JP2010287947A - Apd bias voltage control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect an APD (Avalanche Photo Diode) module from excessive input of an optical signal. <P>SOLUTION: A circuit is provided with: a bias voltage application unit 3 which applies a bias voltage to the APD module 1; an APD current monitor unit 4 which outputs a monitor current according to an APD current generated by the APD module 1; and a bias voltage control unit 5 which controls the bias voltage according to the monitor current output from the APD current monitor unit 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an APD bias voltage control circuit for protecting an APD (Avalanche PhotoDiode) module from an excessive input of an optical signal, for example.

  As a receiving module of an optical communication system, an APD module using an APD element is known. This APD module is used by applying a high bias voltage of about 30 V to the APD element, so that an electronic avalanche phenomenon occurs when an optical signal is input, and it corresponds to a multiplication factor determined by the applied bias voltage. Since the APD current flows, a sufficient current can be generated even when an optical signal with a very low intensity is input.

  In the APD bias voltage control circuit for controlling the bias voltage applied to the APD module, the bias voltage to be applied is changed depending on the input power of the optical signal. The weaker the input power of the optical signal, the higher the bias voltage is increased. Control is performed so as to increase the magnification. The stronger the input power of the optical signal, the lower the bias voltage and the lower the multiplication factor. As a result, the multiplication factor can be controlled in response to fluctuations in the input power of the optical signal, and the output level of the electrical signal output from the APD module can be maintained constant.

  However, in the conventional APD bias voltage control circuit, when the optical fiber is connected from the state where there is no optical signal input, or when the optical signal input sharply increases when the transmitter / receiver module is turned on, etc. When the input power of the optical signal rises in a short time of several ms to several hundred ms from the state where no optical signal is input, the control of the bias voltage contributing to the multiplication factor cannot follow the input power of the optical signal, and the APD module There is a problem that the APD current generated by the APD module exceeds the maximum rating and the APD module may be damaged.

  Also, when the optical signal is constantly increased and excessively input, the bias voltage decreases and the multiplication factor decreases, but there is a non-lower region that does not decrease below a certain region. When the optical signal is excessively input in the state, the APD current generated by the APD module increases beyond the maximum rating, and there is a problem that the APD module may be damaged.

  On the other hand, the APD bias voltage that limits the instantaneous excessive current generated due to the transient response of the optical amplifier without degrading the original performance and protects the light receiving element and the preamplifier from the excessive current. There is a control circuit (see, for example, Patent Document 1).

  There is also an APD bias voltage control circuit that protects the APD module even when the input power of the optical signal changes suddenly (see, for example, Patent Document 2). There is also an APD bias voltage control circuit that reduces the output voltage of the high voltage generation circuit until the bias voltage becomes an unamplifiable voltage of the APD module when the light reception level of the APD module exceeds the maximum light reception level (for example, And Patent Document 3).

JP-A-9-93203 JP 2000-244419 A JP 2004-336320 A

  However, the APD bias voltage control circuit disclosed in Patent Document 1 controls a voltage from a voltage source using a voltage comparator and a subtractor, and is applied to an APD module using a self-bias resistor. There is a problem that cannot be done.

  The APD bias voltage control circuit disclosed in Patent Document 2 relates to protection against instantaneous excessive input of an optical signal, and can protect the APD module against steady excessive input of an optical signal. There is a problem that it cannot be done. On the other hand, the APD bias voltage control circuit disclosed in Patent Document 3 is a method of directly changing the output voltage of a high voltage generation circuit using a DC / DC converter, and peripheral circuit components constituting the DC / DC converter. Due to this time constant, it takes time to change the voltage, and depending on the degree, there is a problem that the APD module may not be protected by following an excessive input of an instantaneous optical signal.

  The present invention has been made to solve the above-described problems, and provides an APD bias voltage control circuit that can protect an APD module from an excessive input of an optical signal and can be applied to a self-bias resistance system. The purpose is that.

  An APD bias control circuit according to the present invention includes a bias voltage application unit that applies a bias voltage to an APD module, an APD current monitor unit that outputs a monitor current according to an APD current generated by the APD module, and an APD current monitor unit And a bias voltage control unit that controls the bias voltage in accordance with the monitor current output by.

  According to the present invention, since it is configured as described above, the APD current generated by the APD module does not exceed the maximum rating, the APD module can be protected from an excessive input of an optical signal, and the self-bias can be protected. It can be applied to the resistance method.

It is a figure which shows the structure of the APD bias voltage control circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the change of the bias voltage by the change of the optical signal in Embodiment 1 of this invention, a multiplication factor, and APD electric current. It is a figure which shows the change of the bias voltage by a change of the optical signal in Embodiment 2 of this invention, a multiplication factor, and APD electric current.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
1 is a diagram showing a configuration of an APD bias voltage control circuit according to Embodiment 1 of the present invention.
As shown in FIG. 1, the APD bias voltage control circuit applies the bias voltage Vb and the APD module 1 that generates the APD current Iapd when the optical signal Pin is input with the bias voltage Vb applied. A constant voltage source 2 that supplies a high voltage Vhv necessary for the operation, a bias voltage application unit 3 that generates a bias voltage Vb from the high voltage Vhv supplied by the constant voltage source 2 and applies the bias voltage Vb to the APD module 1, and an APD module 1, a self-bias resistor R1 that causes a voltage drop according to the APD current Iapd generated by 1 and changes the bias voltage Vb applied to the APD module 1, and a monitor current according to the APD current Iapd generated by the APD module 1 The APD current monitor unit 4 that outputs Imon and the APD current monitor unit 4 The monitor current Imon is converted into a voltage, and the bias voltage Vb is obtained by sending the bias command voltage Vset to the bias voltage applying unit 3 from the resistor R2 that is output as the monitor signal Vmon and the monitor signal Vmon that is output from the resistor R2. And a bias voltage control unit 5 to be controlled.

  Here, as shown in FIG. 1, the APD module 1 generates an electronic avalanche phenomenon when an optical signal Pin is input in a state where a bias voltage Vb is applied, and an increase determined by the applied bias voltage Vb. An APD element 6 that generates an APD current Iapd corresponding to the magnification M, and a transimpedance amplifier (TIA) 7 that converts the APD current Iapd generated by the APD element 6 into a voltage and outputs the voltage as an output electric signal Vout. The

Next, the operation of the APD bias voltage control circuit configured as described above will be described.
First, the constant voltage source 2 supplies the bias voltage application unit 3 with the high voltage Vhv necessary for generating the bias voltage Vb. Next, the bias voltage application unit 3 generates the bias voltage Vb from the high voltage Vhv supplied from the constant voltage source 2 based on the bias command voltage Vset for controlling the bias voltage Vb sent from the bias voltage control unit 5. And applied to the APD module 1.

  Next, the APD element 6 of the APD module 1 generates an electronic avalanche phenomenon when the optical signal Pin is input with the bias voltage Vb sent from the bias voltage application unit 3 through the self-bias resistor R1 applied. Then, the APD current Iapd corresponding to the multiplication factor M determined by the applied bias voltage Vb is generated. Next, the TIA 7 of the APD module 1 converts the APD current Iapd generated by the APD element 6 into a voltage and outputs the voltage as an output electric signal Vout.

  On the other hand, the APD current monitor unit 4 outputs a monitor current Imon corresponding to the APD current Iapd generated by the APD element 6 of the APD module 1. Next, the resistor R2 converts the monitor current Imon output by the APD current monitor unit 4 into a voltage and outputs it as a monitor signal Vmon.

  Next, the bias voltage control unit 5 controls the bias voltage Vb by sending a bias command voltage Vset for controlling the bias voltage Vb to the bias voltage application unit 3 from the monitor signal Vmon output by the resistor R2.

Next, control of the bias voltage Vb by the bias voltage control unit 5 will be described.
FIG. 2 is a diagram showing changes in the bias voltage Vb, multiplication factor M, and APD current Iapd due to changes in the optical signal Pin in Embodiment 1 of the present invention, and FIG. 2 (a) is a diagram showing changes in the optical signal Pin. 2 (b) is a diagram showing a change in the bias voltage Vb, FIG. 2 (c) is a diagram showing a change in the multiplication factor M, and FIG. 2 (d) shows a change in the APD current Iapd. FIG. Here, the dotted line in FIG. 2 shows each change in the conventional APD bias voltage control circuit, and the solid line shows each change in the APD bias voltage control circuit according to Embodiment 1 of the present invention.

  First, as shown in FIG. 2 (a), when the optical signal Pin is hardly input to the APD module 1, the APD current Iapd generated by the APD module 1 almost flows as shown in FIG. 2 (d). No state. Therefore, the monitor signal Vmon output by the resistor R2 via the APD current monitor unit 4 is hardly output, and the bias voltage control unit 5 does not input the optical signal Pin from the monitor signal Vmon to the APD module 1. Can be judged.

  In this way, when the bias voltage control unit 5 determines from the monitor signal Vmon that the optical signal Pin is not input to the APD module 1, the bias voltage control unit 5 then applies the bias voltage application unit 3 to the APD module 1. A bias command voltage Vset indicating that the bias voltage Vb is set to a value lower than a specified value in normal use is sent.

  Next, the bias voltage application unit 3 lowers the bias voltage Vb applied to the APD module 1 based on the bias command voltage Vset sent from the bias voltage control unit 5 as shown in FIG. Reduce to value. Along with this, the multiplication factor M also decreases as shown in FIG.

  In this state, as shown in FIG. 2A, a strong optical signal having a steep rise characteristic in a short time that an APD current Iapd exceeding the maximum rating flows in the conventional APD bias voltage control circuit. Even when Pin is input to the APD module 1, the bias voltage Vb is set to a value lower than the specified value so that the multiplication factor M is lowered. Therefore, as shown in FIG. The APD current Iapd generated by the module 1 can be kept within the maximum rating, and the APD module 1 can be protected.

  After that, when the bias voltage control unit 5 determines from the monitor signal Vmon that the steep rise of the optical signal Pin is eliminated and the multiplication factor M is increased, the APD current Iapd generated by the APD module 1 does not exceed the maximum rating. Subsequently, a bias command voltage Vset indicating that the bias voltage Vb applied to the APD module 1 is raised to a specified value in normal use is sent to the bias voltage application unit 3.

  Next, the bias voltage application unit 3 raises the bias voltage Vb applied to the APD module 1 to a specified value based on the bias command voltage Vset sent from the bias voltage control unit 5 as shown in FIG.

  As described above, according to the first embodiment, the APD current Iapd is monitored by the bias voltage controller 5, and the bias applied to the APD module 1 when the optical signal Pin is not input to the APD module 1. Since the control is performed such that the voltage Vb is lowered and the bias voltage Vb is increased to a specified value after the input of the optical signal Pin is detected, the APD current Iapd generated by the APD module 1 does not exceed the maximum rating. The APD module 1 can be protected from an instantaneous excessive input of the optical signal Pin, and can be applied to a self-bias resistance system.

Embodiment 2. FIG.
The APD bias control circuit according to the first embodiment of the present invention is configured to lower the bias voltage Vb applied to the APD module 1 when the optical signal Pin is not input to the APD module 1. The APD bias control circuit according to the second embodiment of the invention is configured to lower the bias voltage Vb applied to the APD module 1 when the optical signal Pin is constantly increased and excessively input to the APD module 1. Is.
The APD bias control circuit according to the second embodiment of the present invention is the same as the configuration of the APD bias control circuit according to the first embodiment of the present invention shown in FIG. 1, and will be described below with reference to FIG. Do.

Next, control of the bias voltage by the bias voltage control unit 5 will be described.
FIG. 3 is a diagram showing changes in bias voltage, multiplication factor, and APD current due to changes in the optical signal according to Embodiment 2 of the present invention, and FIG. 3 (a) is a diagram showing changes in the optical signal Pin. 3 (b) is a diagram showing changes in the bias voltage Vb, FIG. 3 (c) is a diagram showing changes in the multiplication factor M, and FIG. 3 (d) is a diagram showing changes in the APD current Iapd. Here, the dotted line in FIG. 3 shows each change in the conventional APD bias voltage control circuit, and the solid line shows each change in the APD bias voltage control circuit according to the second embodiment of the present invention.

  As shown in FIG. 3A, when the optical signal Pin is constantly increased and excessively input to the APD module 1, the APD voltage generated by the APD module 1 is shown in FIG. Since Iapd also increases, when the bias voltage Vb applied to the APD module 1 is decreased by the self-bias resistor R1, the multiplication factor M is decreased as shown in FIG.

  However, as indicated by the dotted line in FIG. 3 (c), when the multiplication factor M decreases to a certain region, it is in a stopped state that does not decrease below that. If the optical signal Pin is further excessively input to the APD module 1 in a state where the multiplication factor M has stopped decreasing, the APD current Iapd generated by the APD module 1 further increases. The bias voltage control unit 5 indicates that the optical signal Pin is constantly increased and excessively input to the APD module 1 from the monitor signal Vmon, and the APD current Iapd generated by the APD module 1 may exceed the maximum rating. When the determination is made, a bias command voltage Vset indicating that the bias voltage Vb to be applied to the APD module 1 is set to a value lower than a specified value for normal use is sent to the bias voltage application unit 3.

  Next, the bias voltage application unit 3 lowers the bias voltage Vb applied to the APD module 1 based on the bias command voltage Vset sent from the bias voltage control unit 5 as shown in FIG. Reduce to value. As a result, the bias voltage Vb applied to the APD module 1 is lowered, and the multiplication factor M can be lowered to a region not normally lowered as shown in FIG. Then, even when a strong optical signal Pin that constantly increases so that the APD current Iapd exceeds the maximum rating is input to the APD module 1, the APD current Iapd generated by the APD module 1 is kept within the maximum rating. The APD module 1 can be protected.

  As described above, according to the second embodiment, when the APD current Iapd is monitored by the bias voltage control unit 5 and the optical signal Pin is constantly increased and excessively input to the APD module 1, the APD Since the control is performed such that the bias voltage Vb applied to the module 1 is lowered, the APD current Iapd generated by the APD module 1 does not exceed the maximum rating, and the optical signal Pin is constantly excessively input. The APD module 1 can be protected from the above, and can be applied to a self-bias resistance system.

1 APD module, 2 constant voltage source, 3 bias voltage application unit, 4 APD current monitor unit, 5 bias voltage control unit, 6 APD element, 7 TIA.

Claims (3)

A bias voltage application unit for applying a bias voltage to an APD (Avalanche PhotoDiode) module;
An APD current monitor unit that outputs a monitor current corresponding to the APD current generated by the APD module;
An APD bias voltage control circuit comprising: a bias voltage control unit that controls the bias voltage in accordance with a monitor current output by the APD current monitor unit.   2. The APD according to claim 1, wherein the bias voltage control unit sets the bias voltage lower than a predetermined value when it is determined from the monitor current that the optical signal is not input to the APD module. Bias voltage control circuit.   The bias voltage control unit sets the bias voltage lower than a specified value when it is determined from the monitor current that the optical signal is constantly increased and excessively input to the APD module. The APD bias voltage control circuit according to claim 1.

Images