JP2015115621A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion device capable of conducting a short circuit pass of a photodiode only in non-power feeding without installing a switch.SOLUTION: The photoelectric conversion device for converting an optical signal into an electric signal in an optical transmission system includes: a photodiode 1 for converting the optical signal into the electric signal; reverse voltage application means +Vc for applying a reverse voltage to the photodiode 1 in power feeding; a shirt circuit pass 5 for short-circuiting between the cathode side and the anode side of the photodiode 1; and a diode 4 arranged in the short circuit pass 5 and set so that a direction from the anode side of the photodiode 1 to the cathode side is a forward direction.

Description

  The present invention relates to a photoelectric conversion device that receives an optical signal and converts it into an electrical signal in an optical transmission system, and more particularly to a photoelectric conversion device that can convert an optical signal into an electrical signal and output it even in a non-powered state.

  In an optical transmission system using an optical fiber, an optical line terminator is arranged on the receiver side. The optical line termination device has a photoelectric conversion device that converts an optical signal into an electrical signal, and outputs an RF signal or an FM signal transmitted by the optical signal. Such photoelectric conversion devices are widely used in notification broadcasting systems that transmit information on disasters such as earthquakes, regional information, or administrative information.

  Announcement broadcasts notify information in an emergency such as a disaster, but in such a case, there is a high possibility of a power outage. For this reason, it is necessary that the photoelectric conversion device operates to convert an optical signal into an electric signal even during a power failure. As such a photoelectric conversion device capable of converting an optical signal into an electric signal even when no power is supplied, for example, there is a device described in Patent Document 1.

  In the photoelectric conversion device of Patent Document 1, a reverse voltage is applied to a photodiode during power feeding, and an electric signal output from the photodiode is amplified by an amplifying unit and then output from an output terminal. Output can be performed. In addition, when no power is supplied, the anode side and the cathode side of the photodiode are short-circuited by a short circuit when the switch is turned on, and the electrical signal output from the photodiode in the non-bias mode is output from the output terminal. Conversion output can be performed.

JP 2012-257283 A

  In a conventional photoelectric conversion device, a short circuit that short-circuits both sides of the photodiode is provided, and a switch that is turned on only when no power is supplied to the short circuit, so that an output from the photodiode can be taken out when there is no power. Although it is configured as described above, it is necessary to operate the switch provided on the short circuit by some means when the power supply state is changed to the non-power supply state. For this reason, the circuit configuration is slightly complicated and the number of parts is increased. There was a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a photoelectric conversion device capable of conducting a short circuit of a photodiode only when no power is supplied without providing a switch.

In order to solve the above problem, a photoelectric conversion device according to the invention of claim 1 is a photoelectric conversion device that converts an optical signal into an electrical signal in an optical transmission system.
A photodiode for converting the optical signal into the electrical signal;
Reverse voltage application means for applying a reverse voltage to the photodiode during power feeding;
A short circuit for short-circuiting the cathode side and the anode side of the photodiode;
And a diode provided in the short circuit and having a forward direction from the anode side to the cathode side of the photodiode.

  According to the first aspect of the present invention, the reverse voltage applied to the photodiode is maintained during power supply, and the photocurrent from the photodiode flows through the short circuit when no power is supplied, thereby extracting an optical signal.

  The photoelectric conversion device according to a second aspect of the invention is characterized in that the diode is formed of a germanium diode or a Schottky barrier diode.

  According to the invention of claim 2, the forward voltage drop of the diode can be suppressed.

  Furthermore, the photoelectric conversion device according to the invention of claim 3 is characterized in that the diode has a forward voltage drop of 0.1 V or less.

  According to the invention of claim 3, it is possible to prevent the output level from being lowered due to the destruction of the internal electric field of the photodiode.

  According to the photoelectric conversion device of the present invention, the operation at the time of power supply and no power supply can be switched by the action of a diode, and it is not necessary to provide a switch or the like, so that it can operate even with no power supply with a simple circuit configuration. can do.

It is a circuit diagram of the photoelectric conversion apparatus in this embodiment.

  Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a circuit diagram of the photoelectric conversion device according to this embodiment. The photoelectric conversion device of this embodiment is used in a notification broadcasting system, and is provided in an optical line termination device installed in each home. An optical cable from an optical fiber network is connected to the optical line termination device, and the photoelectric conversion device converts an optical signal from the optical cable into an electrical signal and outputs it.

  The photoelectric conversion device includes a photodiode 1 for converting an optical signal into an electric signal, an FM output terminal 6 that outputs an FM signal out of the converted electric signal, and an RF output that outputs an RF signal out of the converted electric signal. The terminal 7 is connected via a line. The cathode side of the photodiode 1 is connected to a positive power source + Vc via a coil L2, and the anode side of the photodiode 1 is grounded via a coil L3 and a resistor R1. That is, the positive power source + Vc corresponds to a reverse voltage applying unit that applies a reverse voltage to the photodiode 1 during power feeding. Note that the coil L3 and the resistor R1 are grounded via a capacitor C2.

  A line is drawn from between the cathode of the photodiode 1 and the positive power source + Vc, and a band pass filter 2 and an FM output terminal 6 that can extract only the frequency band of the FM broadcast from the electric signal are connected to the line. ing.

  A line is also drawn from between the anode of the photodiode 1 and the resistor R1, and a capacitor C1, an amplifier 3 and an RF output terminal 7 are connected to the line. Only the AC component of the electric signal converted by the photodiode 1 can be taken out by the capacitor C1, and further amplified by the amplifier 3, so that it can be output from the RF output terminal 7 as an RF signal.

  The anode side and the cathode side of the photodiode 1 are connected by a short circuit 5. In the short circuit 5, a coil L1 and a diode 4 are arranged. The diode 4 is connected so that the direction from the anode side to the cathode side of the photodiode 1 in the short circuit 5 is a forward direction. This diode 4 is constituted by a germanium diode or a Schottky barrier diode having a small forward voltage drop.

  An operation of the photoelectric conversion device during power feeding will be described. At the time of power feeding, a reverse voltage is applied to the photodiode 1 by the positive power source + Vc. In this state, an optical signal from the optical cable is photoelectrically converted, and an electric signal is output from the photodiode 1. The AC component of the output electric signal is taken out by the capacitor C1, amplified by the amplifier 3, and then output from the RF output terminal 7. A signal in the frequency band of the FM broadcast is passed through the bandpass filter 2. Via the FM output terminal 6. At this time, since a voltage is applied to the short circuit 5 in the reverse direction of the diode 4, no current flows through the short circuit 5. Note that the RF signal does not flow into the power supply or ground due to the action of the coil L2, the coil L3, and the capacitor C2.

  Next, the operation of the photoelectric conversion device when no power is supplied will be described. When power supply to the photoelectric conversion device is stopped due to a power failure or the like, no voltage is applied to the photodiode 1 by the positive power source + Vc. In this case, the photodiode 1 is in a non-bias mode, and when light energy exceeding the band gap is incident from the optical cable, the light energy is absorbed by the depletion layer, and the light intensity is increased by generation and drift of conduction electrons and holes. Proportional electromotive force is generated.

  Due to the electromotive force of the photodiode 1, a current flows through the short circuit 5 in the forward direction of the diode 4. As described above, since a voltage is applied in the reverse direction of the diode 4 during power feeding, no current flows through the short circuit 5, but when no power is fed, the electromotive force generated by the photodiode 1 in the no-bias mode is forward in the diode 4. Since it is applied, a current flows through the short circuit 5. As a result, an FM broadcast frequency band signal of the electrical signal is output from the FM output terminal 6 via the bandpass filter 2.

  Due to the direct current component of the current from the photodiode 1, a self-bias voltage is generated in the short circuit 5. Since the resistance of the line is sufficiently small, the self-bias voltage is mainly determined by the value of the forward voltage drop of the diode 4. If the self-bias voltage is large, the internal electric field of the photodiode 1 is destroyed and the output level is lowered. Therefore, it is necessary to reduce the self-bias voltage. Therefore, it is necessary to select a diode 4 having a small forward voltage drop as the diode 4 that defines the self-bias voltage. In the present embodiment, a germanium diode or a Schottky barrier diode having a small forward voltage drop is used as the diode 4. In particular, it is possible to prevent the output level of the photodiode 1 from being lowered by selecting one having a forward voltage drop of 0.1 V or less.

  Thus, the short circuit 5 for short-circuiting both ends of the photodiode 1 is provided in the photoelectric conversion device, and the diode 4 having the forward direction from the anode side to the cathode side of the photodiode 1 is provided in the short circuit 5. Thus, the reverse voltage applied to the photodiode 1 is maintained during power feeding, and the photocurrent from the photodiode 1 can flow through the short circuit 5 and take out an optical signal when there is no power feeding. In addition, since the operation at the time of feeding and without feeding is switched by the action of the diode 4, such a function can be realized with a simple circuit configuration. Furthermore, by selecting a diode 4 having a forward voltage drop of 0.1 V or less, it is possible to prevent a decrease in output level due to destruction of the internal electric field of the photodiode 1.

  Although the embodiment of the present invention has been described above, the application of the present invention is not limited to this embodiment, and can be applied in various ways within the scope of its technical idea.

1 Photodiode 2 Bandpass filter 3 Amplifier 4 Diode 5 Short circuit 6 FM output terminal 7 RF output terminal

Claims (3)

In a photoelectric conversion device that converts an optical signal into an electrical signal in an optical transmission system,
A photodiode for converting the optical signal into the electrical signal;
Reverse voltage application means for applying a reverse voltage to the photodiode during power feeding;
A short circuit for short-circuiting the cathode side and the anode side of the photodiode;
And a diode provided in the short circuit and having a forward direction from the anode side to the cathode side of the photodiode.   The photoelectric conversion device according to claim 1, wherein the diode is a germanium diode or a Schottky barrier diode.   The photoelectric conversion device according to claim 1, wherein the diode has a forward voltage drop of 0.1 V or less.

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