JP3193799B2 - Communication terminal device - Google Patents

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 supplied from a home device.

When a home terminal and a communication terminal are connected by a bus through a connector, in order to simplify the structure of the communication terminal, a power supply is not provided in the communication terminal itself, but a power supply circuit of the home terminal is provided. It is necessary to supply a DC power supply from.

[0003]

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

The in-home device 20 includes a transmitting circuit 1 and a receiving circuit 2, and transformers 4 and 5 are connected to the transmitting circuit 1 and the receiving circuit 2. A power supply circuit 3 is connected to a middle point of the transformers 4 and 5.

The terminal device 30-1 corresponding to the home device 20
30-3 also include a receiving circuit 6 and a transmitting circuit 7, respectively. Transformers 9 and 10 are connected to these, and a feeder 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 is transmitted via the transformer 4 → connector CT20 → home cable CB → connectors CT30-1 to CT30-3 → transformer 9 to the terminal devices 30-1 to 30-. 3 is received by the receiving circuit 6.

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

[0008] In order to perform four-wire full-duplex communication in this manner, communication signals are balanced-transmitted by the transformers 4, 5, 910.

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

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

In such a case, the problem is that when the terminal device A inserts another communication terminal device B or C during communication, the connection form is a connector, so that the inserted terminal device B or C is inserted.
May not be connected at the same time. In such a case, a transient current at the time of insertion flows between the signal lines, which adversely affects a signal during communication.

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

The power supply current at this time is applied to each of the transformers 4, 5,
Since the current is shunted from the midpoint between 9 and 10, no signal is generated on the side of the transmitting circuits 1 and 7 and the receiving circuits 2 and 9 connected to each other.

At this time, for example, the operation of the transformer 4 is shown in FIG.
And 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 to each other, they cancel each other out, and no signal is generated on the side of the transmission / reception circuit.

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. For example, as shown in FIG. 3, only the cables B and C are connected. In some cases, the cables A and D are not connected.

The power supply current at this time is only the current as shown in the figure, and flows from the middle point of the transformers 4 and 5 to only one winding.

At this time, for example, the operation of the transformer 4 is shown in FIG.
(A) shows a case where only the current I1 flows, and (b) shows a case where only the current I2 flows.

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

Therefore, in Japanese Patent Application 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 into A and B.

That is, while the switch circuit 12 is in the OFF state, the high resistance initial load 14 is connected to the middle point of the transmission / reception transformers 9 and 10 on the side of the terminal device 30-1. Then, when the home device 20 and the terminal device 30-1 are connected by the connectors CT20 and CT30-1 in this state, 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 are securely connected to the current detection units 13A and 13B.
, The power supply current from the in-home device 20 is supplied 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 disclosed in Japanese Patent Application Laid-Open No. 2-246596, there are the following problems. (1) Since the current detection unit is inserted in the main signal line, it adversely affects the communication signal flowing through the 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 into both signal lines, which increases the circuit scale. (3) Since a current always flows through the initial load, the power from the in-home device is wastefully consumed. If the load is lightened to prevent this, the detection value of the current detection unit becomes low and the detection becomes difficult.

Accordingly, the present invention performs four-wire full-duplex communication with an in-home device, communication signals are balanced-transmitted by a transformer, and a DC feed current superimposed from the midpoint of the transformer in the in-home device. In a communication terminal device applied to a power receiving circuit connected between the midpoints of the transmitting and receiving transformers of the own station, a new communication terminal device can be inserted during communication without a simple circuit configuration and without initial load. The purpose is to prevent adverse effects.

[0025]

In order to achieve the above object, a communication terminal device according to the present invention is provided between reception signal lines to detect and smooth a reception signal as shown in principle in FIG. A signal detection circuit 11 that outputs a converted DC signal of a constant voltage, and the power receiving circuit 8 and the midpoint of the receiving transformer 9 are connected only when a DC signal is output from the signal detection circuit 11. A switch circuit 12 is provided.

In the present invention, the signal detection circuit 11
It is composed of a rectifier circuit and a smoothing circuit, and can be set so that the time constant of the smoothing circuit becomes the constant voltage over the completion time of the insertion 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 a reception signal a on the reception signal line of the terminal device 30, and converts the reception signal a to a positive or negative signal. A negative signal b or c (both signals 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 the output reaches a certain value as shown in the figure, the switch circuit 12 receives the signal and switches the switch operation state e from OFF to ON. Therefore, the power supply current f is simultaneously switched from OFF to ON as shown in the figure. , The power receiving circuit 8 operates.

In this case, the time constant of the smoothing operation of the signal detection 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 FIG. , D are considered.

As described above, since the power supply current flows after the connector has been completely inserted after a lapse of time T from the insertion of the connector, the current does not flow to only 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, B, a transformer T1 having both ends connected thereto, and diodes D1 and D2 having respective anodes connected to opposing ends of two windings on the secondary side of the transformer T1 and having respective cathodes connected in common. And this diode D
1 and D2 and a common connection terminal F of the secondary winding.
And a smoothing capacitor C1 connected between the two.

As the switch circuit 12, the common connection terminal E of the diodes D1 and D2 is used as the gate terminal G,
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 can be used.

In the operation of such an embodiment, 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 form of full-wave rectification. Is 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 when the voltage reaches a constant voltage, the FET 13 is turned on. As a result, the supply current from the middle point of the transformer 9 becomes F
The power is supplied to the power receiving circuit 8 via the ET 13.

[0035]

As described above, according to the communication terminal apparatus of the present invention, the reception signal is detected and supplied to the switch circuit in the form of a smoothed DC signal of a constant voltage, whereby the reception circuit is connected to the reception circuit. Since the power supply current is supplied by connecting to the middle point of the side transformer, the power supply current flows after the connector is completely connected, and data errors may occur even if another terminal device is inserted during communication. Connection can be made without any occurrence, and a high quality data service can be provided.

[Brief description of the 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 showing the operation principle of the communication terminal device according to the present invention.

FIG. 3 is a circuit diagram showing one 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.

FIG. 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. 4;

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

FIG. 7 is a diagram showing a flow of power supply current when a connector is not normally connected in the full duplex communication system of FIG. 4;

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 Application Laid-Open No. 2-246596.

[Explanation of symbols]

1, 7 transmission circuit 2, 6 reception circuit 3 power supply circuit 4, 5, 9, 10 transformer 8 power reception 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)
Connectors A, B, C, D Signal lines In the figures, the same symbols indicate the same or corresponding parts.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 29/00 H04L 5/14

Claims (2)

(57) [Claims] 1. A four-wire full-duplex communication is performed with an in-home device (20), communication signals are balanced-transmitted by transformers (4, 5, 9, 10), and the transformer of the in-home device (20) is transmitted. A communication terminal device (30) that applies a DC feed current superimposed from the midpoint of (4,5) to a power receiving circuit (8) connected between the midpoints of the transmitting and receiving transformers (9,10) of the own station (30) 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 constant-voltage DC signal
And a switch circuit (12) for connecting the power receiving circuit (8) and the midpoint of the receiving transformer (9) only when a DC signal is output from the signal detection circuit (11). A communication terminal device characterized by the above-mentioned. 2. The signal detection circuit (11) is composed of a rectifier circuit and a smoothing circuit, and a time constant of the smoothing circuit is set so as to become the constant voltage over a completion time of insertion of the connector. The communication terminal device according to claim 1, wherein