JPH06244893A - Communication terminal equipment - Google Patents

Abstract

PURPOSE:To prevent any adverse influence caused by inserting the new communication terminal equipment during communication with simple configuration while unnecessitating any initial load by detecting a received signal, applying it to a switch circuit in the shape of a smoothed and fixed voltage, connecting a power reception circuit and the midpoint of a reception side transformer and applying a feeding current. CONSTITUTION:A signal detection circuit 11 detects the received signal in the received signal line of a terminal equipment 30, turns the received signal to the signal of a positive or negative polarity and outputs it as a smoothed DC voltage signal. Only when the DC signal is outputted from the signal detection circuit 11, a switch circuit 12 connects a power reception circuit 8 and the midpoint of a reception side transformer 9. Namely, when the DC voltage signal at a fixed value is outputted from the signal detection circuit 11, the switch operating state of the switch circuit 12 receiving this signal is changed over from OFF to ON, and the power reception circuit 8 is operated. Therefore, even when the other terminal equipment is inserted during communication, it can be connected without generating data error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication terminal device, and more particularly to a communication terminal device having a power receiving circuit fed from a home device.

When the in-home device and the communication terminal device are connected to the bus by a connector, in order to simplify the structure of the communication terminal device, the communication terminal device itself is not provided with a power supply device and the power feeding circuit of the in-home device is provided. DC power must be supplied from the

[0003]

2. Description of the Related Art FIG. 4 shows a conventional general communication terminal device 30-1 having a power receiving circuit fed from a home device.
30-3 is shown connected to one home device 20 by a home cable CB having connectors CT20, CT30-1 to CT30-3, respectively, and the configuration of the terminal device A is the terminal device A. The same applies to B and C.

The in-home device 20 is provided with a transmission circuit 1 and a reception circuit 2, to which transformers 4 and 5 are connected, and a feeding circuit 3 is connected to the midpoint of the transformers 4 and 5.

Terminal device 30-1 corresponding to in-home device 20
30 to 3 also include a receiving circuit 6 and a transmitting circuit 7, respectively, to which transformers 9 and 10 are connected, and a feeding circuit 8 is connected to the midpoint of the transformers 9 and 10.

The transmission signal from the transmission circuit 1 of the home device 20 passes through the transformer 4 → connector CT20 → home cable CB → connectors CT30-1 to CT30-3 → transformer 9 and the terminal devices 30-1 to 30-. 3 is received by the receiving circuit 6.

On the contrary, from the transmission circuit 7 of each of the terminal devices 30-1 to 30-3, the transformer 10 to the connectors CT30-1 to CT30-1.
The signal is received by the receiving circuit 2 of the home device 2 via T30-3 → home cable CB → connector CT20 → transformer 5.

In this way, in order to carry out the 4-wire full-duplex communication, the communication signals are balanced-transmitted by the transformers 4, 5, and 910.

On the other hand, since power is supplied to each of the terminal devices 30-1 to 30-3, the DC power supply current from the power supply circuit 3 of the in-home device 20 is superimposed from the midpoint of the transformers 4 and 5, and the same route as the communication signal is supplied. Via the receiving side transformer 9,1
The power is supplied to the power receiving circuit 8 from the midpoint of 0.

Here, the above-described connection form is a form in which a plurality of terminal devices can communicate at the same time. For example, if only the terminal device A is connected, the terminal devices B and C are communicating during this communication. May be added or connected by moving.

A problem in such a case is that when the terminal device A inserts the other communication terminal devices B and C during communication, since the connection form is a connector, the inserted terminal devices B and C are inserted.
There is a case where the signal lines of 1 are not connected at the same time, and in such a case, a transient current at the time of insertion flows between the signal lines, which adversely affects the signal during communication.

This phenomenon will be described with reference to FIG. 5. FIG. 5 shows the case where the terminal device 30-1 is normally connected to the home device 20, and the terminal device 30-1 is connected to the home device 20 from the home device 20. The power supply current flows in the directions indicated by the arrows.

The power supply current at this time is set to the respective transformers 4, 5,
Since current is shunted from the midpoints of 9 and 10, no signal is generated on the side of the transmitting circuits 1 and 7 and the receiving circuits 2 and 9 that are respectively connected.

The operation of, for example, the transformer 4 at this time is shown in FIG.
, The current I shunted from the midpoint of the transformer 4
Since the current values of 1 and I2 are equal and the directions of the currents are opposite, they cancel each other and no signal is generated on the transmission / reception circuit side.

However, as shown in FIG. 7, when the connector is inserted, the four cables A to D are not always connected at the same time. Therefore, for example, as shown in FIG. 3, only the cables B and C are connected. , The cables A and D may be unconnected.

At this time, the power supply current becomes only current as shown in the figure, and flows only from the midpoint of the transformers 4 and 5 to the winding on one side.

The operation of, for example, the transformer 4 at this time is shown in FIG.
FIG. 7A shows a case where only the current I1 flows, and FIG. 7B shows a case where only the current I2 flows.

In any case, the current I3 flows through the circuit side of the transformer 4 and a signal component is generated. When this signal component is generated, it affects the communication signal from the transmission circuit 1 and causes a data error.

Therefore, in Japanese Patent Laid-Open No. 2-246596, a switch circuit 12 is provided in series with the receiving circuit 8 on the side of the terminal device 30-1 as shown in FIG. The operation is performed according to the detection results of the current detection units 13A and 13B inserted in A and B.

That is, in the state where the switch circuit 12 is off now, the high-resistance initial load 14 is connected to the midpoint of the transmission / reception transformers 9 and 10 on the side of the terminal device 30-1. Then, when the in-home device 20 and the terminal device 30-1 are connected by the connectors CT20 and CT30-1 in this state, a current flows through the cables A to D by the initial load 14 and the detection units 13A and 13B are turned on.

As a result, the switch circuit 12 is also turned on, and a power supply current is supplied to the power receiving circuit 8.

Therefore, the connectors CT20 and CT30-
1 is surely connected, the current detector 13A, 13B
By detecting by (1), the power supply current from the in-home device 20 is applied to the power receiving circuit 8, and the problems as shown in FIGS. 7 and 8 can be avoided.

[0023]

However, in the case of the conventional example according to Japanese Patent Laid-Open No. 2-246596, there are the following problems. (1) Since the current detector is inserted in the main signal line, it adversely affects the communication signal flowing through this signal line, and the circuit becomes complicated to eliminate the influence. (2) Since the fact that the connector is connected is detected by the power supply current from the power supply circuit 3, it is necessary to insert a current detection unit in both signal lines, which increases the circuit scale. (3) Since the current always flows through the initial load, the power from the home device is wasted, and if the load is reduced to prevent this, the detection value of the current detection unit becomes low and detection becomes difficult.

Therefore, according to the present invention, 4-wire full-duplex communication is performed with the home device, the communication signal is balanced and transmitted by the transformer, and the DC power supply current superposed from the midpoint of the transformer of the home device is transmitted. In a communication terminal device to be applied to a power receiving circuit connected between the midpoints of the transmitting side and receiving side transformers of its own station, by inserting a new communication terminal device during communication with a simple circuit configuration and without requiring an initial load. The purpose is to prevent adverse effects.

[0025]

In order to achieve the above object, a communication terminal apparatus according to the present invention is provided between received signal lines to detect a received signal and smooth it, as shown in principle in FIG. The signal detection circuit 11 for outputting in the form of a converted DC signal of a constant voltage, and the power receiving circuit 8 and the middle point of the receiving side transformer 9 are connected only when the DC signal is output from the signal detection circuit 11. The switch circuit 12 is provided.

In the present invention, the signal detection circuit 11 is
It is composed of a rectifying circuit and a smoothing circuit, and the time constant of the smoothing circuit can be set to be the constant voltage after the insertion completion time of the connector.

[0027]

The operation of the configuration of FIG. 1 will be described with reference to the time chart of FIG. 2. The signal detection circuit 11 detects the reception signal a on the reception signal line of the terminal device 30, and detects the reception signal a as positive polarity or A negative polarity signal b or c (both are positive signals in the illustrated example) is output as a smoothed DC voltage signal d.

The DC voltage signal d from the signal detection circuit 11 is
When it reaches a certain value and is output as shown in the figure, the switch circuit 12 that receives it switches the switch operating state e from OFF to ON, so that the power supply current f is also switched from OFF to ON at the same time as shown in the figure. The power receiving circuit 8 operates.

In this case, the time constant of the smoothing operation of the signal detecting circuit 11 is set so that the smoothed DC voltage reaches a constant value in a time longer than the connector insertion completion time as shown in the figure, and the opposing signal line C is set. , D it is desirable to consider the connection state of the connector.

In this way, since the power supply current flows after the connector has been completely inserted after the time T has elapsed from the insertion of the connector, the current does not flow only on one side of the transformer and a data error occurs. Is preventing.

[0031]

FIG. 3 is a circuit diagram showing an embodiment of the communication terminal device according to the present invention shown in FIG. 1. In this embodiment, the signal detection circuit 11 includes a reception signal line A from a connector CT30, A transformer T1 having both ends connected to B, and diodes D1 and D2 having respective anodes connected to opposite ends of two windings on the secondary side of the transformer T1 and having respective cathodes commonly connected And this diode D
1, D2 common connection terminal E and secondary winding common connection terminal F
And a smoothing capacitor C1 connected between and.

In the switch circuit 12, the common connection terminal E of the diodes D1 and D2 is the gate terminal G,
It is possible to use an FET in which the drain terminal D is connected to the middle point of the transformer 9 and the source terminal S is connected to the power receiving circuit 8.

In the operation of this embodiment, since the connector CT30 is connected, the reception signal line A,
When the received signal from B is input to the transformer T1, the positive current I1 of the transformer T1 flows through the diode D1 and the negative current I2 flows through the diode D2 to charge the capacitor C1 in a full-wave rectified form. To be done.

The voltage of the capacitor C1 gradually increases in accordance with the time constant as shown by the DC voltage d in FIG. 2, and the FET 13 is turned on when it reaches a constant voltage value. As a result, the feeding current from the middle point of the transformer 9 becomes F
It is supplied to the power receiving circuit 8 via the ET 13.

[0035]

As described above, according to the communication terminal device of the present invention, the received signal is detected and applied to the switch circuit in the form of a smoothed DC signal of a constant voltage, thereby receiving and receiving the signal. Since it is configured to connect the middle point of the side transformer to supply the power supply current, the power supply current will flow after the connector is completely connected, and even if another terminal device is inserted during communication, a data error will occur. It is possible to connect without generating and to provide high quality data service.

[Brief description of drawings]

FIG. 1 is a block diagram showing a principle configuration of a communication terminal device according to the present invention.

FIG. 2 is a time chart diagram showing the operating principle of the communication terminal device according to the present invention.

FIG. 3 is a circuit diagram showing an embodiment of a communication terminal device according to the present invention.

FIG. 4 is a block diagram showing a general full-duplex communication system between a home device and a terminal device.

5 is a diagram showing a flow of a power supply current when a connector is normally connected in the full-duplex communication system of FIG.

FIG. 6 is a diagram showing a transformer operation when the connector connection is normal.

7 is a diagram showing a flow of a power supply current when a connector is not properly connected in the full-duplex communication system of FIG.

FIG. 8 is a diagram showing a transformer operation when the connector connection is not normal.

FIG. 9 is a block diagram showing a conventional example according to Japanese Patent Laid-Open No. 2-246596.

[Explanation of symbols]

1,7 transmitter circuit 2,6 receiver circuit 3 power supply circuit 4,5,9,10 transformer 8 power receiver circuit 11 signal detection circuit 12 switch circuit 20 home device 30 (30-1 to 30-3) terminal device CT20, CT30 ( CT30-1 to CT30-3)
Connector A, B, C, D signal line In the figure, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A four-wire full-duplex communication with a home device (20), the communication signals are balanced-transmitted by the transformers (4,5, 9, 10), and the transformer of the home device (20) is also transmitted. Communication terminal device (30) that applies DC power supply current superimposed from the midpoint of (4,5) to the power receiving circuit (8) connected between the midpoints of the transmitter and receiver transformers (9, 10) of the local station In the above, a signal detection circuit (11) provided between the reception signal lines to detect the reception signal and output it in the form of a smoothed DC signal of a constant voltage (11)
And a switch circuit (12) for connecting the power receiving circuit (8) and the middle point of the receiving side transformer (9) only when a DC signal is output from the signal detection circuit (11). A communication terminal device. 2. The signal detection circuit (11) is composed of a rectifying circuit and a smoothing circuit, and the time constant of the smoothing circuit is set so as to become the constant voltage after the insertion completion time of the connector. The communication terminal device according to claim 1, wherein the communication terminal device is provided.