JPH09271007A - Two-way catv system and device with incoming confluent noise removed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce confluent noise as much as possible in a two-way CATV system. SOLUTION: A signal transmitter arranged in a terminal equipment T1 and capable of transmitting only an incoming band signal is provided with level detection means 31 to 33 for detecting the level of an incoming band signal on a signal line, a comparing means 34 for comparing the level detected by the means 31 to 33 with a prescribed level and a switching means 30 inserted into the signal line and allowed to be set up to an on-state when the level of the incoming band signal is higher than the prescribed level as the result of the means 34 and set up to an OFF state in the other case. Only when an incoming band signal is sent from each demander, a demander's terminal equipment T1 is connected to a transmission line, and when the signal is not sent, the equipment T1 is completely separated from the transmission line, so that noise collected from the demander's terminal equipment T1 is not sent to the incoming fand of the transmission line and confluent noise can be effectively suppressed as less as possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and apparatus for suppressing upstream combined noise in a bidirectional CATV system.

[0002]

2. Description of the Related Art Conventionally, in an interactive CATV system, a signal for descrambling or
BACKGROUND ART A request for an image sent from a center device, a reply to an inquiry from the center device, safety information of a terminal device, and the like are transmitted to the center device using an upstream band.

This bidirectional CATV transmission line is formed in a tree shape with the center device as the apex, and the upstream band signal transmitted from the consumer to the center device uses a low group band such as 10 to 50 MHz. For this reason, 27 MHz band signals for citizen's radio, radio waves such as amateur radio, and various noises that are picked up by each customer flow into all the customers connected to the transmission line into the center device. Become. This ingress noise interferes with the reception of the upstream band signal transmitted from the consumer.

In order to suppress this ingress noise in the center device, the upstream amplifier is deactivated when the upstream signal is not transmitted to the upstream band signal amplifier of the trunk line or the branch line, and the upstream signal is transmitted when the upstream signal is transmitted. A technique for operating an amplifier is known (Actual exploitation 59-1).
No. 01571). Further, in the branch portion from the trunk line to the branch line, the device that monitors the upstream band signal transmitted through the branch line for each channel and controls the filter so that only the band in which the upstream band signal exists is passed to the trunk line side. It is known (Japanese Patent Laid-Open No. 1-293785). Further, there is known a technique in which each customer is provided with a switch that is turned on by a command when a terminal device sends an upstream band signal (Japanese Patent Laid-Open No. 5-304672).

[0005]

In the first method, it is judged whether or not the upstream band signal is transmitted in units of branch lines.
However, a large number of customers are connected to the branch line, and if one customer sends an upstream band signal,
Even if no other customer is sending the upstream band signal, this amplifier is in operation and ready to send the upstream band signal to the trunk line. Therefore, the ingress noise is not reduced because the transmission path is in a propagable state with respect to a large number of consumers who do not transmit the upstream band signal.

In the second method, the propagation possible state and the propagation impossible state of the transmission path are switched for each channel of the upstream band, but again, the number of consumers connected to one channel is large. . As a result, the transmission line to the trunk line can be propagated to a large number of consumers who are not transmitting the upstream band signal, so that the effect of reducing the ingress noise is small.

Furthermore, the third method manages whether or not the transmission path of the upstream band is cut off in the terminal device. However, when there is an intention to transmit data to the center device, the transmission path in the upstream band is in a propagable state continuously for the intended period. Because of this,
Even when the upstream band signal is not transmitted, the center device and the terminal device are connected in the upstream band. Therefore, during this time, noise is propagated to the center device,
Since many such devices are connected to the transmission line, there is a problem that the ingress noise becomes large while such an upstream band signal is not actually transmitted.

The present invention has been made to solve the above problems, and an object of the present invention is to effectively and as much as possible reduce ingress noise in a bidirectional CATV system.

[0009]

The invention of claim 1 is a bidirectional CATV system which enables bidirectional communication between a center device and a terminal device by frequency separation of an upstream band and a downstream band. In the security device provided at the entrance of each consumer, the surge absorber that absorbs a surge entering from the transmission line and the consumer-side terminal are provided to separate the upstream band and the downstream band. The upstream band signal output from the first duplexer on the customer side, the second duplexer on the center device side, and the terminal device installed in the consumer is passed through the upstream band signal of the first duplexer. A level detection means for extracting the level of the upstream band signal from the terminal, a comparison means for comparing the level detected by the level detection means with a predetermined level, and a first demultiplexer and a second demultiplexer. Upstream band signal between Is inserted into the upstream band circuit for transmitting,
The comparison means is provided with a switch means that is turned on when the level of the upstream band signal is higher than a predetermined level and turned off in other cases.

The upstream band signal transmitted from the terminal device of the consumer to the center device is input to the level detecting means via the first demultiplexer of the protector. The level detecting means detects the signal level of the upstream band, and the comparing means compares the signal level with a predetermined level. Also, the switch means is inserted in the upstream band circuit between the second demultiplexer and the first demultiplexer, and the switch means is used when the detected upstream band signal level is higher than a predetermined level. Is turned on, and conversely, it is turned off when the signal level of the upstream band signal is lower than a predetermined level. As a result, the terminal device of the customer and the transmission path are connected to each other only for a period during which the upstream band signal to be transmitted to the center apparatus is substantially present. It can be effectively reduced.

Further, the invention of claim 2 is arranged in each consumer of a bidirectional CATV system capable of bidirectional communication between a center device and a terminal device by frequency separation of an up band and a down band. In the signal transmitter that is connected to the signal line for transmitting the upstream band signal to the center device and passes only the upstream band signal, the level detecting means for detecting the level of the upstream band signal on the signal line and the level detecting means are used. Comparison means for comparing the detected level with a predetermined level, and an ON state when the level of the upstream band signal inserted into the signal line by the comparison means is higher than the predetermined level,
In other cases, switch means that is turned off is provided.

By providing such a signal transmitter in the circuit for transmitting the upstream band signal of the terminal device of each consumer, transmission with the terminal device is performed during the period when the signal level of the upstream band signal does not exceed the predetermined level. The path is disconnected from the upstream band, and the terminal device and the transmission path are connected to each other in the upstream band only while the signal level of the upstream band signal exceeds a predetermined level. As a result, by installing this signal transmitter in each customer, it is possible to extremely effectively reduce the ingress noise in the center device.

Further, the invention of claim 3 is a protector used in the system of claim 1. By installing this protector at the eaves of each customer, it is possible to extremely effectively reduce the ingress noise in the center device as described above.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on specific embodiments. FIG. 1 shows the configuration of a signal transmitter according to a specific embodiment of the present invention and the overall configuration of a system using the signal transmitter. A center device C is connected to one end of the frequency-multiplexed transmission line L, and a large number of bidirectional amplifiers R are arranged in the transmission line L. This transmission line L is connected via the relay terminal of this bidirectional amplifier,
It is branched into a large number of branch lines, and the terminal device T1 of the consumer is connected to the branch lines via a protector 70. In this system, the upstream band is the low group band and the downstream band is the high group band.

The terminal device T1 includes a demultiplexer 10 for separating a low group band and a high group band, a demodulator 12 for receiving a high group downlink band signal, converting it into a predetermined frequency band, and demodulating it into data, and a demodulator. It has a television receiver 11 for displaying a video by inputting a signal output from the digital camera 12. With this device, the video transmitted from the center device C can be received. On the other hand, the terminal device T1 is provided with a device for transmitting a signal to the center device C. That is, RAM / ROM
A CPU 20 that executes a predetermined process according to a program or data stored in 21 is provided, and the CPU 20 includes a demodulator 12, an input / output interface 22, and a demodulator 12.
A keyboard 23 for inputting various kinds of data, a switch / sensor 24 for taking in various kinds of information such as security, etc. are connected, and a modulator 25 for modulating the data generated by the CPU 20 and sending it to the transmission path is provided. CP
U20 inputs data from the center device C via the demodulator 12, inputs the state of the switch / sensor 24, and outputs the state data to the modulator 25.
The status data is modulated into a low-group upstream band signal and sent to the transmission path, and the security information of each customer is sent to the center device.

Further, the following devices, which are characteristic parts of the present invention, are provided. PIN between modulator 25 and duplexer 10
A diode switch 30 is provided. The PIN diode switch 30 responds to the applied bias voltage by
It switches between a passing state and a blocking state. In addition, a band pass filter 31 for inputting the output of the modulator 25 and passing a signal in a predetermined band, a diode 32 for rectification, a capacitor 3
3. A comparator 34 for outputting a voltage to the PIN diode switch 30 is provided. The reference voltage Vt by resistance division is input to the inverting input terminal of the comparator 34.

In such a device, when there is no output of the modulator 25, the level of the output signal of the bandpass filter 31 is also low, and therefore, the average voltage V input to the non-inverting input terminal of the comparator 34 after rectification. The level of is also low. Therefore,
The average voltage V is lower than the reference voltage Vt, and the output of the comparator 34 is low level. As a result, since no bias voltage is applied to the PIN diode switch 30, the PIN diode switch 30 is cut off, and the transmission line and the terminal device T1 are connected in the upstream low group band.
Is disconnected, and noise picked up in the customer is not sent to the transmission line.

On the other hand, if there is an output from the modulator 25,
The level of the output signal of the bandpass filter 31 becomes high,
Therefore, the level of the average voltage V input to the non-inverting input terminal of the comparator 34 after rectification is also high. Therefore, the average voltage V is higher than the reference voltage Vt, and the output of the comparator 34 becomes high level. As a result, a bias voltage is applied to the PIN diode switch 30, and the PIN diode switch 30 is in the pass state, the transmission line and the terminal device T1 are in the connection state for the upstream low group band, and the output signal of the modulator 25 is sent to the transmission line. become.

Since each customer is provided with such a device, each terminal device is connected to the transmission line only when the data is substantially sent to the center device C as a signal in the upstream low group band. Therefore, the ingress noise can be effectively reduced.

The level detecting means is composed of a band pass filter 31, a diode 32 and a capacitor 33, the comparing means is composed of a comparator 34, and the switching means is a PIN.
It is composed of a diode switch 30. Further, the signal transmitter includes a band pass filter 31, a diode 32, a capacitor 33, a comparator 34, and a PIN diode switch 30.
It consists of.

Next, the second embodiment will be described. In this embodiment, a protector provided at the eaves of a customer is provided with the above function. That is, instead of the signal transmitter described in the first embodiment, the protector 70 shown in FIG. 1 has the above-mentioned function. FIG. 2 is a circuit diagram of the protector. Terminal 41 is a terminal connected to the center side, terminal 4
2 is a terminal connected to the terminal device T1 side. The arrester 45 and the capacitors 46 and 49 are components constituting a conventional protector, and the arrester 45 is a circuit that absorbs a surge. In addition to this, in the present invention, the first demultiplexer 44 is connected to the terminal 42 via the capacitor 50, and
A second demultiplexer 43 is arranged closer to the center device than 4 is. The downlink band circuit for passing the high-group downlink band signal between the first demultiplexer 44 and the second demultiplexer 43 is one line and constitutes an all-pass circuit.

The circuit connecting the first demultiplexer 44 and the second demultiplexer 43 to the lower group band side is an upstream band circuit, and the PIN diode switch 30 is inserted in the circuit. The PIN diode switch 30 disconnects or connects the transmission line and the terminal device T1 with respect to the upstream band. Then, in order to supply a bias voltage to the PIN diode switch 30, a bandpass filter 31,
Diode 32 for rectification, capacitor 33, voltage
A comparator 34 for outputting to the PIN diode switch 30 is provided. The reference voltage Vt by resistance division is input to the inverting input terminal of the comparator 34.

In such an apparatus, the first demultiplexer 44
When no signal is detected at the terminal for passing the upstream band signal, the level of the output signal of the bandpass filter 31 is also low, and therefore the level of the average voltage V input to the non-inverting input terminal of the comparator 34 after rectification is also. Low. Therefore, the average voltage V is lower than the reference voltage Vt, and the output of the comparator 34 is low level. As a result, since no bias voltage is applied to the PIN diode switch 30, the PIN diode switch 30 is cut off, the transmission line and the terminal device T1 are disconnected from each other in the up low group band, and the noise picked up in the customer is sent to the transmission line. Not done.

On the other hand, when a signal is detected at the terminal of the first demultiplexer 44 that passes the upstream band signal, the level of the output signal of the bandpass filter 31 becomes high, and therefore, after the rectification, the comparator 34 outputs the signal. The level of the average voltage V input to the non-inverting input terminal is also high. Therefore, the average voltage V is higher than the reference voltage Vt, and the output of the comparator 34 becomes high level. As a result, a bias voltage is applied to the PIN diode switch 30, and the PIN diode switch 30 is in the pass state, and the transmission line and the terminal device T1 are in the connection state for the upstream low group band, and the output signal of the modulator 25 is transmitted to the transmission line. become.

Since the protector 70 is provided in each customer, each terminal device is connected to the transmission line only when the data is substantially sent to the center device C as a signal of the upstream low group band. Therefore, the ingress noise can be effectively reduced.

As with the signal transmitter of the first embodiment, the level detecting means includes a band pass filter 31 and a diode 3.
2, a capacitor 33, and the comparison means is a comparator 3
4 and the switch means is a PIN diode switch 30.

A device for supplying power to the protector 70 is required. In the protector of FIG. 2, DC power is supplied to the above-described active circuit of the protector 70 from the DC power supply (DC12V) of another system supplied from the consumer or another system through the automatic voltage regulator 51. It

In addition to the above DC power supply, as shown in FIG. 3, AC power is superposed on the transmission line L so that the choke coil 52 and the capacitor 53 are connected to the live line of the terminal 41. Connect the series circuit of the choke coil 52
AC power may be separated via the. In this method, the AC voltage separated by the choke coil 52 is transferred to the transformer 5
The voltage is transformed at 4 and converted to DC at the full-wave rectification circuit 55.
The DC voltage thus obtained is stabilized by the automatic voltage regulator 56 and supplied to the active circuit of the protector 70.

Further, in addition to the above-mentioned power supply system, AC power may be superposed on the signal and supplied from the customer as shown in FIG. In that case, the terminal 60 on the consumer side is connected to the coil 60.
AC power may be taken out via a low-pass filter composed of a capacitor 61 and a capacitor 61, and DC power may be supplied to the active circuit of the protector 70 via an automatic voltage regulator 62 having rectification and voltage adjustment functions. .

When the AC power is not superposed on the signal and supplied from the center device side of the transmission line, as shown in FIG. 4, a small power surge is provided between the terminal 41 and the second demultiplexer 43. It is also possible to insert a coil 48 for releasing the electric current to the ground in parallel with the arrester 45.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a signal transmitter and a CATV system using the signal transmitter according to a first specific example of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a protector according to a second specific example of the present invention.

FIG. 3 is a circuit diagram showing a power supply system of the protector.

FIG. 4 is a circuit diagram showing another power supply method of the protector.

[Explanation of symbols]

 C ... Center device T1 ... Terminal device L ... Transmission line R ... Relay amplifier 10 ... Demultiplexer 43 ... Second demultiplexer 44 ... First demultiplexer 30 ... PIN diode switch 31 ... Bandpass filter 34 ... Comparator 25 … Modulator 20… CPU

Claims (3)

[Claims] 1. In a bidirectional CATV system capable of bidirectional communication between a center device and a terminal device by frequency separation of an up band and a down band, a protector disposed at the entrance of each customer. In addition, the first duplexer on the customer side and the center device side, which are arranged between the surge absorption circuit that absorbs surges entering from the transmission line and the customer side terminal, separate the upstream band and the downstream band from each other. Of the second demultiplexer of the first demultiplexer and the upstream band signal output from the terminal device installed in the consumer are taken out from the terminal of the first demultiplexer that passes the upstream band signal, and the level of the upstream band signal is determined. Level detecting means for detecting, comparing means for comparing the level detected by the level detecting means with a predetermined level, and an upstream band signal between the first demultiplexer and the second demultiplexer for the center device. Bandwidth to be transmitted to A two-way CATV, which is inserted in the path and is provided with switching means that is turned on when the level of the upstream band signal is higher than a predetermined level by the comparison means and is turned off otherwise. system. 2. A bidirectional CATV system, which enables bidirectional communication between a center device and a terminal device by frequency separation of an up band and a down band, is installed in each customer and goes up to the center device. In a signal transmitter that is connected to a signal line that sends a band signal and that passes only an upstream band signal, a level detection unit that detects the level of the upstream band signal on the signal line, and a level detected by the level detection unit. A comparing means for comparing with a predetermined level, and a switching means inserted into the signal line and turned on when the level of the upstream band signal is higher than a predetermined level by the comparing means, and turning off otherwise. And a signal transmitter characterized by being provided. 3. A protector arranged at the entrance of each customer in a two-way CATV system capable of two-way communication between a center device and a terminal device by frequency separation of an up band and a down band. , A consumer-side first demultiplexer that is provided between a surge absorption circuit that absorbs a surge that enters from a transmission line and a consumer-side terminal and separates the upstream band and the downstream band from the center device side. An upstream band signal output from the second demultiplexer and the terminal device installed in the consumer is taken out from a terminal of the first demultiplexer that passes the upstream band signal, and the level of the upstream band signal is detected. Level detecting means, comparing means for comparing the level detected by the level detecting means with a predetermined level, and an upstream band signal between the first demultiplexer and the second demultiplexer for the center device side. Up band transmitted to And a switching means that is inserted into a frequency band circuit and is turned on when the level of the upstream band signal is higher than a predetermined level by the comparison means, and turned off in other cases. .