A high-compatibility optical power monitoring circuit and monitoring method

Abstract

The present invention discloses a highly compatible optical power monitoring circuit and monitoring method, including a controller, a driver, a laser, an optional tube mirror circuit, a voltage follower, a reference power supply voltage, a first resistor, a second resistor, a third resistor, a fourth resistor and a fifth resistor; the controller is connected to the driver, the controller is connected to the ground through the first resistor, and the controller is connected to the voltage follower; the voltage follower is connected to the optional tube mirror circuit through the second resistor; the optional tube mirror circuit is connected to the laser; the optional tube mirror circuit is connected to the positive power supply voltage through the fourth resistor, or is connected to the negative power supply voltage through the fifth resistor; the laser is connected to the driver; the reference power supply voltage is respectively connected to the optional tube mirror circuit and the first resistor through the third resistor. The present invention achieves the purpose of being compatible with different device pin definition circuit designs by selecting different triodes, does not require repeated board making, increases product compatibility, and reduces development costs.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber communication technology, and in particular to a highly compatible optical power monitoring circuit and monitoring method. Background Art

[0002] PD (Photo-Diode) is mainly used in optical modules to monitor the size of the transmitted optical power, realize the APC (Automatic Optical Power Control) function and provide the DDMI (Digital Diagnostic Monitoring Interface) of the transmitted optical power. Among them, the transmitted optical power monitoring is to read the size of the driver chip (driver) ADC value through the MCU (Micro Controller Unit) through the IIC (Inter-Integrated Circuit), and then after the MCU conversion, it is updated in real time and stored in the corresponding protocol area.

[0003] At present, in the application of optical modules, different device manufacturers have different definitions of PD pins. There are two common wiring methods, one of which is to connect the PD anode to GND, and the other is to connect the PD cathode to GND. The circuit design has poor compatibility and requires different circuit designs to drive, resulting in repeated board design, which greatly increases product development costs.

[0004] In view of this, it is necessary to design a high compatibility circuit to solve the defects in the prior art. Summary of the invention

[0005] The present invention provides a highly compatible optical power monitoring circuit and monitoring method to solve the deficiencies of the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a highly compatible optical power monitoring circuit, including a controller, a driver, a laser, an optional tube mirror circuit, a voltage follower, a reference power supply voltage, a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor;

[0008] The first end of the controller is connected to the first end of the driver, the second end of the controller is connected to the ground through the first resistor, and the third end of the controller is connected to the first end of the voltage follower;

[0009] The second end of the voltage follower is connected to the first end of the optional tube mirror circuit through the second resistor;

[0010] The second end of the optional tube mirror circuit is connected to the first end of the laser; the third end of the optional tube mirror circuit is connected to the positive power supply voltage through the fourth resistor, or is connected to the negative power supply voltage through the fifth resistor;

[0011] The second end of the laser is connected to the second end of the driver;

[0012] The reference power supply voltage is connected to the first end of the optional tube mirror circuit and the first resistor respectively through the third resistor.

[0013] Further, in the high-compatibility optical power monitoring circuit, the optional tube mirror circuit is a PNP tube mirror circuit, and the PNP tube mirror circuit includes a first PNP tube and a second PNP tube;

[0014] The emitter of the first PNP tube and the emitter of the second PNP tube are connected in parallel, connected in series with the fourth resistor, and then connected to the positive power supply voltage;

[0015] The collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube are connected in parallel and then connected to the laser;

[0016] The collector of the second PNP tube is connected between the controller and the first resistor.

[0017] Further, in the high-compatibility optical power monitoring circuit, the optional tube mirror circuit is an NPN tube mirror circuit, and the NPN tube mirror circuit includes a first NPN tube and a second NPN tube;

[0018] The emitter of the first NPN tube and the emitter of the second NPN tube are connected in parallel, connected in series with the fifth resistor, and then connected to the negative power supply voltage;

[0019] The collector of the first NPN tube, the base of the first NPN tube and the base of the second NPN tube are connected in parallel and then connected to the laser;

[0020] The collector of the second NPN tube is connected in series with the second resistor and then connected to the voltage follower, or is connected in series with the third resistor and then connected to the reference power supply voltage.

[0021] Further, in the high-compatibility optical power monitoring circuit, the voltage follower is composed of an operational amplifier;

[0022] The output end of the operational amplifier is connected in series with the second resistor and then connected to the collector of the second NPN tube;

[0023] The non-inverting input terminal of the operational amplifier is connected to the controller, and the inverting input terminal of the operational amplifier is connected to the output terminal of the operational amplifier.

[0024] Furthermore, in the high-compatibility optical power monitoring circuit, the controller and the driver are connected via an I2C bus.

[0025] Furthermore, the highly compatible optical power monitoring circuit further includes a sixth resistor and a seventh resistor;

[0026] A first end of the sixth resistor is connected to a serial clock line in the I2C bus, and a second end thereof is connected to a positive power supply voltage;

[0027] A first end of the seventh resistor is connected to a serial data line in the I2C bus, and a second end of the seventh resistor is connected to a positive power supply voltage.

[0028] Further, in the high-compatibility optical power monitoring circuit, the driver includes a laser diode and a photodiode;

[0029] One end of the photodiode is grounded; the other end of the photodiode is connected to the collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube, or connected to the collector of the first NPN tube, the base of the first NPN tube and the base of the second NPN tube;

[0030] The cathode of the laser diode is connected between the photodiode and the ground, and the anode of the laser diode is connected to the driver.

[0031] In a second aspect, an embodiment of the present invention provides a highly compatible optical power monitoring method, which is performed by using the highly compatible optical power monitoring circuit as described in the first aspect, and the method includes:

[0032] Determining whether the photodiode in the laser is anode-grounded or cathode-grounded;

[0033] If the anode of the photodiode is grounded, the optional tube mirror circuit is selected as a PNP tube mirror circuit, the second resistor, the third resistor and the fifth resistor are disconnected, and the ADC samples the voltage of the first resistor;

[0034] If the cathode of the photodiode is grounded, the optional tube mirror circuit is selected as an NPN tube mirror circuit, and it is determined whether there is a constant reference power supply voltage in the circuit;

[0035] If yes, the first resistor, the second resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the third resistor;

[0036] If not, a stable reference power supply voltage is provided by the voltage follower, the first resistor, the third resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the second resistor.

[0037] The embodiments of the present invention provide a highly compatible optical power monitoring circuit and monitoring method, which have a simple circuit design structure and can achieve compatibility with circuit designs with different device pin definitions by selecting different transistors. Not only does the PCB occupy a small space, but it also does not require repeated board making, thereby increasing the compatibility of the product development platform and reducing the product development cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1 It is a structural schematic diagram of a highly compatible optical power monitoring circuit provided by an embodiment of the present invention;

[0040] Figure 2 It is a specific structural diagram of a highly compatible optical power monitoring circuit provided by an embodiment of the present invention;

[0041] Figure 3 It is a flowchart of a highly compatible optical power monitoring method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] In the description of the present invention, it is to be understood that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally disposed component. When a component is considered to be "disposed on" another component, it may be directly disposed on the other component or there may be a centrally disposed component.

[0044] In addition, terms such as "long", "short", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention. They do not indicate or imply that the device or component referred to must have this specific direction or operate with a specific direction structure, and should not be understood as a limitation of the present invention.

[0045] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0046] Embodiment 1

[0047] Please refer to Figure 1 and Figure 2 The embodiment of the present invention provides a highly compatible optical power monitoring circuit, including a controller (i.e., an MCU unit circuit), a driver (i.e., a laser driver chip circuit), a laser, an optional tube mirror circuit, a voltage follower, a reference power supply voltage (such as a reference power supply voltage 2.5V provided inside the MCU), a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), and a fifth resistor (R5);

[0048] The first end of the controller is connected to the first end of the driver, the second end of the controller is connected to the ground through the first resistor, and the third end of the controller is connected to the first end of the voltage follower;

[0049] The second end of the voltage follower is connected to the first end of the optional tube mirror circuit through the second resistor;

[0050] The second end of the optional tube mirror circuit is connected to the first end of the laser; the third end of the optional tube mirror circuit is connected to the positive power supply voltage (i.e. Figure 1 and 2 VCC, which is the module power supply voltage), or connected to the negative power supply voltage (i.e. Figure 1 and 2 -VCC, which can be obtained by the module power supply voltage through the charge pump negative voltage conversion circuit) connection;

[0051] The second end of the laser is connected to the second end of the driver;

[0052] The reference power supply voltage is connected to the first end of the optional tube mirror circuit and the first resistor respectively through the third resistor.

[0053] Wherein, the controller and the driver are connected via an I2C bus.

[0054] Since the I2C drain is open-circuited, preferably, the high-compatibility optical power monitoring circuit must be provided with two pull-up resistors for realizing level inversion, which are the sixth resistor (R6) and the seventh resistor (R7);

[0055] A first end of the sixth resistor is connected to a serial clock line in the I2C bus, and a second end thereof is connected to a positive power supply voltage;

[0056] A first end of the seventh resistor is connected to a serial data line in the I2C bus, and a second end of the seventh resistor is connected to a positive power supply voltage.

[0057] It should be noted that the monitoring function is realized by the controller (referring to MCU, i.e. Figure 2 U1 in the figure) configures the driver (referring to Driver, i.e. Figure 2 The output bias current (Ibias) is controlled by the ADC value of the U2) register to drive the laser (J1) to emit light. The light power is input into the ADC of the MCU for sampling after being mirrored by the current of the photodiode (i.e., PD, specifically the backlight photodiode, MPD for short) in this embodiment. The MCU then converts and processes it and stores it in the protocol storage address.

[0058] In one embodiment, the optional tube mirror circuit (i.e. Figure 2 U3) in the embodiment may be a PNP tube mirror circuit, wherein the PNP tube mirror circuit includes a first PNP tube and a second PNP tube;

[0059] The emitter of the first PNP tube and the emitter of the second PNP tube are connected in parallel, connected in series with the fourth resistor, and then connected to the positive power supply voltage;

[0060] The collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube are connected in parallel and then connected to the laser;

[0061] The collector of the second PNP tube is connected between the controller and the first resistor.

[0062] In another embodiment, the optional tube mirror circuit (i.e. Figure 2 U3) in the embodiment may be an NPN tube mirror circuit, wherein the NPN tube mirror circuit includes a first NPN tube and a second NPN tube;

[0063] The emitter of the first NPN tube and the emitter of the second NPN tube are connected in parallel, connected in series with the fifth resistor, and then connected to the negative power supply voltage;

[0064] The collector of the first NPN tube, the base of the first NPN tube and the base of the second NPN tube are connected in parallel and then connected to the laser;

[0065] The collector of the second NPN tube is connected in series with the second resistor and then connected to the voltage follower, or is connected in series with the third resistor and then connected to the reference power supply voltage.

[0066] Specifically, the principle analysis and calculation of the PNP tube mirror circuit (NPN tube mirror circuit) are as follows:

[0067] Since the two PNP (NPN) tubes have the same characteristics, the voltage drop U of T1 tube is EBO and U ECO equal, T1 tube always works in the amplification area. EBO Equal, so the base current and collector current of tubes T1 and T2 are equal.

[0068]

[0069] When β>>2, I monitor =I MPD =I C , so V ADC =I monitor ·R.

[0070] In this embodiment, the voltage follower is composed of an operational amplifier (OPA);

[0071] The output end of the operational amplifier is connected in series with the second resistor and then connected to the collector of the second NPN tube;

[0072] The non-inverting input terminal of the operational amplifier is connected to the controller, and the inverting input terminal of the operational amplifier is connected to the output terminal of the operational amplifier.

[0073] In this embodiment, the driver includes a laser diode and a photodiode;

[0074] One end of the photodiode is grounded; the other end of the photodiode is connected to the collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube, or connected to the collector of the first NPN tube, the base of the first NPN tube and the base of the second NPN tube;

[0075] The cathode of the laser diode is connected between the photodiode and the ground, and the anode of the laser diode is connected to the driver.

[0076] An embodiment of the present invention provides a highly compatible optical power monitoring circuit with a simple circuit design structure. By selecting different transistors, the purpose of being compatible with circuit designs with different device pin definitions is achieved. Not only does the PCB occupy a small space, but it also does not require repeated board making, thereby increasing the compatibility of the product development platform and reducing the product development cost.

[0077] Embodiment 2

[0078] Please refer to Figure 3 The embodiment of the present invention provides a high-compatibility optical power monitoring method, the method is performed by using the high-compatibility optical power monitoring circuit as described in the first embodiment, and the method specifically includes the following steps:

[0079] S201, determining whether the photodiode in the laser is anode-grounded or cathode-grounded.

[0080] S202: If the anode of the photodiode is grounded, the optional tube mirror circuit is selected as a PNP tube mirror circuit, the second resistor, the third resistor and the fifth resistor are disconnected, and the ADC samples the voltage of the first resistor.

[0081] It should be noted that after selecting the PNP tube mirror circuit, when the transmitter works normally, the test value of the optical power meter is Po, K is a fixed coefficient taking into account all other factors such as backlight current conversion efficiency, A is the 12-bit ADC sampling value of the MCU, and Vref is the MCU reference power supply voltage of 2.4V.

[0082] The optical power is

[0083]

[0084] The optical transmitter manufacturer can obtain the K value through software calibration once during production. After the system is networked, there is no need to cut off the optical path for measurement to monitor the optical power in real time.

[0085] S203. If the cathode of the photodiode is grounded, the optional tube mirror circuit is selected as an NPN tube mirror circuit, and it is determined whether there is a constant reference power supply voltage in the circuit; if so, execute step S204, if not, execute step S205.

[0086] S204 , the first resistor, the second resistor, and the fourth resistor are disconnected, and the ADC samples the voltage of the third resistor.

[0087] S205 , providing a stable reference power supply voltage through the voltage follower, disconnecting the first resistor, the third resistor and the fourth resistor, and sampling the voltage of the second resistor by ADC.

[0088] It should be noted that after selecting the NPN tube mirror circuit, when the transmitter works normally, the test value of the optical power meter is Po, K is a fixed coefficient taking into account all other factors such as backlight current conversion efficiency, A is the 12-bit ADC sampling value of the MCU, and Vref is the MCU reference power supply voltage of 2.4V.

[0089] The optical power is

[0090]

[0091] The optical transmitter manufacturer can obtain the K value through software calibration once during production. After the system is networked, there is no need to cut off the optical path for measurement to monitor the optical power in real time.

[0092] The embodiment of the present invention provides a highly compatible optical power monitoring method with a simple circuit design structure. By selecting different transistors, the purpose of being compatible with circuit designs with different device pin definitions is achieved. Not only does the PCB occupy a small space, but it also does not require repeated board making, thereby increasing the compatibility of the product development platform and reducing the product development cost.

[0093] Thus far, the description of the above-described embodiments is provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a specific embodiment are generally not subject to the limitations of the specific embodiment, but when applicable, they can be interchanged and used for selected embodiments even if not specifically shown or described. In many respects, the same element or feature also can be changed. This variation is not considered to be a departure from the present disclosure, and all such modifications are intended to be included in the scope of the present disclosure.

[0094] Example embodiments are provided so that the present disclosure will be thorough and the scope will be fully conveyed to those skilled in the art. In order to thoroughly understand the embodiments of the present disclosure, numerous details are set forth, such as examples of specific parts, devices, and methods. Obviously, for those skilled in the art, it is not necessary to use specific details, the example embodiments can be implemented in many different forms, and neither should be construed as limiting the scope of the present disclosure. In certain example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0095] Here, specialized vocabulary is used only for the purpose of describing specific example embodiments, and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a" and "the" used herein may be intended to include plural forms as well. The terms "including" and "having" are inclusive, and therefore specify the presence of the claimed features, wholes, steps, operations, elements and / or components, but do not exclude the presence or additional presence of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof. Unless the order of execution is clearly indicated, the method steps, processing and operations described herein are not interpreted as necessarily needing to be performed in the specific order discussed and shown. It should also be understood that additional or optional steps may be adopted.

[0096] When an element or layer is referred to as being "on ...", "engaged with ...", "connected to" or "coupled to" another element or layer, it may be directly on another element or layer, engaged with another element or layer, connected to or coupled to another element or layer, or there may be an intervening element or layer. In contrast, when an element or layer is referred to as being "directly on ...", "directly engaged with ...", "directly connected to" or "directly coupled to" another element or layer, there may be no intervening element or layer. Other words used to describe element relationships should be interpreted in a similar manner (e.g., "between ..." and "directly between ...", "adjacent" and "directly adjacent", etc.). The term "and / or" used herein includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts are not limited by these terms. These terms may only be used to distinguish one element, component, region or part from another element, component, region or part. Unless clearly indicated by the context, the use of terms such as "first", "second" and other numerical terms herein does not imply sequence or order. Therefore, the first element, component, region, layer or part discussed below can adopt the terminology of the second element, component, region, layer or part without departing from the teaching of the exemplary embodiment.

[0097] Spatially relative terms, such as "inside", "outside", "below", "below...", "lower", "above", "upper", etc., may be used herein for ease of description to describe the relationship between one element or feature and one or more other elements or features as shown in the figure. Spatially relative terms may be meant to include different orientations of the device in addition to the orientation depicted in the figure. For example, if the device in the figure is flipped, the elements described as "below other elements or features" or "below elements or features" will be oriented as "above other elements or features". Therefore, the example term "below..." may include both upward and downward orientations. The device can be oriented in other ways (rotated 90 degrees or other orientations) and interpreted with the spatially relative descriptions herein.

Claims

1. A highly compatible optical power monitoring circuit, characterized in that: It includes a controller, a driver, a laser, an optional tube mirror circuit, a voltage follower, a reference power supply voltage, a first resistor, a second resistor, a third resistor, a fourth resistor and a fifth resistor; The first end of the controller is connected to the first end of the driver, the second end of the controller is connected to the ground through the first resistor, and the third end of the controller is connected to the first end of the voltage follower; The second end of the voltage follower is connected to the first end of the optional tube mirror circuit through the second resistor; The second end of the optional tube mirror circuit is connected to the first end of the laser; the third end of the optional tube mirror circuit is connected to the positive power supply voltage through the fourth resistor, or is connected to the negative power supply voltage through the fifth resistor; The second end of the laser is connected to the second end of the driver; The reference power supply voltage is connected to the first end of the optional tube mirror circuit and the first resistor respectively through the third resistor; The laser includes a laser diode and a photodiode; The method performed by the high-compatibility optical power monitoring circuit includes: Determining whether the photodiode in the laser is anode-grounded or cathode-grounded; If the anode of the photodiode is grounded, the optional tube mirror circuit is selected as a PNP tube mirror circuit, the second resistor, the third resistor and the fifth resistor are disconnected, and the ADC samples the voltage of the first resistor; If the cathode of the photodiode is grounded, the optional tube mirror circuit is selected as an NPN tube mirror circuit, and it is determined whether there is a constant reference power supply voltage in the circuit; If yes, the first resistor, the second resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the third resistor; If not, a stable reference power supply voltage is provided by the voltage follower, the first resistor, the third resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the second resistor.

2. The optical power monitoring circuit with high compatibility according to claim 1, characterized in that: The optional tube mirror circuit is a PNP tube mirror circuit, and the PNP tube mirror circuit includes a first PNP tube and a second PNP tube; The emitter of the first PNP tube and the emitter of the second PNP tube are connected in parallel, then connected in series with the fourth resistor, and then connected to the positive power supply voltage; The collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube are connected in parallel and then connected to the laser; The collector of the second PNP tube is connected between the controller and the first resistor.

3. The optical power monitoring circuit with high compatibility according to claim 1, characterized in that: The optional tube mirror circuit is an NPN tube mirror circuit, and the NPN tube mirror circuit includes a first NPN tube and a second NPN tube; The emitter of the first NPN tube and the emitter of the second NPN tube are connected in parallel, connected in series with the fifth resistor, and then connected to the negative power supply voltage; The collector of the first NPN tube, the base of the first NPN tube and the base of the second NPN tube are connected in parallel and then connected to the laser; The collector of the second NPN tube is connected in series with the second resistor and then connected to the voltage follower, or is connected in series with the third resistor and then connected to the reference power supply voltage.

4. The optical power monitoring circuit with high compatibility according to claim 3, characterized in that: The voltage follower is composed of an operational amplifier; The output end of the operational amplifier is connected in series with the second resistor and then connected to the collector of the second NPN tube; The non-inverting input terminal of the operational amplifier is connected to the controller, and the inverting input terminal of the operational amplifier is connected to the output terminal of the operational amplifier.

5. The optical power monitoring circuit with high compatibility according to claim 1, characterized in that: The controller and the driver are connected via an I2C bus.

6. The optical power monitoring circuit with high compatibility according to claim 5, characterized in that: Also including a sixth resistor and a seventh resistor; A first end of the sixth resistor is connected to a serial clock line in the I2C bus, and a second end thereof is connected to a positive power supply voltage; A first end of the seventh resistor is connected to a serial data line in the I2C bus, and a second end of the seventh resistor is connected to a positive power supply voltage.

7. The optical power monitoring circuit with high compatibility according to claim 2, characterized in that: One end of the photodiode is grounded; the other end of the photodiode is connected to the collector of the first PNP tube, the base of the first PNP tube and the base of the second PNP tube; The cathode of the laser diode is connected between the photodiode and the ground, and the anode of the laser diode is connected to the driver.

8. The optical power monitoring circuit with high compatibility according to claim 3, characterized in that: One end of the photodiode is grounded; the other end of the photodiode is connected to the collector of the first NPN transistor, the base of the first NPN transistor and the base of the second NPN transistor; The cathode of the laser diode is connected between the photodiode and the ground, and the anode of the laser diode is connected to the driver.

9. A high-compatibility optical power monitoring method, implemented by the high-compatibility optical power monitoring circuit according to any one of claims 1 to 8, characterized in that: The method comprises: Determining whether the photodiode in the laser is anode-grounded or cathode-grounded; If the anode of the photodiode is grounded, the optional tube mirror circuit is selected as a PNP tube mirror circuit, the second resistor, the third resistor and the fifth resistor are disconnected, and the ADC samples the voltage of the first resistor; If the cathode of the photodiode is grounded, the optional tube mirror circuit is selected as an NPN tube mirror circuit, and it is determined whether there is a constant reference power supply voltage in the circuit; If yes, the first resistor, the second resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the third resistor; If not, a stable reference power supply voltage is provided by the voltage follower, the first resistor, the third resistor and the fourth resistor are disconnected, and the ADC samples the voltage of the second resistor.

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