JP2001128135A - Distribution compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a cable modem to receive a down signal in a prescribed reception level and to prevent attenuation in an up signal from the cable modem. SOLUTION: The down signal inputted from an input terminal IN passes an HPF 21, a branching device 22, an equalizer 23, a variable attenuator 24, a down amplifier 25, and an HPF 26 and is outputted from a first output terminal OUT1. The down signal is attenuated and branched by the branching device 22 after passing the HPF 21, has the level adjusted by a variable attenuator 27, passes an HPF 28 to be set to the prescribed reception level of the cable modem and is outputted from a second output terminal OUT2. The up signal which is transmitted from the cable modem and is inputted from the second output terminal OUT2 passes an LPF 29 to have the extent of attenuation minimized and is outputted from the input terminal IN.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distribution compensator for a cable modem in a CATV system to transmit and receive at an appropriate level.

[0002]

2. Description of the Related Art In recent CATV systems, a cable modem is connected to a cable television network, and a personal computer is connected to the cable television network via the cable modem to use various network services. ing. One example of such a CATV system is shown in FIG. C shown in FIG.
From the head end 51a provided in the CATV center 51 in the ATV system 200, various program signals and various data are transmitted to trunk lines constituting a plurality of cable television networks. The various program signals and various data transmitted to the main line propagate through the main line, and the bidirectional main line amplifiers (AMP) 52a, 52 provided at predetermined distances.
The signal is amplified at b and the frequency characteristics are equalized and propagated.

[0003] This trunk line is branched in some places by a branch amplifier or a branching device, propagates through the branch trunk line, is further distributed by a distributor, and passes through tap-offs 53a and 53b.
It is drawn into each facility and each home via the protectors 54a and 54b. Thereby, each facility and each home can receive various program signals and various data. Home terminals 55a and 55 are provided at each facility and each home.
b, and the home terminals 55a, 55b
, Various program signals are decoded or selected. Thereby, the home terminals 55a, 55
A desired program can be enjoyed by the televisions 57a and 57b connected to the terminal b.

Further, personal computers 58a and 58b installed in facilities and homes can be connected to a cable television network. In this case, the personal computer 58a,
58b is connected to a cable television network via cable modems 56a and 56b. At this time, for example, the upstream signals transmitted when connecting to the Internet from the personal computers 58a and 58b are transmitted to the cable modems 56a and 56b.
b. The user goes up to the CATV center 51 via the cable television network and is sent to the Internet provider 59 via the router 51b provided in the CATV center 51. As a result, the personal computers 58a and 58b installed in each facility and each home are connected to the Internet via the Internet provider 59, and can receive Internet services. When the CATV center 51 can provide another network service, the personal computers 58a, 5 installed in each facility or each home via the cable TV network are similarly provided to the CATV center 51.
8b, other network services can be received from the CATV center 51.

[0005]

By the way, the upstream frequency band in a cable television network is slightly different depending on the cable modem, but is 5 to 55 MHz, and the downstream frequency band is 70 to 770 MHz. The transmission level of the cable modems 56a and 56b, that is, the upstream signal level is 68 to 118d depending on the specification.
Bμ, and the received signal level, that is, the downstream signal level, is 45 to 75 dBμ according to the specification. On the other hand, the level of various program signals in the cable television network is set to 60 to 90 dBμ. These various program signals are of course the level of the downstream signal, and various amplifiers inserted into the cable television network amplify the downstream signal and propagate it so that the level of the downstream signal is secured. I have.

[0006] Then, the level of the downstream signal directed to the personal computers 58a and 58b installed in each facility and each home is set to the level of 60 to 90 dBμ similarly to the various program signals, and is propagated on the network. For this reason, the personal computers 58a, received by the cable modems 56a, 56b,
The level of the downstream signal toward 58b is also set to a level of 60 to 90 dBμ, and if the received signal level of the cable modems 56a and 56b becomes excessive, the cable modems 56a and 56b may cause a data error. become.

FIG. 6 shows a conventional distribution method in consideration of the above-mentioned problem of distribution to a home terminal and a cable modem. In this distribution method, the distributor 10 is provided to the filter unit 70.
4 are connected in cascade, and an input terminal IN of the filter unit 70 is connected to a cable television network. The downstream signal input to the input terminal IN of the filter unit 70 is a high-pass filter (HP
F) After passing through 101, the signal is amplified by a predetermined level in the downstream amplifier 102. Further, the signal passes through the HPF 103, is output from the output terminal OUT, and is divided into two by the distributor 104. One distribution output distributed by the distributor 104 is supplied to the home terminal, and the other distribution output is supplied to the cable modem. Note that the downstream signal cannot pass through the LPF 105 and is blocked by the LPF 105. Also, the upstream signal output from the cable modem is
The signal is input to the output terminal OUT of the filter unit 70 via the distributor 104, and the low-pass filter (LPF) 10
6, 105 and output from the input terminal IN to the cable television network. The upstream signal is HPF1
03 and cannot be passed through the HPF 103.

In such a distribution method, the downstream signal is amplified by the downstream amplifier 102 to increase the level.
At the home terminal, it can be received at a sufficient level. Further, since the upstream signal is output as it is without increasing the level, it can be transmitted at a specified level. However, since the cable modem is supplied with the same level of down signal as the home terminal,
If the received signal level of the cable modem becomes excessive, the cable modem may cause a data error. Further, since the noise from the home terminal comes to the center via the LPFs 106 and 105, the noise is affected by the signal noise.

Next, FIG. 7 shows a conventional distributor for distributing to a home terminal and a cable modem. In the distributor 80 shown in FIG. 7, the input terminal IN of the distributor 80 is connected to a cable television network. The downstream signal input from the input terminal IN is split by the splitter 111, and the attenuated split output is output to the second output terminal O
The signal is output from the UT 2 and supplied to the cable modem. On the other hand, the downstream signal passing through the splitter 111 passes through the HPF 112, is amplified by a predetermined level in the downstream amplifier 113, passes through the HPF 114, is output from the first output terminal OUT1, and is supplied to the home terminal. The upstream signal output from the cable modem is input from the second output terminal and applied to the branch terminal of the branch unit 111. The upstream signal attenuated in the splitter 111 is transmitted from the input terminal IN to the cable television network.

In such a distributor 80, the downstream signal is amplified by the downstream amplifier 113 to increase the level, so that the home terminal can receive the signal at a sufficient level. In addition, since the cable modem is supplied with the downstream signal attenuated by a predetermined level in the branching unit 111,
The reception signal level of the cable modem is prevented from being over-input. Further, since the noise from the home terminal is blocked by the HPF 114, the amplifier 113, and the HPF 112, the flow noise is prevented from going to the center. However, since the level of the upstream signal input from the second output terminal OUT2 is attenuated in the branching unit 111, the level may be lower than a prescribed level.

Therefore, the present invention provides a distribution compensator that allows a cable modem to receive a downlink signal at a prescribed reception level and minimizes the amount of attenuation of an uplink signal that is a transmission signal from the cable modem. It is intended to provide.

[0012]

To achieve the above object, a distribution compensator of the present invention distributes a downstream signal input from an input terminal to a first output terminal and a second output terminal. A distribution compensator for outputting an upstream signal input from the second output terminal from the input terminal, wherein a frequency band of a downstream signal provided between the input terminal and the first output terminal is determined. A first filter unit having a characteristic of passing the signal, a branching unit for branching an output of the first filter unit, and a frequency band of an upstream signal provided between the second output terminal and the input terminal. Second filter means having characteristics to be adjusted, level adjusting means provided between the branch terminal of the branching means and the second output terminal for adjusting the level of the branch output of the branching means, Characteristics to pass the frequency band And a third filter means,
A down signal input from the input terminal is output to the first output terminal via the first filter means and the branch means, and the first filter means, a branch terminal of the branch means, An up signal output from the second output terminal via the level adjusting means and the third filter means and input from the second output terminal is output from the input terminal via the second filter means. Has been output.

[0013] In the distribution compensator of the present invention,
The second filter means may include an amplification means for amplifying the upstream signal.

According to the present invention, the level of the downstream signal branched by the branching means is adjusted and output from the second output terminal to which the cable modem is connected. The down signal whose level has been reduced to the specified reception level by the means is received by the cable modem. Then, the specified level up signal output from the cable modem input from the second output terminal passes through the second filter almost without being attenuated and is output from the input terminal. This allows the cable modem to receive the downlink signal at the prescribed reception level, and to transmit the transmission signal from the cable modem with the attenuation of the uplink signal at the prescribed level being minimized. Further, the downstream signal can be distributed to the home terminal without being attenuated. Further, since the level of the downstream signal can be adjusted by the level adjusting means, the cable modem can receive the downstream signal at the desired level of the downstream signal. For this reason, a cable modem having a different prescribed reception level can be used.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A distribution compensator according to the present invention
FIG. 1 shows a configuration example of a CATV system when applied to a TV system. In the CATV system 100 shown in FIG.
From “a”, various program signals and various data are transmitted to the trunk lines constituting a plurality of cable television networks. The various program signals and various data transmitted to the main line are propagated along the main line, amplified by the bidirectional main line amplifiers (AMP) 2a and 2b provided at predetermined distances, and transmitted with equalized frequency characteristics. Go.

This trunk line is branched into branch trunk lines by branch amplifiers and branch devices and propagates along the branch trunk line, and is further distributed by distributors via tap-offs 3a and 3b, as well as protectors 4a and 4b and main trunks. It is drawn into each facility or each home via distribution compensators 10a and 10b, which will be described later, according to the present invention. Thereby, each facility and each home can receive various program signals and various data. Home terminals 5a and 5b for each facility and home
Are provided, and various program signals are decoded or selected in the home terminals 5a and 5b. Thereby, a desired program can be enjoyed by the televisions 7a and 7b connected to the home terminals 5a and 5b.

Further, personal computers 8a and 8b installed in facilities and homes are connected to the cable television network, and the personal computers 8a and 8b are connected to the cable modems 6a and 8b.
6b. In addition, the protectors 4a, 4b
The coaxial cable drawn from the distribution compensator 10a, 1
0b, which are connected to the input terminals of the distribution compensators 10a and 10b.
One distributed output of the downstream signal distributed by the above is supplied to the home terminals 5a and 5b, and the other distributed output is supplied to the cable modems 6a and 6b. The distribution output supplied to the home terminals 5a and 5b is converted into a level-adjusted downstream signal as described later, and is output from the cable modem 6a.
The distribution output supplied to 6b is a down signal adjusted to a specified level. Also, the cable modems 6a, 6
b sent from the distribution compensators 10a and 10b
Through the input terminal without attenuating the protector 4a,
4b.

As described above, when the distribution compensators 10a and 10b distribute the downlink signal, the downlink signal from the cable television network is attenuated to a specified level and received by the cable modems 6a and 6b. Home terminal 5 at a sufficient level without attenuation
a, 5b. This prevents the cable modems 6a and 6b from being over-input and causing a data error, and the home terminals 5a and 5b can output good image and audio signals to the televisions 7a and 7b. . Since the transmission signals of the cable modems 6a and 6b, which are the upstream signals, pass through the distribution compensators 10a and 10b without being attenuated, the transmission signals from the cable modems 6a and 6b are at a specified transmission level without being attenuated. It will be transmitted to cable television networks.

The CATV system 1 configured as described above
At 00, for example, when the personal computer 8a is connected to the Internet, the transmission signal transmitted from the personal computer 8a is transmitted to the cable modem 6a, the distribution compensator 10a, the security device 4a.
The signal goes up to 1 via the cable television network to the CATV center at the prescribed transmission level transmitted from the cable modem 6a without being attenuated via a. Then, in the CATV center 1, the router 1 provided
b to the Internet provider 9. In this way, the personal computer 8a installed in the facility or home is connected to the Internet via the Internet provider 9.

Then, various data taken in through the Internet provider 9 are transmitted to the C through the router 1b.
The data is taken into the ATV center 1 and transmitted from the head end 1a to the main line. As a result, the signal is attenuated to a specified level by the distribution compensator 10a via the cable television network and further via the tap-off 3a and the protector 4a, and is received by the cable modem 6a without causing a data error. Thus, the personal computer 8a is connected to the Internet and can receive Internet services. PC 8
Similarly, the cable modem 6b and the distribution compensator 10b
You will be able to connect to the Internet via. If the CATV center 1 can provide other network services, the CA
Other network services can be received from the CATV center 1 by connecting the personal computers 8a and 8b installed in each facility and each home to the TV center 1 via a cable television network.

Next, FIG. 2 is a functional block diagram showing an example of the configuration of the distribution compensator 10 according to the embodiment of the present invention.
As shown in FIG. 2, the distribution compensator 10 according to the present invention
One input terminal IN and two output terminals OUT1 and OUT2
And An input terminal IN is provided with a first high-pass filter (HP
F) 21 and a low-pass filter (LPF) 29 having a characteristic of passing the frequency band of the upstream signal are connected.
An equalizer (EQ) 23 for compensating a frequency characteristic of a downstream signal via a splitter 22 is provided to the first high-pass filter 21.
Are further connected, and a variable attenuator 24 for adjusting the level of the downstream signal, and a downstream amplifier 25 for amplifying the downstream signal
Are cascaded. Then, a second high-pass filter (HPF) 26 having a characteristic of passing the frequency band of the downstream signal is cascade-connected to the downstream amplifier 25, and the output of the second high-pass filter 26 is output from the first output terminal OUT1. I have.

The low-pass filter 29 has an input terminal I
It is connected between N and the second output terminal OUT2.
Note that the branch terminal of the branching device 22 and the second output terminal OUT2
Between the variable attenuator 27 and a third high-pass filter (HPF) 2 having a characteristic of passing the frequency band of the downstream signal.
8 is connected.

The operation of the thus configured distribution compensator 10 according to the present invention will be described. The downstream signal input to the input terminal IN passes through the first high-pass filter 21, passes through the splitter 22 with almost no attenuation, and is supplied to the equalizer 23. The equalizer 23 equalizes the frequency characteristics of the downlink signal, and the equalizer 23 is provided with a changeover switch for switching the equalizer characteristics. By switching this switch, the best frequency characteristics are obtained. Then, the level is adjusted by the variable attenuator 24 and the downstream amplifier 25 so that the level of the downstream signal becomes a sufficient level. The level-adjusted downstream signal passes through the second high-pass filter 26 and is transmitted from the first output terminal OUT1 to the home terminals 5a and 5b. As a result, the home terminal 5
In a and 5b, the frequency characteristics are equalized and a sufficient level of a down signal can be received. Note that the downstream signal is blocked by the low-pass filter 29 and is not output from the second output terminal OUT2 via the low-pass filter 29.

Also, from the branch terminal of the branching device 22, 10
The downstream signal is branched by being attenuated by about dB, and the branched downstream signal is supplied to the second output terminal O in the variable attenuator 27.
Level adjustment is performed so that the level of the downstream signal output from the UT 2 becomes the specified reception level of the cable modems 6a and 6b. The level-adjusted downstream signal passes through the third high-pass filter 28 and is output from the second output terminal OUT2. The output from the second output terminal OUT2 is received by the cable modems 6a and 6b. As a result, the cable modems 6a and 6b receive the downlink signal whose level has been adjusted to the prescribed reception level.

The upstream signal transmitted from the cable modems 6a and 6b at a specified level is supplied to the low-pass filter 29.
And output from the input terminal IN. In addition, the upstream signal input from the second output terminal OUT2 is blocked by the third high-pass filter 28 to prevent further transmission. Also, the upstream signal output from the low-pass filter 29 is blocked by the first high-pass filter 21 to prevent further transmission. As a result, the upstream signals transmitted from the cable modems 6a and 6b at the prescribed level are transmitted from the input terminal IN of the distribution compensator 10 to the cable television network without substantially attenuating and go up to the center 1. .

The low-pass filter 29 is connected to the low-pass filter 29 shown in FIG.
The configuration shown in FIG. The low-pass filter 29 shown in FIG. 3A includes a first low-pass filter LPF1 and a second low-pass filter LPF1.
Is provided between the low-pass filter LPF2 and the upstream amplifier AMP for amplifying the upstream signal. As a result, the level of the upstream signal can be enhanced and transmitted from the distribution compensator 10 to the cable television network. FIG. 3B shows an example of a circuit configuration of the variable attenuator 24 and the variable attenuator 27. Variable attenuator 24 (2
7) is a first resistor R1 connected in series between the input and output terminals.
A variable resistor VR1, and a second resistor R2 connected in series between the variable resistor VR1 and the ground. Input terminal a
Is connected to the variable terminal of the variable resistor VR1, and by varying the variable resistor VR1, a level-adjusted downstream signal is output from the output terminal b. The level adjustment range is determined by the first resistor R1 and the second resistor R2.

The input terminal IN and the first output terminal OUT1 in the distribution compensator 10 of the present invention shown in FIG.
Frequency characteristics of the input terminal IN and the second output terminal OUT
An example of the frequency characteristic of No. 2 is shown in FIG. 4, and the operation of the distribution compensator 10 will be described with reference to FIG. As shown in FIG. 4, the frequency characteristic of the input terminal IN-the first output terminal OUT1 is a substantially flat frequency characteristic at 70 to 770 MHz covering the downstream frequency band in the cable television network, and the gain is about 20 dB. It has been. As a result, various program signals can be received at sufficient levels in the home terminals 5a and 5b. Further, the frequency characteristics of the input terminal IN and the second output terminal OUT2 are obtained at a frequency of 5 to 55 MHz covering an upstream frequency band in a cable television network.
It has a pass loss of 2.5 dB or less, and has a substantially flat frequency characteristic with a pass loss of about -12 dB at 70 to 770 MHz covering the downstream frequency band. Thereby, the cable modems 6a, 6
b, the down signal whose level has been adjusted to the prescribed reception level is received, and the up signal transmitted at the prescribed level from the cable modems 6a and 6b is transmitted from the input terminal IN of the distribution compensator 10 to the cable without substantial attenuation. It will be sent to the TV network.

[0028]

As described above, according to the present invention, the level of the downstream signal branched by the branching means is adjusted and output from the second output terminal to which the cable modem is connected. The level signal is lowered by the level adjusting means, and the down signal having the specified reception level is received by the cable modem. Then, the specified level up signal output from the cable modem input from the second output terminal passes through the second filter almost without being attenuated and is output from the input terminal. This allows the cable modem to receive the downlink signal at the prescribed reception level, and to transmit the transmission signal from the cable modem with the attenuation of the uplink signal at the prescribed level being minimized. Further, the downstream signal can be distributed to the home terminal without being attenuated. Further, since the level of the downstream signal can be adjusted by the level adjusting means, the cable modem can receive the downstream signal at the desired level of the downstream signal. For this reason, a cable modem having a different prescribed reception level can be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a CATV system when a distribution compensator according to the present invention is applied to a CATV system.

FIG. 2 is a diagram illustrating an example of a configuration of a distribution compensator according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a modified example of a low-pass filter in a distribution compensator according to an embodiment of the present invention, and a circuit configuration of a variable attenuator.

FIG. 4 is a diagram illustrating an example of a frequency characteristic in the distribution compensator according to the embodiment of the present invention;

FIG. 5 is a diagram showing a conventional configuration example of a CATV system.

FIG. 6 is a diagram showing a conventional distribution method for distribution to a home terminal and a cable modem.

FIG. 7 is a diagram showing a configuration of a conventional distributor for distributing to a home terminal and a cable modem.

[Explanation of symbols]

1,51 Center 1a, 51a Headend 1b, 51b Router 2a, 2b, 52a, 52b Bidirectional trunk amplifier (AM
P) 3a, 3b, 53a, 53b Tap-off 4a, 4b, 54a, 54b Protector 5a, 5b, 55a, 55b Home terminal 6a, 6b, 56a, 56b Cable modem 7a, 7b, 57a, 57b Television 8a, 8b, 58a , 58b Personal computer 9, 59 Internet provider 10, 10a, 10b Distribution compensator 21 First high-pass filter 22 Splitter 23 Equalizer 24 Variable attenuator 25 Down-amplifier 26 Second high-pass filter 27 Variable attenuator 28 Third high-pass filter 29 low-pass filter 70 filter unit 80 distributor 100, 200 CATV system 102, 113 down-amplifier 104 distributor 111 brancher 101, 103, 112, 114 high-pass filter

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroyuki Tanabe 4-7-4 Kitamachi, Warabi-shi, Saitama Japan Antenna Co., Ltd. Warabi Plant F-term (reference) 5C056 FA02 FA03 FA05 GA01 GA05 HA01 HA14 HA15 5C064 BA01 BB05 BC14 BD01 BD07 BD08

Claims (2)

[Claims] 1. A down signal input from an input terminal is transmitted to a first terminal.
A distribution compensator that distributes an upstream signal input from the second output terminal to the output terminal and a second output terminal, and outputs the upstream signal from the input terminal, wherein the input terminal and the first output A first filter having a characteristic of passing a frequency band of a downstream signal provided between the first filter and a terminal; a branching unit for branching an output of the first filter; a second output terminal and the input terminal A second filter unit having a characteristic of passing a frequency band of an uplink signal provided between the first and second output terminals; and a branch of the branching unit provided between a branch terminal of the branching unit and the second output terminal. A level adjusting means for adjusting an output level; and third filter means having a characteristic of passing a frequency band of the downstream signal, wherein the downstream signal input from the input terminal is connected to the first filter means and the branch. Means And output from the second output terminal via the first filter means, the branch terminal of the branch means, the level adjusting means and the third filter means. A distribution compensator wherein the upstream signal input from the second output terminal is output from the input terminal via second filter means. 2. The distribution compensator according to claim 1, wherein said second filter means includes amplification means for amplifying said upstream signal.