DC component simulation elimination system and elimination method

Abstract

The invention discloses a DC component simulation elimination system and elimination method.The elimination system comprises a photoelectric detection module, an elimination module, a simulation comparison output module and a control module, controlling the first elimination digital-to-analog converter to sequentially traverse from the highest weight elimination gear to determine a first elimination gear combination; after a first elimination gear combination is determined, a transmitting element is turned on, a first elimination digital-to-analog converter is controlled to counteract an ambient light signal, and when a sleep period of a current sampling period is executed, a second elimination digital-to-analog converter is controlled to sequentially traverse from the highest weight elimination gear, determining a second elimination gear combination according to the comparison result of the current elimination gear to offset the direct current component in the reflected light signal; according to the application, the elimination gear combination can be dynamically determined step by step, the direct current component in the ambient light signal and the reflected light signal is effectively eliminated, and the accuracy and reliability of the detection result are ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of health monitoring, and particularly relates to a DC component analog elimination system and method. BACKGROUND

[0002] In the field of wearable health monitoring devices, the heart rate and blood sample monitoring technology of PPG (Photo Plethysmo Graphy) has been widely applied. The core of the technology is to use a photoelectric detection module to detect the light signal reflected by the skin tissue, and to extract the weak AC (Alternating Current) component caused by the blood volume pulse to calculate the physiological parameters of the wearer, such as the heart rate and blood oxygen of the wearer.

[0003] However, in the light signal received by the photoelectric detection module, the AC component expressing the physiological information is much smaller than the DC (Direct Current) component generated by the static reflection of the skin tissue and the background environment. In most cases, the AC component expressing the physiological information is only in the order of nanoamperes, while the DC component generated by the static reflection of the skin tissue and the background environment can reach hundreds of microamperes. If the DC component not containing physiological information changes is not eliminated, or the DC component is not eliminated sufficiently, it will lead to the saturation distortion of the collected signal and cannot guarantee the reliability of the detection data and the detection result. SUMMARY

[0004] The application provides a DC component analog elimination system and method, which can dynamically determine the elimination gear combination by steps, effectively eliminate the DC component in the environmental light signal and the reflected light signal, and ensure the accuracy and reliability of the detection result.

[0005] To solve the above technical problems, the application provides a DC component analog elimination system, which comprises: A photoelectric detection module comprising a transmitting element for transmitting a light signal and a receiving element for collecting a receiving signal and converting it into a receiving current, wherein the receiving signal comprises an environmental light signal and a reflected light signal of the light signal reflected by a target object; An elimination module coupled to the output end of the receiving element, comprising a first elimination digital-to-analog converter and a second elimination digital-to-analog converter configured with a plurality of elimination gears with different weights; An analog comparison output module coupled to the output end of the elimination module, configured to convert the receiving current after elimination by the elimination module into a receiving voltage and compare it with a reference voltage, and output a comparison result of over-elimination or under-elimination; A control module coupled to the output end of the analog comparison output module, configured to: The transmitting element is closed after triggering cancellation, the first cancellation digital-to-analog converter is controlled to sequentially traverse from the highest weight cancellation gear, and the first cancellation gear combination is determined according to the comparison result of the current cancellation gear. The transmitting element is opened after determining the first cancellation gear combination, the first cancellation digital-to-analog converter is controlled to offset the ambient light signal according to the first cancellation gear combination, when the sleep period of the current sampling period is executed, the second cancellation digital-to-analog converter is controlled to sequentially traverse from the highest weight cancellation gear, the second cancellation gear combination is determined according to the comparison result of the current cancellation gear, and the direct current component in the reflected light signal is offset according to the second cancellation gear combination.

[0006] As a further improvement of the present application, when the transmitting element is closed, the receiving signal collected by the receiving element is the ambient light signal. When the transmitting element is opened, the transmitting element is used for transmitting a light signal with a preset intensity, the receiving signal collected by the receiving element is the ambient light signal, and the reflected light signal after being reflected by the target object.

[0007] As a further improvement of the present application, the output end of the first cancellation digital-to-analog converter is coupled with the output end of the receiving element, the output end of the second cancellation digital-to-analog converter is coupled with the output end of the receiving element, and the input end of the analog comparison output module is coupled with the output end of the cancellation module.

[0008] As a further improvement of the present application, the first cancellation digital-to-analog converter and the second cancellation digital-to-analog converter are both configured with corresponding adjustment circuits, each adjustment circuit includes a plurality of cancellation gears arranged in parallel, and each cancellation gear is provided with a current source matched with the weight thereof. The control module is connected with the plurality of current sources arranged in the first cancellation digital-to-analog converter and the second cancellation digital-to-analog converter.

[0009] As a further improvement of the present application, the control module is used for controlling the corresponding cancellation digital-to-analog converter to start from the highest weight corresponding cancellation gear, and based on the comparison result corresponding to the current cancellation gear, when the comparison result is under-cancellation, the current source corresponding to the current cancellation gear is connected, and when the comparison result is over-cancellation, the current source corresponding to the current cancellation gear is disconnected.

[0010] As a further improvement of this application, the control module is also used to enable or disable the current source corresponding to the next weight after completing the on / off switching of the current source corresponding to the current weight, based on the updated comparison result output by the analog comparison output module, in descending order of weight, until all current sources corresponding to the elimination level are traversed, thereby generating the first elimination level combination for canceling the ambient light signal and the second elimination level combination for canceling the DC component in the reflected light signal.

[0011] As a further improvement of this application, the control module is used to control the on / off state of the current source corresponding to each elimination level in the first elimination digital-to-analog converter according to the first elimination level combination, and to weight and superimpose the output of the current source in the conducting state to generate an elimination current corresponding to the first elimination level combination to cancel the ambient light signal. The control module is further configured to control the on / off state of the current source corresponding to each elimination level in the second elimination digital-to-analog converter according to the second elimination level combination, and to weight and superimpose the outputs of the current sources in the conducting state to generate an elimination current corresponding to the second elimination level combination to cancel the DC component in the reflected light signal.

[0012] As a further improvement of this application, the analog comparison output module includes a transimpedance amplifier coupled to the output terminal of the cancellation module, and an analog comparator coupled to the output terminal of the transimpedance amplifier. The transimpedance amplifier is used to convert the received current, after being eliminated by the elimination module, into a received voltage. The analog comparator is used to compare the received voltage with a reference voltage and output a comparison result representing over-cancellation or under-cancellation; Specifically, when the received voltage is greater than the reference voltage, the analog comparator outputs an under-cancelled comparison result; when the received voltage is less than the reference voltage, the analog comparator outputs an over-cancelled comparison result.

[0013] As a further improvement of this application, the number of elimination levels is at least 8, and the weight corresponding to each elimination level is allocated in binary.

[0014] Based on the above-described DC component analog cancellation system, this application also provides a DC component analog cancellation method, which includes the following steps: After trigger elimination, the transmitting element is turned off, and the ambient light signal when the transmitting element is turned off is received and converted into ambient photocurrent. The ambient light current is superimposed bit by bit with the output current of the first elimination digital-to-analog converter to eliminate it. The eliminated ambient light current is converted into an ambient light voltage and compared with a reference voltage. The corresponding comparison result is output, and a first elimination level combination is generated based on the comparison result. The system controls the emitting element to emit a light signal of a preset intensity, receives a received signal containing a reflected light signal and the ambient light signal, and controls the first cancellation digital-to-analog converter to cancel the ambient light signal according to the first cancellation level combination. When the current sampling period reaches the sleep period, the received current after being eliminated by the second elimination digital-to-analog converter is converted into a received voltage and compared with the reference voltage, and the comparison result of over-elimination or under-elimination is output. Based on the comparison result, a second elimination level combination is generated, and the second elimination digital-to-analog converter is controlled to cancel the DC component in the reflected light signal according to the second elimination level combination.

[0015] The DC component analog cancellation system and cancellation method provided in this application have the following beneficial effects: This application generates an ambient light cancellation current with the same amplitude but opposite direction to the ambient light current through a first cancellation digital-to-analog converter, avoiding the influence of ambient light and ensuring that the received signal in subsequent processing only includes valid information reflected by the target object. Then, the adjustment circuit of the second cancellation digital-to-analog converter is controlled to traverse sequentially from the highest weight cancellation level. The received current after ambient light cancellation is converted into a received voltage through a transimpedance amplifier. The analog comparator compares the received voltage with a reference voltage and outputs the result of over-cancellation or under-cancellation. By enabling or disabling the current cancellation level, the final second cancellation level combination is dynamically generated, ensuring that the second cancellation digital-to-analog converter can accurately cancel the DC component in the reflected photocurrent according to the cancellation level combination. This effectively removes the DC components of the ambient light signal and the reflected light signal in the received signal, enabling the subsequent analog-to-digital converter to accurately acquire the AC signal related to heart rate changes, ensuring the accuracy and reliability of the heart rate detection results. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is a schematic diagram of the DC component simulation elimination system provided in an embodiment of this application.

[0018] Figure 2 A functional block diagram of the DC component analog elimination system provided in the embodiments of this application.

[0019] Figure 3 The schematic diagram of the adjustment circuit in the DC component analog elimination system provided in the embodiments of this application is shown.

[0020] Figure 4 This is a schematic diagram of the sampling period in the DC component analog elimination system provided in this application embodiment.

[0021] Figure 5 This is a schematic diagram of the DCC triggering structure in the DC component simulation elimination system provided in this application embodiment.

[0022] Figure 6 A flowchart of the DC component simulation elimination method provided in the embodiments of this application. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] In the field of wearable health monitoring devices, PPG (Photo Plethysmo Graphy) heart rate and blood sample monitoring technology has been widely used. The core of this technology is to use a photoelectric detection module to detect the light signal reflected by the skin tissue and extract the weak AC (Alternating Current) component caused by blood volume pulsation to calculate the wearer's physiological parameters, such as monitoring the wearer's heart rate and blood oxygen.

[0028] However, in the light signal received by the photoelectric detection module, the AC component, which expresses physiological information, is much smaller than the DC (Direct Current) component generated by the static reflection of skin tissue and the background environment. In most cases, the AC component, which expresses physiological information, is only in the nanoampere range, while the DC component generated by the static reflection of skin tissue and the background environment can reach hundreds of microamperes. If the DC component, which does not contain physiological information changes, is not eliminated, or if the DC component is not eliminated sufficiently, it will lead to saturation distortion of the acquired signal and make it impossible to guarantee the reliability of the detection data and results.

[0029] Please refer to Figures 1-6 This application provides a DC component analog elimination system and elimination method, which can dynamically determine the elimination level combination step by step, effectively eliminate the DC component in ambient light signal and reflected light signal, and ensure the accuracy and reliability of detection results.

[0030] Please refer to Figure 1 This is a schematic diagram of the DC component analog elimination system provided in the embodiments of this application. The DC component analog elimination system includes a photoelectric detection module, an elimination module, an analog comparison output module, and a control module.

[0031] As an optional implementation, the photoelectric detection module includes a transmitting element and a receiving element, wherein the transmitting element is used to transmit light signals, and the receiving element is used to collect and receive signals and convert the received signals into received current. The received signals include ambient light signals and reflected light signals after the transmitted light signals are reflected by the target object.

[0032] In an optional embodiment, the above-mentioned emitting element can be set as an LED (Light Emitting Diode) emitting tube, and the receiving element can be set as a PD (Photodiode) receiving tube. The LED emitting tube emits a light signal of a preset intensity, and the receiving tube is used to receive the light signal reflected by the target object (such as the wearer's skin tissue).

[0033] Meanwhile, due to its inherent characteristics, the receiving tube can convert the received ambient light signal into ambient photocurrent and the received reflected light signal reflected by the target object into reflected photocurrent. This application will not elaborate further on this.

[0034] As an optional implementation, the elimination module is coupled to the output of the receiving element, and the elimination module includes a first elimination digital-to-analog converter and a second elimination digital-to-analog converter configured with multiple elimination levels of different weights.

[0035] Specifically, this application places the first elimination digital-to-analog converter in the elimination module between the receiving element and the transimpedance amplifier. The first elimination digital-to-analog converter generates an elimination current with the same amplitude and opposite direction as the ambient light current, so as to achieve accurate elimination of the ambient light signal and avoid interference caused by ambient light in the subsequent detection process.

[0036] Furthermore, after the first digital-to-analog converter eliminates ambient light, the transmitting element emits a light signal of a preset intensity, which is then canceled by the second digital-to-analog converter to avoid the two types of interference from coupling with each other and affecting the elimination accuracy.

[0037] Please refer to Figure 2 The diagram below shows the functional block diagram of the DC component analog cancellation system provided in this application embodiment. This application couples the output terminal of the analog comparison output module with the output terminal of the cancellation module to convert the received current after cancellation by the cancellation module into a received voltage, and then compares the received voltage with the reference voltage to output the comparison result of over-cancellation or under-cancellation.

[0038] In an optional embodiment, this application converts the received current eliminated by the elimination module into a received voltage through a transimpedance amplifier (TIA) in the analog comparison output module. Since voltage signals have higher compatibility in signal amplification, threshold comparison, noise suppression and other processing stages, this application preferably uses a transimpedance amplifier to convert the weak received current signal into an easily processed received voltage signal, providing a suitable signal form for subsequent operations such as comparison of the received voltage with the reference voltage and analog-to-digital conversion, thereby ensuring the accuracy and effectiveness of DC component elimination and physiological parameter measurement.

[0039] Furthermore, the received voltage is compared with the reference voltage by the analog comparator in the analog comparison output module, and the comparison result representing over-cancellation or under-cancellation is output.

[0040] In this embodiment, the control module is coupled to the output of the analog comparison output module. The control module is configured to turn off the transmitting element after triggering elimination, control the first elimination digital-to-analog converter to traverse sequentially from the highest weight elimination level, and determine the first elimination level combination based on the comparison result of the current elimination level.

[0041] Furthermore, after determining the first elimination level combination, the transmitting element is activated, and the first elimination digital-to-analog converter is controlled to cancel the ambient light signal according to the first elimination level combination.

[0042] Furthermore, when the current sampling period reaches the sleep period, the second elimination digital-to-analog converter is controlled to traverse from the highest weight elimination level in sequence, and the second elimination level combination is determined according to the comparison result of the current elimination level, so as to cancel the DC component in the reflected light signal according to the second elimination level combination.

[0043] It should be noted that when the transmitting element is off, the receiving element collects the ambient light signal; when the transmitting element is on, the transmitting element is used to emit a light signal of preset intensity, and the receiving element collects the ambient light signal and the reflected light signal after being reflected by the target object (such as the wearer's skin tissue).

[0044] As an optional implementation method, please refer to Figure 3The diagram shows the schematic of the adjustment circuit in the DC component digital cancellation system provided in this application. The first and second cancellation digital-to-analog converters provided in this application are both configured with multiple cancellation levels with different weights. When cancellation is triggered, since the transmitting element is in the off state, the receiving element receives the ambient light signal. The control module controls the first cancellation digital-to-analog converter to traverse sequentially from its highest weight cancellation level. According to the comparison result of the analog comparator corresponding to the current weight, the cancellation level corresponding to the current weight is selected to be enabled or disabled until all cancellation levels are traversed to generate the final first cancellation level combination.

[0045] After determining the first elimination level combination, the transmitting element is activated, and the first elimination digital-to-analog converter is controlled to cancel the ambient light signal according to the first elimination level combination. When the current sampling period's sleep period is reached, the control module controls the second elimination digital-to-analog converter to traverse sequentially from its highest weight elimination level. According to the comparison result of the analog comparator corresponding to the current weight, the elimination level corresponding to the current weight is selected to be enabled or disabled until all elimination levels are traversed to generate the final second elimination level combination. Then, the second elimination digital-to-analog converter cancels the DC component in the reflected light signal according to the second elimination level combination.

[0046] Taking heart rate detection as an example, the human heart rate is usually in the range of 0.67-4Hz (where 0.67Hz corresponds to 40 beats / minute and 4Hz corresponds to 240 beats / minute). According to the Nyquist sampling theorem, the sampling rate should be set to at least twice the highest frequency of the signal, such as 8Hz. However, the heart rate detection signal is not a single fundamental frequency. If it is sampled at only 8Hz, some signal characteristics will be lost. Therefore, in order to meet the signal sampling requirements, this application preferably sets the sampling rate to 25Hz, with a corresponding sampling period of 40 milliseconds. Multiple samples can be taken within each 40-millisecond sampling period.

[0047] In an optional embodiment, 4 to 7 signal samples can be performed within each 40-millisecond sampling period, and the time interval between two adjacent samples is called the sampling gap Slot. The sampling gap Slot between each sample can be set from 100 microseconds to 3 milliseconds.

[0048] In other words, multiple sampling intervals are set within a sampling period. After all the preset signal sampling is completed within the sampling period, the system can enter a sleep period and wait for the next sampling period to arrive.

[0049] For example, please refer to Figure 4This is a schematic diagram of the sampling period in the DC component analog elimination system provided in this application embodiment. This application sets multiple sampling gaps in a sampling period PRF (Pulse Repetition Frequency), namely Slot0, Slot1, Slot2 and Slot3. Signal is acquired in the sampling gap. This application sets multiple sampling gaps Slot in a concentrated manner, and the remaining time period in the sampling period PRF(0) is recorded as the sleep (SLEEP) period.

[0050] Under the above sampling mechanism, this application utilizes the sleep period to traverse the elimination levels and cancels the DC component in the reflected light signal according to the elimination level combination result. The DCC (DC Cancellation) adjustment stage is set to be performed during the sleep period, which does not interrupt the normal sampling process of the system, does not occupy additional system resources, and will not affect the continuous acquisition of reflected light signals (such as heart rate detection signals), thus effectively saving power consumption.

[0051] Next, we will focus on explaining the first and second digital-to-analog converters and their respective elimination levels. Please continue reading... Figure 3 In this application, the output terminal of the first elimination digital-to-analog converter is coupled to the output terminal of the receiving element, the output terminal of the second elimination digital-to-analog converter is coupled to the output terminal of the receiving element, and the input terminal of the analog comparison output module is coupled to the output terminal of the elimination module.

[0052] It should be noted that a digital-to-analog converter (DAC) converts an input digital signal into an analog signal for output. Therefore, this application couples the output of the first DAC with the output of the receiving element, and uses the analog current signal output by the first DAC to cancel the ambient light signal collected by the receiving element. Similarly, the output of the second DAC is coupled with the output of the receiving element, and uses the analog current signal output by the second DAC to cancel the DC component in the reflected light signal collected by the receiving element.

[0053] Furthermore, this application couples the output of the cancellation module with the input of the analog comparison output module. This can also be understood as the output of the cancellation module being the output node formed by the output of the first cancellation digital-to-analog converter, the output of the second cancellation digital-to-analog converter, and the output of the receiving element, thereby achieving the cancellation of the DC component in the ambient light signal and the reflected light signal.

[0054] As an optional implementation, both the first elimination digital-to-analog converter and the second elimination digital-to-analog converter are equipped with corresponding adjustment circuits. Each adjustment circuit includes several elimination levels arranged in parallel, and each elimination level is equipped with a current source adapted to its weight.

[0055] For details, please continue to refer to... Figure 3 Each elimination level is equipped with a current source that matches its weight. This application connects the control module to several current sources in the first elimination digital-to-analog converter and to several current sources in the second elimination digital-to-analog converter. That is, the control module is connected to several current sources in the first elimination digital-to-analog converter and the second elimination digital-to-analog converter respectively.

[0056] In this embodiment, the first elimination digital-to-analog converter can control the on / off state of the current source corresponding to each elimination level according to the determined first elimination level combination, and weight and superimpose the output of the current source in the conducting state to generate the elimination current corresponding to the first elimination level combination, so as to cancel the ambient light signal.

[0057] Correspondingly, the second elimination digital-to-analog converter can control the on / off state of the current source corresponding to each elimination level according to the determined second elimination level combination, and weight and superimpose the output of the current source in the conducting state to generate the elimination current corresponding to the second elimination level combination, so as to cancel the DC component in the reflected light signal.

[0058] It should be noted that after the first elimination level combination is determined, the controlling element emits a light signal of preset intensity, and the receiving unit receives the reflected light signal after being reflected by the target object. Setting the light signal of preset intensity here can ensure that the AC and DC components in the reflected light signal are within the known amplitude range, and ensure that the subsequent adjustment circuit can determine the elimination level combination based on the known AC and DC components, thereby judging whether the elimination of the current DC component is reasonable.

[0059] If the emitting element emits a light signal of random intensity after canceling out ambient light, the AC and DC components in the corresponding reflected light signal are random and chaotic, which cannot provide a stable reference for the adjustment circuit. Those skilled in the art should know this.

[0060] It is understandable that when the transmitting element emits a light signal of preset intensity, the receiving unit collects the received signal, which includes the ambient light signal and the reflected light signal of the light signal of preset intensity reflected by the target object. At this time, the first elimination digital-to-analog converter will cancel the ambient light signal in the received signal according to the first elimination level combination, and then the second elimination digital-to-analog converter will cancel the DC component in the reflected light signal.

[0061] The following will explain in detail how to determine the first elimination gear combination and the second elimination gear combination. When the first elimination gear combination is determined, the control module controls the first elimination digital-to-analog converter to start from the elimination gear corresponding to the highest weight, and determines the on / off state of the corresponding current source based on the comparison result corresponding to the current elimination gear.

[0062] In this embodiment of the application, the ambient light signal is converted into ambient light current by an analog comparison output module, and then the ambient light current is converted into ambient light voltage and compared with a reference voltage. When the ambient light voltage is greater than the reference voltage, the under-cancelled comparison result is output, and when the ambient light voltage is less than the reference voltage, the over-cancelled comparison result is output.

[0063] Specifically, when the comparison result output by the analog comparison output module is under-elimination, the current source corresponding to the current elimination level is connected; when the comparison result is over-elimination, the current source corresponding to the current elimination level is disconnected.

[0064] It is understood that the comparison results of the above under-elimination indicate that the elimination current needs to be increased, while the comparison results of the above over-elimination indicate that the elimination current needs to be decreased. Of course, this application does not impose further restrictions on the specific value of the above reference voltage, and it can be adjusted according to actual needs.

[0065] In other words, the control module controls the first elimination digital-to-analog converter to start from the elimination level corresponding to the highest weight, and determines the on / off state of the corresponding current source according to the comparison result corresponding to the current elimination level. After completing the on / off state of the current source with the current weight (highest weight), based on the updated comparison result output by the analog comparison output module, it continues to turn on / off the current source corresponding to the next weight (second highest weight) in descending order of weight, and so on, until all current sources corresponding to the elimination levels are traversed, generating the final first elimination level combination used to eliminate ambient light current.

[0066] Once the first elimination level combination is determined, the emitting element emits a light pulse of preset intensity. The first elimination digital-to-analog converter cancels the ambient light signal according to the first elimination level combination. The control module further controls the second elimination digital-to-analog converter to start from the elimination level corresponding to the highest weight and determine the on / off state of the corresponding current source according to the comparison result corresponding to the current elimination level.

[0067] In this embodiment, the input terminal of the analog comparison output module is coupled to the output terminal of the elimination module, enabling the received current after elimination by the elimination module to be converted into a received voltage for comparison with a reference voltage.

[0068] Specifically, since the received signal includes ambient light signal and reflected light signal reflected by the target object, and the first cancellation digital-to-analog converter cancels the ambient light signal according to the first cancellation level combination, the received current after cancellation by the cancellation module is the current part remaining in the received signal after canceling the ambient light signal.

[0069] Furthermore, the analog comparison output module converts the received current after elimination by the elimination module into a received voltage and compares it with a reference voltage, outputting the comparison result of over-elimination or under-elimination. When the received voltage is greater than the reference voltage, the comparison result of under-elimination is output, and when the received voltage is less than the reference voltage, the comparison result of over-elimination is output.

[0070] Similarly, the control module controls the second elimination digital-to-analog converter to start from the elimination level corresponding to the highest weight, and determines the on / off state of the corresponding current source according to the comparison result of the current elimination level. After completing the on / off state of the current source with the current weight (highest weight), based on the updated comparison result output by the analog comparison output module, it continues to turn on / off the current source corresponding to the next weight (second highest weight) in descending order of weight, and so on, until all current sources corresponding to the elimination levels are traversed, generating the final second elimination level combination used for eliminating ambient light current.

[0071] Specifically, when the comparison result output by the analog comparison output module is under-elimination, the current source corresponding to the current elimination level is connected; when the comparison result is over-elimination, the current source corresponding to the current elimination level is disconnected.

[0072] In an optional embodiment, the control module controls the on / off state of the current source corresponding to each elimination level in the first elimination digital-to-analog converter according to the first elimination level combination, and weights and superimposes the output of the current source currently in the conducting state to generate an elimination current corresponding to the first elimination level combination to cancel the ambient light signal.

[0073] Furthermore, the control module controls the on / off state of the current source corresponding to each elimination level in the second elimination digital-to-analog converter according to the second elimination level combination, and weights and superimposes the output of the current source currently in the conducting state to generate an elimination current corresponding to the second elimination level combination to cancel the DC component in the reflected light signal.

[0074] As an optional implementation, the analog comparison output module provided in this application includes a transimpedance amplifier coupled to the output terminal of the cancellation module, and an analog comparator coupled to the output terminal of the transimpedance amplifier.

[0075] In this embodiment, the transmitting element and the receiving element are arranged opposite to each other. The first and second elimination digital-to-analog converters are both located between the receiving element and the transimpedance amplifier. The transimpedance amplifier is coupled to the output terminal of the elimination module. The relevant description of the output terminal of the elimination module will not be elaborated here.

[0076] Furthermore, the received current after cancellation by the cancellation module is converted into a received voltage by the transimpedance amplifier. By coupling an analog comparator to the output of the transimpedance amplifier, the analog comparator compares the received voltage with the reference voltage, thereby outputting a comparison result that represents over-cancellation or under-cancellation.

[0077] Specifically, when the received voltage is greater than the reference voltage, the analog comparator outputs an under-cancelled comparison result; when the received voltage is less than the reference voltage, the analog comparator outputs an over-cancelled comparison result.

[0078] The working principle of the DC component analog cancellation system provided in this application will be described in detail below with reference to specific embodiments. Please refer to... Figure 5 The diagram below is a schematic diagram of the DC component analog elimination system provided in this application embodiment. The preferred sampling rate of 25Hz and sampling period of 40ms will be used as an example for further explanation.

[0079] Please refer to the first sampling period PRF (0) in the figure. During the process of moving from the first sampling gap slot0 to the second sampling gap slot1, the system will trigger the DCC (DC Cancellation) adjustment stage when it detects that the current received signal (CH0) has not been effectively eliminated. This includes determining the first elimination level combination for eliminating ambient light. After the first elimination level combination is determined, the second elimination level combination for eliminating DC components is then determined.

[0080] Specifically, the DCC adjustment phase will begin during the SLEEP sleep period after the completion of the acquisition of slots 0, 1, 2 and 3 of the current sampling period PRF (0).

[0081] In this embodiment, there are two feasible ways to perform ambient light elimination. One is to perform ambient light elimination before the system officially collects physiological signals. The other is to perform it during the sampling process when the system detects that a DC component in the currently received signal has not been effectively eliminated. To ensure elimination accuracy, the system controls the transmitting element to turn off during the sampling process, so that the receiving element only collects the ambient light signal. During this period, the control module controls the first elimination digital-to-analog converter to traverse all its elimination levels, quickly determine the first elimination level combination that matches the current ambient light, and then controls the transmitting element to emit a light signal of a preset intensity. Subsequently, the control module controls the second elimination digital-to-analog converter to traverse its elimination levels and determine the second elimination level combination used to eliminate the DC component of the reflected light. It is understood that both methods can effectively eliminate ambient light. However, the first method cannot cope with interference caused by wearer movement or sudden changes in ambient light, which may cause the current ambient light signal to be inconsistent with the characteristics of the ambient light signal before sampling and ambient light elimination, affecting the accuracy of subsequent DC component elimination.

[0082] In contrast, the preferred second method of this application can dynamically eliminate ambient light during the sampling process, capture changes in the current ambient light in real time, and avoid errors caused by changes in wearing status or wearing environment, thereby more accurately matching the current environment of the actual wearer.

[0083] Furthermore, the emitting element is controlled to emit a light signal with a preset intensity of LED code=40. Taking the determination of the second elimination level combination that matches the light signal with a preset intensity of LED code=40 as an example, the specific steps of determining the first elimination level combination and eliminating ambient light through the first elimination digital-to-analog converter will not be elaborated on here.

[0084] It should be noted that the LED code=40 mentioned above represents the driving intensity of the emitting element through coding, and has no specific dimension. The larger the code value, the higher the driving intensity of the corresponding emitting element, and the greater the intensity of the emitted light signal.

[0085] In this embodiment, controlling the emitting element to emit a light signal of preset intensity (LED code=40) is used to test how to generate a corresponding cancellation mode combination when the emitting element emits a light signal of preset intensity (code=40) to precisely cancel the DC component in the reflected light signal and avoid signal saturation.

[0086] In this embodiment, when the ambient light is eliminated by the first digital-to-analog converter and the emitting element is turned on, the light signal is reflected by the target object (such as the wearer's skin tissue), received by the receiving element and converted into a reflected photocurrent, specifically a reflected photocurrent of 15.11uA.

[0087] At this point, since a second elimination gear combination that can effectively eliminate the current reflected photocurrent has not yet been determined, the second elimination digital-to-analog converter will use the initial or previously determined second elimination gear combination to eliminate the reflected photocurrent.

[0088] Specifically, the current second elimination gear combination is: Figure 5 The second elimination digital-to-analog converter cannot effectively eliminate the reflected photocurrent using the current second elimination gear combination corresponding to Slot 1, which is "DC code CH0 Slot 1".

[0089] Furthermore, this application presets the adjustment range of the adjustment circuit to 64uA, sets 8 elimination levels in each adjustment circuit, and allocates the weight of each elimination level according to a binary ratio.

[0090] In other words, when all current sources in the regulating circuit are turned on, i.e., when the second elimination gear combination DCC code=11111111, and the weight combination corresponding to the second elimination gear combination is 255, the elimination current that the second elimination digital-to-analog converter can achieve is 64uA.

[0091] Similarly, when the elimination gear combination DCC code=00000000, the corresponding weight combination is 0; when the elimination gear combination DCC code=00000001, the corresponding weight combination is 1; when the elimination gear combination DCC code=00000010, the corresponding weight combination is 2; ..., when DCC code=10000001, the corresponding weight combination is 129; ..., when DCC code=11111111, the corresponding weight combination is 255, and so on.

[0092] Since the elimination gear combination of the regulating circuit is DCC code=11111111, the corresponding weight combination is 255, and the corresponding elimination current is 64uA. According to the basic rules of binary encoding, we can obtain DCC code=00000001, the corresponding weight combination is 1, and the corresponding elimination current is 64uA / 256=0.25uA. This application will not enumerate the elimination current corresponding to other weight combinations.

[0093] For ease of explanation, this application names the weight bits corresponding to the 8 weights as the highest weight bit, the second highest weight bit, the third highest weight bit, the fourth highest weight bit, the fifth highest weight bit, the sixth highest weight bit, the seventh highest weight bit, and the lowest weight bit. The current elimination achieved by each weight bit decreases in a power of 2 order, and they are named and arranged from left to right in the DCC code.

[0094] When the DCC adjustment phase begins, the control module controls the current source of the highest weight bit corresponding to the elimination level in the adjustment circuit of the second elimination digital-to-analog converter to be turned on. At this time, DCC code=10000000, the corresponding weight combination is 128, and the corresponding elimination current is 64uA / 2=32uA.

[0095] Since the current reflected photocurrent is 15.11uA, a total of 32uA is eliminated by adjusting the circuit. At this time, a receiving current of approximately -17uA (15.11-32=-16.89uA) will be obtained. The receiving voltage generated by this receiving current after passing through the transimpedance amplifier is a negative voltage. Then, the analog comparator compares this receiving voltage with the reference voltage.

[0096] For example, this application sets the reference voltage to 0V. When the received voltage is less than the reference voltage, the comparison result of over-cancellation will be output, indicating that the highest weight bit should not be retained, and the cancellation code is 00000000.

[0097] Next, the comparison of the second highest weight bit begins. The control module further controls the current source of the elimination level corresponding to the second highest weight bit to be turned on. At this time, DCC code=01000000, the corresponding weight combination is 64, and the corresponding elimination current is 64uA / 4=16uA.

[0098] Since the current reflected photocurrent is 15.11uA, a total of 16uA is eliminated by adjusting the circuit. At this time, a receiving current of -0.89uA will be obtained. The receiving voltage generated by the transimpedance amplifier is a negative voltage. The analog comparator compares the receiving voltage with the reference voltage and outputs the comparison result of the over-elimination, indicating that the second highest weight bit should also not be retained. The elimination code remains 00000000.

[0099] Next, the comparison of the third highest weight bit begins. The control module controls the current source of the elimination level corresponding to the third highest weight bit to be turned on. At this time, DCC code=00100000, the corresponding weight combination is 32, and the corresponding elimination current is 64uA / 8=8uA.

[0100] Since the current reflected photocurrent is 15.11uA, a total of 8uA is eliminated by adjusting the circuit, resulting in a receiving current of 7.11uA. This receiving current is then passed through a transimpedance amplifier to generate a positive receiving voltage. The analog comparator compares this receiving voltage with the reference voltage and outputs the under-cancellation comparison result, indicating that the third highest weight bit should be retained. At this time, the cancellation code is updated to 00100000.

[0101] Next, the comparison of the fourth highest weighted bit begins. While retaining the third highest weighted bit, the control module controls the current source of the elimination gear corresponding to the fourth highest weighted bit to be turned on, and connects the elimination gear corresponding to the fourth highest weighted bit into the adjustment circuit. At this time, DCC code=00110000, the corresponding weight combination is 48, and the corresponding elimination current is 64uA / 16+8uA=12uA.

[0102] At this point, a receiving current of 3.11uA will be obtained. This receiving current is a positive receiving voltage generated by the transimpedance amplifier. The analog comparator compares this receiving voltage with the reference voltage and outputs the under-cancellation comparison result, indicating that the fourth highest weight bit should be retained. At this time, the cancellation code is updated to 00110000.

[0103] Next, the comparison of the fifth highest weight bit begins. While retaining the third and fourth highest weight bits, the control module controls the current source of the elimination level corresponding to the fifth highest weight bit to be turned on. At this time, DCC code=00111000, the corresponding weight combination is 56, and the corresponding elimination current is 64uA / 32+12uA =14uA.

[0104] At this point, a receiving current of 1.11uA will be obtained. This receiving current is used to generate a positive receiving voltage through a transimpedance amplifier. The analog comparator compares this receiving voltage with the reference voltage and outputs the under-cancellation comparison result, indicating that the fifth highest weight bit should be retained. At this time, the cancellation code is updated to 00111000.

[0105] When entering the comparison of the sixth highest weight bit, the control module, while retaining the third, fourth, and fifth highest weight bits, controls the current source of the elimination level corresponding to the sixth highest weight bit to be turned on. At this time, DCC code=00111100, the corresponding weight combination is 60, and the corresponding elimination current is 64uA / 64+14 uA =15uA.

[0106] At this point, a receiving current of 0.11uA will be obtained. This receiving current is a positive receiving voltage generated by the transimpedance amplifier. The analog comparator compares this receiving voltage with the reference voltage and outputs the under-cancellation comparison result, indicating that the sixth highest weight bit should be retained. At this time, the cancellation code is updated to 00111100.

[0107] When entering the comparison of the seventh highest weight bit, the control module retains the third, fourth, fifth, and sixth highest weight bits, and controls the current source of the elimination gear corresponding to the seventh highest weight bit to be turned on. At this time, DCCcode=00111110, the corresponding weight combination is 62, and the corresponding elimination current is 64uA / 128+15uA =15.5uA.

[0108] At this point, a receiving current of -0.39uA will be obtained. This receiving current is a transimpedance amplifier that generates a negative receiving voltage. The analog comparator compares this receiving voltage with the reference voltage and outputs the over-cancellation comparison result, indicating that the seventh highest weight bit should not be retained, and the cancellation code remains 00111100.

[0109] Next, the comparison of the lowest weight bit begins. The control module controls the current source of the elimination gear corresponding to the third, fourth, fifth, sixth and lowest weight bits to be turned on. At this time, the elimination gear combination DCC code=00111101, the corresponding weight combination is 61, and the corresponding elimination current is 64uA / 256+15uA =15.25uA.

[0110] At this point, a receiving current of -0.14uA will be obtained. This receiving current is used to generate a negative receiving voltage through a transimpedance amplifier. The analog comparator compares this receiving voltage with the reference voltage and outputs the over-cancellation comparison result, indicating that the least weighted bit should not be retained. The cancellation code is finally determined to be 00111100.

[0111] Thus, by iterating through the elimination levels of each weight from high to low, the final second elimination level combination is determined as DCC code=00111100, which is... Figure 5 The “New DC code CH0 Slot1” is determined to be 00111100. The weight combination corresponding to this elimination gear combination is 60, and the corresponding elimination current is 64uA / 64+14=15uA.

[0112] It should be noted that this second cancellation mode combination can cancel most of the DC component in the reflected photocurrent, and the received current is extremely small at this time, which can effectively avoid circuit saturation and ensure that the subsequent AC signal can be accurately acquired by the analog-to-digital converter.

[0113] Understandably, once the final second elimination gear combination is determined, the system will continue to return to the sleep period of the sampling period PRF (0). In the next sampling period PRF (1), the updated second elimination gear combination DCC code=00111100 can be used directly to eliminate the DC component.

[0114] It should be understood that this application does not limit the specific value of the output of each current source. The output of each current source is set according to its corresponding weight, and the proportional relationship of the binary distribution is satisfied. That is to say, the weight of each elimination level should present a power of 2 relationship, that is, in any two adjacent elimination levels, the higher weight is twice the lower weight.

[0115] Thus, this application generates an ambient light cancellation current with the same amplitude but opposite direction to the ambient light current through a first cancellation digital-to-analog converter, avoiding the influence of ambient light and ensuring that the received signal in subsequent processing only includes valid information reflected by the target object. Then, the adjustment circuit of the second cancellation digital-to-analog converter sequentially traverses from the highest-weighted cancellation level, converting the received current after ambient light cancellation into a received voltage through a transimpedance amplifier. The analog comparator compares the received voltage with a reference voltage and outputs the result of over-cancellation or under-cancellation. By enabling or disabling the current cancellation level, the final second cancellation level combination is dynamically generated, ensuring that the second cancellation digital-to-analog converter can accurately cancel the DC component in the reflected photocurrent according to the cancellation level combination. This effectively eliminates the DC components of both ambient light and reflected light signals in the received signal, enabling the subsequent analog-to-digital converter to accurately acquire AC signals related to heart rate changes, ensuring the accuracy and reliability of heart rate detection results.

[0116] Meanwhile, the weighted order traversal method ensures that the elimination current can efficiently and accurately match the DC component in the ambient light signal and the reflected light signal, avoiding the signal saturation problem caused by the ineffective elimination of the DC component. While ensuring the accuracy of signal acquisition, it improves the reliability and resource utilization efficiency of the system.

[0117] Based on the aforementioned DC component analog cancellation system, this application also provides a DC component analog cancellation method, please refer to... Figure 6 Here is a flowchart of a DC component simulation elimination method provided in this application embodiment. The elimination method includes the following steps: Step S1: After trigger cancellation, turn off the transmitting element, receive the ambient light signal when the transmitting element is turned off and convert it into ambient photocurrent; In this embodiment of the application, the transmitting element is turned off after the trigger is eliminated, and the receiving element only receives the ambient light signal generated by the ambient light and converts the ambient light signal into ambient light current.

[0118] Step S2: The ambient light current is superimposed bit by bit with the output current of the first elimination digital-to-analog converter to eliminate it. The eliminated ambient light current is converted into an ambient light voltage and compared with a reference voltage. The corresponding comparison result is output. The first elimination level combination is generated according to the comparison result. Furthermore, the control module controls the first elimination digital-to-analog converter to sequentially traverse from the elimination level with the highest bit weight to determine the first elimination level combination used to eliminate the ambient light signal.

[0119] Step S3: Control the emitting element to emit a light signal of preset intensity, receive a received signal containing the reflected light signal and the ambient light signal, and control the first cancellation digital-to-analog converter to cancel the ambient light signal according to the first cancellation level combination; In this embodiment of the application, after determining the first elimination level combination, the transmitting element is controlled to emit a light signal of preset intensity. At this time, the received signal received by the receiving element includes an ambient light signal and a reflected light signal after the light signal of preset intensity is reflected by the target object. At the same time, the first elimination digital-to-analog converter cancels the ambient light signal in the received signal based on the first elimination level combination determined above.

[0120] Step S4: When the current sampling period reaches the sleep period, the received current after being eliminated by the second elimination digital-to-analog converter is converted into a received voltage and compared with the reference voltage, and the comparison result of over-elimination or under-elimination is output. In this embodiment of the application, when the current sampling period is reached, the control module controls the second elimination digital-to-analog converter to traverse sequentially from the elimination level with the highest bit weight to determine the second elimination level combination used to eliminate the DC component.

[0121] Step S5: Generate a second elimination level combination based on the comparison result, and control the second elimination digital-to-analog converter to cancel the DC component in the reflected light signal according to the second elimination level combination.

[0122] Once the second elimination gear combination is determined, the second elimination digital-to-analog converter is controlled to cancel the DC component in the reflected light signal according to the second elimination gear combination.

[0123] For further details regarding the elimination method and the implementation of the above technical solution, please refer to the description in the DC component analog elimination system provided in the above application embodiments, which will not be repeated here.

[0124] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

[0125] In summary, although the present invention has been disclosed above with reference to preferred embodiments, the above preferred embodiments are not intended to limit the present invention. This description is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A DC component analog cancellation system, characterized by, The application relates to a photoelectric detection device and a control method thereof. The photoelectric detection device comprises: a photoelectric detection module, a cancellation module, an analog comparison output module and a control module. The photoelectric detection module comprises a transmitting element for transmitting a light signal and a receiving element for collecting a receiving signal and converting the receiving signal into a receiving current, wherein the receiving signal comprises an ambient light signal and a reflected light signal reflected by a target object. The cancellation module is coupled to the output end of the receiving element and comprises a first cancellation digital-to-analog converter and a second cancellation digital-to-analog converter which are configured with a plurality of cancellation taps with different weights. The analog comparison output module is coupled to the output end of the cancellation module and is used for converting the receiving current after cancellation by the cancellation module into a receiving voltage and comparing the receiving voltage with a reference voltage to output a comparison result of over-cancellation or under-cancellation. The control module is coupled to the output end of the analog comparison output module and is configured to: turn off the transmitting element after triggering cancellation, control the first cancellation digital-to-analog converter to sequentially traverse from a highest-weight cancellation tap, determine a first cancellation tap combination according to a comparison result of a current cancellation tap, and 2. The DC component analog cancellation system of claim 1, wherein, turn on the transmitting element after determining the first cancellation tap combination, control the first cancellation digital-to-analog converter to offset the ambient light signal according to the first cancellation tap combination, when a sleep period of a current sampling period is executed, control the second cancellation digital-to-analog converter to sequentially traverse from a highest-weight cancellation tap, determine a second cancellation tap combination according to a comparison result of a current cancellation tap, and offset a direct current component in the reflected light signal according to the second cancellation tap combination. When the transmitting element is turned off, the receiving signal collected by the receiving element is the ambient light signal.

3. The DC component analog cancellation system of claim 1, wherein, When the transmitting element is turned on, the transmitting element is used for transmitting a light signal with a preset intensity, and the receiving signal collected by the receiving element is the ambient light signal and the reflected light signal reflected by the target object.

4. The DC component analog cancellation system of claim 1, wherein, The output end of the first cancellation digital-to-analog converter is coupled to the output end of the receiving element, the output end of the second cancellation digital-to-analog converter is coupled to the output end of the receiving element, and the input end of the analog comparison output module is coupled to the output end of the cancellation module. The first cancellation digital-to-analog converter and the second cancellation digital-to-analog converter are both configured with corresponding adjusting circuits, each adjusting circuit comprises a plurality of cancellation taps arranged in parallel, and each cancellation tap is provided with a current source matched with the weight of the cancellation tap.

5. The DC component analog cancellation system of claim 4, wherein, The control module is connected with the plurality of current sources arranged in the first cancellation digital-to-analog converter and the second cancellation digital-to-analog converter. The control module is used for controlling the corresponding cancellation digital-to-analog converter to start from a highest-weight corresponding cancellation tap, based on a comparison result of a current cancellation tap, when the comparison result is under-cancellation, connecting the current source corresponding to the current cancellation tap, and when the comparison result is over-cancellation, disconnecting the current source corresponding to the current cancellation tap.

6. The DC component analog cancellation system of claim 5, wherein, The control module is further configured to, after turning on / off the current source corresponding to the current weight, based on the updated comparison result output by the analog comparison output module, enable or disable the current source corresponding to the next weight in the order from high to low, until all the current sources corresponding to the cancellation gears are traversed, to generate the first cancellation gear combination for canceling the ambient light signal, and to generate the second cancellation gear combination for canceling the direct current component in the reflected light signal.

7. The DC component analog cancellation system of claim 6, wherein, The control module is configured to control the on / off of the current source corresponding to each cancellation gear in the first cancellation digital-to-analog converter according to the first cancellation gear combination, and to superimpose the outputs of the current sources in the on state to generate a cancellation current corresponding to the first cancellation gear combination to cancel the ambient light signal. The control module is further configured to control the on / off of the current source corresponding to each cancellation gear in the second cancellation digital-to-analog converter according to the second cancellation gear combination, and to superimpose the outputs of the current sources in the on state to generate a cancellation current corresponding to the second cancellation gear combination to cancel the direct current component in the reflected light signal.

8. The DC component analog cancellation system of claim 1, wherein, The analog comparison output module comprises a transimpedance amplifier coupled to the output end of the cancellation module, and an analog comparator coupled to the output end of the transimpedance amplifier. The transimpedance amplifier is configured to convert the received current after cancellation by the cancellation module into a received voltage. The analog comparator is configured to compare the received voltage with a reference voltage and output a comparison result representing over-cancellation or under-cancellation. When the received voltage is greater than the reference voltage, the analog comparator outputs an under-cancellation comparison result; when the received voltage is less than the reference voltage, the analog comparator outputs an over-cancellation comparison result.

9. The DC component analog cancellation system of claim 1, wherein, The number of cancellation gears is at least 8, and the weights corresponding to each cancellation gear are assigned in binary.

10. A method for DC component analog cancellation, applied to the DC component analog cancellation system according to any one of claims 1-9, characterized in that, The method comprises the following steps: After triggering cancellation, the emitting element is turned off, the ambient light signal when the receiving emitting element is turned off is received and converted into an ambient light current; The ambient light current and the output current of the first cancellation digital-to-analog converter are superimposed bit by bit to cancel, and the ambient light current after cancellation is converted into an ambient light voltage and compared with a reference voltage to output a corresponding comparison result, and a first cancellation gear combination is generated according to the comparison result; The emitting element emits a light signal of a preset intensity, a receiving signal containing a reflected light signal and the ambient light signal is received, and the first cancellation digital-to-analog converter cancels the ambient light signal according to the first cancellation gear combination; When the sleep period of the current sampling period is executed, the received current after cancellation by the second cancellation digital-to-analog converter is converted into a received voltage and compared with a reference voltage to output an over-cancellation or under-cancellation comparison result; A second cancellation gear combination is generated according to the comparison result, and the second cancellation digital-to-analog converter cancels the direct current component in the reflected light signal according to the second cancellation gear combination.

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