Patent Publication Number: US-2021161413-A1

Title: Photoplethysmogram circuit, biological characteristics detection device and biological characteristics detection method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present disclosure is a continuation of international application No. PCT/CN2019/121910, filed on Nov. 29, 2019, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates to a photoplethysmogram (PPG) circuit; in particular, to a PPG circuit, a biological characteristics detection device and a biological characteristics detection method capable of using multiple receiving channels to reduce power consumption and improve accuracy. 
     BACKGROUND 
     Biological characteristics detection devices have promising applications in detecting biological characteristics, such as human blood pressure, blood flow, blood oxygen, cerebral oxygen, muscle oxygen, blood glucose, microcirculatory peripheral vascular pulse rate, respiratory rate and respiratory volume. The PPG front-end processing module is an important component of these wearable non-invasive detection devices. The accuracy of biological characteristics detection using a biological characteristics detection device is affected by the fact that the phototransducer of the biological characteristics detection device may not be positioned in the exact location of the blood vessels during the measurement or the biological characteristics detection device may be displaced relative to the body during the test. Therefore, it is necessary to address the above-mentioned issues. 
     SUMMARY OF THE INVENTION 
     One purpose of the present application is to disclose a PPG circuit, a biological characteristics detection device and a biological characteristics detection method to address the above-mentioned issues. 
     One embodiment of the present application discloses a PPG circuit, which configured to control a light source and N photoelectric converters to sense biological characteristics of an object under test, wherein N is an integer greater than 1, and the PPG circuit includes: a transmitting channel, configured to control the light source to perform light emitting operations during pulse repetition cycles; K receiving channels, wherein K is an integer greater than 1, and the N photoelectric converters are divided into K sets of photoelectric converter sets, the K receiving channels respectively correspond to the K sets of photoelectric converter sets; and a controller, configured to control the PPG circuit to operates in a partial sampling phase or a full sampling phase, when the controller controls the PPG circuit to operate in the partial sampling phase, the controller activates J receiving channels of the K receiving channels as current receiving channels and activates J sets of photoelectric converter sets of the K sets of photoelectric converter sets corresponding to the J receiving channels to sense received light for performing the sampling operation, so as to generate J biological characteristics sampling results during each of the pulse repetition cycles, wherein J is smaller than K; and when the controller controls the PPG circuit to operate in the full sampling phase, the controller activates all receiving channels of the K receiving channels and activates all of the K sets of photoelectric converter sets to sense the received light for performing the sampling operation, so as to generate K biological characteristics sampling results during each of the pulse repetition cycles, and from the K receiving channels, re-select J receiving channels as the current receiving channels to be activated during the next partial sampling phase according to the K biological characteristics sampling results generated during each of the pulse repetition cycles of the full sampling phases. 
     Another embodiment of the present application discloses a biological characteristics detection device, including: the PPG circuit; the photoelectric converter; and the light source. 
     Another embodiment of the present application discloses a biological characteristics detection method, configured to control a light source and N photoelectric converters to sense biological characteristics of an object under test, wherein N is an integer greater than 1, the N photoelectric converters are divided into K sets of photoelectric converter sets, and the biological characteristics detection method includes: controlling the light source to perform only one light emitting operation during each of the pulse repetition cycles; during a partial sampling phase, only activating J sets of photoelectric converter sets of the K sets of photoelectric converter sets to simultaneously sense received light for performing sampling operation, and generating J biological characteristics sampling results via the activated J sets of photoelectric converter sets during each of the pulse repetition cycles, wherein J is smaller than K; and during the full sampling phase, activating all of the K sets of photoelectric converter sets to simultaneously sense the received light for performing the sampling operation, so as to generate K biological characteristics sampling results during each of the pulse repetition cycles, and from the K receiving channels, re-selecting J receiving channels as the current receiving channels to be activated during the next partial sampling phase according to the K biological characteristics sampling results generated during said each of the pulse repetition cycles of the full sampling phases. 
     The PPG circuit, biological characteristics detection device and biological characteristics detection method of the present application utilize multiple receiving channels to reduce the power consumption and increase the accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a biological characteristics detection device according to embodiments of the present application. 
         FIG. 2  is flow diagram illustrating the operation procedure of the biological characteristics detection device according to embodiments of the present application. 
         FIG. 3  is a schematic diagram illustrating a chip including the biological characteristics detection device applied in an electronic device according to embodiments of the present application, 
     
    
    
     DETAILED DESCRIPTION 
     When measuring pulse cycle or cardiac blood oxygenation using the photoplethysmogram (PPG) technique, light is irradiated onto the skin to detect changes in the volume of blood perfusion to the dermis and subcutaneous tissue. As the volume of perfused blood changes, the amount of light absorbed also changes, and a subcutaneous blood plethysmogram can be obtained from the measured intensity of reflected light to reflect the heart rate and cardiac oxygen status. Biological characteristics detection devices typically use multiple photoconverters corresponding to multiple locations, and sample by using multiple photoconverters in turn during each pulse repetition cycle T PF , or sample by using all photoconverters simultaneously which are connected in parallel so as to collect subcutaneous blood plethysmograms of different locations at one time during each pulse repetition cycle T PF . 
     With respect to the method that photoelectric converters are used for sampling in turns, one has to drive the light source to emit light each time when the photoelectric converters perform the sampling process; that is, during each pulse repetition cycle, the light source has to be driven multiple times to sample the multiple photoelectric converters in turns, which leads to significant increase in the power consumption. With respect to the method that multiple photoelectric converters are connected in parallel, if only one or a few of the multiple photoelectric converters contain the valid information, such approach would greatly increase the requirement of the receiving channel to a dynamic range specification, thereby increasing the power consumption of the receiving channel of the biological characteristics detection device. Moreover, connecting multiple photoelectric converters in parallel would greatly increase the parasitic capacitance effect, causing more difficulties in the stability design of the current-to-voltage converter of the receiving channel of the biological characteristics detection device and an increase in the noise amplification effect thereof, and the power consumption of the current-to-voltage converter will increase significantly if it is intended to achieve the noise level and circuit stability of a single photoelectric converter. 
     The present application uses multiple receiving channels in a biological characteristics detection device to reduce the power consumption and increase the accuracy of such device. 
       FIG. 1  is a functional block diagram of a biological characteristics detection device according to embodiments of the present application. The biological characteristics detection device  100  includes a PPG circuit  103 , a light source  108  and N photoelectric converters, wherein the N photoelectric converters are divided into K sets of photoelectric converter sets  110 _ 1 ˜ 110 _K, wherein N and K are integers greater than 1; in the present embodiment, each set of the photoelectric converter sets  110 _ 1 ˜ 110 _K includes N/K photoelectric converters that are parallelly connected, and N/K is an integer greater than 0; however, the present application is not limited thereto, in some embodiments, each set of the photoelectric converter sets  110 _ 1 ˜ 110 _K may include different numbers of photoelectric converters. The PPG circuit  103  is configured to control the light source  108  and N photoelectric converters to sense biological characteristics of an object under test  101 , e.g., the blood pressure, blood flow, blood oxygen, cerebral oxygen, muscle oxygen, blood glucose, microcirculatory peripheral vascular pulse rate, respiratory rate, respiratory volume, etc. of a living organism, and periodically generate biological characteristics sampling result D R  according to a pulse repetition cycle T PF . In some embodiments, the N photoelectric converters are photodiodes, and the light source  108  is a light-emitting diode (LED); however, the present application is not limited thereto. 
     The PPG circuit  103  includes a transmitting channel  102 , K sets of receiving channels  104 _ 1 ˜ 104 _K and a controller  106 , wherein the transmitting channel  102  is configured to perform a light-emission operation EP; the K sets of receiving channels  104 _ 1 ˜ 104 _K are configured to perform a sampling operation SP. When the transmitting channel  102  performs the light-emission operation E, the transmitting channel  102  controls the light source  108  to generate incident light EL onto the object under test  101  which results in a reflective light RL carrying biological characteristics information. The K sets of receiving channels  104 _ 1 ˜ 104 _K correspond to said K sets of photoelectric converter sets  110 _ 1 ˜ 110 _K, when any one receiving channel of the K sets of receiving channels  104 _ 1 ˜ 104 _K performs the sampling operation SP, it controls a corresponding photoelectric converter set of the K sets of photoelectric converter sets  110 _ 1 ˜ 110 _K to sense received light, so as to generate current to the any one receiving channel. The received light includes the reflective light RL with the biological characteristics information; however, light leakage will take place if there is a gap between the biological characteristics detection device  100  and the object under test  101 , thereby leading to the received light additionally including ambient light AL. 
     The controller  106  is configured to control the light source  108  to perform the light-emission operation EP once during each pulse repetition cycle T PF , and specifically, during each pulse repetition cycle T PF , the controller  106  controls a portion (i.e., during a partial sampling phase; for example, J sets, and J is 1) or all (i.e., during a full sampling phase) of the K sets of photoelectric converter sets  110 _ 1 ˜ 110 _K to perform the sampling operation SP. The transmitting channel  102  includes a light source driver  112 , which is configured to drive the light source  108 ; for example, if the light source  108  is an LED, the light source driver  112  is an LED driver. The receiving channels  104 _ 1 ˜ 104 _K includes current-to-voltage converters  114 _ 1 ˜ 114 _K and are configured to convert the current outputted by the photoelectric converter sets  110 _ 1 ˜ 110 _K into voltage. In some embodiments, the controller  106  is implemented using a digital circuit, and the transmitting channel  102  may further include a digital-to-analog converter  116  coupled between the light source driver  112  and the controller  106 ; the receiving channels  104 _ 1 ˜ 104 _K may further include an analog-to-digital converter  118 _ 1 ˜ 118 _K coupled between the current-to-voltage converters  114 _ 1 ˜ 114 _K and the controller  106 . 
     With respect to hear rate or cardiac/blood oxygen measurement, the object under test is generally the finger or wrist, and the biological characteristics detection device generally use multiple photoelectric converters corresponding to multiple location, and wherein only one or two locations thereof may provide valid biological characteristics sampling results. The controller  106  of the biological characteristics detection device  100  according to the present application enters the full sampling phase from the partial sampling phase every preset update interval T, so as to re-select J (e.g., one) receiving channels which are most effective for sampling the biological characteristics from the K receiving channels  104 _ 1 ˜ 104 _K corresponding to the K sets of photoelectric converter sets  110 _ 1 ˜ 110 _K as the current receiving channels RXS. The current receiving channels RXS are used during each pulse repetition cycle T PF  for simultaneous sampling operation SP, so as to generate biological characteristics sampling result D R  periodically. Since the full sampling phase is carried out once every preset update interval T to compare biological characteristics sampling results D R  sampled by all the receiving channels  104 _ 1 ˜ 104 _K, and if there are other candidates better than the current receiving channels RXS that are currently in use, such better receiving channel(s) will be set as the current receiving channels RXS. In the present application, during each pulse repetition cycle T PF , the light source  108  is only driven once; in the present embodiment, the preset update interval T is greater than 1 second, such as 30 seconds, and the length of the pulse repetition cycle T PF  is in millisecond level, e.g., several millisecond; therefore, the preset update interval T is much greater than pulse repetition cycle T PF . 
       FIG. 2  is flow diagram illustrating the operation procedure of the biological characteristics detection device according to embodiments of the present application. In Step  202 , during the partial sampling phase, the controller  106  controls J current receiving channels RXS of the K receiving channels  104 _ 1 ˜ 104 _K to simultaneously perform the sampling operation SP during each pulse repetition cycle T PF , so as to generates J biological characteristics sampling results D R  during each pulse repetition cycle T PF . In this phase, the K-J receiving channels other than the current receiving channels RXS will not perform the sampling operation SP; in other words, during each pulse repetition cycle T PF , the simultaneous sampling operation SP will only be performed once; in other words, during each pulse repetition cycle T PF , the light source  108  will only be irradiated once. 
     In the present embodiment, when the duration of Step  202  lasts for a preset update interval T, the biological characteristics detection device  100  enters the full sampling phase, i.e., Step  204 , in which the controller  106  controls all K receiving channels  104 _ 1 ˜ 104 _K to simultaneously perform sampling operation during each pulse repetition cycle T PF , so as to generate K biological characteristics sampling results D R . The full sampling phase will last for M pulse repetition cycles T PF , wherein M is an integer greater than 1, so as to collect sufficient biological characteristics sampling results D R  that can be used in Step  206  for determining which J receiving channels from the K receiving channels  104 _ 1 ˜ 104 _K to be selected as the current receiving channels RXS, according to M*K biological characteristics sampling results D R , and then returns to Step  202 . It should be noted that, during the M pulse repetition cycles T PF  of the full sampling phase, and before the current receiving channels RXS have been determined and updated, the controller  106  still uses the biological characteristics sampling results D R  of the previous current receiving channels RXS. 
     Specifically, in Step  206 , the controller  106  can generate K quality factors FOM corresponding to the K receiving channels  104 _ 1 ˜ 104 _K according to M*K biological characteristics sampling results D R , and determine the current receiving channels RXS according to the K quality factors FOM. In the present application, the quality factor FOM can be any self-defined factors; in one embodiment, the controller  106  generates the K quality factors FOM according to a ratio of the DC component to the AC component of the M*K biological characteristics sampling results D R . In a further embodiment, the controller  106  generates the K quality factors FOM according to the signal intensity of the M*K biological characteristics sampling results D R  at a specific frequency band. In yet another embodiment, the controller  106  further receives a gravity sensing signal G and generates the K quality factors FOM according to the M*K biological characteristics sampling results D R  and the gravity sensing signal G. 
     Compared with the existing approach where multiple photoelectric converters are sampled alternatively during each pulse repetition cycle T PF , thereby driving the light source multiple times during each pulse repetition cycle T PF , the biological characteristics detection device  100  according to the present application will only be driven once during each pulse repetition cycle T PF ; therefore, embodiments of the present application may save more power. Also, compared with another conventional approach where all photoelectric converter are parallelly connected and sampled together, the biological characteristics detection device  100  according to the present application divides all photoelectric converter into multiple sets and increases the number of the receiving channel to correspond to the multiple sets of photoelectric converters; in this way, only the photoelectric converters that are divided into the same set are parallelly connected instead of connecting all the photoelectric converter in parallel, therefore, it poses less impact to the dynamic range specification and suffers less parasitic capacitance effects. Furthermore, even during the M pulse repetition cycles T PF  of the full sampling phase, before the current receiving channels RXS are determined and updated, the controller  106  still uses the biological characteristics sampling result D R  from the previous current receiving channels RXS, and hence the measurement of the heart rate and cardiac/blood oxygen level performed by the biological characteristics detection device  100  is not interrupted. 
     The PPG circuit  103  according to the present application can be implemented using a chip  32 , wherein the chip  32  can be a semiconductor chip implemented using various processes, and the N photoelectric converters and the light source  108  are disposed outside the chip  32  where the PPG circuit resides. Yet, the present application is not limited thereto; in some embodiments, the N photoelectric converters and/or the light source  108  can also be disposed in the chip  32  where the PPG circuit resides. 
       FIG. 3  is a schematic diagram illustrating a chip  32  including the biological characteristics detection device  100  according to embodiments of the present application, applied in an electronic device  30 . Referring to  FIG. 3 , the electronic device  30  includes a chip  32 . The electronic device  30  may be a wearable electronic device, e.g., watch, necklace or any other smart wearable device. The electronic device  30  may also be a handheld electronic device, such as a smart phone, digital personal assistant, hand-held computing system or tablet computer, etc. 
     In view of the foregoing, the biological characteristics detection device  100  according to the present application and the related chip  32  and electronic device  30  uses multiple receiving channels, which only increase the overall power consumption slightly but at the same time significantly increase the accuracy of biological characteristics detection devices with multiple photoelectric converters in sensing biological characteristics. 
     The foregoing only discloses some preferred embodiments of the present application and is not intended to limit the scope of the present application. The present application is subject to various changes and variations to persons having ordinary skill in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present disclosure are to be included within the scope of the present application.