JP2010199953A - Optical reception circuit, optical reception device, and method of protecting optical reception circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a failure of an optical element or a reception circuit due to a transient response in turning on/off power, in an optical reception circuit used in a reception part of an optical transceiver or the like. <P>SOLUTION: This optical reception circuit includes: a photoelectric conversion element having a multiplication factor controllable by the value of a control voltage; a multiplication factor controlling circuit for controlling the multiplication factor of the photoelectric conversion element by the intensity of light entered in the photoelectric conversion element; and an amplifier circuit supplied with power from a power source for amplifying an electric signal output from the photoelectric conversion element, and forcibly lowers the multiplication factor when the voltage drop of the power source is detected. A failure in the case of turning on the power again in the state where strong light is entered immediately after the power is turned off while light is not received can be prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiver circuit, an optical receiver, and a method for protecting an optical receiver circuit. In particular, the present invention relates to an optical receiving circuit used in a light receiving unit of an optical transceiver.

  In optical communication such as a PON (Passive Optical Network) system, an optical transceiver including an optical transmission circuit that converts an electrical signal into an optical signal and transmits the optical signal and a received optical signal that converts the received optical signal into an electrical signal is used. .

  FIG. 1 is a block diagram of a conventional optical receiving circuit 100. The avalanche photodiode 1 is used as a photoelectric conversion element and converts incident light into a current. The high voltage generation circuit 3 applies a high voltage to the cathode of the avalanche photodiode 1 and controls the avalanche photodiode to break down by the incidence of light. The preamplifier circuit 2 converts the current output from the avalanche photodiode 1 into a voltage and amplifies it. The resistor R1 and the capacitor C1 reduce the noise component from the high voltage generation circuit 3 and stabilize the operation of the optical receiving circuit.

  The resistor R1 and the capacitor C1 function as a low-pass filter. When a strong light is incident on the avalanche photodiode on average and a large current flows, the reverse bias voltage is reduced to increase the multiplication factor of the avalanche photodiode. Reduce. On the other hand, when light that is weak on average enters the avalanche photodiode, the charge supplied from the high voltage generation circuit 3 is accumulated in the capacitor C1, thereby increasing the reverse bias voltage of the avalanche photodiode, and the avalanche photodiode. Increase the multiplication factor.

  Further, in Patent Document 1, a current detection circuit that detects a current flowing in an avalanche photodiode (APD) is provided in the optical receiver circuit of FIG. 1, and a detection voltage that is converted into a voltage by the current detection circuit is a predetermined voltage. The output voltage of the high voltage generation circuit is controlled so as to be substantially the same as the reference voltage, and the voltage applied to the APD is controlled arbitrarily or constant according to the light intensity of the input optical signal. It is described to prevent preamplifier damage.

  Further, in Patent Document 2, when a strong optical signal is input, the cathode of the avalanche photodiode does not drop below a certain voltage in order to prevent a DC bias from being applied to the avalanche photodiode due to a voltage drop due to resistance. An avalanche photodiode bias circuit is described.

JP 2005-354548 A Japanese Utility Model Publication No. 62-85013

  The following analysis is given in the present invention. In the above optical receiver, there is a possibility that a failure of the optical element or the receiving circuit may occur due to a transient response at power-off or power-on. In particular, when no light is incident before the power is turned off, a large charge is accumulated in the capacitor C1, and the multiplication factor of the photoelectric conversion element is high. Even after the power is turned off, the charge of the capacitor C1 is held for a while. If strong light is incident in that state and the power is turned on again in that state, the photoelectric conversion element will receive strong light with a high gain, which may cause failure of the optical element and the receiving circuit. There is sex.

  An optical receiving circuit according to one aspect of the present invention includes a photoelectric conversion element whose multiplication factor can be controlled by the magnitude of a control voltage, and an amplification factor that controls the multiplication factor of the photoelectric conversion element by the amount of light incident on the photoelectric conversion element. A magnification control circuit, an amplification circuit that amplifies an electric signal supplied from a power source and output from the photoelectric conversion element, a protection circuit that forcibly reduces the multiplication factor when a voltage drop of the power source is detected, including.

  An optical receiver according to another aspect of the present invention is an optical receiver including a photoelectric conversion element whose multiplication factor can be controlled by the magnitude of a control voltage, and the control is performed when the optical receiver is turned off. A first protection means for shorting the voltage to ground; and a second protection for controlling the control voltage so that a potential difference from the power supply voltage does not exceed a certain voltage due to an increase in the power supply voltage when the optical receiver is turned on. Means.

  According to still another aspect of the present invention, there is provided a method for protecting an optical receiving circuit, a photoelectric conversion element capable of controlling a multiplication factor according to a magnitude of a control voltage, an amplification circuit that amplifies an electric signal output from the photoelectric conversion element, A method for protecting an optical receiver circuit, comprising: a high voltage generation circuit that applies a control voltage to a photoelectric conversion element; and a capacitor that holds the control voltage, wherein the electric charge accumulated in the capacitor when the optical receiver circuit is powered off And forcibly discharging the optical receiver circuit in a state where the multiplication factor is low irrespective of the multiplication factor of the photoelectric conversion element before the power is turned off.

  According to the present invention, it is possible to obtain an optical receiving circuit capable of preventing a failure of an optical element or a receiving circuit due to a transient response at power-on or power-off. In particular, a failure is prevented when the power is turned off in a state where no light is incident and the power is turned on in a state where a strong light is incident immediately after that.

It is a block diagram which shows the structure of the conventional optical receiver circuit. It is a block diagram of the optical receiver circuit by one Example of this invention. It is a timing diagram which shows the transient response of the optical receiver circuit by one Example of this invention. It is a timing diagram which shows the transient response of the optical receiver circuit used as a comparative example. It is a timing diagram which shows another transient response of the optical receiver circuit by one Example of this invention. It is a timing diagram which shows another transient response of the optical receiver circuit used as a comparative example. It is a block diagram of the optical receiver circuit by another Example of this invention.

  Embodiments of the present invention will be described with reference to the drawings as necessary. In addition, drawing quoted in description of embodiment and the code | symbol of drawing are shown as an example of embodiment, and, thereby, the variation of embodiment by this invention is not restrict | limited.

An optical receiver circuit according to an embodiment of the present invention includes, for example, a photoelectric conversion element 1 whose multiplication factor can be controlled by the magnitude of a control voltage (cathode voltage), and a photoelectric conversion element 1 as shown in FIGS. The multiplication control circuit R1 that controls the multiplication factor of the photoelectric conversion element 1 according to the amount of incident light, the amplification circuit 2 that amplifies the electrical signal that is supplied with power from the power supply Vcc and that is output from the photoelectric conversion element 1, and the power supply Vcc A protection circuit 4 that forcibly lowers the multiplication factor when a voltage drop is detected;
including. When the protection circuit 4 detects a drop in the power supply voltage, it discharges the charge of the capacitor C1, so the control voltage (cathode voltage) of the photoelectric conversion element is lowered and the multiplication factor of the photoelectric conversion element is lowered. Therefore, when the power is turned off, the power is turned off while the charge in the capacitor C1 is discharged. Therefore, no matter how strong light is incident when the power is turned on, even if the power is turned on, the charge of the capacitor C1 is discharged. Therefore, the multiplication factor of the photoelectric conversion element is low, and the optical element and the receiving circuit are not damaged. Absent.

  The optical receiver circuit according to the embodiment of the present invention further includes a capacitor C1 that holds a control voltage as shown in FIGS. 2 and 7, for example, and the protection circuit 4 controls the power supply voltage Vcc and the capacitor. The protection circuit 4 includes a power supply voltage detection circuit 41 that compares the voltages and a discharge circuit (42, R4) that discharges the charge of the capacitor C1 when the power supply voltage detection circuit 41 detects a decrease in the power supply voltage Vcc. is there. In other words, the control voltage of the photoelectric conversion element held by the capacitor is compared with the power supply voltage, and if the power supply voltage drops, control is performed so that the control voltage becomes lower than the power supply voltage. The power is turned off while the control voltage is lowered.

  In addition, in the optical receiver circuit according to the embodiment of the present invention, as shown in FIGS. 2 and 7, for example, the protection circuit 4 is supplied with the control voltage held by the capacitor C1 as a power source, and the control voltage held by the capacitor is supplied. Compare the divided voltage with the power supply voltage. Since the protection circuit 4 is supplied with power from the capacitor C1, it operates as long as the charge remains in the capacitor C1 even after the power is turned off. Therefore, it is possible to reliably discharge the charge of the capacitor C1 when the power is turned off. Even if the charge of the capacitor C1 is not completely discharged, the object can be achieved if the multiplication factor of the photoelectric conversion element can be lowered.

  In the optical receiver circuit according to the embodiment of the present invention, for example, as shown in FIGS. 2 and 7, a resistor R <b> 5 is connected between the capacitor C <b> 1 and the photoelectric conversion element 1. The resistor R5 can prevent an overcurrent from flowing from the photoelectric conversion element 1 to the discharge circuit (42, R4) during discharge.

  In the optical receiver circuit according to the embodiment of the present invention, for example, as shown in FIG. 2, the photoelectric conversion element 1 is an avalanche photodiode 1 whose anode is connected to the input terminal of the amplifier circuit 2. 1 further includes a high voltage generation circuit 3 that applies a control voltage to the cathode of one, and the multiplication factor control circuit R1 has a resistor R1 having one end connected to the high voltage output terminal of the high voltage generation circuit 3 and the other end connected to one end of the capacitor C1. The other end of the capacitor C1 is grounded. In order to operate the avalanche photodiode, since it is necessary to apply a high reverse bias voltage to the cathode, a high voltage generation circuit is provided. Since the multiplication factor of the avalanche photodiode depends on the reverse bias voltage, the multiplication factor decreases when the capacitor C1 is discharged. Since the other end of the capacitor C1 is installed, there is no problem because the operation starts from a state where the multiplication factor is low when the power is normally turned on. However, as described above, when there is no light incident before the power is turned off, the power is turned off in a state where charges are accumulated in the capacitor C1, and thus the above configuration is necessary.

  Further, in the optical receiver circuit according to the embodiment of the present invention, for example, as shown in FIG. 2, when the protection circuit 4 is the first protection circuit, the cathode voltage of the avalanche photodiode 1 is a constant voltage with respect to the power supply voltage. It further includes a second protection circuit 5 that is controlled so as not to decrease below. If the high voltage generating circuit 3 is not operating when the power is turned on, the avalanche photodiode 1 is forward-biased and a large current may flow from the amplifier circuit 2 to the capacitor C1. According to the above configuration, the second protection circuit can prevent excessive forward biasing by the second protection circuit 5 even if the high voltage generation circuit 3 is not operating.

  In the optical receiver circuit according to the embodiment of the present invention, for example, as shown in FIG. 2, the second protection circuit 5 is diode-connected in the forward direction between the power supply Vcc and the high voltage output terminal of the high voltage generation circuit 3. Transistor or a forward-connected diode. The control voltage of the avalanche photodiode can be controlled so as not to become a certain voltage or less with respect to the power supply voltage Vcc by the transistor connected in the forward direction or the diode connected in the forward direction.

  Further, in the optical receiver circuit according to the embodiment of the present invention, for example, as shown in FIG. 7, the photoelectric conversion element is the photodiode 1 whose anode is connected to the input terminal of the amplifier circuit 2, and the control voltage is the photodiode. The multiplication factor control circuit has a resistor R1 having one end connected to the power source and the other end connected to one end of the capacitor, and the other end of the capacitor C1 being grounded.

  An optical receiver according to an embodiment of the present invention is an optical receiver 10 including a photoelectric conversion element whose multiplication factor can be controlled by the magnitude of a control voltage as shown in FIG. The first protection means 4 for shorting the control voltage to the ground when the power of the device 10 is turned off, and the control voltage so that a potential difference from the power voltage does not exceed a certain voltage due to the rise of the power voltage when the optical receiver 10 is turned on. 2nd protection means which controls.

  The optical receiver circuit protection method according to an embodiment of the present invention includes, as shown in FIG. 2, for example, a photoelectric conversion element 1 whose multiplication factor can be controlled by the magnitude of a control voltage, and an electric power output from the photoelectric conversion element. A method of protecting an optical receiver circuit 10 including an amplifier circuit 2 that amplifies a signal, a high voltage generation circuit 3 that applies a control voltage to a photoelectric conversion element, and a capacitor C1 that holds the control voltage. Regardless of the step of forcibly discharging the charge accumulated in the capacitor C1 when the power is turned off and the multiplication factor of the photoelectric conversion element 1 before the power is turned off, the optical receiver circuit 10 is turned on with a low multiplication factor. And a step of performing.

  Further, in the method for protecting the optical receiver circuit 10 according to the embodiment of the present invention, for example, as shown in FIG. 2, in the step of turning on the optical receiver, the potential difference from the control voltage becomes a constant voltage as the power supply voltage increases. The method further includes the step of operating the high voltage generation circuit 3 after the power is turned on after the step of turning on the power while keeping the potential difference between the power supply voltage and the control voltage below a certain voltage so as not to exceed. By operating the high voltage generation circuit later when the power is turned on, it is possible to prevent an inrush current when the power is turned on, but this may cause the photoelectric conversion element to be forward-biased when the power is turned on. As the voltage rises, the power is turned on while maintaining the potential difference between the power supply voltage and the control voltage below a certain voltage so that the potential difference from the control voltage does not exceed the certain voltage. Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 2 is a block diagram of the optical receiver circuit 10 according to the first embodiment. 2, parts that are the same in configuration and operation as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. In FIG. 2, a first protection circuit 4 and a second protection circuit 5 are provided.

  The first protection circuit 4 includes resistors R2, R3, a power supply voltage Vcc, and a reverse bias voltage divided by the resistors R2, R3 that divide the reverse bias voltage of the avalanche photodiode 1 accumulated in the capacitor C1 (point A). The power supply voltage detection circuit (comparator) 41 that outputs a low level signal when the power supply voltage Vcc is lower and the output signal of the power supply voltage detection circuit 41 are turned on. Connected to the PNP transistor 42 for discharging the reverse bias voltage accumulated in the capacitor C1 (point A), the collector resistor R4 of the PNP transistor 42, and the capacitor C1 (point A) and the cathode of the avalanche photodiode 1. The resistor R5 is included. The power supply of the power supply voltage detection circuit 41 is connected to the capacitor C1 (point A), and power is supplied from the capacitor C1. The resistor R4 limits the current when the PNP transistor 42 is turned on, and the PNP transistor 42 and the resistor R4 release the charge of the capacitor C1 (point A) when the power supply voltage detection circuit 41 detects a drop in the power supply voltage. Functions as a discharge circuit. Further, the resistor R5 has a function of limiting a current flowing backward from the amplifier circuit 2 and the avalanche photodiode 1 when the PNP transistor 42 is turned on and the cathode voltage of the avalanche photodiode 1 is lowered.

  The resistors R2 and R3 are set to have a large resistance value that does not wastefully discharge the charge of the capacitor C1, and the potential at the point B divided by the resistors R2 and R3 is always the power supply in the normal specification state. A resistance value is set such that the voltage is lower than the voltage Vcc. This is because the PNP transistor is not turned on during normal use but turned on when the power is turned off.

  The second protection circuit 5 includes an NPN transistor whose base and collector are connected to the power supply Vcc and whose emitter is connected to the output terminal (point E) of the high voltage generation circuit 3. The second protection circuit prevents the potential at the point E from dropping more than a certain voltage from the power supply voltage Vcc, and when the high voltage generating circuit 3 is not functioning, the avalanche photodiode is forward-biased via the avalanche photodiode 1. This prevents the current from flowing back from the amplifier circuit 2 to the capacitor C1 or the high voltage generation circuit 3.

  The resistor R1 controls the reverse bias voltage of the cathode that becomes the control voltage of the avalanche photodiode due to the voltage drop caused by the flowing current. That is, when the amount of light incident on the avalanche photodiode is large, the current flowing through the avalanche photodiode 1 increases, so that the voltage drop due to the resistor R1 increases, the reverse bias voltage applied to the avalanche photodiode 1 decreases, and the avalanche photodiode 1 decreases. The multiplication factor of the photodiode 1 is reduced.

  On the other hand, when no light is incident on the avalanche photodiode 1, since only a dark current flows through the avalanche photodiode, the current flowing through the resistor R1 decreases and the voltage drop due to the resistor R1 also decreases, so the reverse bias voltage increases. The multiplication factor of the avalanche photodiode increases. That is, the resistor R1 automatically increases the multiplication factor according to the amount of light received by decreasing the multiplication factor of the avalanche photo die auto when the light amount is large, and conversely increasing the multiplication factor when the light amount is small. Functions as a magnification control circuit.

  Next, the operation of the optical receiver circuit 10 of the first embodiment shown in FIG. 2 will be described from the operation of the first protection circuit. FIG. 3 is a timing diagram in which the magnitude of the optical reception power received by the avalanche photodiode 1, the voltage of the power supply voltage Vcc, and the voltages at points A to G are plotted in time series.

  In FIG. 3, after the power supply Vcc is once cut off at the timing T2, the power supply is turned on again at the timing T5. The received optical power that is incident while the power supply from T2 to T5 is cut off increases from minus infinity to Pr. The state where the optical reception power is minus infinity is a state where no optical signal is incident on the avalanche photodiode 1, and the state where the optical reception power is Pr is a state where a strong optical signal is received. That is, the optical signal is not incident before the power supply is cut off at the timing T2, whereas a strong optical signal is inputted from the timing T4 while the power supply is turned off. The power is turned on again at T5. The elapsed time from the timing T2 to the timing T5 is shorter than the time during which the capacitor C1 is naturally discharged.

  Prior to timing T2, since no optical signal is incident, the avalanche photodiode 1 is not turned on, and the high voltage (point E, Vapd) output from the high voltage generation circuit 3 is applied to the capacitor C1 via the resistor R1. Accumulated (point A). At this time, the potential at the point B to which the potential obtained by dividing the potential at the point A by the resistors R2 and R3 is higher than the potential at the point C to which the power supply voltage Vcc is connected. Is output (point D), and the PNP transistor 42 is in an OFF state. At this time, the cathode voltage (point F) of the avalanche photodiode 1 is a potential (Vapd−Vr1−Vr5) which is a voltage drop (Vr1, Vr5) caused by the resistance R1 and the resistance R5 from the voltage (Vapd) at the point E. Become. Since only a dark current flows through the avalanche photodiode 1, both Vr1 and Vr5 have small values, and a high voltage is applied to the point F. Therefore, the avalanche photodiode 1 has a high multiplication factor.

  Next, the power supply Vcc is disconnected at timing T2. Immediately after the power supply Vcc is cut off, the potential at the point A of the capacitor C1 maintains that state. Therefore, the power supply voltage detection circuit 41 continues to operate as long as charge remains in the capacitor C1 even after the power supply Vcc is cut off. However, since the potential at the point C connected to the power supply Vcc is lowered, the output (point D) of the power supply voltage detection circuit 41 is inverted, the PNP transistor 42 is turned on, and the charge accumulated in the capacitor C1 (point A) is reduced. discharge. That is, the PNP transistor 42 becomes conductive and discharges the charge of the capacitor C1 after the power source is cut off. As the potential at point A decreases, the potential at points E and F also decreases.

  Next, reception of strong light is started from timing T4. However, at this time, the optical receiver circuit 10 itself does not operate because the optical receiver circuit 10 is powered off.

  Next, the power supply Vcc is turned on again at timing T5. When the power supply Vcc is turned on, the avalanche photodiode 1 and the preamplifier circuit 2 start operating immediately, but the charge accumulated in the capacitor C1 (point A) is discharged by the first protection circuit. The voltages at points A, E, and F all start from a low voltage. Therefore, the multiplication factor of the avalanche photodiode 1 starts from a low state, and even if the power is turned on while strong light is incident on the avalanche photodiode 1, the power is turned on with a low multiplication factor. Therefore, the optical receiving circuit 10 is protected.

  Here, for comparison, in the optical receiver circuit of FIG. 1, as in FIG. 3, the power is turned off in the absence of light incidence, the reception of a strong optical signal is started immediately thereafter, and the power is turned on again immediately thereafter. The operation in this case will be described with reference to the timing chart of FIG.

  In FIG. 4, as in FIG. 3, the power is turned off at timing T <b> 2 in the absence of light incidence, and a strong optical signal is started at timing T <b> 3 during power off, and the power is turned on again at timing T <b> 4 immediately thereafter. FIG. The operation before timing T2 is the same as that in FIG. However, in FIG. 1, since the first protection circuit is not provided, the potential of the cathode (point J) of the avalanche photodiode is kept high for a while even after the power is turned off at timing T2. Therefore, immediately after the power is turned on again at the timing T4, the process starts from a state of receiving strong light with a high multiplication factor. Accordingly, since the avalanche photodiode 1 operates so as to rapidly extract the charge of the capacitor C1 immediately after the power is turned on again at the timing T4, a surge that instantaneously exceeds the rating to the avalanche photodiode 1 or the preamplifier circuit 2 Current may flow, leading to failure.

  Next, returning to the optical receiver circuit 10 of the first embodiment shown in FIG. 2, the operation of the second protection circuit 5 will be described with reference to the timing chart of FIG. FIG. 5 is a timing diagram illustrating the power supply Vcc and voltage waveforms at points A to G in the optical receiver circuit 10 according to the first embodiment. In FIG. 5, the power supply Vcc rises from the ground level (GND) to Vcc at timing T1. Immediately after the power is turned on, the high voltage generation circuit 3 has not started operation. The high voltage generation circuit 3 needs to generate a high voltage via a circuit such as a DC-DC converter, and it is necessary to prevent an inrush current to the optical transceiver including the optical reception circuit 10 when the power is turned on. It is.

  However, since power is supplied to the preamplifier circuit 2 at the same time as the power is turned on, the avalanche photodiode 1 is forward-biased when the voltages at the points E and A are at the ground level. A current flows backward from the feedback circuit of the amplifier circuit 2 to the capacitor C <b> 1 through the avalanche photodiode 1. When the capacitance of the capacitor C1 is large, the current that flows instantaneously may exceed the forward current proof strength of the avalanche photodiode 1, leading to destruction of the avalanche photodiode.

  Therefore, the second protection circuit 5 follows the rise of the power supply Vcc at the timing T1, and raises the voltage at the point E to a voltage Vcc-Vf that is lower by the voltage drop Vf of the second protection circuit. Along with this, the potentials at points A and F also rise. The rising voltages are lower by Vcc−Vf−Vr1 and Vcc−Vf−Vr1−Vr5 in consideration of voltage drops of the resistors R1 and R5, respectively. Note that the rise of the potential at the point A rises at the timing T3 with a delay by a time constant due to the resistor R1 and the capacitor C1.

  The potential at point G rises to a constant voltage (Vpda) at timing T2 due to the bias voltage of the preamplifier circuit 2, but the second protection circuit 5 gives a constant voltage to points A and F, so that the avalanche The potential difference is not so great that the photodiode 1 is destroyed by the forward current. The first protection circuit starts operating when the potential at the point A rises. However, since the power supply Vcc is applied to the point C of the first protection circuit simultaneously with the rise of the power supply Vcc, the power supply voltage detection circuit 41 is always high. The level is output to point D, and the PNP transistor 42 is not turned on.

  Next, at timing T4, the high voltage generation circuit 3 starts operating, and starts supplying a voltage higher than Vcc-Vf supplied by the second protection circuit 5 to the point E. As the potential at point E increases, the potential at points A and F also increases. Further, when a certain time elapses, the high voltage generating circuit outputs a steady-state voltage Vapd at the point E, and accordingly, the points A and F rise to a certain stable voltage, and the power-on operation is completed.

  That is, the avalanche photodiode 1 is forward-biased because a constant voltage is applied to the points E, A, and F by the second protection circuit 5 until the high voltage generation circuit 3 starts operating immediately after the power is turned on. It can be prevented that a large current flows from the preamplifier circuit 2 to the capacitor C1 and the optical receiver circuit 10 is destroyed.

  For comparison, FIG. 6 shows a timing chart when the optical receiver circuit 100 in FIG. 1 is turned on under the same conditions as those in FIG. In FIG. 6, the power supply Vcc rises at the timing T1, and at the timing T2, the preamplifier circuit 2 starts its operation, and after the timing T2, the input bias voltage Vpda is applied to the K point as its input terminal. At this timing T2, the high voltage generation circuit 3 has not yet reached a high voltage supply. Here, in FIG. 1, there is provided means for applying a constant voltage to the cathode (point J) of the avalanche photodiode 1 when the high voltage generation circuit 3 such as the second protection circuit of the first embodiment is not operating. It is not done. Accordingly, there is a possibility that the avalanche photodiode is forward-biased and destroyed after the preamplifier circuit 2 is started up (timing T2) until the high voltage generation circuit 3 can supply a high voltage. Note that the avalanche photodiode is not biased in the forward direction after the high voltage generating circuit generates a high voltage due to T3.

  FIG. 7 is a block diagram of the optical receiver circuit 11 according to the second embodiment. The present invention can also be applied to photoelectric conversion elements such as PIN photodiodes and phototransistors other than avalanche photodiodes. In FIG. 7, a PIN photodiode is used as the photoelectric conversion element 1 instead of the avalanche photodiode. Since the PIN photodiode does not require a high voltage as a control voltage (reverse bias voltage), the high voltage generation circuit 3 is not provided, and the reverse bias voltage is directly applied from the power supply Vcc. Therefore, since there is no fear of destruction of the photoelectric conversion element 1 due to the forward current caused by the delay in the rise of the power supply of the high voltage generation circuit, the second protection circuit is not provided. Other configurations and operations are basically the same as those of the first embodiment. That is, when there is no light incidence, the power is turned off in a state where a large voltage is applied to the capacitor C1 and the photoelectric conversion element 1, and the reception of strong light is started immediately after the power is turned off. However, if the electric charge remains in the capacitor C1 after the power is turned off, the electric charge accumulated in the capacitor C1 is discharged by the first protection circuit 4 that receives power supply from the capacitor C1. Therefore, when the power is turned on again, the multiplication factor of the photoelectric conversion element 1 starts from a low state, so that a large current flows through the photoelectric conversion element 1 and the amplifier circuit 2 immediately after the power is turned on, causing the destruction. Can be prevented.

In recent years, in a PON system and the like, it is necessary to increase the output of an optical transceiver and improve the minimum light receiving sensitivity characteristic in order to increase the distance and the number of connections. At that time, it is possible to obtain the required characteristics by enlarging the loss budget by using the avalanche photodiode, but at the same time, there is a concern that the avalanche photodiode element may fail at the time of high light receiving power. For example, it may occur that an unexpected operation such as connecting the central office side and the optical path directly when performing the evaluation, or repeatedly repeating the power-off and the power-on while receiving light. Even in such a case, according to the present invention, it is possible to prevent the optical transceiver from failing.

  According to the present invention, it is possible to prevent a failure of an optical element and a receiving circuit due to a transient response when power is turned on and off in a receiving unit of an optical transceiver.

  By applying the present invention, an overcurrent to an optical element and an amplifier circuit that occurs at the time of a transient response is prevented, for example, when an evaluation is performed, the optical path is directly connected to the office building side, or the power is cut off in a state of receiving light, It is possible to prevent a failure even when an unexpected work such as re-insertion is repeated.

  In particular, an optical transceiver using an avalanche photodiode can protect the avalanche photodiode because the forward current and the reverse current resistance are low.

  In a downsized optical transceiver, there is a concern about characteristic deterioration due to noise components from inside and outside of the optical module, so there is a case where it is desired to lower the cutoff frequency of the power supply filter (that is, to increase the capacitance of the capacitor). When the embodiment is not applied, a surge current may flow from a capacitor having a large capacity, and thus a large capacity capacitor cannot be applied.

  By using the embodiment of the present invention, it is possible to connect a large-capacity capacitor, and noise immunity is improved.

  Although the embodiments have been described above, the present invention is not limited only to the configurations of the above embodiments, and of course includes various modifications and corrections that can be made by those skilled in the art within the scope of the present invention. It is.

1: Photoelectric conversion element [avalanche photodiode, PIN photodiode]
2: Amplifier circuit [Preamplifier circuit]
3: High voltage generation circuit 4: Protection circuit [first protection circuit]
5: Second protection circuit [NPN transistor]
10, 11, 100: Optical receiver circuit 41: Power supply voltage detection circuit [comparator]
42: PNP transistor C1: Capacitance R1-R5: Resistance

Claims (11)

A photoelectric conversion element whose multiplication factor can be controlled by the magnitude of the control voltage;
A multiplication factor control circuit for controlling the multiplication factor of the photoelectric conversion element by the amount of light incident on the photoelectric conversion element;
An amplifying circuit that is supplied with power from a power source and amplifies an electrical signal output from the photoelectric conversion element;
A protection circuit for forcibly reducing the multiplication factor when detecting a voltage drop of the power supply;
An optical receiver circuit comprising: A capacitor for holding the control voltage;
A power supply voltage detection circuit for comparing the power supply voltage with a control voltage held by the capacitor; and a discharge of the capacitor when the power supply voltage detection circuit detects a decrease in the power supply voltage. 2. The optical receiver circuit according to claim 1, wherein the optical receiver circuit is a protection circuit including a discharge circuit.   The optical reception according to claim 2, wherein the protection circuit is supplied with a control voltage held by the capacitor as a power supply, and compares the power supply voltage with a voltage obtained by dividing the control voltage held by the capacitor. circuit.   The optical receiver circuit according to claim 2, wherein a resistor is connected between the capacitor and the photoelectric conversion element. The photoelectric conversion element is an avalanche photodiode having an anode connected to an input terminal of the amplifier circuit,
A high voltage generating circuit for applying the control voltage to a cathode of the avalanche photodiode;
The multiplication factor control circuit is a resistor having one end connected to the high voltage output terminal of the high voltage generation circuit and the other end connected to one end of the capacitor.
5. The optical receiver circuit according to claim 2, wherein the other end of the capacitor is grounded. When the protection circuit is a first protection circuit,
A second protection circuit for controlling the cathode voltage of the avalanche photodiode so as not to drop below a certain voltage with respect to the voltage of the power supply;
6. The optical receiver circuit according to claim 5, further comprising:   7. The second protection circuit includes a transistor connected in a forward direction or a diode connected in a forward direction between the power source and a high voltage output terminal of the high voltage generation circuit. Optical receiver circuit. The photoelectric conversion element is a photodiode having an anode connected to an input terminal of the amplifier circuit,
The control voltage is a reverse bias voltage for the photodiode;
The multiplication factor control circuit is a resistor having one end connected to the power source and the other end connected to one end of the capacitor,
5. The optical receiver circuit according to claim 2, wherein the other end of the capacitor is grounded. An optical receiver including a photoelectric conversion element whose multiplication factor can be controlled by the magnitude of a control voltage,
First protection means for short-circuiting the control voltage to ground when the optical receiver is powered off;
Second protection means for controlling the control voltage so that a potential difference from the power supply voltage does not occur above a certain voltage due to an increase in the power supply voltage when the optical receiver is turned on;
An optical receiver characterized by comprising: A photoelectric conversion element whose multiplication factor can be controlled by the magnitude of the control voltage;
An amplification circuit for amplifying an electric signal output from the photoelectric conversion element;
A high voltage generating circuit for applying a control voltage to the photoelectric conversion element;
A capacity for holding the control voltage;
A method for protecting an optical receiver circuit including:
Forcibly discharging the charge accumulated in the capacitor when the optical receiver circuit is powered off;
Regardless of the multiplication factor of the photoelectric conversion element before turning off the power, turning on the optical receiver circuit in a state where the multiplication factor is low;
A method for protecting an optical receiver circuit, comprising: In the step of turning on the optical receiver, the power is turned on while maintaining the potential difference between the power supply voltage and the control voltage below a certain voltage so that the potential difference from the control voltage does not exceed a certain voltage as the power supply voltage increases. And
11. The method of protecting an optical receiver circuit according to claim 10, further comprising the step of operating the high voltage generation circuit after the power is turned on after the step of turning on the power.

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