Avalanche photodiode protection circuit in PON and PON optical modem

Abstract

The avalanche photodiode protection circuit in PON and the PON optical modem provided in the present application relate to the field of optical communication technology. In the present application, the avalanche photodiode protection circuit in PON includes a bias control input processing unit and an avalanche photodiode protection unit. The bias control input terminal is used to obtain the diode bias voltage, and when the illumination intensity of the target avalanche photodiode exceeds the preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds the preset current, and the avalanche photodiode protection unit responds to the photocurrent of the target avalanche photodiode exceeding the preset current, and reduces the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Based on the above content, the problem that the target avalanche photodiode is easily damaged by overload in the prior art can be improved.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to an avalanche photodiode protection circuit in a PON and a PON optical modem. Background Art

[0002] In existing access network optical modules and optical modem applications, the photoelectric signal conversion device commonly used in 10G PON (Passive Optical Network) modules is an avalanche photodiode (APD). When using an APD for photoelectric conversion, a high bias voltage needs to be applied to one end of the APD. As a result, when the input optical signal is strong or intense (i.e., the light intensity is high), a large photocurrent will be generated on the APD. Therefore, when the photocurrent exceeds the maximum current allowed by the APD die, the APD will be damaged. Summary of the Invention

[0003] In view of this, the purpose of the present application is to provide an avalanche photodiode protection circuit in a PON and a PON optical modem, so as to improve the problem in the prior art that the target avalanche photodiode is easily damaged due to overload.

[0004] To achieve the above objectives, this application adopts the following technical solutions:

[0005] An avalanche photodiode protection circuit in a PON, comprising:

[0006] a bias control input processing unit, wherein a first terminal of the bias control input processing unit serves as a bias control input terminal, and the bias control input terminal is used to obtain a diode bias voltage;

[0007] an avalanche photodiode protection unit, wherein a first end of the avalanche photodiode protection unit is connected to a second end of the bias control input processing unit, a second end of the avalanche photodiode protection unit is connected to a target avalanche photodiode, and the avalanche photodiode protection unit is configured to apply the diode bias voltage to the target avalanche photodiode so that the target avalanche photodiode performs photoelectric conversion;

[0008] Moreover, when the illumination intensity of the target avalanche photodiode exceeds a preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds a preset current. In response to the photocurrent of the target avalanche photodiode exceeding the preset current, the avalanche photodiode protection unit reduces the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced, thereby completing the overload protection of the target avalanche photodiode.

[0009] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the avalanche photodiode protection unit includes:

[0010] a first resistor, wherein a first end of the first resistor serves as a first end of the avalanche photodiode protection unit and is connected to a second end of the bias control input processing unit, and a second end of the first resistor serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode;

[0011] a first transistor, wherein the first transistor is a PNP transistor, and an emitter of the first transistor is connected to the first end of the first resistor;

[0012] a second resistor, wherein a first end of the second resistor is connected to a second end of the first resistor, and a second end of the second resistor is connected to a base of the first transistor;

[0013] a third resistor, wherein a first end of the third resistor is connected to the collector of the first transistor, and a second end of the third resistor is grounded;

[0014] Moreover, when the illumination intensity of the target avalanche photodiode exceeds the preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds the preset current. In response to the photocurrent of the target avalanche photodiode exceeding the preset current, the first transistor reduces the diode bias voltage applied to the target avalanche photodiode by connecting the emitter and the collector of the first transistor, thereby reducing the photocurrent of the target avalanche photodiode and completing the overload protection of the target avalanche photodiode.

[0015] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the resistance value of the first resistor is 400-1000 ohms, and the resistance value of the third resistor is 100-1000 ohms.

[0016] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the avalanche photodiode protection unit further includes:

[0017] A fourth resistor, wherein a first end of the fourth resistor is connected to the second end of the first resistor, and a second end of the fourth resistor serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode.

[0018] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the avalanche photodiode protection unit further includes:

[0019] an inductor element, wherein a first end of the inductor element is connected to the second end of the fourth resistor, and a second end of the inductor element serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode;

[0020] A first capacitor, wherein a first end of the first capacitor is connected to the second end of the inductor element, and a second end of the first capacitor is grounded.

[0021] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the bias control input processing unit includes:

[0022] A current source, wherein the current source is used to copy and output the photocurrent of the target avalanche photodiode to form a target RSSI current, and the target RSSI current is used to reflect the light intensity of the target avalanche photodiode.

[0023] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the current source includes:

[0024] a second transistor, wherein the second transistor is a PNP transistor, and a collector of the second transistor serves as a second terminal of the bias control input processing unit and is connected to a first terminal of the avalanche photodiode protection unit;

[0025] a third transistor, wherein the third transistor is a PNP transistor, and the base of the third transistor is connected to the collector of the third transistor, and the base of the third transistor is connected to the base of the second transistor;

[0026] a fourth transistor, wherein the fourth transistor is a PNP transistor, a base of the fourth transistor is connected to the collector of the second transistor, an emitter of the fourth transistor is connected to the collector of the third transistor, and the collector of the fourth transistor is used to output the target RSSI current;

[0027] a fifth resistor, wherein a first end of the fifth resistor serves as a first end of the bias control input processing unit for obtaining the diode bias voltage, and a second end of the fifth resistor is connected to the emitter of the second transistor;

[0028] a sixth resistor, wherein a first end of the sixth resistor is connected to the first end of the fifth resistor, and a second end of the sixth resistor is connected to the emitter of the third transistor.

[0029] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the current source further comprises:

[0030] a seventh resistor, wherein a first end of the seventh resistor is connected to the collector of the fourth transistor, and a second end of the seventh resistor is used to output the target RSSI current.

[0031] In a preferred embodiment of the present application, in the avalanche photodiode protection circuit in the PON, the current source further comprises:

[0032] A second capacitor, wherein a first end of the second capacitor is connected to the second end of the seventh resistor, and a second end of the second capacitor is grounded.

[0033] Based on the above, this application also provides a PON optical modem, including:

[0034] Target avalanche photodiode;

[0035] The avalanche photodiode protection circuit in the PON is connected to the target avalanche photodiode to protect the target avalanche photodiode from overload.

[0036] The avalanche photodiode protection circuit and PON optical modem in the PON provided by the present application include a bias control input processing unit and an avalanche photodiode protection unit. The bias control input terminal is used to obtain a diode bias voltage, and when the illumination intensity of the target avalanche photodiode exceeds a preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds a preset current, and the avalanche photodiode protection unit responds to the photocurrent of the target avalanche photodiode exceeding the preset current by reducing the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Based on the above content, due to the presence of the avalanche photodiode protection unit, when the photocurrent of the target avalanche photodiode exceeds the preset current, the diode bias voltage applied to the target avalanche photodiode is reduced, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Therefore, the problem that the target avalanche photodiode is easily damaged by overload in the prior art can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0038] Figure 1 This is a structural block diagram of the PON optical modem provided in an embodiment of the present application.

[0039] Figure 2 This is an application block diagram of the avalanche photodiode protection circuit in the PON provided in an embodiment of the present application.

[0040] Figure 3 This is a circuit schematic diagram of the avalanche photodiode protection circuit in the PON provided in an embodiment of the present application.

[0041] Figure 4 A schematic diagram of the bias stabilization time when receiving strong light provided in an embodiment of the present application.

[0042] Icon: R1-first resistor; Q1-first transistor; R2-second resistor; R3-third resistor; R4-fourth resistor; L-inductor; C1-first capacitor; Q2-second transistor; Q3-third transistor; Q4-fourth transistor; R5-fifth resistor; R6-sixth resistor; R7-seventh resistor; C2-second capacitor; APD-target avalanche photodiode. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0045] like Figure 1 As shown, an embodiment of the present application provides a PON optical modem (exemplarily, the PON optical modem can be applied to scenarios such as FTTR). The PON optical modem may include a target avalanche photodiode and a PON avalanche photodiode protection circuit. In detail, the PON avalanche photodiode protection circuit is connected to the target avalanche photodiode and can be used to protect the target avalanche photodiode from overload.

[0046] Exemplarily, the PON optical modem may further include a DC-DC device, which may be connected to the avalanche photodiode protection circuit in the PON. In this way, the diode bias voltage output by the DC-DC device may be applied to the target avalanche photodiode through the avalanche photodiode protection circuit in the PON, so that the target avalanche photodiode performs photoelectric conversion. Moreover, when the illumination intensity of the target avalanche photodiode exceeds a preset illumination intensity (which may be configured according to actual needs), the photocurrent of the target avalanche photodiode exceeds a preset current. In response to the photocurrent of the target avalanche photodiode exceeding the preset current (which may also be configured according to actual needs), the avalanche photodiode protection circuit in the PON reduces the diode bias voltage applied to the target avalanche photodiode, thereby reducing the photocurrent of the target avalanche photodiode to complete the overload protection of the target avalanche photodiode.

[0047] Combine Figure 2 The present application also provides an avalanche photodiode protection circuit for a PON. The avalanche photodiode protection circuit for a PON can be applied to the aforementioned PON optical modem. Furthermore, the avalanche photodiode protection circuit for a PON can include a bias control input processing unit and an avalanche photodiode protection unit.

[0048] Specifically, the first end of the bias control input processing unit serves as a bias control input end, which is used to obtain a diode bias voltage. For example, it can be connected to the output end of the aforementioned DC-DC device, meaning that the diode bias voltage can be provided by the aforementioned DC-DC device. Furthermore, the first end of the avalanche photodiode protection unit is connected to the second end of the bias control input processing unit, and the second end of the avalanche photodiode protection unit is connected to a target avalanche photodiode. The avalanche photodiode protection unit is used to apply the diode bias voltage to the target avalanche photodiode, causing the target avalanche photodiode to perform photoelectric conversion. Furthermore, when the illumination intensity of the target avalanche photodiode exceeds a preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds a preset current. In response to the photocurrent exceeding the preset current, the avalanche photodiode protection unit reduces the diode bias voltage applied to the target avalanche photodiode, thereby reducing the photocurrent of the target avalanche photodiode and providing overload protection for the target avalanche photodiode.

[0049] Based on the above content, due to the presence of the avalanche photodiode protection unit, when the photocurrent of the target avalanche photodiode exceeds the preset current, the diode bias voltage applied to the target avalanche photodiode is reduced, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Therefore, the problem in the prior art that the target avalanche photodiode is easily damaged by overload can be improved.

[0050] In the first aspect, it should be noted that the specific circuit structure of the bias control input processing unit is not limited and can be selected according to actual needs.

[0051] For example, in an alternative embodiment, in order to obtain the diode bias voltage and also perform current sampling to facilitate monitoring of the optical signal intensity, the bias control input processing unit may include a current source.

[0052] The current source is used to copy and output the photocurrent of the target avalanche photodiode to form a target RSSI (Received Signal Strength Indicator) current. The target RSSI current is used to reflect the light intensity of the target avalanche photodiode. Exemplarily, this current value is proportional to the received light signal intensity.

[0053] It is understandable that the specific circuit structure of the current source is not limited and can be selected according to actual needs. For example, in an alternative embodiment, in order to avoid the situation where the input current and the output current have a large difference due to the base current mismatch of the conventional mirror current source, thereby causing the receiving RSSI current monitoring to be inaccurate, the current source is combined with the base current mismatch of the conventional mirror current source. Figure 3 , the current source may further include a second transistor Q2, a third transistor Q3, a fourth transistor Q4, a fifth resistor R5 and a sixth resistor R6.

[0054] Specifically, the second transistor Q2 is a PNP transistor, and the collector of the second transistor Q2 serves as the second terminal of the bias control input processing unit and is connected to the first terminal of the avalanche photodiode protection unit. The third transistor Q3 is a PNP transistor, and the base of the third transistor Q3 is connected to the collector of the third transistor Q3, and the base of the third transistor Q3 is connected to the base of the second transistor Q2. The fourth transistor Q4 is a PNP transistor, and the base of the fourth transistor Q4 is connected to the collector of the second transistor Q2, and the emitter of the fourth transistor Q4 is connected to the collector of the third transistor Q3. The collector of the fourth transistor Q4 is used to output the target RSSI current. The first terminal of the fifth resistor R5 serves as the first terminal of the bias control input processing unit, and is used to obtain the diode bias voltage. The second terminal of the fifth resistor R5 is connected to the emitter of the second transistor Q2. A first end of the sixth resistor R6 is connected to the first end of the fifth resistor R5 , and a second end of the sixth resistor R6 is connected to the emitter of the third transistor Q3 .

[0055] It is understandable that, in other embodiments, based on the above implementation content, the current source may further include at least one of the seventh resistor R7 and the second capacitor C2. For example, it may include only the seventh resistor R7, or only the second capacitor C2, or it may include both the seventh resistor R7 and the second capacitor C2. In this way, a filtering network for the RSSI current can be formed with at least one of the seventh resistor R7 and the second capacitor C2 to ensure the reliability of the output target RSSI current.

[0056] For example, in an alternative embodiment, when the seventh resistor R7 is included, a first end of the seventh resistor R7 is connected to the collector of the fourth transistor Q4, and a second end of the seventh resistor R7 is used to output the target RSSI current. For another example, in another alternative embodiment, when the seventh resistor R7 is included, a second capacitor C2 is further included, such that a first end of the second capacitor C2 is connected to the second end of the seventh resistor R7, and a second end of the second capacitor C2 is grounded.

[0057] Secondly, it should be noted that the specific circuit structure of the avalanche photodiode protection unit is not limited and can be selected according to actual needs.

[0058] For example, in an alternative embodiment, in order to be able to reliably protect the target avalanche photodiode APD from overload through the avalanche photodiode protection unit, and to ensure the reliable operation of the target avalanche photodiode APD, for example, in a conventional scheme, the protection circuit can quickly lower the voltage to close to 0 and maintain the target protection avalanche photodiode when strong light is incident. However, in this protection method, the bias voltage on the target avalanche photodiode APD is reduced to 0, which will cause the target avalanche photodiode APD to be unable to continue to work normally to achieve photoelectric conversion. Moreover, since the target avalanche photodiode APD is not working, it is impossible to determine whether the input light signal at this time has returned to normal from strong light. If the light signal is still strong light, the target avalanche photodiode APD will be immediately damaged when it is reconnected due to excessive photocurrent generated by the strong light. In addition, in another conventional solution, a current limiting resistor can be set to generate a larger voltage drop when the current increases to reduce the bias voltage on the target avalanche photodiode APD, thereby avoiding excessive current when a strong light signal illuminates the target avalanche photodiode APD. However, because a large amount of charge is still stored on the decoupling capacitor, when the light intensity is high, it takes milliseconds for the bias voltage on the target avalanche photodiode APD to drop from high voltage to low voltage; the large current generated during this time may still cause the target avalanche photodiode APD to be damaged, thereby failing to effectively achieve overload protection of the target avalanche photodiode APD, and because different target avalanche photodiodes APD have different optimal operating point voltages, it is difficult to select a good series voltage divider resistor; if the value is too small, the target avalanche photodiode APD cannot be well protected, resulting in breakdown when the light is strong, and if the value is too large, the target avalanche photodiode APD enters saturation state prematurely. Based on this, the avalanche photodiode protection unit may include a first resistor R1, a first transistor Q1, a second resistor R2, and a third resistor R3.

[0059] In detail, the first end of the first resistor R1 serves as the first end of the avalanche photodiode protection unit and is connected to the second end of the bias control input processing unit, and the second end of the first resistor R1 serves as the second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode APD. The first transistor Q1 is a PNP transistor, and the emitter of the first transistor Q1 is connected to the first end of the first resistor R1. The first end of the second resistor R2 is connected to the second end of the first resistor R1, and the second end of the second resistor R2 is connected to the base of the first transistor Q1. The first end of the third resistor R3 is connected to the collector of the first transistor Q1, and the second end of the third resistor R3 is grounded.

[0060] Moreover, when the light intensity of the target avalanche photodiode APD exceeds the preset light intensity, the photocurrent of the target avalanche photodiode APD exceeds the preset current. In response to the photocurrent of the target avalanche photodiode APD exceeding the preset current, the first transistor Q1 turns on the emitter and collector of the first transistor Q1 to reduce the diode bias voltage applied to the target avalanche photodiode APD, so that the photocurrent of the target avalanche photodiode APD is reduced, thereby completing the overload protection of the target avalanche photodiode APD.

[0061] Specifically, during normal operation, the first transistor Q1 is disconnected. When the incident light is large enough to make the photocurrent flowing between the emitter and the base reach a certain value, the first transistor Q1 will be turned on, which is equivalent to connecting a load in parallel to the target avalanche photodiode APD. The overall load impedance is reduced. If the output bias voltage is to be maintained unchanged, the output power consumption of the DC-DC device will increase. Once the output limit of the DC-DC device is reached, the bias voltage will decrease with the increase of incident light within a certain range. The decrease in bias voltage leads to a decrease in the multiplication factor, thereby reducing the current flowing through the target avalanche photodiode APD, which plays a protective role. At the same time, as the current flowing through the first transistor Q1 increases, the voltage drop across the first resistor R1 will also increase, making the base current too large, resulting in a small voltage difference between the collector and the emitter, and the transistor saturates. After that, if the incident light continues to increase, the bias voltage of the target avalanche photodiode APD will tend to a stable value (such as Figure 4 shown).

[0062] It can be understood that the first resistor R1 determines the magnitude of the incident light for the first transistor Q1 to be turned on and off. The larger the resistance value, the smaller the incident light required for the first transistor Q1 to be turned on, and the larger the Vbe (voltage difference between the base and the emitter) under the same incident light, which is conducive to increasing the current passing through the first transistor Q1, thereby reducing the bias voltage and current of the target avalanche photodiode APD. For example, since the target avalanche photodiode APD exceeds 2mA, it will cause damage to the target avalanche photodiode APD. Therefore, the value of the first resistor R1 is between 400-1K ohms. The third resistor R3 acts as a parallel load. When the first transistor Q1 is turned on, the smaller the resistance value is under the same bias voltage, the easier it is to lower the bias voltage and current of the target avalanche photodiode APD. The value of the third resistor R3 is several hundred ohms, that is, 100-1000 ohms. The specific parameters of other resistors can be selected according to actual conditions.

[0063] The experimental data when the optical fiber is connected to 5dBm (optical signal strength) are as follows:

[0064]

[0065] It can be understood that, based on the above embodiment, in an alternative embodiment, the avalanche photodiode protection unit may further include a fourth resistor R4.

[0066] Specifically, the first end of the fourth resistor R4 is connected to the second end of the first resistor R1, and the second end of the fourth resistor R4 serves as the second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode (APD). In this way, the fourth resistor R4 can serve as a debugging resistor to facilitate measurement of the current of the target avalanche photodiode (APD) during verification.

[0067] It can be understood that, based on the above embodiment, in an alternative embodiment, the avalanche photodiode protection unit may further include an inductor element L and a first capacitor C1.

[0068] Specifically, the first end of the inductor element L is connected to the second end of the fourth resistor R4, and the second end of the inductor element L serves as the second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode (APD). The first end of the first capacitor C1 is connected to the second end of the inductor element L, and the second end of the first capacitor C1 is grounded. Thus, the inductor element L and the first capacitor C1 form a voltage filtering network for the target avalanche photodiode (APD).

[0069] In summary, the avalanche photodiode protection circuit and PON optical modem in the PON provided by the present application include a bias control input processing unit and an avalanche photodiode protection unit. The bias control input terminal is used to obtain a diode bias voltage, and when the illumination intensity of the target avalanche photodiode exceeds a preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds a preset current, and the avalanche photodiode protection unit responds to the photocurrent of the target avalanche photodiode exceeding the preset current, and reduces the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Based on the above content, due to the presence of the avalanche photodiode protection unit, when the photocurrent of the target avalanche photodiode exceeds the preset current, the diode bias voltage applied to the target avalanche photodiode is reduced, so that the photocurrent of the target avalanche photodiode is reduced to complete overload protection. Therefore, the problem that the target avalanche photodiode is easily damaged by overload in the prior art can be improved.

[0070] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An avalanche photodiode protection circuit in a PON, characterized in that: include: a bias control input processing unit, wherein a first terminal of the bias control input processing unit serves as a bias control input terminal, and the bias control input terminal is used to obtain a diode bias voltage; an avalanche photodiode protection unit, wherein a first end of the avalanche photodiode protection unit is connected to a second end of the bias control input processing unit, a second end of the avalanche photodiode protection unit is connected to a target avalanche photodiode, and the avalanche photodiode protection unit is configured to apply the diode bias voltage to the target avalanche photodiode so that the target avalanche photodiode performs photoelectric conversion; Furthermore, when the light intensity of the target avalanche photodiode exceeds a preset light intensity, the photocurrent of the target avalanche photodiode exceeds a preset current. In response to the photocurrent of the target avalanche photodiode exceeding the preset current, the avalanche photodiode protection unit reduces the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced, thereby completing overload protection of the target avalanche photodiode. Wherein, the avalanche photodiode protection unit includes: a first resistor, wherein a first end of the first resistor serves as a first end of the avalanche photodiode protection unit and is connected to a second end of the bias control input processing unit, and a second end of the first resistor serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode; a first transistor, wherein the first transistor is a PNP transistor, and an emitter of the first transistor is connected to the first end of the first resistor; a second resistor, wherein a first end of the second resistor is connected to a second end of the first resistor, and a second end of the second resistor is connected to a base of the first transistor; a third resistor, wherein a first end of the third resistor is connected to the collector of the first transistor, and a second end of the third resistor is grounded; Moreover, when the illumination intensity of the target avalanche photodiode exceeds the preset illumination intensity, the photocurrent of the target avalanche photodiode exceeds the preset current. In response to the photocurrent of the target avalanche photodiode exceeding the preset current, the first transistor reduces the diode bias voltage applied to the target avalanche photodiode by connecting the emitter and the collector of the first transistor, thereby reducing the photocurrent of the target avalanche photodiode and completing the overload protection of the target avalanche photodiode.

2. The avalanche photodiode protection circuit in PON according to claim 1, characterized in that: The resistance value of the first resistor is 400-1000 ohms, and the resistance value of the third resistor is 100-1000 ohms.

3. The avalanche photodiode protection circuit in PON according to claim 2, characterized in that: The avalanche photodiode protection unit further includes: A fourth resistor, wherein a first end of the fourth resistor is connected to the second end of the first resistor, and a second end of the fourth resistor serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode.

4. The avalanche photodiode protection circuit in PON according to claim 3, characterized in that: The avalanche photodiode protection unit further includes: an inductor element, wherein a first end of the inductor element is connected to the second end of the fourth resistor, and a second end of the inductor element serves as a second end of the avalanche photodiode protection unit and is connected to the target avalanche photodiode; A first capacitor, wherein a first end of the first capacitor is connected to the second end of the inductor element, and a second end of the first capacitor is grounded.

5. The avalanche photodiode protection circuit in a PON according to any one of claims 1 to 4, characterized in that: The bias control input processing unit includes: A current source, wherein the current source is used to copy and output the photocurrent of the target avalanche photodiode to form a target RSSI current, and the target RSSI current is used to reflect the light intensity of the target avalanche photodiode.

6. The avalanche photodiode protection circuit in PON according to claim 5, characterized in that: The current source comprises: a second transistor, wherein the second transistor is a PNP transistor, and a collector of the second transistor serves as a second terminal of the bias control input processing unit and is connected to a first terminal of the avalanche photodiode protection unit; a third transistor, wherein the third transistor is a PNP transistor, and the base of the third transistor is connected to the collector of the third transistor, and the base of the third transistor is connected to the base of the second transistor; a fourth transistor, wherein the fourth transistor is a PNP transistor, a base of the fourth transistor is connected to the collector of the second transistor, an emitter of the fourth transistor is connected to the collector of the third transistor, and the collector of the fourth transistor is used to output the target RSSI current; a fifth resistor, wherein a first end of the fifth resistor serves as a first end of the bias control input processing unit for obtaining the diode bias voltage, and a second end of the fifth resistor is connected to the emitter of the second transistor; a sixth resistor, wherein a first end of the sixth resistor is connected to the first end of the fifth resistor, and a second end of the sixth resistor is connected to the emitter of the third transistor.

7. The avalanche photodiode protection circuit in PON according to claim 6, characterized in that: The current source further comprises: a seventh resistor, wherein a first end of the seventh resistor is connected to the collector of the fourth transistor, and a second end of the seventh resistor is used to output the target RSSI current.

8. The avalanche photodiode protection circuit in PON according to claim 7, characterized in that: The current source further comprises: A second capacitor, wherein a first end of the second capacitor is connected to the second end of the seventh resistor, and a second end of the second capacitor is grounded.

9. A PON optical modem, characterized in that: include: Target avalanche photodiode; The avalanche photodiode protection circuit in a PON according to any one of claims 1 to 8, wherein the avalanche photodiode protection circuit in the PON is connected to the target avalanche photodiode for overload protection of the target avalanche photodiode.

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