JP5248345B2 - Optical receiver terminal - Google Patents

Description

  The present invention relates to an optical receiving terminal capable of outputting a reception output even during a power failure.

In cable television (CATV) and a joint reception system, video and audio are distributed by FTTH (Fiber To The Home), which is a data communication service for homes using optical fibers. This video and audio distribution is received by the optical receiving terminal. A circuit block diagram showing the configuration of a conventional optical receiving terminal is shown in FIG.
In the optical receiving terminal 100 shown in FIG. 3, a series circuit of a Zener diode ZD, a resistor R21, a coil L20, and a photodiode PD is connected between a power supply (+ Vcc) and ground, and the photodiode PD is connected by a Zener diode ZD and a resistor R21. A bias is applied. An optical signal input from an optical fiber or the like is received by the photodiode PD, and the optical signal is converted into an electrical signal. This electric signal is taken out from the connection point between the photodiode PD and the coil L, supplied to the first amplifying unit 110 via the capacitor C20 that extracts only the signal component, and amplified with a predetermined amplification degree. The amplified electric signal is gain-controlled in the variable attenuating unit 111, supplied to the second amplifying unit 113, and amplified with a predetermined amplification degree. The photocurrent Ipd flowing through the photodiode PD has a magnitude corresponding to the intensity of the optical signal, and a signal corresponding to the photocurrent Ipd is taken out from the connection point between the Zener diode ZD and the resistor R21 as a control signal, and the control unit 112. To be applied. The control unit 112 controls the attenuation amount of the variable attenuation unit 111 so that the level of the applied control signal is constant. Thereby, the level of the electric signal output from the second amplifying unit 113 is controlled to be constant.

  The voltage-current characteristic when a reverse voltage is applied to the Zener diode ZD is a logarithmic function characteristic. Therefore, when the photocurrent Ipd that flows through the photodiode PD that receives the optical signal changes according to the optical signal power, the bias voltage Vd of the photodiode PD changes with a logarithmic function characteristic. Therefore, when a bias is applied to the photodiode PD by the Zener diode ZD, the electrical signal converted in the photodiode PD due to the nonlinear characteristic of the Zener diode ZD changes with a logarithmic function characteristic with respect to the optical input power. Become. The variable attenuation unit 111 is configured by using, for example, a PIN diode, and the attenuation amount of the variable attenuation unit 111 changes logarithmically non-linearly with respect to the control amount. As described above, the electrical signal that changes with the logarithmic function characteristic with respect to the optical input power is amplified by the first amplifying unit 110 and supplied to the variable attenuating unit 111, so that the attenuation amount is logarithmically functioned. From the variable attenuating unit 111 that changes, an electric signal having a substantially constant level is output.

  The electric signal output from the second amplifying unit 113 is connected to a branch circuit including a resistor R22 and a resistor R23 connected in series, and a resistor R24 having one end connected to a connection point between the resistor R22 and the resistor R23. Is input via. The other end of the resistor R24 is connected to one end of the capacitor C23, and the other end of the capacitor C23 is connected to the monitor terminal J102. Further, a capacitor C22 is connected in series to the capacitor C21, and the other end of the capacitor C22 is connected to the output terminal J101. The electrical signal via the capacitor C21 is mainly output from the output terminal J101, and the electrical signal branched by the branch circuit is output from the monitor terminal J102.

JP 2004-236259 A

  When the conventional optical receiver terminal 100 receives optical signals such as video and audio distributed by FTTH, the optical receiver terminal 100 needs to be supplied with power. An FM broadcast reception signal will not be output. There is a need for an FTTH video distribution system that can transmit emergency broadcasts even during power outages in large-scale disasters. By the way, some photodiodes PD that convert an optical signal into an electrical signal can output an electrical signal even in a zero bias mode in which power is not supplied. Therefore, it is conceivable to use such a photodiode PD. However, in the conventional optical receiving terminal 100, the Zener diode ZD is used to detect the photocurrent Ipd that varies depending on the optical input level. However, when the photodiode PD is operated with zero bias when no power is supplied, the photodiode PD is used. There is a problem that a converted electric signal cannot be obtained unless it is terminated with a resistor. In addition, if the photodiode PD is terminated with a resistor when power is supplied, the photocurrent Ipd does not vary according to the level of the input optical signal, and the control unit 112 is controlled according to the level of the optical signal. In other words, the control signal is not applied, and the electric signal level cannot be controlled to be constant.

  Accordingly, the present invention provides an optical receiving terminal that can extract an electrical signal obtained by converting an optical signal from a photodiode even during a power failure, and prevents the photodiode from being terminated by a resistor during normal operation. It is aimed.

In order to achieve the above object, an optical receiving terminal of the present invention is applied with a bias by a bias means connected in series between a power source and a ground, and a photodiode that converts an input optical signal into an electric signal; Amplifying means for amplifying the electrical signal extracted from one end of the photodiode; and a branch for branching the amplified electrical signal output from the amplifying means to an output signal terminal and a monitor signal terminal When the circuit and the power supply are supplied, the movable contact connected to one end of the resistor is switched to the normally opened contact side, and when the power is cut off, the movable contact is switched to the photodiode. and a switching means for automatically switching the normally-closed contact point side, which is connected to one end, when said power supply is disconnection, the opposite ends of the resistor terminating the photodiode Et retrieved said electrical signals, are the most important feature that the output from the monitor signal terminal through the branch circuit.

  According to the present invention, when the power is turned off, an electrical signal obtained by converting the input optical signal is taken out from both ends of the resistor constituting the branch circuit terminating the photodiode, and is monitored via the branch circuit. Therefore, an electrical signal obtained by converting an optical signal from the photodiode can be taken out even during a power failure. In addition, when power is supplied, the photodiode is not terminated by the resistor, so that the photocurrent varies according to the level of the optical signal, and the control means for controlling the level of the electric signal to be constant. Thus, the electric signal level is controlled to be constant.

It is a circuit block diagram which shows the structure of the optical receiver terminal of 1st Example of this invention. It is a circuit block diagram which shows the structure of the optical receiver terminal of 2nd Example of this invention. It is a circuit block diagram which shows the structure of the conventional optical receiver terminal.

FIG. 1 is a circuit block diagram showing the configuration of the optical receiving terminal according to the first embodiment of the present invention.
In the optical receiver terminal 1 according to the first embodiment of the present invention shown in FIG. 1, a series circuit of a Zener diode ZD, a resistor R1, a coil L, and a photodiode PD is connected between a power source (+ Vcc) and the ground. A bias is applied to PD by a Zener diode ZD and a resistor R1. An optical signal input from an optical fiber or the like is received by the photodiode PD. Then, the photocurrent Is1 flowing through the photodiode PD becomes a magnitude corresponding to the intensity of the optical signal, and the optical signal is converted into an electric signal. This electric signal is taken out from the connection point between the photodiode PD and the coil L, supplied to the first amplifying unit 10 via the capacitor C1 for extracting only the signal component, and amplified with a predetermined amplification degree. The amplified electric signal is gain-controlled in the variable attenuating unit 11 and supplied to the second amplifying unit 13 to be amplified with a predetermined amplification degree. Also, the photocurrent Is1 flowing through the photodiode PD has a magnitude corresponding to the intensity of the optical signal, and a signal corresponding to the photocurrent Is1 is taken out from the connection point between the Zener diode ZD and the resistor R1 as a control signal, and the control unit 12 To be applied. The control unit 12 controls the attenuation amount of the variable attenuation unit 11 so that the level of the applied control signal becomes constant. As a result, the level of the electric signal output from the second amplifying unit 13 is controlled to be constant.

  The voltage-current characteristic when a reverse voltage is applied to the Zener diode ZD is a logarithmic function characteristic. Therefore, when the photocurrent Is1 flowing through the photodiode PD that receives the optical signal changes according to the optical signal power, the bias voltage Vd of the photodiode PD changes with a logarithmic function characteristic. Therefore, when a bias is applied to the photodiode PD by the Zener diode ZD, the electrical signal converted in the photodiode PD due to the nonlinear characteristic of the Zener diode ZD changes with a logarithmic function characteristic with respect to the optical input power. Become. The variable attenuating unit 11 is configured by using, for example, a PIN diode, and the attenuation amount of the variable attenuating unit 11 changes in a logarithmic non-linear manner with respect to the control amount. As described above, the electrical signal that changes with the logarithmic function characteristic with respect to the optical input power is amplified by the first amplifying unit 10 and supplied to the variable attenuating unit 11, so that the attenuation amount is logarithmically functioned. From the variable attenuating unit 11 that changes, an electric signal having a substantially constant level is output.

  The output from the second amplifying unit 13 is supplied to the branch circuit 14. The branch circuit 14 is a branch circuit using a transformer, and includes a first transformer T1 in which a first primary winding P1 and a first secondary winding S1 are wound around a core, and a second primary winding. A second transformer T2 in which a wire P2 and a second secondary winding S2 are wound around a core is provided. The electric signal output from the second amplifying unit 13 is input to one end of the first primary winding P1, and the capacitor C2 is connected to the output terminal J1 from which the electric signal converted from the optical signal is output at the other end. And is connected to the other end of the second primary winding P2. One end of the first secondary winding S1 is connected to the ground, and the other end is connected to the other end of the second secondary winding S2 and to one end of the resistor R2. One end of the second primary winding P2 is connected to the ground, and the other end is connected to the other end of the first primary winding P1. One end of the second secondary winding S2 is connected to the monitor terminal J2 via the capacitor C3, and the other end is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the ground. In this case, the monitor signal output from the monitor terminal J2 is a signal obtained by distributing the electrical signal input to the branch circuit 14 at the winding ratio of the transformer T1 and the transformer T2.

  The characteristic configuration of the optical receiving terminal 1 according to the first embodiment of the present invention is such that the photodiode PD is terminated by the resistor R2 via the relay RY when the power supply + Vcc is not supplied. The relay RY has a movable contact a, a normally closed contact b, a normally open contact c, and a relay coil for switching these relay contacts. Although not shown, the relay coil is connected between the power source + Vcc and the ground. Thus, the power source + Vcc is always supplied to the relay coil. Thereby, when the power source + Vcc is supplied, the relay coil of the relay RY is driven, and the movable contact a is automatically switched to the normally open contact c side as shown in FIG. Therefore, the photodiode PD is not terminated by the resistor R2 because the normally closed contact b is opened. In this case, the electrical signal obtained by converting the optical signal extracted from the connection point between the photodiode PD and the coil L is supplied to the first amplifying unit 10 via the capacitor C1. Further, the control signal taken out from the connection point between the Zener diode ZD and the resistor R1 is supplied to the control unit 12, and the variable attenuating unit 11 is controlled by the control unit 12 and output from the second amplifying unit 13. The signal level is controlled to be constant.

  Further, since the power source + Vcc is not supplied during a power failure, no bias is supplied to the photodiode PD, and the relay coil of the relay RY is not driven, so that the movable contact a is automatically switched to the normally closed contact b side. become. As a result, the photodiode PD is terminated by the resistor R2 connected to the movable contact a, and the intensity of the optical signal as shown in the circuit composed of the photodiode PD and the resistor R2 in the zero bias state is illustrated. The photocurrent Is2 having a magnitude corresponding to the current flows. The electrical signal obtained by converting the optical signal extracted from both ends of the resistor R2 is mainly output from the monitor terminal J2 via the branch circuit 14. The first amplifying unit 10, the variable attenuating unit 11, the control unit 12, and the second amplifying unit 13 do not operate because the power source + Vcc is not supplied.

Next, FIG. 2 is a circuit block diagram showing the configuration of the optical receiving terminal according to the second embodiment of the present invention.
The optical receiving terminal 2 of the second embodiment according to the present invention shown in FIG. 2 differs from the optical receiving terminal 1 of the first embodiment only in the configuration of the branch circuit, and the other configurations are the same. A different configuration will be described.
In the optical receiving terminal 2 of the second embodiment, the output from the second amplifying unit 13 is supplied to the branch circuit 24 via the capacitor C4, and is output from the output terminal J1 via the capacitor C2 and branched. An electric signal is output from the monitor terminal J2 via the capacitor C3. The branch circuit 24 is a branch circuit using a resistor, in which a resistor R3 and a resistor R2 are connected in series, and a resistor R4 is connected to a connection point between the resistor R3 and the resistor R2. One end of the resistor R3 is connected to a connection point between the capacitor C4 and the capacitor C2, and the other end of the resistor R2 is grounded. Further, the other end of the resistor R4 is connected to one end of the capacitor C3. In the branch circuit 24, the electric signal input via the capacitor C4 is divided by the series circuit of the resistor R3 and the resistor R2, and the divided electric signal is output from the monitor terminal J2 via the resistor R4 and the capacitor C3. Is output.

  The other configuration is the same as that of the optical receiving terminal 1 of the first embodiment, but the characteristic configuration of the optical receiving terminal 2 according to the second embodiment of the present invention is also a photodiode when the power source + Vcc is not supplied. The PD is terminated by a resistor R2 via a relay RY. The relay RY has a movable contact a, a normally closed contact b, a normally open contact c, and a relay coil for switching these contacts. Although not shown, the relay coil is connected between the power source + Vcc and the ground. Thus, the power supply + Vcc is always supplied to the relay coil. Thereby, when the power supply + Vcc is supplied, the relay coil of the relay RY is driven, and the movable contact a is automatically switched to the normally open contact c side as shown in FIG. Therefore, the photodiode PD is not terminated by the resistor R2 because the normally closed contact b is opened. In this case, the electrical signal obtained by converting the optical signal extracted from the connection point between the photodiode PD and the coil L is supplied to the first amplifying unit 10 via the capacitor C1. Further, the control signal taken out from the connection point between the Zener diode ZD and the resistor R1 is supplied to the control unit 12, and the variable attenuating unit 11 is controlled by the control unit 12 and output from the second amplifying unit 13. The signal level is controlled to be constant.

  Further, since the power source + Vcc is not supplied during a power failure, no bias is supplied to the photodiode PD, and the relay coil of the relay RY is not driven, so that the movable contact a is automatically switched to the normally closed contact b side. become. As a result, the photodiode PD is terminated by the resistor R2 connected to the movable contact a, and the intensity of the optical signal as shown in the circuit composed of the photodiode PD and the resistor R2 in the zero bias state is illustrated. The photocurrent Is2 having a magnitude corresponding to the current flows. An electrical signal obtained by converting the optical signal extracted from both ends of the resistor R2 is mainly output from the monitor terminal J2 via the branch circuit 24. The first amplifying unit 10, the variable attenuating unit 11, the control unit 12, and the second amplifying unit 13 do not operate because the power source + Vcc is not supplied.

The optical receiving terminal according to the present invention is not limited to an optical receiving terminal used for CATV or a joint receiving system, and any optical receiving terminal that receives an optical signal can be applied. Since the optical receiving terminal according to the present invention shares the monitor terminal and the terminal that outputs an electrical signal obtained by converting the optical signal at the time of a power failure, the optical receiving terminal can be reduced in size and cost.
Further, in connecting the relay contact of the relay RY, the movable contact a is connected to the connection point between the photodiode PD and the coil L, one end of the capacitor C1 is connected to the normally open contact c, and the resistor R2 is connected to the normally closed contact b. One end may be connected. Even if such a connection is made, the relay coil of the relay RY is not driven at the time of a power failure, so that the photodiode PD is terminated by the resistor R2 through the movable contact a-normally closed contact b.

DESCRIPTION OF SYMBOLS 1 Optical receiving terminal, 2 Optical receiving terminal, 10 1st amplification part, 11 Variable attenuation part, 12 Control part, 13 2nd amplification part, 14 Branch circuit, 24 Branch circuit, 100 Optical receiving terminal, 110 1st Amplifying unit, 111 Variable attenuating unit, 112 Control unit, 113 Second amplifying unit

Claims (3)

A bias is applied by a bias means connected in series between the power source and the ground, and a photodiode that converts an input optical signal into an electrical signal;
Amplifying means for amplifying the electrical signal extracted from one end of the photodiode;
A branch circuit for branching and outputting the amplified electrical signal output from the amplification means to an output signal terminal and a monitor signal terminal;
When the power is supplied, the movable contact connected to one end of the resistor is switched to the open normally-open contact side, and when the power is cut off, the movable contact is connected to one end of the photodiode. Switching means for automatically switching to the normally closed contact side ,
When the power is cut off, the electrical signal extracted from both ends of the resistor that terminates the photodiode is output from the monitor signal terminal through the branch circuit. .   The amplification means is configured by connecting a first amplifier, a variable attenuator and a second amplifier in cascade, and the attenuation amount of the variable attenuator according to the magnitude of the photocurrent flowing through the photodiode. The optical receiving terminal according to claim 1, wherein: is controlled. The optical receiving terminal according to claim 1, wherein the switching unit is configured by a relay .

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