A fast dimming method and dimming system for PPG sensor

Abstract

This application discloses a fast dimming method and dimming system for PPG sensors. The dimming method includes controlling a first digital-to-analog converter (DAC) to eliminate ambient light, causing a second DAC to output a reference current corresponding to the dimming target; adjusting the drive current of the light-emitting diode (LED) based on the binary divider method and the polarity of the transimpedance amplifier output signal; sampling the output signal of the transimpedance amplifier using an analog-to-digital converter (ADC), comparing the sampled values ​​with the convergence interval corresponding to the dimming target, and updating the convergence and non-convergence counts; adjusting the drive current based on the updated convergence and non-convergence counts to make the sampled values ​​approach the dimming target; repeating the above steps until the number of samples reaches a preset minimum number of samples and the number of convergences reaches a preset convergence threshold, at which point dimming is considered complete. This application can shorten the dimming time of PPG sensors and improve the accuracy and stability of dimming.

Description

Technical Field

[0001] This application belongs to the field of PPG sensor technology, specifically relating to a fast dimming method and dimming system for PPG sensors. Background Technology

[0002] Photoplethysmo mapping (PPG) is an optical measurement technique that measures blood oxygen saturation and heart rate by detecting changes in light absorption. A PPG sensor typically consists of an emitter and a receiver. The emitter comprises a light-emitting diode (LED) and its driving circuitry, used to emit light of a specific wavelength into human tissue. The receiver comprises a photodetector (PD) and signal processing circuitry, used to receive the light signal reflected or transmitted through human tissue, convert it into a current signal, and quantize it.

[0003] Due to factors such as human skin color, sensor placement, motion state, and humidity, the ratio between the LED driving current and the photodetector output current, i.e., the CTR (Current Transfer Ratio), will change in an unknown and dynamic manner.

[0004] In the relevant dimming scheme, a dimming target value and the corresponding convergence range are first set. Then, the LED driving current is gradually adjusted in a binary search method within the preset LED current range. Each time the LED driving current is changed, a sampling measurement is performed through an analog-to-digital converter. The obtained ADC code value is compared with the dimming target value, and the direction of the next LED driving current adjustment is determined based on the comparison result.

[0005] However, the CTR may change slowly during dimming, and each adjustment of the LED drive current requires a complete sampling measurement by the analog-to-digital converter. The entire dimming process requires multiple samplings, resulting in long dimming time, insufficient accuracy, and poor stability. Summary of the Invention

[0006] This application provides a fast dimming method and dimming system for PPG sensors, which can shorten the dimming time of PPG sensors and improve the accuracy and stability of dimming.

[0007] To address the aforementioned technical problems, this application provides a rapid dimming method for a PPG sensor. The PPG sensor includes a light-emitting diode, a photodetector, and an analog front-end coupled to the photodetector. The analog front-end includes a first digital-to-analog converter for eliminating ambient light, a second digital-to-analog converter for outputting a reference current, a transimpedance amplifier, and an analog-to-digital converter coupled to the transimpedance amplifier. The dimming method includes the following steps: The first digital-to-analog converter is controlled to eliminate ambient light, and the input code value of the second digital-to-analog converter is configured so that the second digital-to-analog converter outputs a reference current corresponding to the dimming target; Based on the binary division method and the polarity of the output signal of the transimpedance amplifier, the driving current of the light-emitting diode is adjusted until the receiving current of the photodetector is close to the reference current. The output signal of the transimpedance amplifier is sampled by the analog-to-digital converter, and the sampled value is compared with the convergence interval corresponding to the dimming target. The number of convergences and non-convergences are updated according to the comparison result. The drive current is adjusted based on the updated convergence count and non-convergence count to make the sampled value approach the dimming target; Repeat the above steps of sampling, comparison, number update, and drive current adjustment until the number of samplings reaches the preset minimum number of samplings and the number of convergences reaches the preset convergence threshold, at which point dimming is considered complete.

[0008] As a further improvement to this application, the adjustment of the driving current of the light-emitting diode based on the binary divider method and the polarity of the output signal of the transimpedance amplifier until the receiving current of the photodetector is close to the reference current includes: The adjustment range of the drive current is set, and the adjustment range has an upper limit value and a lower limit value; Set the current drive current to the midpoint between the upper limit value and the lower limit value; The current drive current is adjusted based on the polarity of the output signal of the transimpedance amplifier so that the difference between the received current of the photodetector and the reference current is less than a preset difference.

[0009] As a further improvement to this application, the adjustment of the current drive current based on the polarity of the transimpedance amplifier output signal includes: If the output signal of the transimpedance amplifier is positive, the upper limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper limit and the lower limit is determined as the new current drive current. If the output signal of the transimpedance amplifier is negative, the lower limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper limit and the lower limit is determined as the new current drive current.

[0010] As a further improvement to this application, the step of comparing the sampled values ​​obtained by sampling with the convergence interval corresponding to the dimming target, and updating the number of convergences and non-convergences based on the comparison result, includes: If the sampled value is within the convergence interval, the convergence count is incremented by one, and the non-convergence count is cleared to zero. If the sampled value is not within the convergence interval, the number of non-convergence counts is incremented by one.

[0011] As a further improvement to this application, adjusting the drive current based on the updated convergence count and non-convergence count includes: When the sampled value is within the convergence interval, the driving current is adjusted in the direction approaching the dimming target with a minimum step size; When the sampled value is not in the convergence interval and the current number of non-convergences is less than the preset non-convergence threshold, the driving current is adjusted in the direction approaching the dimming target with the smallest step size, and the count of the convergences is kept from being zero. When the sampled value is not in the convergence interval and the current number of non-convergences is greater than or equal to the preset non-convergence threshold, the driving current is adjusted in the direction approaching the dimming target with a preset step size, and the number of convergences is cleared.

[0012] As a further improvement to this application, adjusting the drive current in a direction approaching the dimming target includes: When the sampled value is greater than the dimming target, the driving current is reduced; when the sampled value is less than the dimming target, the driving current is increased.

[0013] As a further improvement of this application, the preset step size does not exceed a preset ratio of the code value corresponding to the current drive current, and is not less than the minimum step size.

[0014] As a further improvement to this application, the rapid dimming method further includes: If the number of samplings reaches the preset maximum number of samplings and the dimming is not yet determined to be complete, the dimming is determined to have failed.

[0015] As a further improvement of this application, the preset non-convergence threshold is 2 times, the preset minimum sampling number is 3 times, and the preset maximum sampling number is 5 times.

[0016] As a further improvement to this application, this application also provides a fast dimming system for a PPG sensor, used to execute the fast dimming method for a PPG sensor, the dimming system comprising: A configuration unit is used to control the first digital-to-analog converter to eliminate ambient light and to configure the input code value of the second digital-to-analog converter so that the second digital-to-analog converter outputs a reference current corresponding to the dimming target. The judgment unit is used to adjust the driving current of the light-emitting diode based on the binary method and the polarity of the output signal of the transimpedance amplifier until the receiving current of the photodetector is close to the reference current. The update unit is used to sample the output signal of the transimpedance amplifier through the analog-to-digital converter, compare the sampled value with the convergence interval corresponding to the dimming target, and update the number of convergences and non-convergences according to the comparison result. An adjustment unit is configured to adjust the drive current based on the updated number of convergences and the number of non-convergences, so that the sampled value approaches the dimming target. The execution unit is used to repeatedly perform the above steps of sampling, comparison, number update and drive current adjustment until the number of sampling reaches the preset minimum number of sampling and the number of convergences reaches the preset convergence threshold, at which point the dimming is determined to be complete.

[0017] This application provides a rapid dimming method and system for PPG sensors. In the coarse adjustment stage, a first digital-to-analog converter (DAC) is controlled to eliminate ambient light, and a second DAC is configured to output a reference current corresponding to the dimming target. Based on the binary division method and utilizing the polarity of the transimpedance amplifier output signal, the driving current of the light-emitting diode (LED) is directly adjusted until the receiving current of the photodetector approaches the reference current. The coarse adjustment process does not rely on DAC sampling and can be completed in a very short time. In the fine adjustment stage, the DAC samples the output signal of the transimpedance amplifier, compares the sampled value with the convergence interval corresponding to the dimming target, updates the convergence and non-convergence counts based on the comparison results, and adjusts the driving current based on the updated counts to bring the sampled value closer to the dimming target. This method can distinguish between accidental and continuous deviations, thus enabling fine adjustment with a minimum or preset step size.

[0018] Subsequently, the steps of sampling, comparison, count update, and adjustment are repeated until the number of samples reaches the preset minimum number of samples and the number of convergences reaches the preset convergence threshold. Only then is dimming considered complete, avoiding premature termination of dimming due to single or accidental convergence. Compared to traditional solutions that require multiple analog-to-digital converter samplings and additional confirmation samplings, this application quickly approximates the dimming target through coarse adjustment, and only requires a small number of samples to complete fine adjustment, thereby reducing the total number of samplings and shortening the dimming time. At the same time, because the dimming process is faster, the LED drive current can quickly stabilize, effectively improving the accuracy and stability of dimming and ensuring the detection accuracy of the sensor. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only a part of the embodiments of this application, and not all of the embodiments. For those skilled in the art, other drawings obtained from these drawings without creative effort are all within the scope of protection of this application.

[0020] Figure 1 A flowchart illustrating a rapid dimming method for a PPG sensor provided in an embodiment of this application.

[0021] Figure 2 This is a flowchart illustrating the process of setting intermediate values ​​in a rapid dimming method for a PPG sensor provided in an embodiment of this application.

[0022] Figure 3 This is a flowchart illustrating the determination of a new current drive current in a fast dimming method for a PPG sensor provided in an embodiment of this application.

[0023] Figure 4 This is a flowchart illustrating the updating of the convergence and non-convergence counts in a fast dimming method for a PPG sensor provided in an embodiment of this application.

[0024] Figure 5 This is a flowchart illustrating the adjustment of the drive current in a fast dimming method for a PPG sensor provided in an embodiment of this application.

[0025] Figure 6 This is a flowchart illustrating the determination of dimming failure in a fast dimming method for a PPG sensor provided in an embodiment of this application.

[0026] Figure 7 Figure 1 shows a specific embodiment of the fast dimming method for a PPG sensor provided in this application.

[0027] Figure 8 for Figure 7The diagram shown illustrates the coarse adjustment stage in the specific embodiment.

[0028] Figure 9 for Figure 7 The diagram shown illustrates the fine-tuning stage in the specific embodiment.

[0029] Figure 10 A functional block diagram of a fast dimming system for a PPG sensor provided in an embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0031] To make the description of this disclosure more detailed and complete, illustrative descriptions of the implementation methods and specific embodiments of this application are provided below; however, this is not the only form of implementing or utilizing the specific embodiments of this application. The implementation methods cover the features of multiple specific embodiments and the method steps and their order for constructing and operating these specific embodiments. However, other specific embodiments can also be used to achieve the same or equivalent functions and step sequences. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0033] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The word "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more. Other quantifiers should be understood similarly. The preferred embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. Furthermore, the embodiments of this application and the features in the embodiments can be combined with each other without conflict.

[0034] Photoplethysmo mapping (PPG) is an optical measurement technique that measures blood oxygen saturation and heart rate by detecting changes in light absorption. A PPG sensor typically consists of an emitter and a receiver. The emitter comprises a light-emitting diode (LED) and its driving circuitry, used to emit light of a specific wavelength into human tissue. The receiver comprises a photodetector (PD) and signal processing circuitry, used to receive the light signal reflected or transmitted through human tissue, convert it into a current signal, and quantize it.

[0035] Due to factors such as human skin color, sensor placement, movement, and humidity, the ratio between the LED drive current and the photodetector output current, i.e., the CTR (Current Transfer Ratio), will vary dynamically and unpredictably. If the LED drive current is set too low, the noise of the circuit components will significantly affect the data sampling accuracy; if the LED drive current is set too high, it may cause the signal processing circuit at the receiving end to enter a saturation state and fail to measure normally. Therefore, the LED drive current needs to be properly adjusted before each data sampling begins.

[0036] In related technologies, the receiving circuit of a PPG sensor typically adopts a TIA (Trans Impedance Amplifier) ​​architecture, and sets up an ambient light cancellation type digital-to-analog converter to cancel ambient light, and a DC component cancellation type digital-to-analog converter to cancel the DC component in the PPG signal.

[0037] During the dimming process, a dimming target value and the corresponding convergence range need to be set first. Then, the LED driving current is gradually adjusted in a binary search within the preset LED current range. Each time the LED driving current is changed, a sampling measurement is performed through an analog-to-digital converter. The obtained ADC code value is compared with the dimming target value, and the direction of the next LED driving current adjustment is determined based on the comparison result.

[0038] However, the CTR may change slowly during dimming, and each adjustment of the LED drive current requires a complete sampling measurement by the ADC (Analog-to-Digital Converter). The entire dimming process requires multiple samplings, resulting in long dimming time, insufficient accuracy, and poor stability.

[0039] In view of this, please refer to Figures 1-10This application proposes a fast dimming method and dimming system for PPG sensors, which can shorten the dimming time of PPG sensors and improve the accuracy and stability of dimming.

[0040] In an optional embodiment, the fast dimming method for a PPG sensor provided in this application can be applied to a PPG sensor, which includes a light-emitting diode, a photodetector, and an analog front-end coupled to the photodetector. The analog front-end includes a first digital-to-analog converter for eliminating ambient light, a second digital-to-analog converter for outputting a reference current, a transimpedance amplifier, and an analog-to-digital converter coupled to the transimpedance amplifier.

[0041] Specifically, light-emitting diodes (LEDs) are used to emit light of specific wavelengths into human tissue, while photodetectors are used to receive the light signals reflected or transmitted through human tissue and convert them into photocurrent output. Since the photocurrent output by the photodetector contains ambient light components, DC components, and AC components carrying physiological information, directly amplifying the photocurrent containing these components can easily lead to saturation of the transimpedance amplifier, thus failing to effectively extract weak AC signals.

[0042] To this end, this application includes a first digital-to-analog converter (DAC) and a second DAC in the analog front-end. The first DAC is used to eliminate ambient light, and the second DAC is configured to output a reference current corresponding to the dimming target during the coarse adjustment stage. This reference current is compared with the remaining photocurrent after ambient light elimination to determine the adjustment direction of the current driving current of the LED. After ambient light elimination, the remaining photocurrent is input to a transimpedance amplifier and converted into a voltage signal, which is then sampled and quantized by the DAC.

[0043] Based on this, please refer to Figure 1 This is a flowchart of a fast dimming method for a PPG sensor provided in an embodiment of this application. The dimming method includes the following steps: Step S1: Control the first digital-to-analog converter to eliminate ambient light, configure the input code value of the second digital-to-analog converter, and make the second digital-to-analog converter output a reference current corresponding to the dimming target; In this embodiment of the application, the light-emitting diode is used to emit light of a specific wavelength to human tissue, and the photodetector is used to receive the light signal reflected or transmitted by the human tissue and convert it into photocurrent output. Therefore, the photocurrent output by the photodetector includes both the current reflected or transmitted to the photodetector after the light-emitting diode irradiates the human tissue and the current generated by the ambient light directly irradiating the photodetector.

[0044] If the ambient light signal is not eliminated, the transimpedance amplifier may enter a saturated state. At the same time, the ambient light itself is unrelated to the dimming target and will cause some interference to the adjustment of the LED drive current. Therefore, this application sets a first digital-to-analog converter to eliminate the ambient light. As to how to eliminate the ambient light through the first digital-to-analog converter, it is a conventional technology in the field of PPG sensor technology, and this application will not elaborate on it here.

[0045] Furthermore, the input code value of the second digital-to-analog converter needs to be configured so that the output of the second digital-to-analog converter corresponds to the dimming target.

[0046] It is understandable that the dimming target is a predetermined value, corresponding to a specific reference current. When sampling under this reference current, the photocurrent output by the photodetector will not be too small to be overwhelmed by circuit noise, nor too large to cause the transimpedance amplifier to saturate.

[0047] Specifically, if the photocurrent output by the photodetector is too small, the signal amplitude sampled by the analog-to-digital converter will be low, resulting in a poor signal-to-noise ratio and affecting data accuracy; if the photocurrent is too large, the output of the transimpedance amplifier may reach the upper limit of the power supply voltage, causing clipping distortion and failing to accurately reflect changes in light intensity.

[0048] To obtain this reference current, the code value that the second digital-to-analog converter should input can be calculated based on the dimming target. After writing the code value into the second digital-to-analog converter, the current output by the second digital-to-analog converter is the reference current corresponding to the dimming target.

[0049] Step S2: Based on the binary division method and the polarity of the output signal of the transimpedance amplifier, adjust the driving current of the light-emitting diode until the receiving current of the photodetector is close to the reference current; In this embodiment, after ambient light elimination and reference current configuration, the driving current of the light-emitting diode (LED driving current) needs to be adjusted so that the receiving current of the photodetector is close to the reference current. Since there is a positive correlation between the receiving current of the photodetector and the driving current of the LED, but the specific proportionality coefficient (i.e., the current transfer ratio) is unknown, the required LED driving current cannot be directly calculated.

[0050] In an optional embodiment, this application employs a binary method to adjust the drive current of the light-emitting diode and uses the polarity of the transimpedance amplifier output signal as the judgment criterion. Since the transimpedance amplifier simultaneously receives the received current from the photodetector and the reference current output by the second digital-to-analog converter during the adjustment process, the polarity of the transimpedance amplifier output signal reflects the magnitude relationship between the received current of the photodetector and the reference current.

[0051] Furthermore, based on the polarity of the output signal of the transimpedance amplifier, it can be determined whether the current driving current of the LED is too large or too small relative to the dimming target. The driving current of the LED is then adjusted until the receiving current of the photodetector gradually approaches the reference current. The entire coarse adjustment process does not require sampling by an analog-to-digital converter, effectively shortening the dimming time.

[0052] As an optional implementation method, please refer to Figure 2 This is a flowchart illustrating the process of setting an intermediate value in a fast dimming method for a PPG sensor provided in this application embodiment. The step of adjusting the driving current of the light-emitting diode based on the binary search method and the polarity of the transimpedance amplifier output signal until the receiving current of the photodetector is close to the reference current includes: Step S20: Set the adjustment range of the drive current, wherein the adjustment range has an upper limit value and a lower limit value; Step S21: Set the current drive current to the midpoint between the upper limit value and the lower limit value; Step S22: Adjust the current drive current based on the polarity of the output signal of the transimpedance amplifier so that the difference between the received current of the photodetector and the reference current is less than a preset difference.

[0053] In this embodiment of the application, before the binary search method begins, it is necessary to determine the adjustment range of the driving current. This adjustment range has an upper limit and a lower limit, which are expressed in code value form, corresponding to the maximum and minimum code values ​​that the driving current of the light-emitting diode can reach, respectively.

[0054] The transmitter consists of a light-emitting diode and its driving circuit, used to emit light of a specific wavelength into human tissue. The upper limit corresponds to the code value corresponding to the maximum driving current that the driving circuit can output, and the lower limit corresponds to the code value corresponding to the minimum driving current.

[0055] This application limits the adjustment range to between the upper limit code value and the lower limit code value. In each subsequent iteration, the upper limit value or the lower limit value will be updated according to the comparison result, thereby narrowing the adjustment range and making the driving current of the light-emitting diode gradually converge to the vicinity of the dimming target.

[0056] Furthermore, after determining the upper and lower limits of the adjustment range, the current driving current of the LED is set to the midpoint between the upper and lower limits to ensure that the adjustment range can be halved after each comparison, thereby approaching the dimming target with fewer comparisons.

[0057] In an optional embodiment, after the drive current of the light-emitting diode is set, the transimpedance amplifier outputs a corresponding polarity signal based on the comparison result between the received current of the photodetector and the reference current. This application adjusts the upper or lower limit of the adjustment range according to the polarity of the output signal of the transimpedance amplifier, and then recalculates a new intermediate value as the drive current of the light-emitting diode for the next time.

[0058] After repeating this process several times, the receiving current of the photodetector corresponding to the driving current of the light-emitting diode will get closer and closer to the reference current until the difference between the two is less than a preset difference. This preset difference can be understood as the allowable error range in the coarse adjustment stage. Its size can be set according to the actual application requirements. This application does not impose specific restrictions on it.

[0059] As an optional implementation method, please refer to Figure 3 This is a flowchart illustrating the fast dimming method for a PPG sensor provided in this application, in which a new current drive current is determined. The step of adjusting the current drive current based on the polarity of the transimpedance amplifier output signal includes: Step S220: If the output signal of the transimpedance amplifier is positive, then update the upper limit of the adjustment range to the current drive current, and determine the midpoint between the updated upper limit and the lower limit as the new current drive current; Step S221: If the output signal of the transimpedance amplifier is negative, then update the lower limit of the adjustment range to the current drive current, and determine the midpoint between the updated upper limit and the lower limit as the new current drive current.

[0060] In this embodiment, when the polarity of the transimpedance amplifier output signal is positive, it indicates that the receiving current of the photodetector is greater than the reference current, and the currently set driving current of the light-emitting diode is too large. Since the receiving current of the photodetector is positively correlated with the driving current of the light-emitting diode, the upper limit of the adjustment range needs to be updated to the code value corresponding to the current driving current of the light-emitting diode, while the lower limit remains unchanged. Then, the current driving current of the light-emitting diode is set to the midpoint between the updated upper and lower limits, and the next comparison continues.

[0061] When the polarity of the output signal of the transimpedance amplifier is negative, it indicates that the receiving current of the photodetector is less than the reference current, and the driving current of the currently set LED is too small. At this time, the lower limit of the adjustment range needs to be updated to the code value corresponding to the driving current of the current LED, while the upper limit remains unchanged.

[0062] Then, the current driving current of the LED is set to the midpoint between the updated upper and lower limits. Through the above comparison method, the adjustment range is halved in each iteration, and the driving current code value of the LED converges to the code value corresponding to the dimming target.

[0063] Furthermore, the coarse adjustment stage does not rely on analog-to-digital converter sampling; comparison can be completed solely through the polarity of the transimpedance amplifier output signal, thus shortening the dimming time compared to traditional schemes that require waiting for analog-to-digital converter sampling for each adjustment.

[0064] Step S3: Sample the output signal of the transimpedance amplifier through the analog-to-digital converter, compare the sampled value with the convergence interval corresponding to the dimming target, and update the number of convergences and non-convergences based on the comparison result; In the embodiments of this application, after the coarse adjustment stage is completed, the receiving current of the photodetector is close to the reference current, and then the fine adjustment stage will begin.

[0065] Specifically, this application samples the output signal of the transimpedance amplifier using an analog-to-digital converter to obtain a digitized sample value, then compares the sample value with the convergence interval corresponding to the dimming target, and updates the number of convergences and non-convergences based on the comparison result.

[0066] It should be noted that the convergence range is a numerical range centered on the dimming target. If the sampled value falls within this convergence range, it means that the current drive current is already appropriate. If the sampled value falls outside this convergence range, it means that the current drive current still needs to be adjusted.

[0067] To track the convergence status during the fine-tuning process, this application sets convergence counts and non-convergence counts. The convergence count records the number of samples where the current sample value is within the convergence interval, while the non-convergence count records the number of consecutive samples that are not within the convergence interval. The convergence count and non-convergence count are updated based on the comparison results, providing a basis for subsequent adjustment of the drive current.

[0068] As an optional implementation method, please refer to Figure 4 This is a flowchart illustrating the updating of convergence and non-convergence counts in a fast dimming method for a PPG sensor provided in this application embodiment. The step of comparing the sampled values ​​obtained from sampling with the convergence interval corresponding to the dimming target, and updating the convergence and non-convergence counts based on the comparison result, includes: Step S30: If the sampled value is within the convergence interval, increment the convergence count by one and clear the non-convergence count to zero; Step S31: If the sampled value is not within the convergence interval, then increment the number of non-convergence count by one.

[0069] In an optional embodiment, when the sampled value obtained by the analog-to-digital converter is within the convergence interval corresponding to the dimming target, it indicates that the current driving current of the light-emitting diode has enabled the receiving current of the photodetector to reach an acceptable accuracy range, and the convergence count can be incremented by one.

[0070] Meanwhile, since the sampled value is within the convergence interval corresponding to the dimming target, it indicates that the current sampling is converged and the previous continuous non-convergence state has been broken. Therefore, the number of non-convergence counts is cleared to zero, and the continuous non-convergence situation is recorded again so that it can be accurately identified in subsequent judgments whether there are multiple consecutive non-convergences.

[0071] Conversely, if the sampled value obtained by the analog-to-digital converter is not within the convergence interval corresponding to the dimming target, it indicates that the current driving current of the light-emitting diode has not yet enabled the receiving current of the photodetector to reach an acceptable accuracy range, and further adjustment is required.

[0072] Furthermore, the number of non-convergences needs to be incremented by one to record the number of consecutive non-convergences, while the number of convergences remains unchanged. By recording the number of non-convergences, it is possible to determine in subsequent adjustments whether larger step size adjustments are needed to cope with possible sudden changes in the current transfer ratio.

[0073] It should be noted that the number of consecutive convergences does not need to be recorded, but the number of consecutive non-convergences should be recorded. This is because an occasional non-convergence may be caused by noise or instantaneous fluctuations in the current transfer ratio, and does not necessarily indicate that the drive current deviates significantly from the target. Only multiple consecutive non-convergences indicate that the current drive current has indeed deviated from the convergence range, requiring adjustments with larger step sizes. Therefore, the number of non-convergences is recorded as consecutive non-convergences, while the number of convergences is recorded cumulatively and does not need to be consecutive. Those skilled in the art should understand this.

[0074] Step S4: Adjust the driving current based on the updated convergence count and non-convergence count to make the sampled value approach the dimming target; In this embodiment, the convergence count is the cumulative number of times the sampled value is within the convergence interval, and the non-convergence count is the number of times the sampled value is continuously not within the convergence interval. Based on the convergence count and non-convergence count updated in step S3, this application adjusts the drive current so that the sampled values ​​obtained by the subsequent analog-to-digital converter gradually approach the dimming target, and finally the sampled values ​​can stably fall within the convergence interval.

[0075] As an optional implementation method, please refer to Figure 5This is a flowchart illustrating the adjustment of the driving current in a fast dimming method for a PPG sensor provided in this application embodiment. The adjustment of the driving current based on the updated convergence count and non-convergence count includes: Step S40: When the sampled value is within the convergence interval, adjust the driving current in the direction approaching the dimming target with a minimum step size; Step S41: When the sampled value is not in the convergence interval and the current number of non-convergences is less than the preset non-convergence threshold, adjust the driving current in the direction approaching the dimming target with the minimum step size, and keep the count of the convergences from being zero. Step S42: When the sampled value is not in the convergence interval and the current number of non-convergences is greater than or equal to the preset non-convergence threshold, adjust the driving current in the direction approaching the dimming target with a preset step size, and at the same time clear the number of convergences.

[0076] In an optional embodiment, if the sampled value obtained by the analog-to-digital converter is within the convergence interval corresponding to the dimming target, it indicates that the photodetector receiving current corresponding to the current driving current of the light-emitting diode is within an acceptable error range.

[0077] However, since the current transfer ratio may change slowly over time, if no adjustment is made to the drive current, the subsequent sampled values ​​may gradually drift out of the convergence range. Therefore, it is still necessary to fine-tune the drive current to make the sampled values ​​move closer to the dimming target.

[0078] Specifically, this application uses the minimum step size as the adjustment step size. Each time, the driving current code value of the light-emitting diode is increased or decreased by one minimum step size. The direction of adjustment is determined according to the relationship between the sampled value and the dimming target. Since the sampled value is already within the convergence range, the small adjustment will not cause the sampled value to jump out of the convergence range, which is beneficial to maintaining the stability of sampling and dimming.

[0079] If the sampled value obtained by the analog-to-digital converter is not within the convergence interval, but the number of non-convergence counts has not yet reached the preset non-convergence threshold, it indicates that this non-convergence may be accidental, caused by factors such as circuit noise or instantaneous fluctuations in the current transfer ratio, and does not necessarily mean that the current drive current has seriously deviated from the target value. In this case, rashly using a larger step size for adjustment may actually lead to drive current overshoot, causing the sampled value to deviate further from the convergence interval.

[0080] Preferably, this application still uses the minimum step size for adjustment, while keeping the convergence count count from being reset. If a certain number of convergence counts have already been accumulated, a single non-convergence will not reset these counts, thus avoiding interference from occasional non-convergence to the dimming process. If the sampled value subsequently re-enters the convergence range, the convergence count can continue to accumulate, thereby reaching the required convergence threshold for dimming completion more quickly and avoiding unnecessary repeated adjustments.

[0081] In an optional embodiment, if the sampled value obtained by the analog-to-digital converter is not within the convergence interval, and the number of non-convergence counts has reached or exceeded a preset non-convergence count threshold, it indicates that multiple consecutive samples are not within the convergence interval. This situation is usually not an occasional disturbance, but rather indicates that the deviation between the current driving current of the LED and the dimming target is large, or that the current transfer ratio has changed significantly, making the original driving current no longer applicable.

[0082] At this point, if the minimum step size is still used for adjustment, many adjustments will be needed to bring the drive current back to the vicinity of the convergence range, significantly extending the dimming time. Therefore, a preset step size larger than the minimum step size needs to be used for adjustment in order to quickly reduce the deviation.

[0083] It should be noted that the specific value of the preset step size can be set according to actual needs, for example, it can be a certain percentage of the current drive current code value, but it should not be less than the minimum step size. The adjustment direction is still determined based on the comparison result between the sampled value and the dimming target, that is, decrease the drive current when the sampled value is greater than the dimming target, and increase the drive current when the sampled value is less than the dimming target.

[0084] Meanwhile, since the drive current has deviated from the convergence range multiple times, the previously accumulated convergence count can no longer reflect the current convergence status. Therefore, the convergence count needs to be reset to zero. After resetting, if subsequent sampling re-enters the convergence range, the convergence count will be re-accumulated from zero, ensuring that the dimming completion condition is based on the latest convergence situation.

[0085] As an optional implementation, adjusting the drive current in a direction approaching the dimming target includes: When the sampled value is greater than the dimming target, the driving current is reduced; when the sampled value is less than the dimming target, the driving current is increased.

[0086] In the embodiments of this application, whether the minimum step size or the preset step size is used as the adjustment step size, the driving current needs to be adjusted in a direction that approaches the dimming target.

[0087] Specifically, if the sampled value is greater than the dimming target, it indicates that the current receiving current of the photodetector is too high. This is usually due to the excessive driving current setting of the light-emitting diode, so the driving current needs to be reduced.

[0088] Conversely, if the sampled value is less than the dimming target, it indicates that the current receiving current is too low and the drive current setting is too small. The drive current needs to be increased to ensure that each adjustment to the drive current is made in the direction that brings the sampled value closer to the dimming target, thus ensuring the effectiveness of the adjustment.

[0089] As an optional implementation, the preset step size does not exceed a preset ratio of the code value corresponding to the current drive current, and is not less than the minimum step size.

[0090] In this embodiment of the application, when the sampled value is not in the convergence interval and the number of consecutive non-convergences reaches or exceeds a preset threshold, a larger adjustment needs to be made using a preset step size.

[0091] On the one hand, in order to quickly bring the drive current back to the vicinity of the convergence range, the preset step size cannot be too small; on the other hand, if the step size is too large, it may cause adjustment overshoot, causing the sampled value to deviate from one side and jump to the other side, which will prolong the dimming time.

[0092] In an optional embodiment, this application sets the preset ratio value to 1 / 32, that is, the preset step size is limited to no more than one-thirty-second of the code value corresponding to the current driving current. This ratio can ensure that the adjustment range is moderate each time, which can effectively respond to large changes in the current transmission ratio without causing drastic fluctuations. At the same time, the preset step size is not less than the minimum step size, ensuring that it can provide a greater adjustment force than the minimum step size when rapid adjustment is required. Of course, the specific value of the above-mentioned preset ratio value can also be adjusted according to actual needs, and this application does not limit it.

[0093] As an optional implementation, the minimum step size is 1 LSB.

[0094] It is understood that the minimum step size refers to the smallest unit in which the drive current code value of the light-emitting diode is adjusted each time. In this application, the minimum step size is set to 1 LSB (Least Significant Bit), where LSB corresponds to a minimum code value change of the drive current digital-to-analog converter. This fine adjustment step size can avoid excessive fluctuations when the sampled value is close to the dimming target, ensuring the stability of the dimming process. At the same time, it also enables the drive current after final convergence to be accurately stabilized near the dimming target.

[0095] Step S5: Repeat the above steps of sampling, comparison, number update and drive current adjustment until the number of sampling reaches the preset minimum number of sampling and the number of convergences reaches the preset convergence threshold, then determine that dimming is complete.

[0096] In this embodiment, after each sampling, the sampled value needs to be compared with the convergence interval corresponding to the dimming target. The number of convergences or non-convergences is updated according to the comparison result. Then, based on the updated number of convergences or non-convergences, the corresponding adjustment step size is selected to adjust the driving current of the light-emitting diode. Then, the next sampling is performed, and so on.

[0097] Furthermore, dimming is considered complete only when both of these conditions are met: the number of samples taken has reached the preset minimum number of samples, and the number of convergences has reached the preset convergence threshold. This setting ensures that the sampled values ​​are not only within the convergence range but also that the number of samples is sufficient, avoiding premature determination of dimming success due to accidental factors.

[0098] As an optional implementation method, please refer to Figure 6 This is a flowchart illustrating the determination of dimming failure in a fast dimming method for a PPG sensor provided in this application embodiment. The fast dimming method further includes: Step S51: When the number of samplings reaches the preset maximum number of samplings and dimming has not yet been determined to be complete, dimming is determined to have failed.

[0099] Understandably, during actual dimming, the number of samples may increase continuously, but the minimum number of samples and the convergence number may not be reached, thus failing to meet the preset convergence threshold. To address this, this application sets a maximum number of samples. If dimming is not considered complete when the actual number of samples reaches this maximum, the dimming is considered a failure, preventing endless dimming in the event of drastic changes in the current transfer ratio or sensor malfunctions.

[0100] As an optional implementation, the preset non-convergence threshold is 2 times, the preset minimum sampling number is 3 times, and the preset maximum sampling number is 5 times.

[0101] In an optional embodiment, this application sets the preset non-convergence threshold to 2 times. If two consecutive samples are not within the convergence interval, it is considered that the drive current deviates significantly, and a preset step size is required for a large adjustment, and the convergence count is reset to zero.

[0102] Optionally, the minimum number of samples can be set to 3, meaning that at least 3 samples need to be completed, and dimming can only be determined to be complete when the number of convergences in these 3 samples reaches a preset convergence threshold.

[0103] For example, the maximum number of samplings can be set to 5. That is, if the number of samplings has reached 5 but the dimming completion condition is still not met, the dimming is determined to have failed. The specific values ​​provided above can be adjusted according to factors such as the sampling rate and the rate of change of current transfer ratio in actual applications, and this application does not impose too many restrictions on them.

[0104] In one specific embodiment provided in this application, please refer to Figure 7 This is a specific embodiment of the fast dimming method for a PPG sensor provided in this application. The PPG sensor includes a light-emitting diode, a photodetector, and an AFE (Analog Front End) coupled to the photodetector. The analog front end includes a first digital-to-analog converter (corresponding to AMB-DAC in the figure) for eliminating ambient light, a second digital-to-analog converter (corresponding to DC-DAC in the figure) for outputting a reference current, a transimpedance amplifier (TIA), and an analog-to-digital converter (ADC) coupled to the transimpedance amplifier. The fast dimming process in this embodiment will be described below with reference to specific values.

[0105] First, perform a rough adjustment; please refer to... Figure 8 ,for Figure 7 The schematic diagram of the coarse adjustment stage in the specific embodiment shown illustrates the process of controlling the first digital-to-analog converter to eliminate ambient light and configuring the input code value of the second digital-to-analog converter so that its output is a reference current corresponding to the dimming target. The dimming target is a predetermined value corresponding to a suitable reference current, ensuring that when sampling is performed under this reference current, the photocurrent output by the photodetector is neither too small and overwhelmed by circuit noise, nor too large and causes the transimpedance amplifier to saturate.

[0106] In this embodiment, the dimming target value is set to a specific value, and the convergence interval is set to ±10% of the dimming target value.

[0107] Furthermore, the adjustment range of the drive current is set, which has an upper limit and a lower limit, corresponding to the maximum and minimum possible code values ​​of the LED drive current, respectively. The current drive current is set to the midpoint between the upper and lower limits.

[0108] The transimpedance amplifier simultaneously receives the receiving current from the photodetector and the reference current output from the second digital-to-analog converter. The polarity of its output signal reflects the magnitude relationship between the receiving current and the reference current. If the transimpedance amplifier output signal is positive, it indicates that the receiving current is greater than the reference current, and the current drive current is too large. In this case, the upper limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper and lower limits is determined as the new current drive current. If the output signal is negative, it indicates that the receiving current is less than the reference current, and the current drive current is too small. In this case, the lower limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper and lower limits is determined as the new current drive current.

[0109] Repeat the above polarity judgment and adjustment range update to make the difference between the received current and the reference current of the photodetector less than a preset difference value, and the entire coarse adjustment process does not require the participation of the analog-to-digital converter (ADC), so it is very fast.

[0110] Further, please refer to Figure 9 ,for Figure 7 The diagram shown in the specific embodiment illustrates the fine-tuning stage. After the coarse-tuning is completed, the fine-tuning stage begins. At this time, the analog-to-digital converter samples the output signal of the transimpedance amplifier to obtain the sampled value, and compares the sampled value with the convergence interval corresponding to the dimming target.

[0111] If the sampled value is within the convergence interval, the convergence count is incremented by one, and the non-convergence count is reset to zero; if the sampled value is not within the convergence interval, the non-convergence count is incremented by one.

[0112] In this specific embodiment, the application sets the preset non-convergence threshold to 2 times, the minimum step size to 1 LSB, the preset step size not exceeding 1 / 32 of the code value corresponding to the current drive current and not less than 1 LSB, the preset minimum sampling number to 3 times, and the preset maximum sampling number to 5 times.

[0113] Furthermore, if the sampled value is within the convergence range, the drive current is adjusted by 1 LSB in the direction of approaching the dimming target. If the sampled value is greater than the dimming target, the drive current is reduced by 1 LSB, and if it is less than the target, the drive current is increased by 1 LSB.

[0114] If the sampled value is not within the convergence interval and the current number of non-convergences is less than 2, the drive current is adjusted by 1 LSB, while the count of convergences is kept from being zeroed.

[0115] If the sampled value is not within the convergence interval, and the current non-convergence count is greater than or equal to 2, it means that the sampled values ​​have been out of the convergence interval for two consecutive times. At this time, the driving current is adjusted by a preset step size, and the adjustment direction is also to make the sampled value approach the dimming target, while the convergence count is cleared to zero.

[0116] After each adjustment, the cycle of sampling, comparison, count update, and adjustment is repeated. The sampling count is incremented after each sampling. When the number of samplings reaches a preset 3 and the number of convergences reaches a preset convergence threshold, the dimming is considered complete.

[0117] If the number of samples has reached the preset maximum of 5 during the sampling process, but the dimming completion condition is still not met, then dimming is deemed to have failed.

[0118] Thus, by combining the above-mentioned coarse and fine adjustments, this application can usually complete dimming within 3 to 5 times. Compared with the traditional method that requires multiple sampling, it significantly shortens the dimming time while ensuring dimming accuracy and stability.

[0119] Based on the above-described fast dimming method for PPG sensors, please refer to [link to relevant documentation]. Figure 10 This is a functional block diagram of a fast dimming system for a PPG sensor provided in an embodiment of this application. This application also provides a fast dimming system for a PPG sensor, comprising: A configuration unit is used to control the first digital-to-analog converter to eliminate ambient light and to configure the input code value of the second digital-to-analog converter so that the second digital-to-analog converter outputs a reference current corresponding to the dimming target. The judgment unit is used to adjust the driving current of the light-emitting diode based on the binary division method and the polarity of the output signal of the transimpedance amplifier until the receiving current of the photodetector is close to the reference current. The update unit is used to sample the output signal of the transimpedance amplifier through the analog-to-digital converter, compare the sampled value with the convergence interval corresponding to the dimming target, and update the number of convergences and non-convergences according to the comparison result. An adjustment unit is configured to adjust the drive current based on the updated number of convergences and the number of non-convergences, so that the sampled value approaches the dimming target. The execution unit is used to repeatedly perform the above steps of sampling, comparison, number update and drive current adjustment until the number of sampling reaches the preset minimum number of sampling and the number of convergences reaches the preset convergence threshold, at which point the dimming is determined to be complete.

[0120] For further details regarding the implementation of the above-mentioned fast dimming system for PPG sensors, please refer to the description of the fast dimming method for PPG sensors provided in the above-mentioned application embodiments, which will not be repeated here.

[0121] This application provides a rapid dimming method and system for PPG sensors. In the coarse adjustment stage, a first digital-to-analog converter (DAC) is controlled to eliminate ambient light, and a second DAC is configured to output a reference current corresponding to the dimming target. Based on the binary division method and utilizing the polarity of the transimpedance amplifier output signal, the driving current of the light-emitting diode (LED) is directly adjusted until the receiving current of the photodetector approaches the reference current. The coarse adjustment process does not rely on DAC sampling and can be completed in a very short time. In the fine adjustment stage, the DAC samples the output signal of the transimpedance amplifier, compares the sampled value with the convergence interval corresponding to the dimming target, updates the convergence and non-convergence counts based on the comparison results, and adjusts the driving current based on the updated counts to bring the sampled value closer to the dimming target. This method can distinguish between accidental and continuous deviations, thus enabling fine adjustment with a minimum or preset step size.

[0122] Subsequently, the steps of sampling, comparison, count update, and adjustment are repeated until the number of samples reaches the preset minimum number of samples and the number of convergences reaches the preset convergence threshold. Only then is dimming considered complete, avoiding premature termination of dimming due to single or accidental convergence. Compared to traditional solutions that require multiple analog-to-digital converter samplings and additional confirmation samplings, this application quickly approximates the dimming target through coarse adjustment, and only requires a small number of samples to complete fine adjustment, thereby reducing the total number of samplings and shortening the dimming time. At the same time, because the dimming process is faster, the LED drive current can quickly stabilize, effectively improving the accuracy and stability of dimming and ensuring the detection accuracy of the sensor.

[0123] It should be noted that, in the several embodiments provided in this application, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed between each other can be through some interfaces, or indirect coupling or communication connection between devices or units, and can be electrical, mechanical, or other forms.

[0124] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0125] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A fast dimming method for a PPG sensor, the PPG sensor comprising a light-emitting diode, a photodetector, and an analog front-end coupled to the photodetector, the analog front-end comprising a first digital-to-analog converter for eliminating ambient light, a second digital-to-analog converter for outputting a reference current, a transimpedance amplifier, and an analog-to-digital converter coupled to the transimpedance amplifier, characterized in that, The dimming method includes the following steps: The first digital-to-analog converter is controlled to eliminate ambient light, and the input code value of the second digital-to-analog converter is configured so that the second digital-to-analog converter outputs a reference current corresponding to the dimming target; Based on the binary division method and the polarity of the output signal of the transimpedance amplifier, the driving current of the light-emitting diode is adjusted until the receiving current of the photodetector is close to the reference current. The output signal of the transimpedance amplifier is sampled by the analog-to-digital converter, and the sampled value is compared with the convergence interval corresponding to the dimming target. The number of convergences and non-convergences are updated according to the comparison result. The drive current is adjusted based on the updated convergence count and non-convergence count to make the sampled value approach the dimming target; Repeat the above steps of sampling, comparison, number update, and drive current adjustment until the number of samplings reaches the preset minimum number of samplings and the number of convergences reaches the preset convergence threshold, at which point dimming is considered complete.

2. The rapid dimming method for a PPG sensor as described in claim 1, characterized in that, The adjustment of the driving current of the light-emitting diode based on the binary search method and the polarity of the output signal of the transimpedance amplifier until the receiving current of the photodetector is close to the reference current includes: The adjustment range of the drive current is set, and the adjustment range has an upper limit value and a lower limit value; Set the current drive current to the midpoint between the upper limit value and the lower limit value; The current drive current is adjusted based on the polarity of the output signal of the transimpedance amplifier so that the difference between the received current of the photodetector and the reference current is less than a preset difference.

3. The rapid dimming method for a PPG sensor as described in claim 2, characterized in that, The adjustment of the current drive current based on the polarity of the transimpedance amplifier output signal includes: If the output signal of the transimpedance amplifier is positive, the upper limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper limit and the lower limit is determined as the new current drive current. If the output signal of the transimpedance amplifier is negative, the lower limit of the adjustment range is updated to the current drive current, and the midpoint between the updated upper limit and the lower limit is determined as the new current drive current.

4. The rapid dimming method for a PPG sensor as described in claim 1, characterized in that, The step of comparing the sampled values ​​obtained by sampling with the convergence interval corresponding to the dimming target, and updating the number of convergences and non-convergences based on the comparison result, includes: If the sampled value is within the convergence interval, the convergence count is incremented by one, and the non-convergence count is cleared to zero. If the sampled value is not within the convergence interval, the number of non-convergence counts is incremented by one.

5. The rapid dimming method for a PPG sensor as described in claim 4, characterized in that, The adjustment of the drive current based on the updated convergence count and non-convergence count includes: When the sampled value is within the convergence interval, the driving current is adjusted in the direction approaching the dimming target with a minimum step size; When the sampled value is not in the convergence interval and the current number of non-convergences is less than the preset non-convergence threshold, the driving current is adjusted in the direction approaching the dimming target with the smallest step size, and the count of the convergences is kept from being zero. When the sampled value is not in the convergence interval and the current number of non-convergences is greater than or equal to the preset non-convergence threshold, the driving current is adjusted in the direction approaching the dimming target with a preset step size, and the number of convergences is cleared.

6. The rapid dimming method for a PPG sensor as described in claim 5, characterized in that, Adjusting the drive current in a direction approaching the dimming target includes: When the sampled value is greater than the dimming target, the driving current is reduced; when the sampled value is less than the dimming target, the driving current is increased.

7. The rapid dimming method for a PPG sensor as described in claim 5, characterized in that, The preset step size does not exceed a preset ratio of the code value corresponding to the current drive current, and is not less than the minimum step size.

8. The rapid dimming method for a PPG sensor as described in claim 5, characterized in that, The rapid dimming method further includes: If the number of samplings reaches the preset maximum number of samplings and the dimming is not yet determined to be complete, the dimming is determined to have failed.

9. The rapid dimming method for a PPG sensor as described in claim 8, characterized in that, The preset threshold for the number of non-convergences is 2, the preset minimum number of samples is 3, and the preset maximum number of samples is 5.

10. A fast dimming system for a PPG sensor, characterized in that, For performing the fast dimming method for a PPG sensor as described in any one of claims 1-9, the dimming system comprises: A configuration unit is used to control the first digital-to-analog converter to eliminate ambient light and to configure the input code value of the second digital-to-analog converter so that the second digital-to-analog converter outputs a reference current corresponding to the dimming target. The judgment unit is used to adjust the driving current of the light-emitting diode based on the binary division method and the polarity of the output signal of the transimpedance amplifier until the receiving current of the photodetector is close to the reference current. The update unit is used to sample the output signal of the transimpedance amplifier through the analog-to-digital converter, compare the sampled value with the convergence interval corresponding to the dimming target, and update the number of convergences and non-convergences according to the comparison result. An adjustment unit is configured to adjust the drive current based on the updated number of convergences and the number of non-convergences, so that the sampled value approaches the dimming target. The execution unit is used to repeatedly perform the above steps of sampling, comparison, number update and drive current adjustment until the number of sampling reaches the preset minimum number of sampling and the number of convergences reaches the preset convergence threshold, at which point the dimming is determined to be complete.

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