JPH03253162A - Loop closing device for telephone line connection terminal equipment - 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] [Object of the Invention] (Industrial Application Field) The present invention relates to a telephone line connection used to close a loop of a telephone line, for example, in a transmission terminal connected to a telephone line. The present invention relates to a terminal loop closing device.

(Prior Art) A conventional loop closing device for a telephone line connection terminal, for example, as shown in FIG. A transformer 51, a resistor 53, and a switch 55 are connected in series between T1 terminals. The transformer 51 has a high impedance of, for example, about 600Ω in AC and low impedance in DC, the resistor 53 determines the DC impedance between the telephone lines, and the switch 55 controls the loop between the telephone lines. It is intended to conclude the

(Problem to be Solved by the Invention) Since the conventional loop closing device for a telephone line connection terminal has a transformer 51, it cannot be made into an IC, and there is a problem that it cannot be made lower in price and smaller in size. .

The present invention has been made in view of the above, and its purpose is to provide a loop closing device for a telephone line connection terminal, which can eliminate a transformer and use an IC, and which can achieve lower costs and smaller size. It's about doing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the loop closing device for a telephone line connection terminal of the present invention includes a resistor connected between telephone lines to close the telephone lines. a variable means, a resistance means connected between the telephone lines in series with the resistance variable means to detect the loop current of the telephone line as a voltage signal, and a voltage signal detected by the resistance means is supplied; operational amplifier means for controlling the variable resistance means according to the voltage; circuit means for processing a voltage on the telephone line to determine a loop current of the telephone line and supplying the voltage to a non-inverting input of the operational amplifier means; and capacitance means connected to the non-inverting input of the operational amplification means to increase the AC impedance of the operational amplification means.

(Function) In the loop closing device for a telephone line connection terminal of the present invention, a variable resistance means is connected between the telephone lines to close the telephone line, and a loop current is generated by the resistance means connected in series to the variable resistance means. detecting a voltage signal corresponding to and supplying it to an operational amplification means, controlling the resistance variable means according to the voltage signal,
Capacitive means is connected to the non-inverting input of the operational amplifier means to increase the alternating current impedance of the telephone line.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram of a loop closing device for a telephone line connection terminal according to an embodiment of the present invention. The loop closing device shown in the figure is used to close a loop of telephone lines in, for example, a transmission terminal connected between telephone lines. It has a variable resistance element 1 consisting of a transistor connected in series between T'l terminals and a resistor 3, and the output of an operational amplifier 5 is connected to the base of the transistor constituting the variable resistance element 1. 1, that is, the impedance between the telephone lines is controlled by the output of the operational amplifier 5.

Further, the connection point between the variable resistance element 1 and the resistor 3 is connected to the inverting input terminal of the operational amplifier 5, whereby a voltage signal corresponding to the loop current of the telephone line detected by the resistor 3 is supplied to the operational amplifier 5. It looks like this. Furthermore, a resistor 7 and a resistor are connected in series between the T2 and T1 terminals of the telephone line, and the connection point of both resistors is connected to the non-inverting input of the operational amplifier 5, thereby adjusting the voltage between the telephone lines to an appropriate value. The voltage is divided into two and supplied to the operational amplifier 5.

Further, a capacitor 11 is connected in parallel to both ends of the resistor 9, so that the capacitor 11 and the resistor 7 constitute a smoothing circuit, and a signal from which alternating current components in the telephone line have been removed is supplied to the operational amplifier 5. It has become.

Although not shown in FIG. 1, since the polarity of telephone lines is reversed depending on the state, it is necessary to take measures such as inserting a rectifier circuit so as not to be affected by the polarity reversal. Such a rectifier circuit is omitted because it does not affect the main idea.

In the loop closing device for a telephone line connection terminal configured as described above, the voltage at the T2 terminal is set to v as shown in FIG.
1Do+V1AC1 The voltage at the connection point between resistor 7 and resistor 9 is v2Dc, and the current flowing through resistor 3 is 110c + I I
Ac, and the resistance values of resistor 3, resistor 7, and resistor 9 are R1, R2, and R3, respectively. In addition, the subscript DC
, AC separates the DC component and AC component, but regarding the voltage V2 at the connection point between resistor 7 and resistor 9, the AC component is smoothed by resistor 7 and capacitor 11, so the voltage V2AC of the AC component is do not have.

The voltage (2DC) at the non-inverting input of the operational amplifier 5 is expressed as follows; however, since the alternating current component is smoothed, the voltage becomes as shown in the following equation.

Also, since the voltage at the inverting input of the operational amplifier 5 is equal to the voltage at the non-inverting input, (I IDC + I IAc ) R1=
V 2DCR3 R3+T2VIDC (2) From this, it can be seen that I+Ac=0.

That is, T2. There is high impedance between the TI terminals in terms of alternating current.

Also, the direct current is becomes.

In the above circuit configuration, if each circuit element is determined so that 20 mA≦I IDc≦120 mA, a loop closing device for a terminal device for telephone line connection can be constructed.

The transmitter/receiver circuit of a normal terminal device has an input/output impedance of -
Since the loop closing device has a value of 600Ω, unless the loop closing device has a high AC impedance, the human output impedance will change. However, by using the loop closing device of the present invention, the terminal This eliminates the effect on the input/output impedance of the transmitter/receiver circuit of the device.

Please note that the telephone line is 72. To close the loop between the TI terminals, (1) turn off the power to the operational amplifier 5 with a switch or the like, or (2) insert a switch or the like between the operational amplifier 5 and the variable resistance element 1 to close the loop. Methods such as (3) short-circuiting both ends of the resistor 9 using a switch or the like may be considered, but method (1) is advantageous in terms of current consumption.

The relationship between voltage VIDC11 and current 11DC in the loop closure device of FIG. 1 is directly proportional as shown in FIG.

FIG. 3 is a circuit diagram of a loop closing device for a telephone line connection terminal according to another embodiment of the present invention. The loop closing device shown in the figure has one end of a resistor 12 connected to the connection point between the resistor 7 and the resistor 9 in FIG. The other points are different, and the other configuration and operation are the same as the loop closing device of FIG.

With this configuration, the relationship between the voltage V+ocll and the current 11DC in the loop closing device can be set as shown in FIG. 4.

〔Effect of the invention〕

As explained above, according to the present invention, a variable resistance means is connected between telephone lines to close the telephone line, and a voltage signal corresponding to a loop current is generated by the resistance means connected in series to the variable resistance means. is detected and supplied to the operational amplification means, the resistance variable means is controlled in accordance with the voltage signal, and the capacitance means is connected to the non-inverting input of the operational amplification means to increase the alternating current impedance of the telephone line. Therefore, a high-impedance loop closure device can be constructed without using a transformer, and a reduction in cost and size can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a loop closing device for a telephone line connection terminal according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between voltage v1Dc and current IIDC of the loop closing device of FIG. 1. FIG. 3 is a circuit diagram of another embodiment of the present invention, and FIG. 4 is a voltage VIDC and a current I IDc of the loop closing device of FIG. 3.
FIG. 5 is a circuit diagram of a conventional loop closing device. 1. - Variable resistance element, 3.7.9... Resistor, 5. - Operational amplifier, 11. - Capacitor.

Claims (1)

[Claims] a variable resistance means connected between the telephone lines to close the telephone line; a resistance means connected between the telephone lines in series with the variable resistance means to detect the loop current of the telephone line as a voltage signal; operational amplification means that is supplied with a voltage signal detected by the resistance means and controls the resistance variable means in accordance with the voltage signal; For a telephone line connection terminal, comprising circuit means for supplying a non-inverting input of an amplifying means, and capacitive means connected to a non-inverting input of the operational amplifying means for increasing the alternating current impedance of the telephone line. Loop closure device.