JPS63234658A - Line monitoring circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] A line monitoring circuit in a digital transmission system monitors the potential state of a two-wire telephone line connected to digital transmission equipment. In order to solve the problem of erroneous detection due to potential difference between the system equipment and the corresponding equipment, the first and second wires of the two-wire telephone line are pulled up using two reference voltages. By configuring the circuit to detect the potential conditions of the two input voltages input to the operational amplifier in this state, it becomes possible to clearly distinguish between a normal mode and an abnormal mode of the potential state of the line.

[Industrial application field]

The present invention relates to a line monitoring circuit for a two-wire telephone line connected to a digital transmission system.

For example, in switching equipment (e.g., analog switching equipment) and transmission equipment (e.g., digital transmission systems) that are connected via a two-wire telephone line, the potential state of the two-wire telephone line changes depending on the connection state. Depending on the state, it is possible to distinguish between a normal connection state and an abnormal connection state.

That is, the potential states of the first line (hereinafter referred to as the A line) and the second line (hereinafter referred to as the B line) of the two-wire telephone line are predefined depending on the communication system.

This potential state includes "negative polarity", "positive polarity" and "
It is displayed as a combination of ``earth air'', but ``earth air'' is generally grounded with the earth where each device is installed to form ``earth air''.

However, such "earth energy" does not necessarily show the same potential no matter where it is, and if a slight potential difference between "earth energy" affects the connection status, it is necessary to take countermeasures. be.

[Conventional technology]

FIG. 4 is a diagram illustrating a conventional example, and FIG. 5 is a diagram illustrating a connection state of devices.

Figure 5 shows the connection state of the equipment that is the premise of this example, and shows the connection state of the equipment, which is the premise of this example.
is a digital terminal equipment, 2 is an analog exchange, and symbol +a is a two-wire telephone line (Line A) connecting digital terminal equipment 1 and analog exchange 2.

(consisting of B line) are shown respectively.

Figure 4 shows a two-wire telephone line (A
This circuit shows a line monitoring circuit 11 that monitors the potential state of the line (consisting of the OP-AM line and the B line), and includes one operational amplifier (hereinafter referred to as OP-AM line).
P) 11a and three Zener diodes D21
~Dz3 and 6 resistors R, I? I~l? It consists of 5.

Note that the symbol V is a reference voltage for determining the potential state of the B line side terminal, and V has a potential of <0, and V((.

(2): E is the voltage applied to the OP-AMP 11a. Also, the three Zener diodes DZ1 to Dz3 are OP-
This is a limiter for protecting the AMP11a.

In this line monitoring circuit 11, the A line side terminal is "-48V"
(However, via a predetermined line resistance), when the B line side terminal is connected to "earth" (However, via a predetermined line resistance), the two input voltages of OP-AMP11a are V,
<V, and for other combinations V,, >Vp
Monitor that.

That is, in the case of Fig. 4 (11), the A line side terminal is "E = -4
8v'', and the B line side terminal is connected to the earth, a normal state (normal mode) in which V<Vp is detected, and the OP-AMP 11a operates in a normal state.

In the case of FIG. 4 (2), the ground potential difference is ΔV, and when ΔV<O, ■7 is A! ? Is the potential of the I side terminal equal to the resistance Bl? 2. I? 3, whereas Vp is the potential of the B line side terminal appearing as it is due to the potential relationship with the reference voltage 3, so V, > V, and an abnormal state (abnormal mode) is detected. be done.

[Problem that the invention seeks to solve]

However, the A line side terminal of the line monitoring circuit 11 described above.

For example, if the terminals on the B line side are both in the "earth" state, and the "earth" state on the line monitoring circuit 11 side is higher than that on the opposing equipment side (
If the potential of the “ground air” on the analog exchange 2 side is high, O
There is a problem in that the two input voltages of the P-AMP 11a become V and <Vp, making it impossible to detect an abnormal state of the line (a).

[Means for solving problems]

FIG. 1 shows a detailed illustration of the invention.

The principle diagram of the present invention shown in FIG. 1 shows a line monitoring circuit 110, whose configuration is as follows: A first resistor (R1) between the first 6% (line A) and the second line (line B). and the potential supplied to the first vA (A line) is set to the first reference voltage (
The second voltage is divided based on V1). Third resistance (1?2
．． R3), a fifth resistance (R5) between the second line (B line) and the second reference voltage (V2), and a second resistance (R2) from the first line (A line). ) via
The OP-AMP 11a is connected to the second line (B line) via a fourth resistor (R4).

[Effect]

In order to divide the voltage of the first line (line A), by setting the first reference voltage (V+) to ■1 > 0 and pulling up the first line (line A), For example, if a potential difference occurs between both "earth air", the first ￥IIA (A line) -
Even if it becomes "earth air" and the second line (line B) - "earth air", it is possible to clearly distinguish it from the normal mode (normal state).

〔Example〕

The gist of the present invention will be specifically explained below with reference to embodiments shown in FIGS. 1 to 3.

FIG. 2 is a diagram for explaining the state in the normal mode in the embodiment of the present invention, and FIG. 3 is a diagram for explaining the state in the abnormal mode in the embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures.

In the line monitoring circuit 110 of this embodiment, in the case of FIG. 3, the line resistance of the line (A line/B line in AL is R6A).

The ground potential difference is 5V, and both A line and B line terminals are “ground air”.
This is the case where the input impedance of OP-AMP11a is very large, and in that case, OP-AMP11a has a very large input impedance.
The voltage input to P11a is V, = 5- [(5-5)
R3/ (ROA+R2+R3)]-5V... (Formula 1) %Formula%)] <5V... (Formula 2) The above (Formula 1) and (Formula 2) are obtained, and V11>Vp to detect an abnormal state. Become.

Also, Fig. 2 shows the normal mode, and ROA<<R1゜Ro
So that n << R5! 11. If you choose R5, V
r#0, V, = 5- [(48+ 5) R3/(
R2+R3) ].

Therefore, if R2 and R3 are selected so that R3/(R2+R3)>5153, then v11<v, and the normal mode shown in FIG. 2 can be distinguished from the abnormal mode shown in FIG. 3.

In this embodiment, a Zener voltage of 12 V or less may be used for the Zener diodes Dz1 to DZ3 for protecting the OP-AMP 11a.

As mentioned above, for example, normal mode is detected (i.e., V, l
<V, is detected), the output of the OP-AMP 11a is the power supply vE! It becomes conductive with the (--12V) side, and its output side becomes "low (L)" and indicates a normal state.

Moreover, when an abnormal mode is detected (that is, Vfi>V is detected), the output of the OP-AMP 11a becomes the power supply Vcc (=+
12V) side, and its output side becomes “high (
H)” to indicate an abnormal condition.

〔Effect of the invention〕

According to the present invention as described above, even if a potential difference occurs between the "earths" of both devices connected by a two-wire telephone line, it is possible to clearly distinguish between an abnormal state and a normal state of the line. I can do it.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the details of the present invention. FIG. 2 is a diagram explaining the state in the normal mode in the embodiment of the present invention. FIG. 3 is a diagram explaining the state in the abnormal mode in the embodiment of the present invention. FIG. 4 is a diagram for explaining a conventional example, and FIG. 5 is a diagram for explaining the connection state of devices. In the figure, 1 is a digital terminal equipment, 2 is an analog exchange, and 11.
110 is a line monitoring circuit, and 11a is an OP-AMP.

Claims (1)

[Scope of Claims] A line monitoring circuit (1
10), a first resistance (R1) between the first line (A line) and a second line (B line), and a potential supplied to the first line (A line). The second and third resistors (R
2, R3), a fifth resistance (R5) between the second line (B line) and the second reference voltage (V_2), and a fifth resistance (R5) between the second line (B line) and the second reference voltage (V_2); A fourth resistor (R4) is connected from the second line (line B) through the second resistor (R2).
) and an operational amplifier (11a) connected through a normal mode when the first line (A line) and the second line (B line) are in a predetermined potential state, and an abnormal mode other than that. The two input voltages (
V_n, V_p), and the two input voltages (V_n, V_p) are connected to the first line (A line).
one through the second resistor (R2) that divides the potential of the voltage based on the first reference voltage (V_1) supplied through the third resistor (R3); Line (B
The fourth resistor (R4) divides the potential of the line) based on the second reference voltage (V_2) supplied through the fifth resistor (R5). line monitoring circuit.