Avalanche photodiode protection circuit in PON and PON optical modem

Abstract

The invention provides an avalanche photodiode protection circuit in a PON and a PON optical modem, and relates to the technical field of optical communication. The avalanche photodiode protection circuit in the PON comprises a bias voltage control input processing unit and an avalanche photodiode protection unit. The bias voltage control input end is used for obtaining diode bias voltage, and when the illumination intensity of a target avalanche photodiode exceeds the preset illumination intensity, the photo-generated current of the target avalanche photodiode exceeds the preset current, and the avalanche photodiode protection unit responds to the situation that the photo-generated current of the target avalanche photodiode exceeds the preset current. And the diode bias voltage applied to the target avalanche photodiode is reduced, so that the photo-generated current of the target avalanche photodiode is reduced, and overload protection is completed. Based on the above content, the problem that the target avalanche photodiode is easy to damage due to overload in the prior art can be improved.

Description

Technical Field

[0001] This application relates to the field of optical communication technologies, and in particular, to an avalanche photodiode protection circuit in a PON and a PON optical network terminal (ONT). Background Art

[0002] In existing access network optical modules & ONTs, the optoelectronic signal conversion device commonly used in 10G PON (Passive Optical Network) modules is an avalanche photodiode (APD, Avalanche Photodiode). Among them, when using an APD for optoelectronic conversion, a relatively high bias voltage needs to be applied to one end of the APD. Thus, when the input optical signal is a large or strong light (i.e., the illumination intensity is relatively high), a large photocurrent will be generated on the APD. Therefore, when the photocurrent exceeds the maximum current allowed by the APD die, it will cause the APD to be damaged. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide an avalanche photodiode protection circuit in a PON and a PON ONT to improve the problem that the target avalanche photodiode is prone to damage due to overload in the existing technology.

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

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

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

[0007] An avalanche photodiode protection unit, wherein the first end of the avalanche photodiode protection unit is connected to the second end of the bias voltage control input processing unit, the second end of the avalanche photodiode protection unit is connected to a target avalanche photodiode, and the avalanche photodiode protection unit is used to apply the diode bias voltage to the target avalanche photodiode so that the target avalanche photodiode performs optoelectronic 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, 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 the overload protection of the target avalanche photodiode.

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

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

[0011] A first triode, wherein the first triode is a PNP-type triode, and the emitter of the first triode is connected to the first end of the first resistor;

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

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

[0014] Moreover, when the light intensity of the target avalanche photodiode exceeds the preset light 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 triode conducts the emitter and the collector of the first triode to reduce the diode bias voltage applied to the target avalanche photodiode, so that the photocurrent of the target avalanche photodiode is reduced to complete the overload protection of the target avalanche photodiode.

[0015] In a preferred embodiment of the present application, in the above-mentioned 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 above-mentioned avalanche photodiode protection circuit in the PON, the avalanche photodiode protection unit further includes:

[0017] A fourth resistor, wherein the first end of the fourth resistor is connected to the second end of the first resistor, and the second end of the fourth resistor serves as the 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 above-mentioned avalanche photodiode protection circuit in the PON, the avalanche photodiode protection unit further includes:

[0019] An inductive element, wherein a first end of the inductive element is connected to a second end of the fourth resistor, and a second end of the inductive 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 inductive element, and a second end of the first capacitor is grounded.

[0021] In a preferred selection of the present application, in the above-mentioned avalanche photodiode protection circuit in the PON, the bias voltage 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 illumination intensity of the target avalanche photodiode.

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

[0024] A second triode, wherein the second triode belongs to a PNP type triode, and a collector of the second triode serves as a second end of the bias voltage control input processing unit and is connected to a first end of the avalanche photodiode protection unit;

[0025] A third triode, wherein the third triode belongs to a PNP type triode, and a base of the third triode is connected to a collector of the third triode, and the base of the third triode is connected to a base of the second triode;

[0026] A fourth triode, wherein the fourth triode belongs to a PNP type triode, and a base of the fourth triode is connected to a collector of the second triode, an emitter of the fourth triode is connected to a collector of the third triode, and a collector of the fourth triode 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 voltage control input processing unit for obtaining the diode bias voltage, and a second end of the fifth resistor is connected to an emitter of the second triode;

[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 an emitter of the third triode.

[0029] In a preferred selection of the present application, in the above-mentioned avalanche photodiode protection circuit in the PON, the current source further includes:

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

[0031] In a preferred selection of the present application, in the above-mentioned avalanche photodiode protection circuit in the PON, the current source further includes:

[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] On the above basis, the present application further provides a PON optical network terminal (ONT), including:

[0034] A target avalanche photodiode;

[0035] The above-mentioned avalanche photodiode protection circuit in the PON, wherein the avalanche photodiode protection circuit in the PON is connected to the target avalanche photodiode and is configured to perform overload protection on the target avalanche photodiode.

[0036] The avalanche photodiode protection circuit in the PON and the PON ONT provided by the present application include a bias control input processing unit and an avalanche photodiode protection unit. The bias control input terminal is configured to obtain a diode bias voltage. And 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. 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 existence 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 in the prior art is easily damaged due to overload can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to make the above objects, features, and advantages of the present application more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows.

[0038] Figure 1 It is a structural block diagram of the PON ONT provided by the embodiment of the present application.

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

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

[0041] Figure 4 This is the schematic diagram of the bias stable time when accessing a large optical power in the embodiment of the present application.

[0042] Icon: R1 - First resistor; Q1 - First triode; R2 - Second resistor; R3 - Third resistor; R4 - Fourth resistor; L - Inductive element; C1 - First capacitor; Q2 - Second triode; Q3 - Third triode; Q4 - Fourth triode; R5 - Fifth resistor; R6 - Sixth resistor; R7 - Seventh resistor; C2 - Second capacitor; APD - Target avalanche photodiode. Detailed implementation manners

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Usually, the components of the embodiments of the present application described and illustrated here 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 drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0045] As Figure 1 shown, the embodiment of the present application provides a PON optical network terminal (exemplarily, the PON optical network terminal can be applied to scenarios such as FTTR). Among them, the PON optical network terminal may include a target avalanche photodiode and an avalanche photodiode protection circuit in the PON. Specifically, the avalanche photodiode protection circuit in the PON is connected to the target avalanche photodiode and can be used to perform overload protection on the target avalanche photodiode.

[0046] Exemplarily, the PON optical network terminal may further include a DC-DC device, and the DC-DC device 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 light intensity of the target avalanche photodiode exceeds a preset light intensity (which can be configured according to actual requirements), the photocurrent of the target avalanche photodiode exceeds a preset current. The avalanche photodiode protection circuit in the PON responds to the photocurrent of the target avalanche photodiode exceeding the preset current (which can also be configured according to actual requirements), 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 the overload protection of the target avalanche photodiode.

[0047] Combined with Figure 2 , an embodiment of the present application further provides an avalanche photodiode protection circuit in a PON. Among them, the avalanche photodiode protection circuit in the PON may be applied to the above-mentioned PON optical network terminal. Moreover, the avalanche photodiode protection circuit in the PON may include a bias voltage control input processing unit and an avalanche photodiode protection unit.

[0048] Specifically, the first end of the bias voltage control input processing unit serves as a bias voltage control input terminal, and the bias voltage control input terminal is used to obtain a diode bias voltage. For example, it may be connected to the output terminal of the above-mentioned DC-DC device, that is, the diode bias voltage may be provided by the above-mentioned DC-DC device. In addition, the first end of the avalanche photodiode protection unit is connected to the second end of the bias voltage control input processing unit, the second end of the avalanche photodiode protection unit is connected to the target avalanche photodiode, and the avalanche photodiode protection unit is used to apply the diode bias voltage to the target avalanche photodiode, so that the target avalanche photodiode performs photoelectric conversion. Moreover, 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. 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 the overload protection of the target avalanche photodiode.

[0049] Based on the above, due to the existence 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 the overload protection. Therefore, the problem that the target avalanche photodiode in the prior art is easily damaged due to overload can be improved.

[0050] In the first aspect, it should be noted that for the bias voltage control input processing unit, the specific circuit composition of the bias voltage 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 be able to sample the current on the basis of obtaining the diode bias voltage for monitoring the optical signal intensity, the bias voltage control input processing unit may include a current source.

[0052] Wherein, 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, and the target RSSI current is used to reflect the illumination intensity of the target avalanche photodiode. Exemplarily, this current value is proportional to the intensity of the received optical signal.

[0053] It can be understood that the specific circuit composition of the current source is also not limited and can be selected according to actual needs. For example, in an alternative embodiment, in order to avoid a large difference between the input current and the output current due to the base current mismatch of the conventional mirror current source, resulting in inaccurate monitoring of the received RSSI current, combined with Figure 3 , the current source may further include a second triode Q2, a third triode Q3, a fourth triode Q4, a fifth resistor R5, and a sixth resistor R6.

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

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

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

[0057] Second, regarding the avalanche photodiode protection unit, it should be noted that the specific circuit composition of the avalanche photodiode protection unit is not limited and can be selected according to actual requirements.

[0058] For example, in an alternative embodiment, in order to enable the avalanche photodiode protection unit to provide reliable overcurrent protection for the target avalanche photodiode APD and to ensure the reliable operation of the target avalanche photodiode APD, for example, in a conventional solution, the protection circuit can quickly pull down the voltage to near 0 and maintain it to protect the avalanche photodiode when a large amount of light is incident. However, in this protection method, reducing the bias voltage on the target avalanche photodiode APD to 0 will cause the target avalanche photodiode APD to stop working properly and thus unable to perform photoelectric conversion. Moreover, since the target avalanche photodiode APD is not working, it is impossible to determine whether the input optical signal has returned to normal from a strong light. If the optical signal is still a strong light, reconnecting the target avalanche photodiode APD will immediately cause damage due to excessive photocurrent generated by the strong light. Additionally, 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 the target avalanche photodiode APD is irradiated by a strong light signal. However, since a large amount of charge is still stored on the decoupling capacitor, when the light intensity is relatively large, it takes milliseconds for the bias voltage on the target avalanche photodiode APD to drop from a high voltage to a low voltage; the large current generated during this time may still cause damage to the target avalanche photodiode APD, thus unable to effectively achieve overcurrent protection for the target avalanche photodiode APD. Also, since the optimal operating point voltages of different target avalanche photodiodes APD are inconsistent, it is difficult to select the series voltage-dividing resistor well; if the selected value is too small, it cannot protect the target avalanche photodiode APD well, resulting in breakdown under strong light, and if the selected value is too large, it will cause the target avalanche photodiode APD to enter the saturation state prematurely. Based on this, the avalanche photodiode protection unit may include a first resistor R1, a first triode Q1, a second resistor R2, and a third resistor R3.

[0059] Specifically, 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 voltage 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 triode Q1 is a PNP type triode, and the emitter of the first triode 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 triode Q1. The first end of the third resistor R3 is connected to the collector of the first triode 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 APD exceeds the preset current. In response to the photocurrent of the target APD exceeding the preset current, the first triode Q1 conducts by connecting its emitter and collector, thereby reducing the diode bias voltage applied to the target APD, reducing the photocurrent of the target APD, and completing the overload protection of the target APD.

[0061] Specifically, during normal operation, the first triode Q1 is off. When the incident light is strong enough to make the photocurrent flowing between the emitter and the base reach a certain value, the first triode Q1 will conduct, which is equivalent to connecting a load in parallel with the target APD. The overall load impedance decreases. If the output bias voltage is to be maintained constant, the output power consumption of the DC-DC device will increase. Once the output limit of the DC-DC device is reached, within a certain range, the bias voltage will decrease as the incident light increases. Since the decrease in the bias voltage leads to a decrease in the multiplication factor, the current flowing through the target APD is reduced, playing a protective role. At the same time, as the current flowing through the first triode Q1 increases, the voltage drop across the first resistor R1 also increases, causing the base current to be too large, resulting in a small voltage difference between the collector and the emitter, and the triode saturates. After that, when the incident light is further increased, the bias voltage of the target APD will tend to a stable value (as Figure 4 shown).

[0062] It can be understood that the first resistor R1 determines the magnitude of the incident light for the conduction and cutoff of the first triode Q1. The larger the resistance value, the smaller the incident light required for the first triode Q1 to conduct, and the larger the Vbe (voltage difference between the base and the emitter) under the same incident light, which is beneficial to increasing the current passing through the first triode Q1, thereby reducing the bias voltage and current of the target APD. Exemplarily, since the damage of the target APD will occur when the current of the target APD exceeds 2 mA, the resistance value of the first resistor R1 is between 400 - 1 kΩ. The third resistor R3 is used as a parallel load. When the first triode Q1 conducts, the smaller the resistance value under the same bias voltage, the easier it is to pull down the bias voltage and current of the target APD. The resistance value of the third resistor R3 is in the range of several hundred ohms, that is, 100 - 1000 Ω. The specific parameters of other resistors can be selected according to the actual situation.

[0063] Among them, the experimental data when the large light is connected with 5 dbm (intensity of the optical signal) are as follows:

[0064]

[0065] It can be understood that, based on the above embodiments, 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 be used as a debugging resistor to facilitate measuring the current magnitude of the target avalanche photodiode APD during verification.

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

[0068] Specifically, the first end of the inductance element L is connected to the second end of the fourth resistor R4, and the second end of the inductance 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 inductance element L, and the second end of the first capacitor C1 is grounded. Based on this, through the inductance element L and the first capacitor C1, a voltage filtering network for the target avalanche photodiode APD can be formed.

[0069] In summary, the avalanche photodiode protection circuit and the PON optical network terminal provided in this application include 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. Moreover, when the light intensity of the target avalanche photodiode exceeds the preset light intensity, the photocurrent of the target avalanche photodiode exceeds the preset current. 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 existence 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 in the prior art is easily damaged due to overload can be improved.

[0070] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope 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 used 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, thereby reducing the photocurrent of the target avalanche photodiode to complete overload protection of the target avalanche photodiode.

2. The avalanche photodiode protection circuit in PON according to claim 1, characterized in that: The avalanche photodiode protection unit comprises: 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 a 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; Furthermore, when the light intensity of the target avalanche photodiode exceeds the preset light intensity, the photocurrent of the target avalanche photodiode exceeds the preset current, and the first transistor responds to the photocurrent of the target avalanche photodiode exceeding the preset current by connecting the emitter and the collector of the first transistor to reduce 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.

3. The avalanche photodiode protection circuit in PON according to claim 2, 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.

4. The avalanche photodiode protection circuit in PON according to claim 3, characterized in that: The avalanche photodiode protection unit also includes: A fourth resistor, wherein a first end of the fourth resistor is connected to a 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.

5. The avalanche photodiode protection circuit in PON according to claim 4, characterized in that: The avalanche photodiode protection unit also includes: an inductor element, wherein a first end of the inductor element is connected to a 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.

6. The avalanche photodiode protection circuit in PON according to any one of claims 1 to 5, characterized in that: The bias control input processing unit comprises: A current source, wherein the current source is used to replicate 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.

7. The avalanche photodiode protection circuit in PON according to claim 6, characterized in that: The current source comprises: A second triode, wherein the second triode is a PNP type triode, and the collector of the second triode serves as the second end of the bias control input processing unit and is connected to the first end of the avalanche photodiode protection unit; A third triode, wherein the third triode is a PNP triode, and the base of the third triode is connected to the collector of the third triode, and the base of the third triode is connected to the base of the second triode; A fourth transistor, wherein the fourth transistor is a PNP transistor, and the base of the fourth transistor is connected to the collector of the second transistor, the 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.

8. The avalanche photodiode protection circuit in PON according to claim 7, 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.

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

10. A PON optical modem, characterized in that: include: Target avalanche photodiode; The avalanche photodiode protection circuit in a PON as described in any one of claims 1 to 9, 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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