JP4937690B2 - Optical subscriber terminal - Google Patents

Description

  The present invention relates to an optical subscriber terminal device installed at a terminal of an optical transmission line when a television signal is transmitted using the optical transmission line.

  2. Description of the Related Art Conventionally, an optical receiver circuit of a transmission system using an optical transmission path is disclosed in, for example, Patent Document 1. According to the technique of Patent Document 1, an optical signal is received by a photodiode, a received light signal is generated, and the received light signal is amplified by an AGC amplifier. The output level of the AGC amplifier is detected, compared with a reference signal in the comparison circuit, and the AGC amplifier is controlled based on the comparison result.

JP-A-5-145360

  When the optical receiver circuit disclosed in Patent Document 1 is implemented in an optical subscriber terminal device in a television signal optical transmission system, the optical signal is generated based on a plurality of television signals in the center device. When the wave number of the television signal is increased or decreased in the center device, the optical modulation degree of the optical signal changes. If the reference signal corresponding to the change in the optical modulation degree cannot be set in the optical subscriber terminal according to the change in the optical modulation degree, distortion occurs or the C / N ratio deteriorates. Therefore, it is desirable that the reference value for AGC control on the optical receiver side can be automatically changed in accordance with the change in the optical modulation degree on the optical transmitter side.

  In such a transmission system, a large number of optical receivers are used, but some of these optical receivers need to disable the reception of television signals due to contract changes or the like. In this case, conventionally, it has been necessary for the worker to go to the installation location of the optical receiver whose contract has been changed and to set the optical receiver in an unreceivable state. However, this work is troublesome.

  Therefore, it may be desired that the amplification means of the optical subscriber terminal device corresponding to the optical receiver can be remotely controlled from the center device side. However, if there is very little possibility that the degree of optical modulation will change, or if cancellation of the reception contract is not expected, enabling remote control will increase the cost of the optical subscriber terminal device. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical subscriber terminal device that can be remotely controlled or disabled from a center device.

  The optical subscriber terminal device according to one aspect of the present invention includes a light receiving unit that receives the optical signal supplied to the optical transmission line by the optical transmission unit of the center apparatus and generates a reception signal. As the light receiving means, a photodiode or a phototransistor can be used. The amplification means amplifies the reception signal from the light receiving means. The amplifying means is controlled by the control means. These light receiving means, amplifying means and control means are provided in one housing. The optical signal includes an optical television signal based on a television signal from a television signal source and light control data based on control data for the amplifying means. In the reception signal from the light receiving means, the control data generated based on the reception television signal corresponding to the television signal generated based on the optical television signal and the light control data. Includes reception control data corresponding to. Based on the reception control data, the control means controls the amplification means. The control means is detachably provided on the casing.

  In the optical subscriber terminal configured as described above, when the control means is mounted, when the optical signal is transmitted from the center apparatus, a reception signal is generated by the light receiving means, and reception control data in the reception signal is received. Is supplied to the control means, and the amplification means is controlled. When the control means is not attached, the amplification means is not controlled. In this way, the amplification means can be easily changed to a controllable state or an uncontrollable state depending on whether or not the control means is attached.

  A modulated signal obtained by modulating a carrier wave based on the control data can be supplied to the optical transmission means. In this case, the light reception signal includes a reception modulation signal corresponding to the modulation signal. The control means includes demodulation means for demodulating the reception control data from the reception modulation signal. This demodulating means is detachably provided on the casing.

  With this configuration, in a state where the demodulating means is not attached, the control state cannot be changed using a portion other than the demodulating means of the control means, but the amplifying means can be controlled.

  For example, the control means can control the reference value for automatic gain control of the amplifying means based on the reception control data, and can also control the start and stop of the operation of the amplifying means.

  By configuring in this way, automatic gain control of the amplification means can be performed with a fixed reference value when the demodulation means is not attached. Further, in the state where the demodulating means is mounted, the reference value can be changed according to an instruction from the center device. Further, when the control means is not attached, automatic gain control becomes impossible and control regarding the operation of the amplification means becomes impossible.

  As described above, according to the present invention, it is possible to remotely control the optical subscriber terminal device from the center device, and when remote control is unnecessary, the control means or the demodulating means forming part thereof is not provided. This can be done by mounting.

  An optical subscriber terminal device according to an embodiment of the present invention is implemented, for example, in an optical transmission system for television signals as shown in FIG. This optical transmission system has a center device 2. The center device 2 is provided in a head end device or the like, for example, and has a television signal source 4. The television signal source 4 is composed of, for example, a plurality of terrestrial television broadcast signals in the UHF band and VHF band, an independent broadcast signal of a joint viewing device, an intermediate frequency signal in the 1 GHz band of satellite broadcast and satellite communication signals, and the like. Outputs a television signal. This television signal is supplied to the optical transmission means, for example, the optical transmission unit 8 via the combiner 6. The optical transmitter 8 converts a television signal into an optical television signal and supplies it to an optical transmission line, for example, an optical fiber 10.

This optical television signal is supplied to the optical subscriber terminal device 12 installed at home. In FIG. 1, only one optical fiber 10 is shown, and the center device 2 and the optical subscriber terminal device 12 are shown connected to both ends of the optical fiber 10. An optical subscriber terminal apparatus 12 is connected to each of the branched optical fiber terminals. Alternatively, the optical fiber branched at each access point is further branched via a coupler or a closure, and the optical subscriber terminal device 12 is connected to the terminal of each branched optical fiber.

  The optical subscriber terminal device 12 includes a light receiving element, for example, a photodiode 14, a cathode of which is supplied with a voltage of + V via a high frequency blocking coil 16, and an anode which is supplied with a reference potential such as a ground via a load resistor 18. Connected to potential. By connecting in this way, a reverse bias is supplied to the photodiode 14. When the optical television signal enters the photodiode, a current corresponding to the optical television signal flows through the photodiode 14, and this is amplified by the amplifying means, for example, the amplifier 22 through the DC blocking capacitor 20. The output signal of the amplifier 22 corresponds to the television signal of the television signal source 4 and is hereinafter referred to as a reception television signal. The received television signal is supplied to amplifying means, for example, a two-stage amplifying unit 26 with AGC, via a branching means, for example, one branching device 24.

  The amplifying unit 26 includes an attenuator 28 including an attenuator, for example, a PIN diode, on the input side, and an output signal of the attenuator 28 is amplified and output by two-stage amplifiers 30 and 32. In order to adjust the attenuation amount of the attenuator 28, a control means, for example, a CPU 34 is provided. The CPU 34 is supplied with the voltage across the load resistor 18, that is, the voltage corresponding to the received television signal, digitized by the A / D converter 36. The CPU 34 compares this digital signal with a predetermined reference value, and generates a control signal for controlling the attenuator 28 so that the difference between the two is reduced. This control signal is converted into an analog signal by the D / A converter 38 and supplied to the attenuator 28 via the on / off circuit 39 and the buffer 40. The on / off circuit 39 is controlled by the CPU 34 and is turned on when the attenuator 28 is controlled, and is turned off when the control is not performed.

  By the way, the number of television signals from the television signal source 4 of the center device 2 may increase or decrease, for example. In this case, the optical modulation degree of the optical television signal output from the optical transmitter 8 changes. If the reference value used for the AGC control by the CPU 34 of the optical subscriber terminal device 12 is fixed at a constant value despite the change in the optical modulation degree, the amplified reception television set output from the amplifier 32 is used. The John signal is deteriorated in C / N ratio or includes distortion. In order to prevent the deterioration of the C / N ratio and the occurrence of distortion, a reference value change instruction accompanying a change in the optical modulation degree is supplied from the center device 2 side to the optical subscriber terminal device 12.

  Therefore, optical modulation degree data representing the optical modulation degree is supplied from the optical transmission unit 8 to the control unit 42 in the center apparatus 2. The control unit 42 supplies the light modulation degree data to a control data generation unit, for example, the data transmission unit 44. The data transmission unit 44 modulates a carrier wave having a predetermined frequency with the optical modulation degree data, and performs, for example, FSK modulation to generate a modulation signal. This modulated signal is combined with the television signal by the combiner 6 and supplied to the optical transmitter 8. Accordingly, the optical transmitter 8 generates light control data based on the modulation signal, for example, the light modulation signal, in addition to the optical television signal. An optical signal composed of the optical television signal and the optical modulation signal is supplied to each subscriber terminal device 12 through the optical fiber 10.

In each optical subscriber unit 12, the output signal amplified by the amplifier 22 based on the current flowing through the photodiode 14 is received including a reception modulation signal corresponding to the optical modulation signal in addition to the reception television signal. Signal. This received signal is supplied to the data demodulator 46 via the one branching device 24, where the received modulated signal is extracted from the received signal. From the extracted reception modulation signal, reception control data, for example, reception modulation degree data corresponding to the modulation degree data is demodulated and supplied to the CPU 34. The data demodulator 46 can be switched between a connected state and a disconnected state with respect to the one branching device 24 and the CPU 34, and as shown in FIG. 2, one surface of the housing 12a of the optical subscriber terminal device 12 is provided. In the state of being attached to the one branching device 24 and the CPU 34, the one branching device 24 and the CPU 34 are not connected to one surface of the housing 12a.

  In the CPU 34, a database in which various received modulation degree data and reference signals corresponding to these are stored in a storage unit (not shown) is constructed, and the received modulation degree data is received from the data demodulator 46. Is supplied, the corresponding reference signal is selected from the database and used as the AGC reference signal. Therefore, even if the optical modulation degree changes on the center device 2 side, the reference signal corresponding to the change is automatically used in each optical subscriber terminal device. Accordingly, it is possible to prevent the deterioration of the C / N ratio and the occurrence of distortion based on the change in the degree of light modulation. When the data demodulator 46 is not connected, the CPU 34 performs AGC control using a preset reference signal as a reference signal of the AGC circuit 8.

In addition, the optical subscriber terminal device 12 is installed in each home, but there are homes that cancel the reception contract even though the reception contract using the optical subscriber terminal device 12 has been made so far. Alternatively, some families have newly signed a reception contract. It is necessary to disable reception using the optical subscriber terminal device 12 after the expiration date of the contract at the home where the reception contract is canceled. Moreover, it is necessary to make it possible to receive from the effective date of the reception contract to the home which newly signed the reception contract.

  Therefore, in each optical subscriber terminal device 12, on / off circuits 48 and 50 are provided in a supply path of a power supply voltage to the amplifiers 30 and 32, for example, + V. When the on / off circuits 48 and 50 are in a first state, for example, an on state, a voltage of + V is supplied to the amplifiers 30 and 32, and the amplifiers 30 and 32 start operating. Therefore, the received television signal can be output to the outside. When the on / off circuits 48, 50 are in the second state, eg, the off state, the + V voltage is not supplied to the amplifiers 30, 32, and the amplifiers 30, 32 stop operating and receive television. Output of the signal to the outside is stopped. The CPU 34 switches the on / off circuits 48 and 50 to an on state or an off state.

  In order for the CPU 34 to perform this switching control, amplifier control data is supplied as control data from the outside to the control unit 42 of the center apparatus 2. The amplifier control data includes an instruction to turn on or off the amplifiers 30 and 32 and data to instruct the optical subscriber terminal apparatus 12 including the amplifiers 30 and 32 to be turned on or off. The amplifier control data is supplied to the data transmission unit 44, and an optical modulation signal obtained by FSK-modulating the carrier wave is transmitted to each optical subscriber terminal apparatus 12 in the same manner as described above.

  In each optical subscriber terminal device 12, the receiving amplifier control data corresponding to the amplifier control data is demodulated from the optical modulation signal by the data demodulator 46 and output to the CPU 34 in the same manner as described above. The CPU 34 determines whether the data indicating the optical subscriber terminal device included in the reception amplification control data matches the data indicating the optical subscriber terminal device allocated to itself. The on / off circuits 48 and 50 are controlled in accordance with an on / off instruction included in the reception amplifier control data. If the data indicating the optical subscriber terminal does not match the data indicating the optical subscriber terminal assigned to itself, the on / off circuits 48 and 50 are not controlled and both are turned on. State. Further, even when the data demodulator 46 is not connected, the on / off circuits 48 and 50 are not controlled, and both the on / off circuits 48 and 50 are in the on state.

  In the control unit 42, when the modulation degree data and the amplifier control data are simultaneously supplied to the data transmission unit 44, the optical transmission unit 8 transmits an optical modulation signal based on the modulation degree data and the amplifier control data.

  In the above-described embodiment, the modulation degree data is supplied from the control unit 42 to the data sending unit 44. However, a database in which various light modulation degrees and reference signals corresponding thereto are associated with the control unit 42 is constructed. When modulation degree data is supplied from the optical transmission unit 8, a reference signal corresponding to the modulation degree data is selected, this reference signal is supplied to the data transmission unit 44, and the carrier wave is modulated by the reference signal and modulated. A signal is generated, and an optical modulation signal based on the modulated signal is transmitted from the optical transmission unit 8 to each optical subscriber terminal device 12, and each optical subscriber terminal device 12 receives the received modulated signal based on the optical modulation signal. It is also possible to demodulate the reference signal by the data demodulator 46 and use this received reference signal as the AGC reference signal in the CPU 34. In this case, the CPU 34 does not require a database.

  In the above-described embodiment, the on / off circuits 48 and 50 are provided for the amplifiers 30 and 32. However, a common on / off circuit is provided for the amplifiers 30 and 32. The start and stop of power supply can also be controlled. In addition, the start / stop of the signal supply from the attenuator 28 of the amplifier 30 can be controlled by the on / off circuit instead of the start / stop of the power supply. Similarly, the output of the output signal of the amplifier 32 can be started. The stop can also be performed by an on / off circuit. Further, although the on / off circuit 39 is provided on the input side of the buffer 40, it is not necessary in some cases.

  In the above embodiment, the current flowing through the photodiode 14 amplified by the amplifier 22 is extracted from the cathode of the photodiode 14, but can also be extracted from the anode side of the photodiode 14. Similarly, the voltage across the load resistor 18 is A / D converted for AGC control, but the voltage between the cathode of the photodiode 14 and the ground potential can also be A / D converted. Further, although the photodiode 14 is used, a phototransistor can be used instead.

It is a block diagram of the optical transmission system using the optical subscriber terminal device of one Embodiment of this invention. It is a perspective view of the optical subscriber terminal device of FIG.

Explanation of symbols

2 Center device 4 Television signal source 8 Optical transmitter (optical transmitter)
10 Optical fiber (optical transmission line)
12 Optical subscriber terminal equipment 14 Photodiode (light receiving means)
26 Two-stage amplifier with AGC (amplifier)
34 CPU (control means)
46 Data demodulator (control means)

Claims (4)

A light receiving means for receiving the optical signal supplied to the optical transmission path by the optical transmission means of the center apparatus and generating a received signal;
Amplifying means for amplifying the received signal from the light receiving means;
Control means for controlling the amplification means;
Provided in one housing, the optical signal includes an optical television signal based on a television signal from a television signal source and light control data based on control data of the amplification means,
The reception signal from the light receiving means includes the reception television signal corresponding to the television signal generated based on the optical television signal and the control signal generated based on the light control data. The data for reception control corresponding to the data is included,
A control means controls the amplifying means based on the reception control data, and the control means is an optical subscriber terminal device that is detachably provided in the casing.   2. The optical subscriber terminal device according to claim 1, wherein a modulated signal obtained by modulating a carrier wave based on the control data is supplied to the optical transmitting means, and the received modulated signal corresponding to the modulated signal is included in the received light signal. The optical subscriber terminal device includes a demodulating unit that demodulates the reception control data from the received modulation signal, and the demodulating unit is detachably provided in the housing.   3. The optical subscriber terminal apparatus according to claim 1, wherein said control means controls a reference value for automatic gain control of said amplifying means based on said reception control data. 3. The optical subscriber terminal apparatus according to claim 1, wherein the control unit controls the start and stop of the operation of the amplification unit.

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