PATENT DOCUMENT

Publication Number: US-10219754-B1
Application Number: US-201514621268-A
Country: US
Kind Code: B1

Title: Modulation and demodulation techniques for a health monitoring system

Abstract:
An electronic device includes one or more light sources for emitting light toward a body part of a user and one or more optical sensors for capturing light samples while each light source is turned on and for capturing dark samples while the light source(s) are turned off. A signal produced by the one or more optical sensors is demodulated produce multiple demodulated signals. Each demodulated signal is received by one or more decimation stages to produce a signal associated with each light source. Each signal associated with the light source(s) is analyzed to estimate or determine a physiological parameter of the user.

Claims:
What is claimed is: 
     
       1. A method for estimating physiological parameters when modulated light from a first light source and a second light source is emitted toward a body part of a user, the method comprising:
 determining a first multiplier value by:
 turning on the first light source; 
 generating a first initial signal in response to capturing a first light sample corresponding to the first light source; 
 demodulating the first initial signal to produce first initial demodulated signals; 
 filtering and decimating the first initial demodulated signals; and 
 determining the first multiplier value based on the filtered and decimated first initial demodulated signals; 
 
 determining a second multiplier value by:
 turning on the second light source; 
 generating a second initial signal in response to capturing a second light sample corresponding to the second light source; 
 demodulating the second initial signal to produce second initial demodulated signals; 
 filtering and decimating the second initial demodulated signals; and 
 determining the second multiplier value based on the filtered and decimated second initial demodulated signals; 
 
 capturing multiple light samples while the first light source and the second light source are turned on to emit modulated light toward the body part of the user and converting the multiple light samples into a captured signal; 
 demodulating the captured signal to produce multiple demodulated signals; 
 performing a first decimation stage by:
 low pass filtering each demodulated signal; and 
 decimating each demodulated signal; 
 
 performing a second decimation stage after the first decimation stage by:
 low pass filtering each demodulated signal; and 
 decimating each demodulated signal; 
 
 demultiplexing each demodulated signal after the second decimation stage to produce a first signal associated with the first light source and a second signal associated with the second light source; 
 multiplying the first signal by the first multiplier value using a first multiplier circuit to obtain a first conditioned signal; 
 multiplying the second signal by the second multiplier value using a second multiplier circuit to obtain a second conditioned signal; and 
 analyzing the first conditioned signal and the second conditioned signal to estimate the physiological parameter of the user. 
 
     
     
       2. The method as in  claim 1 , wherein the capturing multiple light samples comprises capturing multiple light samples while:
 the first light source is turned on and the second light source is turned off; 
 the second light source is turned on and the first light source is turned off; and 
 the first light source and the second light source are turned off after being turned on. 
 
     
     
       3. The method as in  claim 2 , wherein the capturing multiple light samples further comprises capturing one or more light samples after the first light source is turned off and before the second light source is turned on. 
     
     
       4. The method as in  claim 1 , wherein the demodulating the captured signal to produce multiple demodulated signals comprises:
 applying a first demodulation operation of a sine function to the captured signal; and 
 applying a second demodulation operation of a cosine function. 
 
     
     
       5. The method as in  claim 2 , wherein the multiple light samples comprise at least five light samples captured when the first light source is turned on and the second light source is turned off. 
     
     
       6. The method as in  claim 1 , wherein:
 when the first light source is turned on, the first light source emits infrared light; and 
 when the second light source is turned on, the second light source emits visible light.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/047,818, filed Sep. 9, 2014, entitled “Modulation and Demodulation Techniques for a Health Monitoring System,” the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to health monitoring systems, and more particularly to modulation and demodulation techniques for a health monitoring system that includes one or more optical sensors. 
     BACKGROUND 
     Health monitoring devices, such as fitness and wellness devices, are capable of measuring a variety of physiological parameters and waveforms non-invasively via optical sensing. Light is applied to a measurement site, such as a user&#39;s wrist, finger, and ear, and the light is absorbed and scattered throughout the skin. An optical sensor in the health monitoring device captures the light that is reflected from or transmitted through the skin. The optical sensor, however, is subject to interferences caused by fluorescent bulbs, sun light, the electricity grid or network, and motion artifacts that are caused by the relative motion between the optical sensor and the user&#39;s measurement site. Thus, the light collected by the light sensor contains a component from the measurement site and component from one or more interferences. To estimate the physiological parameter and waveform, the optical sensor coverts the collected light into electrical signals, and the signal that represents the interference component is typically subtracted from the signal representing the measurement site component. After subtraction, only the component from the measurement site should remain, which is the component that is used to estimate the physiological parameter. However, subtraction cannot be performed instantaneously. A time delay exists between sampling the light and subtracting the interference component. The time delay can result in the creation of aliases in the signal, and the aliases produce errors in the estimation of the physiological parameter. 
     SUMMARY 
     In one aspect, an electronic device includes one or more light sources for emitting light toward a body part of a user and one or more optical sensors for capturing light samples while each light source is turned on and for capturing dark samples while the light source(s) are turned off. A signal produced by the one or more optical sensors is demodulated produce multiple demodulated signals. Each demodulated signal is received by one or more decimation stages to produce a signal associated with each light source. A demultiplexer and multiplier circuit operably can be connected to an output of the decimation stage. The demultiplexer separates the signals by each associated light source and the multiplier multiplies each signal by one or more respective weights. The weights adjust the signals for variations in temperature and operating parameters of various components in the electronic device. Each signal associated with the light source(s) is analyzed to estimate or determine a physiological parameter of the user. 
     In another aspect, a method for processing the signal received from the light sensor can include capturing multiple light samples while each light source emits light toward the body part of the user and converting the multiple light samples into the signal. The light sources can be modulated (e.g., turned on and off) according to a particular modulation pattern. The signal produced by the optical sensor is then demodulated to produce multiple demodulated signals. Each demodulated signal is associated with a particular light source. Each demodulated signal is then be processed by at least one decimation stage. In one embodiment, each decimation stage includes a low pass filter that receives a demodulated signal and a decimation circuit operably connected to an output of the low pass filter. A demultiplexer and multiplier circuit may then process the signals. Each signal associated with the light source(s) is analyzed to estimate or determine a physiological parameter of the user. 
     In yet another aspect, a method for operating an electronic device that includes multiple light sources, an optical sensor, and a processing device operably connected to the optical sensor can include turning on each light source one at a time and emitting light toward a body part of a user and capturing multiple light samples while each light source emits light toward the body part of the user and converting the multiple light samples into a signal. The signal is converted into a digital signal, and the digital signal is demodulated to produce multiple demodulated signals. Each demodulated signal is then processed by at least one decimation stage. In one embodiment, each decimation stage includes a low pass filter that receives a demodulated signal and a decimation circuit operably connected to an output of the low pass filter. Each signal associated with the light source(s) is analyzed to estimate or determine a physiological parameter of the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
         FIG. 1  a perspective front view of one example of an electronic device that provides health-related information; 
         FIG. 2  depicts a back view of the electronic device  100  shown in  FIG. 1 ; 
         FIG. 3  is an illustrative block diagram of the electronic device  100  shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a flowchart of one example method of operating the health monitoring system  312  in  FIG. 3 ; 
         FIGS. 5-6  depict example modulation patterns suitable for use in blocks  400  and  402  in  FIG. 4 ; 
         FIG. 7  is a data flow diagram of a processing channel that performs blocks  408 ,  410 , and  412  in  FIG. 4 ; 
         FIG. 8  is a flowchart of one example method of determining a matrix used in block  718  of  FIG. 7 ; 
         FIG. 9  is a flowchart of one example method of performing block  800  in  FIG. 8 ; and 
         FIG. 10  is a flowchart of one example method of performing block  802  in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein provide modulation and demodulation techniques that reduce or eliminate undesired interferences and produce demodulated signals that can be analyzed to estimate a physiological parameter of a user. A time multiplexed modulation pattern is used to turn the light sources on and off and to cause the optical sensor to capture multiple light and dark samples. Demodulation operations are applied to the signal produced by the optical sensor to produce a signal associated with each light source. In general, the demodulation operation can be 
             sin   ⁢           ⁢   2   ⁢   π   ⁢     kt   N     ⁢   or   ⁢           ⁢   cos   ⁢           ⁢   2   ⁢   π   ⁢       kt   N     .           
The demodulated signals may then be processed by one or more decimation stages. Each decimation stage can include a low pass filter and a decimation circuit.
 
     Any suitable type of electronic device can include a health monitoring system. Example electronic devices include, but are not limited to, a smart telephone, a headset, a pulse oximeter, a digital media player, a tablet computing device, and a wearable electronic device. A wearable electronic device can include any type of electronic device that can be worn on a limb of a user. The wearable electronic device can be affixed to a limb or body part of a user, such as a wrist, an arm, a finger, a leg, an ear, or a chest. In some embodiments, the wearable electronic device is worn on a limb of a user with a band that attaches to the body and includes a holder or case to detachably or removably hold the electronic device, such as an armband, an ankle bracelet, a leg band, and/or a wristband. In other embodiments, the wearable electronic device is permanently affixed or attached to a band, and the band attaches to the body of the user. 
     As one example, a wearable electronic device can be implemented as a wearable health assistant that provides health-related information (whether real-time or not) to the user, authorized third parties, and/or an associated monitoring device. The wearable health assistant may be configured to provide health-related information or data such as, but not limited to, heart rate data, blood pressure data, temperature data, blood oxygen saturation level data, diet/nutrition information, medical reminders, health-related tips or information, or other health-related data. The associated monitoring device may be, for example, a tablet computing device, phone, personal digital assistant, computer, and so on. 
     As another example, the electronic device can be configured in the form of a wearable communications device. The wearable communications device may include a processor coupled with or in communication with a memory, one or more sensors, one or more communication interfaces, output devices such as displays and speakers, one or more input devices, and a health monitoring system. The communication interface(s) can provide electronic communications between the communications device and any external communication network, device or platform, such as but not limited to wireless interfaces, Bluetooth interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces. The wearable communications device may provide information regarding time, health, statuses or externally connected or communicating devices and/or software executing on such devices, messages, video, operating commands, and so forth (and may receive any of the foregoing from an external device), in addition to communications. 
     Referring now to  FIG. 1 , there is shown a perspective view of one example of an electronic device that provides health-related information. In the illustrated embodiment, the electronic device  100  is implemented as a wearable communication device. Other embodiments can implement the electronic device differently. As described earlier, the electronic device can be a smart telephone, a gaming device, a digital music player, a device that provides time, a health assistant, and other types of electronic devices that provide health-related information. 
     The electronic device  100  includes an enclosure  102  at least partially surrounding a display  104  and one or more buttons  106  or input devices. The enclosure  102  can form an outer surface or partial outer surface and protective case for the internal components of the electronic device  100 , and may at least partially surround the display  104 . The enclosure  102  can be formed of one or more components operably connected together, such as a front piece and a back piece. Alternatively, the enclosure  102  can be formed of a single piece operably connected to the display  104 . 
     The display  104  can be implemented with any suitable technology, including, but not limited to, a multi-touch sensing touchscreen that uses liquid crystal display (LCD) technology, light emitting diode (LED) technology, organic light-emitting display (OLED) technology, organic electroluminescence (OEL) technology, or another type of display technology. A button  106  can take the form of a home button, which may be a mechanical button, a soft button (e.g., a button that does not physically move but still accepts inputs), an icon or image on a display or on an input region, and so on. Other buttons or mechanisms can be used as input/output devices, such as a speaker, a microphone, an on/off button, a mute button, or a sleep button. In some embodiments, the button or buttons  106  can be integrated as part of a cover glass of the electronic device. 
     The electronic device  100  can be permanently or removably attached to a band  108 . The band  108  can be made of any suitable material, including, but not limited to, leather, metal, rubber or silicon, fabric, and ceramic. In the illustrated embodiment, the band is a wristband that wraps around the user&#39;s wrist. The wristband can include an attachment mechanism (not shown), such as a bracelet clasp, Velcro, and magnetic connectors. In other embodiments, the band can be elastic or stretchy such that it fits over the hand of the user and does not include an attachment mechanism. 
       FIG. 2  depicts a back view of the electronic device  100  shown in  FIG. 1 . As described earlier, the electronic device can include one or more sensors, and at least one of these sensors may provide health-related information. As one example, the wearable communication device can include an optical sensor, such as a photoplethysmography (PPG) sensor. A PPG sensor uses light to measure changes in the volume of a part of a user&#39;s body. As the light passes through the user&#39;s skin and into the underlying tissue, some light is reflected, some is scattered, and some light is absorbed, depending on what the light encounters. Blood can absorb light more than surrounding tissue, so less reflected light will be sensed by the PPG sensor when more blood is present. The user&#39;s blood volume increases and decreases with each heartbeat. A PPG sensor detects changes in blood volume based on the reflected light, and one or more physiological parameters of the user can be determined by analyzing the reflected light. Example physiological parameters include, but are not limited to, heart rate and respiration. 
     The electronic device  100  includes one or more apertures  200  in the enclosure  102 . Each aperture is associated with a light source  202 . In one embodiment, each light source is implemented as a light-emitting diode (LED). Four apertures  200  and four light sources  202  are used in the illustrated embodiment. Other embodiments can include any number of light sources  200 . For example, two light sources can be used in some embodiments. 
     The light sources  202  can operate at the same light wavelength range, or the light sources can operate at different light wavelength ranges. As one example, with two light sources one light source may transmit light in the visible wavelength range while the other light source can emit light in the infrared wavelength range. With four light sources, two light sources may transmit light in the visible wavelength range while the other two light sources can emit light in the infrared wavelength range. For example, in one embodiment, at least one light source can emit light in the wavelength range associated with the color green while another light source transmits light in the infrared wavelength range. When a physiological parameter of the user will be determined, the light sources emit light toward the user&#39;s skin and the optical sensor  204  senses an amount of reflected light. The optical sensor  204  may sense the reflected light through an aperture (not shown) that is formed in the electronic device. As will be described in more detail later, a modulation pattern can be used to turn the light sources on and off and sample or sense the reflected light. 
       FIG. 3  is an illustrative block diagram of the electronic device  100  shown in  FIG. 1 . The electronic device  100  can include the display  104 , one or more processing devices  300 , memory  302 , one or more input/output (I/O) devices  304 , one or more sensors  306 , a power source  308 , a network communications interface  310 , and a health monitoring system  312 . The display  104  may provide an image or video output for the electronic device  100 . The display may also provide an input surface for one or more input devices, such as, for example, a touch sensing device and/or a fingerprint sensor. The display  104  may be substantially any size and may be positioned substantially anywhere on the electronic device  100 . 
     The processing device  300  can control some or all of the operations of the electronic device  100 . The processing device  300  can communicate, either directly or indirectly with substantially all of the components of the electronic device  100 . For example, a system bus or signal line  314  or other communication mechanisms can provide communication between the processing device(s)  300 , the memory  302 , the I/O device(s)  304 , the sensor(s)  306 , the power source  308 , the network communications interface  310 , and/or the health monitoring system  312 . The one or more processing devices  300  can be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, the processing device(s)  200  can each be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of such devices. As described herein, the term “processing device” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. 
     The memory  302  can store electronic data that can be used by the electronic device  100 . For example, a memory can store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing and control signals or data for the health monitoring system  312 , data structures or databases, and so on. The memory  302  can be configured as any type of memory. By way of example only, the memory can be implemented as random access memory, read-only memory, Flash memory, removable memory, or other types of storage elements, or combinations of such devices. 
     The one or more I/O devices  304  can transmit and/or receive data to and from a user or another electronic device. One example of an I/O device is button  106  in  FIG. 1 . The I/O device(s)  304  can include a display, a touch sensing input surface such as a track pad, one or more buttons, one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. 
     The electronic device  100  may also include one or more sensors  306  positioned substantially anywhere on the electronic device  100 . The sensor or sensors  306  may be configured to sense substantially any type of characteristic, such as but not limited to, images, pressure, light, touch, heat, position, motion, and so on. For example, the sensor(s)  308  may be an image sensor, a heat sensor, a light or optical sensor, a pressure transducer, a magnet, a gyroscope, an accelerometer, and so on. 
     The power source  308  can be implemented with any device capable of providing energy to the electronic device  100 . For example, the power source  308  can be one or more batteries or rechargeable batteries, or a connection cable that connects the remote control device to another power source such as a wall outlet. 
     The network communication interface  310  can facilitate transmission of data to or from other electronic devices. For example, a network communication interface can transmit electronic signals via a wireless and/or wired network connection. Examples of wireless and wired network connections include, but are not limited to, cellular, Wi-Fi, Bluetooth, IR, and Ethernet. 
     The health monitoring system  312  can include the light sources  202 , one or more optical sensors  204 , and a processing device  316 . The processing device  316  may be any suitable type of processing device. In one embodiment, the processing device  316  is a digital signal processor. The processing device  316  may receive signals from the optical sensor(s)  204  and processes the signals to correlate the signal values with a physiological parameter of the user. As one example, the processing device can apply one or more demodulation operations to the signals received from the optical sensor. Additionally, the processing device may control the modulation (e.g., turning on and off) of the light sources  202  according to a given modulation pattern. In one embodiment, one or more modulation patterns may be stored in memory  302  and accessed by the processing device  316  to modulate the light sources  202 . 
     As discussed earlier, the light sources can emit light in the visible and/or infrared wavelength ranges. The optical sensor or sensors  204  is implemented as a photodetector that senses light and converts the light into an electrical signal that represents the amount of light sensed by the photodetector. In one embodiment, the photodetector can be a photodiode. Other embodiments can use a different type of photodetector, such as a phototube or photoresistor. 
     In another embodiment, the processing device  316  is not included in the health monitoring system  312  and the processing device  300  receives signals from the optical sensor(s)  204  and processes the signals to correlate the signal values with a physiological parameter of the user. Additionally or alternatively, the processing device  300  can control the operations of the light sources (e.g., turn on and off). One or more modulation patterns may be stored in memory  302  and accessed by the processing device  300  to modulate the light sources  202 . 
     It should be noted that  FIGS. 1-3  are illustrative only. In other examples, an electronic device may include fewer or more components than those shown in  FIG. 3 . Additionally or alternatively, the electronic device can be included in a system and one or more components shown in  FIG. 3  are separate from the electronic device but in communication with the electronic device. For example, an electronic device may be operatively connected to, or in communication with a separate display. As another example, one or more applications or data can be stored in a memory separate from the electronic device. As another example, a processing device in communication with the electronic device can control various functions in the electronic device and/or process data received from the electronic device. In some embodiments, the separate memory and/or processing device can be in a cloud-based system or in an associated monitoring device. 
     Referring now to  FIG. 4 , there is shown a flowchart of one example method of operating the health monitoring system  312  in  FIG. 3 . Initially, a light source is turned on to illuminate the user&#39;s skin and the optical sensor senses an amount of reflected or transmitted light (blocks  400 ,  402 ). A determination can then be made at block  404  as to whether or not another light source is to be turned on. For example, in one embodiment, the light sources are turned on sequentially and the optical sensor senses the light multiple times while each light source is turned on. 
     If another light source is to be turned on, the process passes to block  406  where the light source that is currently turned on is turned off. The method then returns to block  400  and repeats until all of the light sources have been turned on and the optical sensor has obtained light samples. 
     When a determination is made at block  404  that all of the light sources have been turned on, the process continues at block  408  where the signal received from the optical sensor is digitized by inputting the signal into an analog-to-digital converter. The digitized signal is then demodulated at block  410 . Demodulating the signal produces multiple demodulated signals, with a demodulated signal associated with each light source. Each demodulated signal is then received and processed by a low pass filter and a decimation circuit (block  412 ). 
     The signals may then be analyzed at block  414  to determine or estimate a physiological parameter of the user. As described earlier, in one embodiment the signals can be analyzed to determine a heart rate of the user. As one example, the processing device  316  can analyze the signals to estimate a physiological parameter of the user. In another example, the processing device  300  can analyze the signals to determine a physiological parameter of the user. And in yet another example, both processing devices  300 ,  316  can perform various steps in the analysis to estimate a physiological parameter of the user. 
     In other embodiments, the light source need not be turned off or on entirely. Instead, certain embodiments may modulate the brightness of the light source in place of or in addition to the turning of lights on and off. In some embodiments, certain light sources may be turned on and off while other light sources are alternately dimmed and brightened. 
       FIGS. 5-6  depict example modulation patterns suitable for use in blocks  400  and  402  in  FIG. 4 .  FIGS. 5 and 6  are described with reference to a health monitoring system that includes four light sources. As described earlier, other embodiments can include fewer or more light sources. The embodiments described hereinafter are described with reference to a thirty sample modulation cycle operating at 4096 hertz. This is provided by way of example and is not required. Other modulation cycle frequencies and/or sampling frequencies may be selected. For example, the modulation cycle frequencies may range, as a non-limiting example, from one hundred hertz to several hundred kilohertz. 
     In many examples, the modulation cycle frequency and the sampling frequency may be interrelated. For example, certain embodiments may be limited by hardware or software to a particular maximum sampling frequency. In such an example, the modulation cycle frequency may be selected such that the transmitted signal can be adequately reconstructed. In some cases, the modulation cycle may be less than half the sampling rate. Stated another way, if a certain embodiment requires a particular bandwidth, the sampling frequency may be at least twice the selected maximum frequency of the selected bandwidth. 
     Other embodiments can obtain a different number of samples and/or operate at a different frequency. The frequency may be determined based on a number of factors, one of which is the harmonics of the electrical network or grid. For example, when an electrical network produces a signal at 60 Hz, the harmonics are multiples of 60 (e.g., 120 Hz, 180 Hz, 240 Hz, etc.). Also, some electrical networks produce a signal at 50 Hz, and the harmonics of multiples of 50 Hz (e.g., 100 Hz, 150 Hz, 200 Hz, etc.). 
     Additionally, some electrical networks can be less reliable at generating a signal with a specific frequency, and the frequency may vary by a certain amount or deviation (e.g., a frequency of 60 Hz may operate at 60+/−1% Hz). And the deviation increases with each harmonic. Thus, in one embodiment, the frequency of the modulation cycle is selected to be in a harmonic gap that exists between the various harmonics and harmonic deviations of at least one electrical network. 
     The illustrated modulation patterns are time-multiplexed modulation patterns that drive the light sources. The time periods when the light sources are turned on and off are multiplexed in time. In  FIG. 5 , the first light source is turned on for the time period  500 . The other three light sources are turned off during the time period  500 . An optical sensor captures a light sample multiple times  502  during the time period  500 . In the illustrated embodiment, the optical sensor obtains five light samples  502 . The first light source is then turned off and the optical sensor captures the light at time  504 . A light sample obtained when all of the light sources are turned off is known as a dark sample. 
     The second light source is then turned on for the time period  506 . Again, the other three light sources are turned off during the time period  506 . The optical sensor captures multiple light samples  508  during the time period  506 . In the illustrated embodiment, the optical sensor obtains five samples  508 . The second light source is then turned off and the optical sensor captures a dark sample at time  510 . 
     Similarly, only the third light source is turned on for the time period  512 , and the optical sensor senses an amount of light multiple times  514  (e.g., five times) during the time period  512 . The third light source is then turned off and the optical sensor captures a dark sample at time  516 . 
     The fourth light source is then turned on for the time period  518 , and the optical sensor obtains multiple light samples  520  (e.g., five times) during the time period  518 . The fourth light source is then turned off and the optical sensor captures multiple dark samples  522 . In the illustrated embodiment, the optical sensor obtains seven dark samples  522 . Thus, the optical sensor captures thirty samples during one modulation cycle  524 . The modulation cycles can repeat a given number of times when estimating a physiological parameter. As described earlier, the modulation cycle can have a frequency of 4096 Hz in one embodiment. 
     The modulation pattern in  FIG. 6  is similar to the modulation pattern in  FIG. 5  except that the optical sensor does not capture dark samples in between the time periods when a light source is turned on. In other words, the optical sensor does not sense dark samples at times  504 ,  510 , and  516 . The light sensor obtains multiple dark samples  600  after the time period  518  has ended (after the fourth light source is turned off). In the illustrated embodiment, the light sensor captures ten dark samples  600 . Like the  FIG. 5  embodiment, the optical sensor obtains thirty samples during one modulation cycle  602 . 
     The analog signal produced by the optical sensor includes information associated with all four light sources. Thus, in one embodiment, the analog signal is demodulated by a single optical sensor to produce four signals. In some cases, each signal is associated with a specific light source. In other examples, two optical sensors may be used to generate eight signals associated with the four light sources. In some cases, the two optical sensors may be physically separated so as to measure light associated with the four light sources from different points along the user&#39;s skin. In other embodiments, more than two optical sensors may be used. 
       FIG. 7  is a data flow diagram of an illustrative processing channel that performs blocks  408 ,  410 , and  412  in  FIG. 4 . The analog signal received from the optical sensor on signal line  700  is converted to a digital signal by analog-to-digital converter  702  in the processing channel  704 . The digital signal is then received by the mixer circuit  706 . The mixer circuit  706  also receives one or more demodulation operations  708 . In general, the demodulation operation can be sin 
               2   ⁢   π   ⁢     kt   N     ⁢   or   ⁢           ⁢   cos   ⁢           ⁢   2   ⁢   π   ⁢           ⁢     kt   N       ,         
where k is defined by 1≤k≤n/2, N represents the number of samples obtained by the optical sensor, and t=0, 1, . . . , N−1. The number of demodulation operations input into the mixer circuit  704  may be based on the number of light sources. In one embodiment, each harmonic of the signal received from the optical sensor has two orthogonal components. Thus, in some cases, the number of harmonics may depend upon the number of channels multiplexed and de-multiplexed. As one example, when the health monitoring system includes two light sources, the demodulation operations can be sin 2π/N or cos 2π/N for the first harmonic frequency. Two signals will be produced after both demodulation operations have been applied to the digital signal by mixer circuit  706 . When the health monitoring system has four light sources, the demodulation operation can be sin 2π/N or cos 2π/N for the first harmonic frequency, and sin 4π/N or cos 4π/N for the second harmonic frequency. Four signals will be produced after the four demodulation operations have been applied to the digital signal by mixer circuit  706 .
 
     The signal output by the mixer circuit  706  is received by a low pass filter  710  and a decimation circuit  712 . The low pass filter  710  and the decimation circuit  712  form a first decimation stage. Embodiments can include any number of decimation stages K. The number of decimation stages K can be based on the frequency of the sampling cycle of the optical sensor and the frequency of the physiological parameter. For example, in the embodiments shown in  FIGS. 5 and 6 , thirty samples are obtained by the optical sensor. When the frequency of the physiological parameter is approximately ten hertz and the frequency of the thirty sample cycle is 4096 hertz, six decimation stages are used with each stage reducing the frequency of the signal by two. 
     After the signal is processed by the low pass filter  714  and decimation circuit  716  in the last decimation stage K, each signal is received by a demultiplexer and multiplier circuit  718 . The demultiplexer separates the signals by associated light source. Thus, the signal associated with the first light source is separated from the signals associated with the other light sources, and so on for each signal. The multiplier circuit then multiplies each signal by respective weights or values. As one example, the values can be stored in a matrix, and each signal is multiplied by the values in a respective row in the matrix. 
     The values in the matrix are a function of the dynamics and components of the health monitoring system. The operations of the components such as the optical sensor, the filters (e.g., high pass filters, low pass filters), the operational amplifiers, and the like, change over time due to temperature and other factors. The values in the matrix adjust the signals for these changes. One method for determining the values in the matrix is described in conjunction with  FIG. 8 . 
     The signals output on signal line  720  represent the signals received from the user&#39;s tissue, and these signals can be analyzed to determine or measure the physiological parameter. As one example, these signals can be analyzed to determine the heart rate of the user. 
       FIG. 8  is a flowchart of one example method of determining the values in a matrix used in block  718  of  FIG. 7 . Initially, the values in the matrix are determined at block  800 .  FIG. 9  is a flowchart of one example method of performing block  800 . In block  900 , a single light source is turned on for a given period of time. The signal produced by the optical sensor is then processed to obtain some of the matrix values. For example, when the health monitoring system includes four light sources, s signal value or amplitude associated with each light source will be output by the decimation circuit  716 . Thus, four signal values will be output by the decimation circuit  716  based on the single light source emitting light toward the user&#39;s skin. These four signal values are included in one row in the matrix. 
     Returning to  FIG. 9 , a determination is then made at block  904  as to whether or not all of the light sources have been individually turned on. If not, the process passes to block  906  where the light source that is currently turned on is turned off. The method then returns to block  900  where another single light source is turned on and the signal produced by the optical sensor processed to obtain matrix values for another row in the matrix. The method in  FIG. 9  repeats until all of the light sources have been turned on and all of the values determined for the matrix. For four light sources, the values in the matrix are as follows: 
     Returning to  FIG. 8 , after the matrix values are determined at block  800  the matrix values can be verified at block  802 .  FIG. 10  is a flowchart of one example method of performing block  802 . Initially, all of the light sources except one are turned on for a given period of time (block  1000 ). The signal produced by the optical sensor is then processed based on the data flow diagram shown in  FIG. 7 . As described earlier, the demultiplexer and multiplier circuit  718  outputs signals that are associated with each light source in the health monitoring system. The signal value associated with the light source that is turned off should have a value that is substantially zero, while the signal values associated with the light sources that are turned on should be greater than zero. 
     Returning to  FIG. 10 , a determination is made at block  1004  as to whether or not the signal value associated with the light source that is turned off equals zero. If not, the method passes to block  1006  where the matrix values in the matrix are recalculated. Thus, the method shown in  FIG. 9  may be repeated and the method shown in  FIG. 10  repeated until it is determined at block  1004  that the signal value associated with each light source equals zero when the respective light source is turned off and the other light sources are turned on. 
     If the signal value equals zero, the process continues at block  1008  where a determination is made as to whether or not all of the light sources have been turned off while the other light sources are turned on. If not, the method passes to block  1010  where the light sources that are currently turned on are turned off. The method then returns to block  1000  where all light sources except another single light source is turned on. The method in  FIG. 10  repeats until all of the light sources have been turned off while the other light sources are turned on and the signal value output from the demultiplexer and multiplier circuit  718  associated with each light source equals zero when the respective light source is turned off and the other light sources are turned on. 
     Returning to  FIG. 8 , if the matrix values are not verified at block  804 , the method returns to block  800  as described earlier. If the matrix values are verified at block  804 , the process continues at block  806  where the matrix is applied in the demultiplexer and multiplier circuit  718  in  FIG. 7 . A determination may then be made at block  808  as to whether or not the matrix values are to be recalculated. As one example, the matrix values can be recalculated after a given period of time has passed. Additionally or alternatively, the matrix values may be recalculated each time a user activates the heath monitoring system. The process waits at block  808  if the matrix values are not recalculated. If the matrix values are to be recalculated, the method returns to block  800 . 
     Various embodiments have been described in detail with particular reference to certain features thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. For example, as described earlier, a health monitoring system can include a different number of light sources (e.g., two or six). Additionally or alternatively, a health monitoring system can be included in, or connected to a different type of electronic device. 
     Even though specific embodiments have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. Likewise, the features of the different embodiments may be exchanged, where compatible.

Metadata:
Filing Date: 20150212
Publication Date: 20190305
Grant Date: 20190305
Priority Date: 20140909
Inventors: LAMEGO, MARCELO M.
Assignee: APPLE INC
CPC Classifications: [{"code": "A61B5/7228", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/7225", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7278", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7203", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/725", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/0059", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7228", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/02416", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/14551", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/14551", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/02416", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7228", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/725", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7278", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7225", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7203", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/0059", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 65495822