JPH1155644A - Level controller for data communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the linearity and stability of a control characteristic of a continuous variable level control circuit by compensating control data with compensation data, converting the compensated control data into an analog signal and supplying it as a control signal to a level varying means. SOLUTION: Attenuation compensation data 12 from a 1st data storing device 11 for attenuation quantity compensation is added to control data that is generated based on the control from a CATV center so that control quantity may be linear, and a microcontroller 85 creates level control data which has been calibrated by it. A D/A converter 89 converts the created level control data into an analog signal and supplies it to a voltage control amplifier 88'. By this, the apparent linearity of a control characteristic is improved. As a result of this, it is possible to control the level of a cable modem 60 by control data based on an instruction from the CATV center, to add the data 12 and to perform level control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a data communication level control device suitable for a cable modem for performing data communication using a CATV network.

[0002]

2. Description of the Related Art Existing CATV (Cable Television) systems transmit audio and video signals in an analog manner. Recently, large transmission capacity has been promoted by combining a coaxial cable and an optical fiber cable as a transmission path. ing. Focusing on the increase in capacity and bidirectionality of CATV,
It can be effectively used as a digital transmission path such as a C-LAN (computer local area network), and a data communication system using a CATV network is being constructed.

A configuration of a data communication system using such a CATV network will be described with reference to FIG.

[0004] The CATV center 51 mainly receives and retransmits a broadcast program, and a center that independently produces a television program and transmits a television signal composed of video and audio signals of an independent program such as a movie. The system unit 52 and C
HFC (Hybrid Fidelity) which is an interface with the ATV network
(ber and Coaxial) interface unit 53 and a modem control unit 54.

[0005] The HFC interface 53 of the CATV center 51 is connected to a CATV network 55 such as an HFC. The CATV network 55 has a plurality of fiber branch units 56 for branch distribution to each user. An optical fiber cable is used for a trunk line between the CATV center 51 and the fiber branch section 56,
A coaxial cable is used between the fiber branching section 56 and the user.

The fiber branching section 5 of the CATV network 55
6 is connected to each user 57, and the user 57 is connected to a television receiver 59 via an adapter 58 for receiving a television program, and further connected to a computer device 61 via a cable modem 60. I have.

The CATV center 51 is connected to a PC-LAN 66 such as the Internet 63, an online service system 64 and a security service system 65 via an optical network 62 composed of optical fibers.

In the CATV system having such a configuration, the CATV center 51 transmits a C
When transmitting the television signal and various information signals (hereinafter, referred to as downlink signals) via the ATV network 55,
Usually, a frequency band of 60 to 860 MHz is used. On the other hand, CA 57 is sent from user 57 to CATV center 51.
When transmitting various information signals (hereinafter, referred to as uplink signals) via the TV network 55, a frequency band of 5 to 50 MHz is normally used.

From the CATV center 51 to the user 57
The downlink signal transmitted to the PC includes the television signal and various information signals related to the television signal, such as a user identification signal, and various information data signals from the PC-LAN 66 connected via the CATV center 51. Exists.

On the other hand, from the user 57, the CATV center 5
The upstream signal transmitted to the PC 1 includes an identification signal relating to the reception of a television signal and a data signal for exchanging various information data with the PC-LAN 66 from the computer device 61.

The CATV center 51 and the user 57
QPS to increase the amount of transmission of signals exchanged between
K (Quadrature Phase Shift Keying) and QAM (Quadrature
Digitally modulated signals such as reAmplitude Modulation) are used.

[0012] In addition to the above-mentioned signals,
Control data for assigning the transmission frequency, transmission level, transmission timing, and the like of the uplink signal from each user 57 to the CATV center 51 is also transmitted.

The CATV center 51 and each user 57
Between, the signal transmission loss differs for each user 57 depending on the home wiring, the trunk equipment of the CATV network 55, and the distance. For this reason, it is necessary to adjust the level of the upstream signal reaching the CATV center 51 from each user 57 within a certain appropriate level, and the control from the CATV center 51 makes the level of the signal reaching the CATV center 51 from each user 57 equal. Level control is performed individually.

As a specific configuration thereof, a cable modem 60 connected to a computer device 61 installed in a user 57 will be described with reference to FIG.

The cable modem 60 is provided with an input terminal 71 to which a coaxial cable is connected from the fiber branching section 56 of the CATV network 55.
A demultiplexer 72 for demultiplexing the downstream signal and the upstream signal is connected. The downstream signal split by the splitter 72 is converted into an IF signal by a high-frequency signal receiving unit (hereinafter, referred to as an RF receiving unit) 73, and the IF signal is converted into an analog / digital converter (hereinafter, A / D converter). The analog signal is converted into a digital signal at 74. The signal converted into a digital signal by the A / D converter 74 is demodulated by a QPSK or QAM demodulator 75 and output to a downstream signal selector 76 and a frame synchronization detector 77. The downstream signal selected by the downstream signal selector 76 is subjected to error correction of the signal by the error corrector 78, decrypted by the encryption processor 79, and input to the buffer memory 80. The buffer memory 80 stores the reception selected and decrypted information data, is converted into computer format information corresponding to the computer device 61 by an internet interface unit 81, and is output from the output terminal 82 to the computer Output to the device 61.

On the other hand, the information input from the computer device 61 is converted into computer format information corresponding to the CATV network 55 or the PC-LAN 66 by the internet interface unit 81,
It is stored in the buffer memory 80. The stored information is encrypted by the encryption processor 79 and the error correction device 83
After the error correction, the output is output to the upstream signal format / timing controller 84. In the upstream signal format / timing controller 84, the upstream signal format stored in the buffer memory 80 is read out by the microcontroller 85 formed of a microcomputer element, the format is changed, and the transmission timing of the upstream signal is determined. Control. The output of the upstream signal format / timing controller 84 is a QPSK or QAM modulator 86
Is modulated by a digital-to-analog converter (hereinafter, D /
The digital signal is converted into an analog signal by an A converter 87, and is transmitted from the input terminal 71 to the CATV network 55 via a high frequency signal level variable device (hereinafter, referred to as an RF transmitter) 88 and a duplexer 72. Is output.

The upstream signal transmitted via the CATV network 55 is received by the CATV center 51 and output to the PC-LAN 66 via the optical network 62. At this time, the modem control unit 54 of the CATV center 51 detects the reception level of the upstream signal of the user 57, and if the reception level is lower than an appropriate value, the cable modem enters the predetermined signal band of the downstream signal. The cable modem 60 that transmits an instruction signal to increase the output of the uplink signal from the cable 60 and receives the instruction signal performs processing according to the processing procedure of the uplink signal, and then controls the microcontroller 85 to increase the level of the uplink signal. After a signal is generated and the control signal is converted from a digital signal to an analog signal by a D / A converter 89, the signal is supplied to the RF transmitter 88 and controlled so as to increase the level of the upstream signal.

If the upstream signal transmitted from the cable modem 60 to the CATV center 51 is equal to or more than an appropriate value, control is performed so that the output level from the cable modem 60 is reduced.

In this way, the transmission level of the upstream signal from the cable modem 60 is optimized based on the control from the CATV center 51.

FIG. 10 shows an output level adjusting circuit of the RF transmitter 88. As the RF transmitter 88, FIG.
10 (A) and the voltage controlled amplifier 88 'shown in FIG.
As shown in (b), a variable attenuator 88 "is generally used. The voltage control amplifier 88 'and the variable attenuator 8 are used.
8 ″ is a modem control unit 54 of the CATV center 51.
Is read by the microcontroller 85, a level control signal is generated based on the read signal, and is converted into an analog signal. The voltage control amplifier 88 'or the variable attenuator 88 " Level control terminal 9
0 is input to adjust the output level.

The voltage controlled amplifier 88 'and the variable attenuator 8
Reference numeral 8 ″ denotes an analog output level adjuster that can be continuously varied by voltage control. On the other hand, the voltage controller 88 ′ or the variable attenuator 8 output from the microcontroller 85.
The level control signal for adjusting the output level of 8 ″ is digital data of 8 to 10 bits. This digital data is converted into an analog voltage by the D / A converter 89 and input to the level control terminal 90. Is done.

The voltage controller 88 'and the variable attenuator 88 "
Does not have a uniform attenuation GR over the entire range of the level control voltage V, as shown in FIG. 10C, and the attenuation varies depending on the control voltage. That is, the voltage controller 88 'and the variable attenuator 88 "have a difference in sensitivity depending on the control voltage.

On the other hand, when the digital data is a-bit data, the output voltage range of the D / A converter is ΔV (DAC)
Then, the change amount per 1 LSB of the minimum change of the digital data, that is, the minimum step voltage is ΔV (DAC) /
^2a . Therefore, the maximum value ΔGRmax of the variation of the minimum voltage step per 1 LSB of the digital data is defined so that the control step of the voltage control amplifier 88 ′ or the variable attenuator 88 ″ is not coarsened.
The operation is performed within the range of the accuracy of the control step from 0 to GRmax / LSB.

However, even if the accuracy of the control step is increased, as described above,
8 ′ or the variable attenuator 88 ″, the attenuation level, that is, the linearity of the control sensitivity cannot be secured in the entire variable range of the level control voltage.
The control amount for B is not constant, and the CATV center 5
In response to the increase / decrease instruction signal to the cable modem 60 from 1, the difference value of the output of the RF transmitter 88 cannot be controlled at once, and the difference value is repeatedly controlled several times. Therefore, there is a problem that it takes time to reach a desired upstream signal level.

Further, the voltage controlled amplifier 88 'or the variable attenuator 88 "constituting the RF transmitter 88 has a large temperature lift and has a frequency characteristic in an up band of 5 to 50 MHz, so that stable accuracy can be obtained. High level control was difficult, and the control range was 30-40 db.
And it was difficult to realize a wider variable range. In addition, it is necessary to select and use the elements constituting the voltage control amplifier 88 'and the variable attenuator 88 "with little variation and time-dependent change. There is a problem that it is difficult to make the control characteristics uniform.

[0026]

When a continuously variable analog voltage control amplifier or a variable attenuator is used for an upstream signal transmitter of a cable modem connected to a CATV network, the entire variable range of the upstream signal transmitter is limited. In addition, the linearity of the control sensitivity cannot be ensured, and it is not possible to quickly respond to a request to increase or decrease the uplink signal level transmitted from the CATV center,
Due to the variation of the elements constituting the upstream signal transmitter and the difference in temperature drift, a difference in control sensitivity also occurs between the upstream signal transmitters for each user, and a signal having a signal level within an appropriate value required by the CATV center is stabilized. There was a problem that could not be secured.

An object of the present invention is to provide a level control device for data communication which improves the linearity and stability of control characteristics of a continuously variable level control circuit and enables high-accuracy and wide-range level control. I have.

[0028]

Means for Solving the Problems C through a two-way communication network
The two-way communication network and the terminal device are disposed so as to couple the ATV center and the terminal device, and the CA
A cable modem having a receiving unit for receiving a downlink signal from a TV center, and a transmitting unit for transmitting an uplink signal to the CATV center; and controlling a transmission level of the uplink signal output from the transmitting unit by a control signal. Controllable level varying means, control data generating means for generating first control data based on control from the CATV center to vary the transmission level of the uplink signal, and characteristics of the level varying means. In order to correct the transmission level of the uplink signal in accordance therewith, a correction data storage means for storing preset correction data and the first control data are corrected by the correction data stored in the storage means. Control signal supply means for converting the obtained control data into an analog signal and supplying it as a control signal to the level varying means A data communication level control apparatus characterized by comprising a.

[0029]

Embodiments of the present invention will be described below with reference to the drawings with reference to FIGS. The same parts as those in FIG. 10A are denoted by the same reference numerals, and detailed description thereof will be omitted. The RF transmitter 88 will be described using an example using a voltage control amplifier 88 '.

FIG. 1 is a block diagram showing a first embodiment of a data communication level control device according to the present invention.

In the first embodiment of the present invention shown in FIG. 1, a microcontroller 85 for controlling the amplification level of the voltage control amplifier 88 'is provided. The microcontroller 85 is constituted by a microcomputer including a central processing unit (CPU), a memory, and the like, and outputs first control data for controlling the amount of attenuation of the voltage control amplifier 88 ′ based on control from the CATV center 51. Generate. Further, the data storage 11 is connected to the microcontroller 85, and the data storage 1
1 stores data 12 for correcting the control characteristics of the voltage control amplifier 88 '. The first control data includes:
The correction data is stored in a memory area in the microcontroller 85, and the correction data is used to determine the maximum slope of the control characteristic of the voltage control amplifier 88 'and the minimum level control required for the cable modem 60 from the modem control unit 54 of the CATV center 51. It has a resolution based on the number of bits determined from the step width. This correction data 12 models the standard control characteristics of the voltage controlled amplifier 88 'of the cable modem 60,
The data is stored in the data storage 11 as correction data.

In the level control device configured as described above, the data storage unit 11 controls the first control data generated under the control of the CATV center 51 so that the control amount becomes linear. , And the calibrated level control data is generated by the microcontroller 85. Therefore, the generated level control data is transferred to the D / A converter 89.
By converting the control signal into an analog signal and supplying the analog signal to the voltage control amplifier 88 ', the apparent linearity of the control characteristic can be improved.

As a result, the cable modem 6 is controlled by the first control data based on the instruction from the CATV center 51.
0 can be controlled, and the level can be controlled in consideration of the correction data 12, so that a difference occurs between the arrival signal level desired by the CATV center 51 from the RF transmitter 88 and the required level. However, since the difference between the levels can be directly provided as differential data from the CATV center 51 to the RF transmitter 88, the RF transmitter 88 must be converged to the output level of the upstream signal required by the CATV center 51 in a short time. Can be.

Next, a second embodiment of the present invention will be described with reference to FIG. The first embodiment of the present invention is different from FIG. 1 in that second and third correction data storages 13 and 16 are provided in addition to the first correction data storage 11, and
The point is that a temperature detector 14 for detecting a temperature change inside the cable modem 60 is added. The temperature detector 14 includes:
The cable modem 60 has a function of detecting a temperature change of the voltage control amplifier 88 '. The second correction data storage 13 stores temperature compensation data 15 for controlling the output level of the voltage control amplifier 88 'in response to a change in temperature. Further, the cable modem 6
To correct the level fluctuation due to the frequency characteristic of the zero voltage control amplifier 88 ′, the frequency characteristic data 17 is stored in the third correction data storage 16.

With such a configuration, the cable modem 6
0 or a change in the output level due to a change in the ambient temperature of the voltage control amplifier 88 '.
, The temperature detected by the temperature detector 14 and the temperature compensation data 1 in the second correction data storage 13.
5, the output level can be controlled in accordance with the temperature change.

Further, the fluctuation of the output signal level caused by the frequency characteristic of the voltage control amplifier 88 ′ can be corrected by using the frequency characteristic data 17 of the third correction data storage 16.

As a result, the accuracy and stability of the signal level control can be improved with respect to the temperature change of the voltage control amplifier 88 'and the level fluctuation due to the transmission frequency.

A third embodiment of the present invention will be described with reference to FIG. The third embodiment has a high-frequency signal measuring instrument 18 such as a spectrum analyzer or a power meter and a modem controller 19 for controlling the cable modem 60 as external devices of the cable modem 60. The high-frequency signal measuring device 18 measures the frequency and the transmission signal level of the upstream signal transmitted from the voltage control amplifier 88 ′, and is provided as one of the facilities for manufacturing the modem 60. The modem controller 19 controls the high-frequency signal measuring device 18 and controls the voltage-controlled amplifier 8
The output signal frequency and output signal level data from 8 'are read, correction data is created based on the read data, and converted into an appropriate format.

Since the output of the high-frequency signal measuring instrument 18 changes according to the characteristics of the voltage control amplifier 88 ', the correction data becomes optimum correction data for the voltage control amplifier 88'. Then, the correction data is transmitted to the micro controller 85 of the cable modem 60, and the micro controller 85 stores the correction data in the correction data storage 11 based on the data of the modem controller 19.

In such a configuration, since the correction data stored in the correction data storage 11 is created by measuring the level control characteristics for each cable modem 60, its internal constituent elements or functions The output level can be corrected so as to suppress the variation in the characteristics of each modem caused by the change with time.

A fourth embodiment of the present invention will be described with reference to FIG. This fourth embodiment is different from the first embodiment shown in FIG.
In addition, a signal line switch 21 is provided between the voltage variable amplifier 88 'of the cable modem 60 and the CATV network 55, and the CATV network 55 is connected to one fixed terminal of the switch 21. The level detector 22 and the A / D converter 23 are arranged in series at the other fixed terminal, and are connected to the microcontroller 85 of the cable modem 59. Further, the movable terminal of the switch 21 is connected to the microcontroller 85.

In such a configuration, the switch 2
1 is normally connected to the CATV network 55 side,
Under the control of the microcontroller 85, it is connected to the level detector 22 at a predetermined timing.
When the output of the voltage variable amplifier 88 is connected to the level detector 22, the microcontroller 85 outputs a command to control the level of the voltage variable amplifier 88, and sequentially varies the output signal level. The sequentially controlled signal levels are detected by the level detector 22, taken into the microcontroller 85 via the A / D converter 23, and stored as data in which correction data is generated based on the taken data. Is stored in the container 11. Accordingly, the correction data is corrected each time the level is detected. In other words, the control characteristics of the output signal level of the variable voltage amplifier 88 change due to temperature characteristics and aging, so the correction data is stored as correction data according to the latest control characteristics of the variable voltage amplifier 88.

Normally, the switch 21 is set to the CATV
The output signal level of the voltage variable amplifier 88 is controlled based on control from the CATV center 51. At this time, the correction data stored in the data storage 11 is read out, and the correction data The output level of the variable voltage control amplifier 88 is corrected according to the control characteristic indicated by

The switch 21 may be switched to the level detector 22 when the cable modem 60 is started or at an appropriate timing during normal operation.

A fifth embodiment of the present invention will be described with reference to FIG. This fifth embodiment is different from the first embodiment of the present invention shown in FIG. 1 in that the voltage variable amplifier 88 'and the CAT
The step variable fixed attenuator 25 is arranged between the V network 55 and the fixed attenuator 25. The control of the fixed attenuator 25 is performed by control data from the microcontroller 85 of the cable modem 60.
One of the fixed attenuators 25 is a short-circuiting piece, and the other is composed of an attenuating element piece having a predetermined attenuation. The short-circuiting piece and the attenuating element piece can be switched by a changeover switch. The amount of attenuation is set to be equal to or less than the variable range of the output level of the upstream signal from the voltage conversion amplifier 88 '.

In this configuration, when the amount of attenuation of the output level from the variable voltage amplifier 88 ′ whose level is controlled by the correction data 12 from the microcontroller 85 and the data storage 11 is small, the fixed Attenuator 25
Supplies control data from the microcontroller 85 so that the output signal passes through the short-circuiting piece, and the fixed attenuator 25
When it is necessary to attenuate the signal level to be output to the CATV network 55 more, control data for switching the fixed attenuator 25 to an attenuating element piece is supplied from the microcontroller 85.

As a result, at least two levels of level control can be ensured by selecting the switching of the fixed attenuator 25. It is apparent that the fixed attenuator 25 can secure a plurality of stages of attenuation ranges by using a plurality of attenuation elements having different attenuation amounts.

Next, a sixth embodiment of the present invention will be described with reference to FIG. In the sixth embodiment, a plurality of variable voltage amplifiers 88 'of the first embodiment of FIG. 1 are arranged in series.

A first variable voltage amplifier 91 and a second voltage control amplifier 92 are connected in series, and the level control terminals 93 and 94 of each of the voltage control amplifiers 91 and 92 have a D / A
Converters 95 and 96 are connected, and D / A converter 9
5 and 96 are connected to the microcontroller 85. Further, a first correction data storage 11 and a first 'correction data storage 11' are connected to the microcontroller 85,
Attenuation correction data 12 is stored in each of the correction data storages 11 and 11 '.

In such a configuration, when the amount of attenuation of the up signal required from the CATV center 51 is small, the microcontroller 85 sends the first voltage control amplifier 91 and the first correction data storage 11 to each other. The level control of the first voltage control amplifier 91 is performed using the correction data 12. At this time, the second voltage control amplifier 92 is supplied with the level control data with the minimum attenuation from the microcontroller 85. Next, when the attenuation of the upstream signal required from the CATV center 51 is large and exceeds the maximum attenuation of the first voltage control amplifier 91, the attenuation of the second voltage control amplifier 92 is added. Thereby, the level control range can be expanded. Further, the addition of the transition from the level control range of the first voltage control amplifier 91 to the level range of the second voltage control amplifier 92 can be continuously expanded by the control of the microcontroller 85. Become. FIG. 6 showing the sixth embodiment is different from FIG.
Although the description has been made using the first and second voltage controlled amplifiers 91 and 92, the level control range can be expanded by providing a plurality of the same type of voltage controlled amplifiers between the first and second voltage controlled amplifiers 91 and 92. It is possible.

Further, a seventh embodiment of the present invention will be described with reference to FIG. In the seventh embodiment, similarly to the sixth embodiment of FIG. 6, a plurality of voltage controlled amplifiers 91 and 92 are connected in series and connected to level control terminals 93 and 94 of the voltage controlled amplifiers 91 and 92. The D / A converter 95 ', the microcontroller 85, and the correction data storage 11 are commonly used. That is, the first and second voltage controlled amplifiers 9
1 and 92 are the microcontroller 85 and the D / A converter 9
Level control is performed simultaneously at 5 '.

In such a configuration, since the first and second voltage controlled amplifiers 91 and 92 are level-controlled by the common control signal from the microcontroller 85 and the D / A converter 95 ', both voltage controlled amplifiers 91 and 92 are controlled. The attenuation amount of the control amplifiers 91 and 92 is added, and the level control range can be expanded. It goes without saying that the data such as the attenuation correction stored in the correction data storage 11 stores the correction data in consideration of the two voltage control amplifiers 91 and 92.

As described above, when data communication is performed using a bidirectional CATV communication network, the transmission level of an uplink signal transmitted to a CATV center via a cable modem is controlled within a predetermined level range. Conventionally, the attenuation characteristic or the sensitivity characteristic of the RF transmitter for uplink signal transmission could not obtain linearity over the entire range, but the present invention stores correction data for correcting the linearity of the RF transmitter. The linearity of the attenuation characteristic or the sensitivity characteristic is improved for the level control data transmitted from the CATV center over the entire control target range, and the level control data transmitted from the CATV center is promptly obtained in response to the level control request from the CATV center. It became possible to converge to the output level.
In addition, by storing correction data for temperature and frequency in addition to the attenuation characteristics of the RF transmitter in the correction data storage unit, it is possible to expand the level control range and to perform level control with higher precision than before. became. Further, a wide range of transmission output level control has become possible.

In the above description of the present invention, a voltage controlled amplifier is used as the RF transmitter, but a variable attenuator having an analog output level adjusting function may be used. When this variable attenuator is used, it goes without saying that correction data considering the attenuation characteristics of the variable attenuator is used.

In the above description, the correction data storage unit according to the third and subsequent embodiments of the present invention has been described using only the attenuation correction data. However, data such as temperature compensation and frequency characteristics are also stored in the correction data storage unit. It is clear that it is also possible to use it.

[0056]

According to the present invention, it is possible to perform level control in consideration of the level control characteristics of the high-frequency signal level varying means of the RF transmitter of the cable modem, to converge in a short time to the upstream signal level required by the CATV center, and Thus, highly accurate level control can be performed. In addition, the level control range can be expanded, and the level control can be easily performed even when the cable modem changes over time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a data communication level control device according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a third embodiment of the present invention.

FIG. 4 is a block diagram showing a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing a sixth embodiment of the present invention.

FIG. 7 is a block diagram showing a seventh embodiment of the present invention.

FIG. 8 is a block diagram showing an overall configuration of a data communication system using a conventional bidirectional CATV network.

FIG. 9 is a block diagram showing a circuit configuration of a conventional cable modem.

FIG. 10 is a block diagram and a damping characteristic diagram for explaining a conventional problem.

[Explanation of symbols]

11: Attenuation correction first data storage unit, 12: Attenuation correction data, 13: Temperature correction second data storage unit, 1
4 temperature detector, 15 temperature correction data, 16 third data storage for frequency correction, 17 frequency correction data, 51 CATV center, 55 CATV network, 60
... Cable modem, 85 ... Microcontroller, 88 ... RF
Transmitter, 89 ... D / A converter, 90 ... Level control terminal.

Claims (8)

[Claims] 1. A terminal arranged between a bidirectional communication network and a terminal device so as to couple the CATV center and the terminal device via the bidirectional communication network, and receiving a downlink signal from the CATV center. A cable modem having a receiving unit and a transmitting unit for transmitting an uplink signal to the CATV center; a level varying unit capable of controlling a transmission level of the uplink signal output from the transmitting unit by a control signal; In order to vary the transmission level of the uplink signal, the CA
Control data generating means for generating first control data based on control from a TV center; and correction data set in advance for correcting the transmission level of the uplink signal according to characteristics of the level varying means. Correction data storing means for correcting the first control data with the correction data stored in the storage means, converting the corrected control data into an analog signal, and supplying the analog signal as a control signal to the level varying means. A data communication level control device, comprising: 2. The level control device for data communication according to claim 1, wherein said control data generation means, said correction data storage means and said control signal supply means are constituted by a microcomputer. 3. The level control device for data communication according to claim 1, wherein said level varying means comprises a voltage controlled amplifier or a variable attenuator. 4. The apparatus according to claim 1, wherein the correction data is data capable of correcting at least one of a temperature characteristic and a frequency characteristic by the level varying means in order to correct the uplink signal level. Level control device for data communication. 5. The level varying means includes a plurality of attenuating circuits arranged in parallel between an output terminal of an upstream signal and a two-way communication network, the attenuation circuits having different signal attenuations, and converting the upstream signal into the plurality of attenuation signals. 2. The data communication level control device according to claim 1, wherein the signal is output after being attenuated through any one of the attenuation circuits. 6. The level varying means comprises a plurality of level varying circuits arranged in series between the uplink signal transmitting means and a bidirectional communication network, and the level varying means converts the uplink signal by the plurality of level varying circuits. 2. The level control device for data communication according to claim 1, wherein each of the levels is controlled and output. 7. A terminal arranged between the two-way communication network and the terminal device so as to couple the CATV center and the terminal device via the two-way communication network, and receiving a downlink signal from the CATV center. A cable modem having a receiving unit and a transmitting unit for transmitting an uplink signal to the CATV center; a level varying unit capable of controlling a transmission level of the uplink signal from the transmitting unit by a control signal; To change the transmission level, the CA
Control data generating means for generating first control data based on control from a TV center; measuring means for measuring an upstream signal coupled to an upstream signal transmission path from the level varying means; and the measuring means Means for generating correction data corresponding to the characteristics of the level varying means based on the measurement result by the correction means, correction data storage means for storing the correction data, and correction for storing the first control data in the storage means. And a control signal supply unit for converting the corrected control data into an analog signal and supplying the control signal to the level varying unit as a control signal. 8. A terminal arranged between the two-way communication network and the terminal device so as to couple the CATV center and the terminal device via the two-way communication network, and receives a downlink signal from the CATV center. A cable modem having a receiving unit and a transmitting unit for transmitting an uplink signal to the CATV center; a level varying unit capable of controlling a transmission level of the uplink signal from the transmitting unit by a control signal; To change the transmission level, the CA
Control data generating means for generating first control data based on control from a TV center; level detecting means for detecting a transmission level of an uplink signal from the level varying means; and an output signal of the level detecting means Switch means that can be selectively switched to the two-way communication network or the level detection means, and switching control of the switch means at a predetermined timing,
Means for supplying an output signal of the level varying means to the level detecting means, for generating correction data according to the characteristics of the level varying means based on the detection result of the level detecting means, and for correcting the data to be stored Data storage means, and control for correcting the first control data with correction data stored in the storage means, converting the corrected control data into an analog signal, and supplying the analog signal as a control signal to the level varying means A level control device for data communication, comprising: signal supply means.