JPH04296186A - Two-way catv system - Google Patents

Abstract

PURPOSE:To suppress incoming confluent noise without giving any economical hindrance to communication with simple circuit constitution. CONSTITUTION:When an incoming signal is sent, a terminal equipment 2 superimposes a DC current onto the incoming signal and sends the result to a tap-off 1 via a drawing line 4. A switch circuit 12 in the tap-off 1 passes through only an outgoing signal sent via a CATV transmission line 3 from a center equipment when no DC current is received and passes through the incoming signal when the DC current is received by the circuit 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-way CATV system, and more particularly to a system for preventing upstream noise from entering from terminal equipment installed in subscriber's homes.

0002

2. Description of the Related Art This type of bidirectional CATV system includes a center device and a plurality of terminal devices connected to the center device via a CATV transmission line and a bidirectional repeater. The terminal device is installed at a subscriber's home or the like. Further, the plurality of terminal devices are connected to the center device in a tree shape. The center device sends downlink signals to multiple terminal devices.
It is transmitted via an ATV transmission line and a bidirectional repeater. Each of the multiple terminal devices CATs the upstream signal to the center device.
It is sent out via a V transmission line and a bidirectional repeater. A line on which downlink signals are transmitted is called a downlink, and a line on which upstream signals are transmitted is called an uplink. The bidirectional repeater includes an amplifier for amplifying downlink and uplink signals, a downlink branch circuit for downlinks, and an uplink branch circuit for uplinks. In such a two-way CATV system, noise generated in each terminal device, etc. is merged on a CATV transmission path via an uplink, and is transmitted to a center device as upstream noise.

In order to suppress this upstream noise, in the conventional two-way CATV system, the two-way repeater has a switch for opening and closing the upstream branch circuit, and the opening and closing of the switch is controlled by control from the center device. The control unit is equipped with a control unit for

0004

As described above, in the conventional two-way CATV system, the center device is always connected to the uplink, regardless of whether each terminal device is transmitting an uplink signal or not. Then, every time noise enters the CATV transmission line, the center device controls the control section of the bidirectional repeater to disconnect the upstream branch circuit (upstream line) from the main line using a switch. Therefore, it takes time to identify the location where the noise is mixed. Furthermore, since the uplink is disconnected from the main line, communication between the center device and the plurality of terminal devices may be interrupted.

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-way CATV system that has a simple circuit configuration and can economically suppress upstream noise without interfering with communication.

[0006]

[Means for solving the problems] Bidirectional CA according to the present invention
The TV system includes a tap-off connected to a center device via a CATV transmission line, and a terminal device connected to the tap-off via a drop-in line, and a downlink signal from the center device is transmitted to the center device via a CATV transmission line. , the tap-off, and the drop-in line to the terminal device, and the uplink signal from the terminal device is sent to the center device via the drop-in line, the tap-off, and the CATV transmission line. In the forward CATV system, the terminal device has means for superimposing a DC current on the upstream signal when transmitting the upstream signal, and the tap-off only passes the downstream signal when not receiving the DC current. and a switch means for passing the upstream signal when receiving the direct current.

[0007]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a bidirectional CA according to an embodiment of the present invention.
A TV system is shown. The two-way CATV system according to this embodiment includes a tap-off 1 connected to a center device (not shown) via a CATV transmission line 3, and a terminal device 2 connected to the tap-off 1 via a drop-in line 2. have Although only one tap-off 1 and one terminal device 2 are shown in FIG. 1, in an actual bidirectional CATV system, a plurality of tap-offs are connected to the CATV transmission line 3, and each tap-off has a plurality of terminal devices. is connected. Four terminal devices can be connected to the illustrated tap-off 1.

[0008] The center device converts downlink signals of the RF band into CA
It is sent to the terminal device 2 via the TV transmission line 3, tap-off 1, and drop-in line 4. The terminal device 2 sends an RF band up signal to the center device via the drop-in line 4, the tap-off 1, and the CATV transmission line 3.

The tap-off 1 has first to fourth branch output terminals 24, 25, 26, and 27, an input terminal 28,
It has an output terminal 29. Input terminal 28 and output terminal 2
9 is connected to the CATV transmission line 3. The fourth branch output terminal 27 is connected to the terminal device 2 via the lead-in line 4. The first to third branch output terminals 24 to 26 are also
Like the fourth branch output terminal 27, it is connected to a terminal device (not shown) via a lead-in line (not shown).

The tap-off 1 includes a branch 11 connected between an input terminal 28 and an output terminal 29, and a branch 11 connected between an input terminal 28 and an output terminal 29.
a switch circuit 12 that is connected to the switch circuit 12 and controls the passage of downlink signals and uplink signals, as will be described later;
2, and second and third couplers 14 and 15 connected to the first coupler 13. The first to fourth branch output terminals 24 to 27 are
First to fourth choke coils 20, 21, 2, respectively.
It is connected to the switch circuit 12 via 2 and 23. The first to fourth capacitors 16, 17, 18, and 19 are connected to the first to fourth branch output terminals 24 to 2, respectively.
It is used to prevent direct current from passing through from 7, and only allows signals to pass through. The first and second branch output terminals 24 and 25 are
They are connected to a second coupler 14 via first and second capacitors 16 and 17, respectively. 3rd and 4th
The branch output terminals 26 and 27 of are connected to the third coupler 15 via third and fourth capacitors 18 and 19, respectively.
It is connected to the.

The terminal device 2 has an input/output terminal 35 connected to the lead-in line 4. Input/output terminal 35 is capacitor 3
It is connected to the communication control unit 31 via 2. The transistor 34 is used as a DC switch element and is driven by the communication control section 31. When the transistor 34 turns on, the direct current is sent to the tap-off 1 side via the choke coil 33.

FIG. 2 shows the switch circuit 12 in the tap-off 1.
An example of the configuration is shown below. The switch circuit 12 selects a high-frequency pass filter 51 that allows only downstream signals to pass, a strap line 53 that allows upstream signals to pass, and one of the high-frequency pass filter 51 and the strap line 53. It has a drop-in line 4 and a switch 50 for connecting to the CATV transmission line 3. The switch 50 is driven by a switch drive circuit 52 as described later. Direct current is supplied to the switch drive circuit 52 from the signal line 30 .

The operation of the bidirectional CATV system of this embodiment will be explained below with reference to FIGS. 1 and 2. The state of the switch circuit 12 in FIG. 2 shows a state in which none of the terminal devices connected to tap-off 1 is transmitting an uplink signal. That is, the switch drive circuit 52 is not supplied with direct current from the signal line 30. Thereby, the switch drive circuit 52 connects the contact of the switch 50 to the high frequency pass filter 51 side. Therefore, the switch circuit 12 is in a state where only the downstream signal passes.

In this state, the communication control section 31 of the terminal device 2
Suppose that the device sends an uplink signal in response to polling from the center device. At this time, the communication control unit 31 turns on the transistor 34 immediately before transmitting the upstream signal. Thereby, the DC current is supplied to the tap-off 1 via the lead-in line 4 in a state where it is superimposed on the upstream signal. At tap-off 1, this supplied DC current is supplied to the switch drive circuit 52 of the switch circuit 12 via the fourth choke coil 23 and the signal line 30. In response to this direct current, the switch drive circuit 52 switches the contact of the switch 50 from the high frequency pass filter 51 side to the strap line 53 side. As a result, the switch circuit 12 enters a state in which both downlink signals and uplink signals are passed. This state is maintained while the uplink signal is being sent from the terminal device 2.

Assume that the communication control section 31 of the terminal device 2 stops sending out uplink signals. At this time, the communication control unit 31
The transistor 34 is turned off to stop supplying direct current. Since the supply of DC current has stopped, the switch circuit 12
The switch drive circuit 52 switches the contact point of the switch 50 again to the high frequency pass filter 51 side to allow only the downlink signal to pass. In this way, since the uplink is connected to the center device only when each terminal device sends an uplink signal, it is possible to reduce the probability that upstream noise is sent to the center device.

The switch circuit 12 in the tap-off 1 may have any circuit configuration as long as it passes the upstream signal using a direct current when the terminal device 2 sends out the upstream signal. FIG. 3 shows another example of the configuration of the switch circuit 12. The illustrated switch circuit 12 includes a first passage 5 for passing downlink signals.
6, a second passageway 57 for passing uplink signals, a CATV transmission line 3 (FIG. 1), and first and second passageways 5.
6 and 57, a first directional coupler that transmits the down signal from the CATV transmission path 3 to the first passage path 56, and transmits the up signal from the second passage path 57 to the CATV transmission path 3; 54, the lead-in line 4 (FIG. 1), and the first and second passageways 56 and 57, and transmits the upstream signal from the drop-in line 4 to the second passageway 57. A second directional coupler 55 that transmits a down signal from the input line to the drop-in line 4, and a switch 5 inserted in the second passage 56.
0, and a switch drive circuit 52 that drives the switch 50 so as to open the switch 50 when not receiving a direct current and close the switch 50 when receiving a direct current.

In the embodiment of FIG. 1, a switch circuit 12 is connected between the branch 11 and the first coupler 13,
The switch circuit 12 has first to fourth branch output terminals 24.
A DC current obtained by ORing four input DC currents is supplied from ~27. However, as shown in FIGS. 4 and 5, the switch circuits may be arranged in two locations and four locations within the tap-off 1, respectively. In the tap-off 1 shown in FIG. 4, the switch circuit 60 connects the first coupler 13 and the second
A switch circuit 61 is connected between the first coupler 13 and the third coupler 15. In tap-off 1 shown in FIG.
is connected between the second coupler 14 and the first branch output terminal 24, and the switch circuit 63 is connected between the second coupler 14 and the second branch output terminal 24.
is connected between the branch output terminal 25 of the switch circuit 6
4 is connected between the third coupler 15 and the third branch output terminal 26, and a switch circuit 65 is connected between the third coupler 15 and the fourth branch output terminal 27. Further, in the embodiment described above, four terminal devices are branch-connected to the tap-off, but the number of terminal devices branch-connected to the tap-off is not limited to this, and may be one or more.

[0018]

[Effects of the Invention] As explained above, the present invention switches between two-way communication and one-way communication with the tap-off based only on the presence or absence of direct current from the terminal device, so it has a simple circuit configuration. Economical and without interfering with communication,
Upstream noise from the terminal device can be suppressed at all times. As a result, even when another terminal device with a different number of carriers communicates with the center device, connection is possible by simply superimposing a DC current on the upstream signal when transmitting the upstream signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating a two-way CATV system according to one embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of the switch circuit in FIG. 1;

FIG. 3 is a block diagram showing another configuration example of the switch circuit in FIG. 1;

FIG. 4 is a block diagram showing another configuration example of the tap-off in FIG. 1;

FIG. 5 is a block diagram showing still another configuration example of the tap-off shown in FIG. 1;

[Explanation of symbols]

1 Tap-off 2 Terminal device 3 CATV transmission line 4 Lead-in line 11 Branch 12 Switch circuit 13, 14, 15 Coupler 16, 17, 18, 19 Capacitor 20, 21, 2
2, 23 Choke coil 24, 25, 26, 27
Branch output terminal 28 Input terminal 29 Output terminal 30 Signal line 31 Communication control section 32 Capacitor 33 Choke coil 34 Transistor 35 Input/output terminal 50 Switch 51 High frequency pass filter 52 Switch drive circuit 53 Strap wires 54, 55 Directional coupler 56 ,57 passage

Claims (3)

[Claims] 1. A tap-off connected to a center device via a CATV transmission line, and a terminal device connected to the tap-off via a drop-in line, wherein the downlink signal from the center device is connected to the CATV transmission. The uplink signal from the terminal device is sent to the center device via the drop-in line, the tap-off, and the CATV transmission line. In the two-way CATV system, the terminal device has means for superimposing a DC current on the upstream signal when transmitting the upstream signal, and the tap-off is configured to superimpose only the downstream signal when not receiving the DC current. A two-way CATV system characterized by having a switch means for passing the upstream signal and for passing the upstream signal when receiving the direct current. 2. The switch means selects a filter circuit that allows only the downlink signal to pass, a pass circuit that allows the uplink signal to pass, and one of the filter circuit and the pass circuit. a switch for connecting to the drop-in line and the CATV transmission line; and a switch for driving the switch so as to select the filter circuit when not receiving the direct current and select the passing circuit when receiving the direct current. The bidirectional CATV system according to claim 1, further comprising a drive circuit. 3. The switch means includes a first passage for passing the downlink signal, a second passage for passing the uplink signal, a connection between the CATV transmission line and the first and second passages. a first direction that is connected to a second passageway, transmits the downlink signal from the CATV transmission path to the first passageway, and transmits the upstream signal from the second passageway to the CATV transmission path; a sexual coupler, connected to the lead-in line and the first and second passageways, transmits the upstream signal from the lead-in line to the second passageway, and transmits the upstream signal from the first passageway; a second directional coupler that transmits a downlink signal to the lead-in line; a switch inserted in the second passage; and a switch that opens when the DC current is not received and receives the DC current. The bidirectional CAT according to claim 1, further comprising a switch drive circuit that drives the switch so as to sometimes close the switch.
V system.