polarity reversal detection circuit in series. Never.

(c) Since the light emitting diode, which is the input circuit of the photocoupler, is connected through a smoothing circuit, there is no deterioration in call quality unlike the conventional case where a polarity reversal detection circuit is inserted in parallel.

(d) Compared to the conventional station line termination circuit shown in Figure 4, the DC voltage drop to the station line can be reduced by 1 g of diode, and the voltage drop of the transistor in the current sink circuit can be increased by that amount. The dynamic range of the station line termination circuit can be expanded.

There are other effects.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the station line termination circuit of the present invention.
! The IH1t diagram and FIGS. 2 to 4 are circuit configuration diagrams of a conventional polarity reversal detection circuit and a station line termination circuit. L, , L2 ... central line, Q, , Q2-... = ) transistor, D, , v2--yeat -F, PC, ,
PC2=-,,-7 Oto coupler, R1-R4,R,□,
Rb2...resistance, C,, C2, C,, capacitor,
T... Trans patent applicant Nippon Tsushin Kogyo Co., Ltd. and one other agent Patent attorney Michio Takayama and one other person Figure 1 Figure 4

Claims (1)

[Claims] In the office line termination circuit that is connected between office lines and acts as a predetermined impedance and also transmits the speech voice signal to the terminal side, it is a transistor that applies the voltage applied to the collector to its base via a smoothing means. Two current sinking circuits having collectors and emitters as input/output terminals are connected in series in opposite directions and connected between the office lines, and a diode is connected in parallel to each of the current sinking circuits in a direction opposite to the current direction. A central office line termination circuit characterized in that a photocoupler input circuit is inserted into at least one base circuit or emitter circuit of a transistor, and polarity reversal of a communication current is detected from the photocoupler output circuit.