JPS6130847A - Coupling circuit of network control unit - Google Patents

Abstract

PURPOSE:To constitute a coupling circuit used for a network control unit without using a coupling transformer by realizing DC separation between inputs of a subscriber line and an MODEM by two photocouplers. CONSTITUTION:A signal on a telephone line 4 is rectified by a diode bridge circuit 10 and a light emitting diode 11a of the photocoupler 11 is connected in series with a photo transistor (TR) 12a of the photocoupler 12 at output terminals 24, 26 to form a closed circuit. Further, a coil 13 and a resistor 14 are connected in parallel with a series circuit of the light emitting diode 11a and the photo-TR12a. An output of the photo-TR11b of the photocoupler 11 is fed to an inverting input (-) of an operational amplifier 15 and a transmission signal is applied to a non-inverting input (+) of the operational amplifier 15 from a data transmitter through an input terminal 5 and a capacitor 20. Further, an output 22 of the operational amplifier 15 is fed to the light emitting diode 12b of the photocoupler 12. Thus, the transmission signal at the input terminal 5 is transmitted to a telephone line 4.

Description

[Detailed description of the invention] Technical field The present invention relates to a coupling circuit for a network control device.

Prior Art In order to connect a data transmission device such as a facsimile machine to a telephone line, it is necessary to interpose a network control device between the telephone line and the data transmission device to control the line network and set up, maintain and restore the line connection. be.

The network control device is provided with a coupling circuit as shown in FIG. 2 in order to close the Luzo circuit on the telephone line and to transmit the transmission signal from the data transmission device to the telephone line. In the circuit shown in the figure, when the hook switch 1 is turned on, a Luzo circuit is formed on the telephone line 4 through the winding 2a of the coupling transformer 2, while a terminal is connected from a data transmission device such as a facsimile device through a modem. 5
A transmission signal input to is amplified by an amplifier 3 and transmitted to a telephone line 4 via a coupling transformer 2.

However, since the conventional coupling circuit uses a coupling transformer to separate the direct current between the line 4 and the data transmission equipment, the structure becomes larger and the weight increases. This also hindered miniaturization.

OBJECTS The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide a coupling circuit whose structure can be made compact.

In order to achieve the above object, the present invention rectifies the signal on the telephone line by a diode bridge circuit, and connects the output of the diode bridge circuit with a light emitting element forming a first optical coupler and a second optical coupler. The light-receiving elements forming a coupler are connected in series, while the output signal of the operational amplifier whose non-inverting input terminal receives the transmission signal output to the telephone line is applied to the light-emitting element forming the second optical coupler. By applying the output of the light receiving element forming the coupler to the inverting input terminal of the operational amplifier, a coupling transformer is not required.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a coupling circuit according to the present invention. In this Figure, elements similar to those shown in Figure 2 are designated with the same reference numerals. The signal on telephone line 4 is
In this embodiment, it is rectified by a diode bridge circuit 10, and the output terminals 24 and 26 of this diode bridge circuit 10 are connected to the series connection of the light emitting diode lla of the optical coupler 11 and the phototransistor 12a of the optical coupler 12. , a closed circuit is formed. Further, a coil 13 and a resistor 14 are connected in parallel to the series circuit of the light emitting diode lla and the phototransistor 12a.

The output of the phototransistor llb of the optical coupler 11 is applied to the inverting input terminal (←) of the operational amplifier 15, and the output is transmitted from the data transmission device through the input terminal 5 and the capacitor 20 to the non-inverting input terminal (→) of the operational amplifier 15. The output 22 of the operational amplifier 15 is added to the optical coupler 1.
20 light emitting diodes 12b.

In this way, in this embodiment, the optical couplers 11 and 12 realize DC separation between the subscriber line 4 side and the modem side input 5. Input resistances 16 and 17 of operational amplifier 15
．． If the resistance values of the optical couplers 11 and 18 are R1, R2, and R3, and the current transfer rates of the optical couplers 11 and 12 are Kl and 2, respectively, then the output current i1 of the operational amplifier 15 flows through the photodiode 12a of the optical coupler 12. Current i2 and current i3 flowing through photodiode llb of optical coupler 11
The following relationship holds true.

i 3 = i ”l・K1-11・K1・K 2
(t) Therefore, the inverting input terminal of the operational amplifier 15 (
The voltage υ2 of → is υ2=i3・R3=R3・il・K1・K2 (2
).

Here, if the operational amplifier 15 is an ideal oil amplifier, vl - υ2, so the voltage υ1 at the non-inverting input terminal (+) of the operational amplifier 15 is expressed as follows.

υ1=R3・K1・K2・zl=R3・K1・j2(3
) Here, since R3 and Kl are constants, the optical coupler 12
The output voltage It i 2 is from the data transmission device to the input terminal 5.
The current 'i2 at the output 24.26 of the diode pre-so circuit 10 is proportional to the transmission signal input to the
flows in response to this transmission signal. In this way, the transmission signal at the input terminal 5 is transmitted to the telephone line 4.

Further, when the voltage of the DC power supply 19 is E, the DC component of the voltage v1 is E-R2/(R1+R2'), and the operating point of the optical coupler 12 is determined by this value.

It is possible to transmit the transmission signal to the telephone line 4 without adding any signal to the telephone line 4 and without distortion.

Next, considering the gain of this coupling circuit when viewed from the input terminal 5, if this gain is 1, that is, OdB, the transmission signal can be transmitted to the telephone line 4 without attenuation.

Now, the DC voltage on the telephone line 4 side is sufficiently large, and the current i2
, the optical coupler 12 can be considered as a current source.

Therefore, when the telephone line 4 is terminated with the same impedance as the resistance value R4 of the resistor 14, the voltage υ0 generated across the resistor 14 is expressed as follows using equation (3).

Therefore, the gain of this circuit is 3 as shown in the following equation.

Here, if K1 is 0.5 and R3=R4, the gain is 3
becomes 1. Therefore, the transmission signal can be sent to the telephone line without attenuation.

Effects As explained above, according to the present invention, the coupling circuit used in the network control device can be constructed without using a coupling transformer, so the device can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a coupling circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example of a coupling circuit. Explanation of symbols of main parts 10・Diode Britno circuit 11, 12・・Optical coupler 11aJ1b・・Light emitting diode 11b, 12a・・Phototransistor 13・・・
Coils 14, 16, 17, 18... Resistor 15... Operational amplifier 19... DC power supply

Claims (1)

[Scope of Claims] A coupling circuit for a network control device interposed between a telephone line and a terminal device to control a telephone line network, the coupling circuit comprising: a rectifier circuit for rectifying a signal on the telephone line; a first optical coupling means including a first light emitting element and a first light receiving element optically coupled to the first light emitting element; a second light emitting element and a second light receiving element optically coupled to the second light emitting element; a second optical coupling means including an element; and an operational amplifier means for receiving a transmission signal from the terminal device at a non-inverting input, and an output of the rectifier circuit includes a first light emitting element and a second light receiving element. a series connection of said operational amplifier means is connected, the output of said operational amplifier means is connected to a second light emitting element, and the output of said first light receiving element is connected to an inverting input of said operational amplifier means. Device coupling circuit.