Patent Publication Number: US-2023135923-A1

Title: Method for calibrating external light for bio-signal measurement, and electronic device and storage medium therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of International Application No. PCT/KR2021/004704 (published as WO2021/261725), filed on Apr. 14, 2021, designating the United States, in the Korean Intellectual Property Receiving Office, and claiming priority to Korean Patent Application KR 10-2020-0078155 filed on Jun. 26, 2020 in the Korean Intellectual Property Office, the disclosures of which are all incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     Certain embodiments relate to an external light calibration method for biometric signal measurement, an electronic device and storage medium therefor. 
     2. Description of Related Art 
     An electronic device may include various sensors capable of sensing a user’s biometric signals and provide various health-care functions. For example, there may be various types of biometric signals, including, but not limited to electrical signals, such as electrocardiography (ECG) and electromyogram (EMG), physical signals, such as blood pressure, body temperature, and photoplethysmogram (PPG), and composition-related signals, such as blood glucose level, oxygen saturation, and body composition. 
     The optical heart rate measurement method can be performed to measure changes in the change rate of absorption or transmittance for an internal light source, by using a photodiode, which is a photoelectronic conversion element. 
     However, the watch-type wearable device does not remain in tight contact with the user’s wrist. Therefore, external light (such as sunlight or indoor light) enters through a gap between the device and the wrist. Due to such wearable device structure, motion causes the photodiode to detect light from the internal light source, as well as the light from the outside. The light from the outside causes noise in the measurement. 
     In particular, since the optical heart rate measurement is a type of measurement using the reflection of the light that is radiated to the surface of the human body (which may also be referred to as light output (or scattered) from the human body (or the skin of the human body)), only detection of the reflected light signal may be of significance. However, if noise is caused due to introduction of external light, the output signal from the PPG sensor may severely fluctuate. This causes unstable acquisition of the biometric signal and resultant deterioration of accuracy and reliability in steady biometric signal measurement. 
     Thus, it would be desirable to prevent performance deterioration resulting from introduction of external light occurring while the wearable electronic device is worn. 
     SUMMARY 
     According to certain embodiments, a wearable electronic device, comprises: at least one light receiving unit; at least one light emitting unit; an external light calibration circuit; and a processor electrically connected with the at least one light receiving unit, at least one light emitting unit, and the external light calibration circuit, wherein the processor is configured to: control the at least one light emitting unit to radiate light during first periods, and not emit light during second periods, and detect light through the at least one light receiving unit during the second periods, and controlling the external light calibration circuit to provide an input to the at least one light receiving unit during first periods, based on the light detected during the second periods; and wherein during the first periods the at least one light receiving unit provides an output based on light received, and the input from the external light calibration circuit. 
     According to certain embodiments, a method for calibrating external light for biometric signal measurement in a wearable electronic device, comprises: radiating light with at least one light emitting unit during first periods and not radiating light during second periods; detecting a light signal output by at least one light receiving unit during the second periods; and providing an input to the at least one light receiving unit during the first periods by an external light calibration circuit, wherein the input is based on the detected light signal; provides an output during the first periods based on light received and the input by the at least one light emitting unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a block diagram illustrating an electronic device in a network environment according to an embodiment; 
         FIG.  1 B  is a front perspective view illustrating an electronic device according to an embodiment; 
         FIG.  1 C  is a rear perspective view illustrating an electronic device as shown in  FIG.  1 B ; 
         FIG.  1 D  is an exploded perspective view illustrating an electronic device as shown in  FIG.  1 B ; 
         FIG.  2    is a view illustrating changes in obtaining a biometric signal due to introduction of external light according to certain embodiments; 
         FIG.  3    is a block diagram schematically illustrating a biometric signal processing device for external light calibration according to certain embodiments; 
         FIG.  4    is a view illustrating an example of placement of a PPG sensor of a wearable electronic device according to certain embodiments; 
         FIG.  5    is a view illustrating a structure of a PPG sensor according to certain embodiments; 
         FIG.  6    is a view illustrating an example of a biometric signal processing circuit for external light calibration in a wearable electronic device according to certain embodiments; 
         FIG.  7    is a view illustrating a method for selectively extracting external light in a filter of an external light calibration circuit according to certain embodiments; 
         FIG.  8    is a flowchart illustrating an operation for performing an external light calibration method in a wearable electronic device according to certain embodiments; 
         FIG.  9    is a view illustrating a signal upon initial external light calibration according to certain embodiments; 
         FIG.  10    is a view illustrating a signal after external light calibration according to certain embodiments; 
         FIG.  11    is a detailed circuit diagram for external light calibration according to certain embodiments; 
         FIG.  12    is a view illustrating an output of each component after external light calibration according to certain embodiments; and 
         FIG.  13    is a view illustrating comparison between the respective outputs of components upon initial external light calibration according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Certain embodiments remove the external light component from the measurement by calibrating for external light that is introduced due to various issues with the measurement environment when measuring the biometric signal and thus allow for stable detection of biometric signals alone. 
     In certain embodiments, it is possible to prevent performance deterioration of biometric signal measurement due to external light introduced while the watch-type wearable electronic device is worn in a loose contact state. 
     According to certain embodiments, it is possible to minimize data loss even with sudden introduction of external light by performing real-time calibration upon the optical heart rate measurement. 
     According to certain embodiments, it is possible to minimize, if not eliminate, the difference in DC component for external light upon optical heart rate measurement and to maintain signal to noise ratio (SNR). This enables acquisition of reliable data and accurate measurement. 
     The terms as used herein are provided merely to describe some embodiments thereof, but not to limit the scope of other embodiments of the present disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. All terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the present disclosure belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some cases, the terms defined herein may be interpreted to exclude embodiments of the present disclosure. 
     This disclosure will begin with a functional description of an electronic device  101  in  FIG.  1 A .  FIGS.  1 B and  1 C  describe the housing of an electronic device  101   b , such as a wearable electronic device. A wearable electronic device can include, among other things, a smartwatch.  FIG.  1 B  describes the front of the electronic device  101   b .  FIG.  1 C  describes the rear of the electronic device  101   b .  FIG.  1 D  discloses an exploded view of an electronic device  101   b . 
     Electronic Device 
       FIG.  1 A  is a block diagram illustrating an electronic device  101  in a network environment  100   a  according to certain embodiments. Referring to  FIG.  1 A , the electronic device  101  in the network environment  100   a  may communicate with an electronic device  102  via a first network  198  (e.g., a short-range wireless communication network), or an electronic device  104  or a server  108  via a second network  199  (e.g., a long-range wireless communication network). The electronic device  101  may communicate with the electronic device  104  via the server  108 . The electronic device  101  may include a processor  120 , memory  130 , an input module  150 , a sound output module  155 , a display module  160 , an audio module  170 , a sensor module  176 , an interface  177 , a connecting terminal  178 , a haptic module  179 , a camera module  180 , a power management module  188 , a battery  189 , a communication module  190 , a subscriber identification module (SIM)  196 , or an antenna module  197 . In some embodiments, at least one (e.g., the display module  160  or the camera module  180 ) of the components may be omitted from the electronic device  101 , or one or more other components may be added in the electronic device  101 . According to an embodiment, some (e.g., the sensor module  176 , the camera module  180 , or the antenna module  197 ) of the components may be integrated into a single component (e.g., the display module  160 ). The processor  120  may execute, for example, software (e.g., a program  140 ) to control at least one other component (e.g., a hardware or software component) of the electronic device  101  coupled with the processor  120 , and may perform various data processing or computation. According to one embodiment, as at least part of the data processing or computation, the processor  120  may store a command or data received from another component (e.g., the sensor module  176  or the communication module  190 ) in volatile memory  132 , process the command or the data stored in the volatile memory  132 , and store resulting data in non-volatile memory  134 . The processor  120  may include a main processor  121  (e.g., a central processing unit (CPU) or an application processor (AP)), or an auxiliary processor  123  (e.g., a graphics processing unit (GPU), a neural processing unit (NPU), an image signal processor (ISP), a sensor hub processor, or a communication processor (CP)) that is operable independently from, or in conjunction with, the main processor  121 . For example, when the electronic device  101  includes the main processor  121  and the auxiliary processor  123 , the auxiliary processor  123  may be configured to use lower power than the main processor  121  or to be specified for a designated function. The auxiliary processor  123  may be implemented as separate from, or as part of the main processor  121 . 
     The term processor shall be understood to refer to both the singular and plural contexts in this document. 
     The auxiliary processor  123  may control at least some of functions or states related to at least one component (e.g., the display module  160 , the sensor module  176 , or the communication module  190 ) among the components of the electronic device  101 , instead of the main processor  121  while the main processor  121  is in an inactive (e.g., sleep) state, or together with the main processor  121  while the main processor  121  is in an active state (e.g., executing an application). The auxiliary processor  123  (e.g., an image signal processor or a communication processor) may be implemented as part of another component (e.g., the camera module  180  or the communication module  190 ) functionally related to the auxiliary processor  123 . 
     The auxiliary processor  123  (e.g., the neural processing unit) may include a hardware structure specified for artificial intelligence model processing. The artificial intelligence model may be generated via machine learning. Such learning may be performed, e.g., by the electronic device  101  where the artificial intelligence is performed or via a separate server (e.g., the server  108 ). Learning algorithms may include, but are not limited to, e.g., supervised learning, unsupervised learning, semi-supervised learning, or reinforcement learning. The artificial intelligence model may include a plurality of artificial neural network layers. The artificial neural network may be a deep neural network (DNN), a convolutional neural network (CNN), a recurrent neural network (RNN), a restricted Boltzmann machine (RBM), a deep belief network (DBN), a bidirectional recurrent deep neural network (BRDNN), deep Q-network or a combination of two or more thereof but is not limited thereto. The artificial intelligence model may, additionally or alternatively, include a software structure other than the hardware structure. 
     The memory  130  may store various data used by at least one component (e.g., the processor  120  or the sensor module  176 ) of the electronic device  101 . The various data may include, for example, software (e.g., the program  140 ) and input data or output data for a command related thereto. The memory  130  may include the volatile memory  132  or the non-volatile memory  134 . 
     The program  140  may be stored in the memory  130  as software, and may include, for example, an operating system (OS)  142 , middleware  144 , or an application  146 . 
     The input module  150  may receive a command or data to be used by other component (e.g., the processor  120 ) of the electronic device  101 , from the outside (e.g., a user) of the electronic device  101 . The input module  150  may include, for example, a microphone, a mouse, a keyboard, keys (e.g., buttons), or a digital pen (e.g., a stylus pen). 
     The sound output module  155  may output sound signals to the outside of the electronic device  101 . The sound output module  155  may include, for example, a speaker or a receiver. The speaker may be used for general purposes, such as playing multimedia or playing record. The receiver may be used for receiving incoming calls. The receiver may be implemented as separate from, or as part of the speaker. 
     The display module  160  may visually provide information to the outside (e.g., a user) of the electronic device  101 . The display  160  may include, for example, a display, a hologram device, or a projector and control circuitry to control a corresponding one of the display, hologram device, and projector. The display  160  may include a touch sensor configured to detect a touch, or a pressure sensor configured to measure the intensity of a force generated by the touch. 
     The audio module  170  may convert a sound into an electrical signal and vice versa. The audio module  170  may obtain the sound via the input module  150 , or output the sound via the sound output module  155  or a headphone of an external electronic device (e.g., an electronic device  102 ) directly (e.g., wiredly) or wirelessly coupled with the electronic device  101 . 
     The sensor module  176  may detect an operational state (e.g., power or temperature) of the electronic device  101  or an environmental state (e.g., a state of a user) external to the electronic device  101 , and then generate an electrical signal or data value corresponding to the detected state. The sensor module  176  may include, for example, a gesture sensor, a gyro sensor, an atmospheric pressure sensor, a magnetic sensor, an acceleration sensor, a grip sensor, a proximity sensor, a color sensor, an infrared (IR) sensor, a biometric sensor, a temperature sensor, a humidity sensor, or an illuminance sensor. 
     The interface  177  may support one or more specified protocols to be used for the electronic device  101  to be coupled with the external electronic device (e.g., the electronic device  102 ) directly (e.g., wiredly) or wirelessly. The interface  177  may include, for example, a high definition multimedia interface (HDMI), a universal serial bus (USB) interface, a secure digital (SD) card interface, or an audio interface. 
     A connecting terminal  178  may include a connector via which the electronic device  101  may be physically connected with the external electronic device (e.g., the electronic device  102 ). The connecting terminal  178  may include, for example, a HDMI connector, a USB connector, a SD card connector, or an audio connector (e.g., a headphone connector). 
     The haptic module  179  may convert an electrical signal into a mechanical stimulus (e.g., a vibration or motion) or electrical stimulus which may be recognized by a user via his tactile sensation or kinesthetic sensation. The haptic module  179  may include, for example, a motor, a piezoelectric element, or an electric stimulator. 
     The camera module  180  may capture a still image or moving images. The camera module  180  may include one or more lenses, image sensors, image signal processors, or flashes. 
     The power management module  188  may manage power supplied to the electronic device  101 . According to one embodiment, the power management module  188  may be implemented as at least part of, for example, a power management integrated circuit (PMIC). 
     The battery  189  may supply power to at least one component of the electronic device  101 . The battery  189  may include, for example, a primary cell which is not rechargeable, a secondary cell which is rechargeable, or a fuel cell. 
     The communication module  190  may support establishing a direct (e.g., wired) communication channel or a wireless communication channel between the electronic device  101  and the external electronic device (e.g., the electronic device  102 , the electronic device  104 , or the server  108 ) and performing communication via the established communication channel. The communication module  190  may include one or more communication processors that are operable independently from the processor  120  (e.g., the application processor (AP)) and supports a direct (e.g., wired) communication or a wireless communication. The communication module  190  may include a wireless communication module  192  (e.g., a cellular communication module, a short-range wireless communication module, or a global navigation satellite system (GNSS) communication module) or a wired communication module  194  (e.g., a local area network (LAN) communication module or a power line communication (PLC) module). A corresponding one of these communication modules may communicate with the external electronic device via a first network  198  (e.g., a short-range communication network, such as Bluetooth™, wireless-fidelity (Wi-Fi) direct, or infrared data association (IrDA)) or a second network  199  (e.g., a long-range communication network, such as a legacy cellular network, a 5G network, a next-generation communication network, the Internet, or a computer network (e.g., local area network (LAN) or wide area network (WAN)). These various types of communication modules may be implemented as a single component (e.g., a single chip), or may be implemented as multi components (e.g., multi chips) separate from each other. The wireless communication module  192  may identify or authenticate the electronic device  101  in a communication network, such as the first network  198  or the second network  199 , using subscriber information (e.g., international mobile subscriber identity (IMSI)) stored in the subscriber identification module  196 . 
     The wireless communication module  192  may support a 5G network, after a 4G network, and next-generation communication technology, e.g., new radio (NR) access technology. The NR access technology may support enhanced mobile broadband (eMBB), massive machine type communications (mMTC), or ultra-reliable and low-latency communications (URLLC). The wireless communication module  192  may support a high-frequency band (e.g., the mmWave band) to achieve, e.g., a high data transmission rate. The wireless communication module  192  may support various technologies for securing performance on a high-frequency band, such as, e.g., beamforming, massive multiple-input and multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, or large scale antenna. The wireless communication module  192  may support various requirements specified in the electronic device  101 , an external electronic device (e.g., the electronic device  104 ), or a network system (e.g., the second network  199 ). The wireless communication module  192  may support a peak data rate (e.g., 20 Gbps or more) for implementing eMBB, loss coverage (e.g., 164 dB or less) for implementing mMTC, or U-plane latency (e.g., 0.5 ms or less for each of downlink (DL) and uplink (UL), or a round trip of 1 ms or less) for implementing URLLC. 
     The antenna module  197  may transmit or receive a signal or power to or from the outside (e.g., the external electronic device). The antenna module may include an antenna including a radiator formed of a conductor or conductive pattern formed on a substrate (e.g., a printed circuit board (PCB)). The antenna module  197  may include a plurality of antennas (e.g., an antenna array). In this case, at least one antenna appropriate for a communication scheme used in a communication network, such as the first network  198  or the second network  199 , may be selected from the plurality of antennas by, e.g., the communication module  190 . The signal or the power may then be transmitted or received between the communication module  190  and the external electronic device via the selected at least one antenna. According to an embodiment, other parts (e.g., radio frequency integrated circuit (RFIC)) than the radiator may be further formed as part of the antenna module  197 . 
     According to certain embodiments, the antenna module  197  may form a mmWave antenna module. The mmWave antenna module may include a printed circuit board, a RFIC disposed on a first surface (e.g., the bottom surface) of the printed circuit board, or adjacent to the first surface and capable of supporting a designated high-frequency band (e.g., the mmWave band), and a plurality of antennas (e.g., array antennas) disposed on a second surface (e.g., the top or a side surface) of the printed circuit board, or adjacent to the second surface and capable of transmitting or receiving signals of the designated high-frequency band. 
     At least some of the above-described components may be coupled mutually and communicate signals (e.g., commands or data) therebetween via an inter-peripheral communication scheme (e.g., a bus, general purpose input and output (GPIO), serial peripheral interface (SPI), or mobile industry processor interface (MIPI)). 
     According to an embodiment, commands or data may be transmitted or received between the electronic device  101  and the external electronic device  104  via the server  108  coupled with the second network  199 . The external electronic devices  102  or  104  each may be a device of the same or a different type from the electronic device  101 . According to an embodiment, all or some of operations to be executed at the electronic device  101  may be executed at one or more of the external electronic devices  102 ,  104 , or  108 . For example, if the electronic device  101  should perform a function or a service automatically, or in response to a request from a user or another device, the electronic device  101 , instead of, or in addition to, executing the function or the service, may request the one or more external electronic devices to perform at least part of the function or the service. The one or more external electronic devices receiving the request may perform the at least part of the function or the service requested, or an additional function or an additional service related to the request, and transfer an outcome of the performing to the electronic device  101 . The electronic device  101  may provide the outcome, with or without further processing of the outcome, as at least part of a reply to the request. To that end, a cloud computing, distributed computing, mobile edge computing (MEC), or client-server computing technology may be used, for example. The electronic device  101  may provide ultra low-latency services using, e.g., distributed computing or mobile edge computing. In another embodiment, the external electronic device  104  may include an Internet-of-things (IoT) device. The server  108  may be an intelligent server using machine learning and/or a neural network. The external electronic device  104  or the server  108  may be included in the second network  199 . The electronic device  101  may be applied to intelligent services (e.g., smart home, smart city, smart car, or healthcare) based on 5G communication technology or IoT-related technology. 
     The sensor module  176  can include a PPG sensor for taking cardio measurements. A PPG sensor can include a light emitting diode (LED) and a photodiode. The light emitting diode can radiate light to the user’s body. The user’s body can reflect light. The photodiode can detect the light reflected by the user’s body. Based on the light detected by the photodiode, the electronic device  101  can provide various health related services. 
     However, additional light, such as indoor light, or sunlight, may also be detected by the photodiode. The foregoing results in a noise component to the optical heart rate measurements. 
     Accordingly, in certain embodiments, the effects of indoor light and sunlight are minimized, if not eliminated by performing real-time calibration upon the optical heart rate measurement. 
     Housing 
       FIG.  1 B  is a front perspective view  100   b  illustrating an electronic device according to an embodiment.  FIG.  1 C  is a rear perspective view  100   c  illustrating an electronic device as shown in  FIG.  1 B . The electronic device  101   b  can be wearable and include wearing members  150   a ,  160   a , such as wrist straps, to fasten the electronic device  101   b  to the body. 
     Moreover, the electronic device  101   b  can include a PPG sensor  165   b . The PPG sensor  165   b  can use LEDS to radiate light towards the user’s body and the user’s body reflects the light. The reflected light is detected by photodiode(s). Additionally, the wearing members  150   a  and  160   a  hold the electronic device  101   b , such that the PPG sensor  165   b  is in close proximity to the user’s body. 
     However, it may still be possible for external light (indoor light, or sun light) to also be detected by the photodiode, thereby introducing a noise component to the biometric signal. Certain embodiments minimize, if not eliminate, the influence of external light. 
     Referring to  FIGS.  1 B and  1 C , The electronic device  101   b  (e.g., the electronic device  101  of  FIG.  1 A ) may include a housing  110   a  including a first surface (or front surface)  110 A, a second surface (or rear surface)  110 B, and a side surface  110 C surrounding the space between the first surface  110 A and the second surface  110 B and wearing members  150   a  and  160   a  connected to at least part of the housing  110   a  and configured to allow the electronic device  101   b  to be detachably worn on the user’s body portion (e.g., his wrist or ankle). According to another embodiment (not shown), the housing may denote a structure forming part of the first surface  110 A, the second surface  110 B, and the side surfaces  110 C of  FIGS.  1 B and  1 C . At least part of the first surface  110 A may have a substantially transparent front plate  112   a  (e.g., a glass plate or polymer plate including various coat layers). The second surface  110 B may be formed of a substantially opaque rear plate  107   a . When the electronic device  101   b  includes a sensor module  165  disposed on the second surface  110 B, the rear plate  107   a  may at least partially include a transparent region. 
     The rear plate  107   a  may be formed of, e.g., laminated or colored glass, ceramic, polymer, metal (e.g., aluminum, stainless steel (STS), or magnesium), or a combination of at least two thereof. The side surface  110 C may be formed by a side bezel structure (or a “side member”)  106   a  that couples to the front plate  112   a  and the rear plate  107   a  and includes a metal and/or polymer. The rear plate  107   a  and the side bezel structure  106   a  may be integrally formed together and include the same material (e.g., a metal, such as aluminum). The wearing members  150   a  and  160   a  may be formed of various materials in various shapes. A uni-body structure or multiple unit links which is flexible may be formed of fabric, leather, rubber, urethane, metal, ceramic, or a combination of at least two thereof. 
     The electronic device  101   b  may include at least one or more of a display  120   a  (refer to  FIG.  1 D ), audio modules  105   a  and  108   a , a sensor module  165 , key input devices  102   a ,  103   a , and  104   a , and a connector hole  109   a . The electronic device  101   b  may exclude at least one (e.g., the key input devices  102   a ,  103   a , and  104   a , connector hole  109   a , or sensor module  165 ) of the components or may add other components. 
     The electronic device  101   b  may include a plurality of electrodes for measuring a biometric signal. At least one of the plurality of electrodes may be placed in at least one of the position of the key input device  102   a ,  103   a , or  104   a , the position of the bezel  106   a , or the position of the display  120   a  or the housing  110   a . Among the key input devices, the wheel key  102   a  may include a rotary bezel. 
     The display  120   a  may be exposed through a substantial portion of, e.g., the front plate  112   a . The display  120   a  may have a shape corresponding to the shape of the front plate  112   a , e.g., a circle, ellipse, or polygon. The display  120   a  may be coupled with, or disposed adjacent, a touch detection circuit, a pressure sensor capable of measuring the strength (pressure) of touches, and/or fingerprint sensor. 
     The display  120   a  may include at least one transparent electrode for measuring biometric signals among the plurality of electrodes for measuring biometric signals. 
     The audio modules  105   a  and  108   a  may include a microphone hole  105   a  and a speaker hole  108   a . The microphone hole  105   a  may have a microphone inside to obtain external sounds. There may be a plurality of microphones to be able to detect the direction of a sound. The speaker hole  108   a  may be used for an external speaker or a receiver for phone talks. According to an embodiment, a speaker may be included without the speaker hole (e.g., a piezo speaker). 
     The sensor module  165  may generate an electrical signal or data value corresponding to an internal operating state or external environmental state of the electronic device  101   b . The sensor module  165 , e.g., a biometric sensor module (e.g., an HRM sensor) placed on the second surface  110 B of the housing  110   a , may include an electrocardiogram (ECG) sensor  165   a  including at least two electrodes  a   1  and  a   2  for ECG measurement and a photoplethysmogram (PPG) sensor  165   b  for heartrate measurement. The electronic device  101   b  may further include sensor modules not shown, e.g., at least one of a gesture sensor, a gyro sensor, an atmospheric pressure sensor, a magnetic sensor, an acceleration sensor, a grip sensor, a color sensor, an infrared (IR) sensor, a biometric sensor, a temperature sensor, a humidity sensor, or an illuminance sensor. 
     The key input devices  102   a ,  103   a , and  104   a  may include a wheel key  102   a  disposed on the first surface  110 A of the housing  110   a  to be rotatabe in at least one direction and/or side key buttons  103   a  and  104   a  disposed on the side surface  110 C of the housing  110   a . The wheel key  102   a  may have a shape corresponding to the shape of the front plate  112   a . The electronic device  101   b  may exclude all or some of the above-mentioned key input devices  102   a ,  103   a , and  104   a  and the excluded key input devices  102   a ,  103   a , and  104   a  may be implemented in other forms, e.g., as soft keys on the display  120   a . The connector hole  109   a  may receive a connector (e.g., a universal serial bus (USB) connector) for transmitting and receiving power and/or data to/from an external electronic device. Another connector hole (not shown) may be included for receiving a connector for transmitting and receiving audio signals to/from the external electronic device. The electronic device  101   b  may further include a connector cover (not shown) to cover at least part of, e.g., the connector hole  109   a  and preventing undesirable materials from entering the connector hole. 
     The wearing members  150   a  and  160   a  may detachably be fastened to at least portions of the housing  110   a  via locking members  151   a  and  161   a . The locking members  151   a  and  161   a  may include components or parts for coupling, such as pogo pins, and, according to an embodiment, may be replaced with protrusions or recesses formed on/in the wearing members  150   a  and  160   a . For example, the wearing members  150   a  and  160   a  may be coupled in such a manner as to be fitted into or over the recesses or protrusions formed on the housing  110 . The wearing members  150   a  and  160   a  may include one or more of a fixing member  152   a , fixing member coupling holes  153   a , a band guide member  154   a , and a band fixing ring  155   a . 
     The fixing member  152   a  may be configured to allow the housing  110   a  and the wearing members  150   a  and  160   a  to be fastened to the user’s body portion (e.g., wrist or ankle). The fixing member coupling holes  153   a  may fasten the housing  110   a  and the wearing members  150   a  and  160   a  to the user’s body portion, corresponding to the fixing member  152   a . The band guide member  154   a  may be configured to restrict movement of the fixing member  152   a  to a certain range when the fixing member  152   a  fits into one of the fixing member coupling holes  153   a , thereby allowing the wearing members  150   a  and  160   a  to be tightly fastened onto the user’s body portion. The band fixing ring  155   a  may limit the range of movement of the wearing members  150   a  and  160   a , with the fixing member  152   a  fitted into one of the fixing member coupling holes  153   a . 
       FIG.  1 D  is an exploded perspective view  100   d  illustrating the electronic device  101   b  of  FIG.  1 B . 
     Referring to  FIG.  1 D , an electronic device  101   b  (e.g., the electronic device  101  of  FIG.   1 A ) may include a side bezel structure  210   a , a wheel key  220   a , a front plate  112   a , a display  120   a , a first antenna  250   a , a second antenna  255   a , a supporting member  260   a  (e.g., a bracket), a battery  270   a , a printed circuit board  280   a , a sealing member  290   a , a rear plate  293   a , and wearing members  295   a  and  297   a . At least one of the components of the electronic device  101   b  may be the same or similar to at least one of the components of the electronic device  101   b  of  FIGS.  1 A or  1 C  and no duplicate description is made below. The supporting member  260   a  may be disposed inside the electronic device  101   b  to be connected with the side bezel structure  210   a  or integrated with the side bezel structure  210   a . The supporting member  260   a  may be formed of, e.g., a metal and/or non-metallic material (e.g., polymer). The display  120   a  may be joined onto one surface of the supporting member  260   a , and the printed circuit board  280   a  may be joined onto the opposite surface of the supporting member  260   a . A processor, memory, and/or interface may be mounted on the printed circuit board  280   a . The processor may include one or more of, e.g., a central processing unit, an application processor, a graphic processing unit (GPU), a sensor processor, or a communication processor. 
     The memory may include, e.g., a volatile or non-volatile memory. The interface may include, e.g., a high definition multimedia interface (HDMI), a universal serial bus (USB) interface, a secure digital (SD) card interface, and/or an audio interface. The interface may electrically or physically connect, e.g., the electronic device  101   b  with an external electronic device and may include a USB connector, an SD card/multimedia card (MMC) connector, or an audio connector. 
     The battery  270   a  may be a device for supplying power to at least one component of the electronic device  101   b . The battery  270   a  may include, e.g., a primary cell which is not rechargeable, a secondary cell which is rechargeable, or a fuel cell. At least a portion of the battery  270   a  may be disposed on substantially the same plane as the printed circuit board  280   a . The battery  270   a  may be integrally or detachably disposed inside the electronic device  101   b . 
     The first antenna  250   a  may be disposed between the display  120   a  and the supporting member  260   a . The first antenna  250   a  may include, e.g., a near-field communication (NFC) antenna, a wireless charging antenna, and/or a magnetic secure transmission (MST) antenna. The first antenna  250   a  may perform short-range communication with an external device, wirelessly transmit/receive power necessary for charging, or transmit magnetic-based signals including payment data or short-range communication signals. According to an embodiment, an antenna structure may be formed by a portion or combination of the side bezel structure  210   a  and/or the supporting member  260   a . 
     The second circuit board  255   a  may be disposed between the circuit board  280   a  and the rear plate  293   a . The second circuit board  255   a  may include an antenna, e.g., a near-field communication (NFC) antenna, a wireless charging antenna, and/or a magnetic secure transmission (MST) antenna. The second circuit board  255   a  may perform short-range communication with an external device, wirelessly transmit/receive power necessary for charging, or transmit magnetic-based signals including payment data or short-range communication signals. According to an embodiment, an antenna structure may be formed by a portion or combination of the side bezel structure  210   a  and/or the rear plate  293   a . According to an embodiment, when the electronic device  101   b  (e.g., the electronic device  101   b  of  FIGS.  1 B or  1 C ) includes a sensor module (e.g., the sensor module  165  of  FIG.  1 B ), a sensor element (e.g., a photoelectric conversion element or electrode pad) separate from the second circuit board  255   a  or the sensor circuit disposed on the second circuit board  255   a  may be disposed. For example, an electronic component provided as the sensor module  165  may be disposed between the circuit board  280   a  and the rear plate  293   a . 
     The sealing member  290   a  may be positioned between the side bezel structure  210   a  and the rear plate  293   a . The sealing member  290   a  may be configured to block moisture or foreign bodies that may enter the space surrounded by the side bezel structure  210   a  and the rear plate  293   a , from the outside. 
     According to certain embodiments described below, examples of measurable biometric signals may include electrical signals, such as electrocardiogram (ECG), electroencephalography (EEG), and electromyography (EMG), physical signals, such as blood pressure, body temperature, and PPG, and composition-related signals, such as blood glucose level, oxygen saturation, and body composition. However, the measurable biometric signals are not limited thereto. Further, although the description focuses primarily on an example of correcting external light for a PPG signal for optical heartbeat measurement, this is merely for convenience of description, and embodiments are not limited thereto. 
     PPG Sensor 
       FIG.  2    is a view  200  illustrating changes in obtaining a biometric signal due to introduction of external light according to certain embodiments. 
     Referring to  FIG.  2   , biometric signal measurement is performed continuously for 24 hours while the wearable electronic device  201  is worn by the user. Various noises other than the biometric signal may be superposed according to the user’s movement and posture while wearing the wearable electronic device  201 . The foregoing leads to a higher change of an error in analyzing the biometric signal waveform. For example, as shown in  FIG.  2   , when external light introduction to the optical biometric signal  215  starts ( 205 ), the biometric signal may fall outside of the input dynamic range  220 . In this case, if the external noise corresponding to the external light enters the biometric signal, e.g., PPG sensor, of the wearable electronic device  201 , it may be difficult to determine whether the light entering the PPG sensor is external light or reflected light. In particular, when falling outside of the input dynamic range  220 , the signal may be saturated, rendering it possible to measure the biometric signal. 
     The wearable electronic device  201  calibrates for external light calibration  230  in realtime at the time of introduction of the external light  210  while measuring the optical biometric signal  215 , so that only minimum data loss  240  occurs. Therefore, although the external light  210  may be included in the optical biometric signal  215 , the input dynamic range  220  may be stably maintained so that a calibrated optical biometric signal  225  waveform is output as if a baseline calibration  250  operation was performed. Further, according to certain embodiments, although the external light is introduced together, the wearable electronic device  201  may maintain SNR without a difference in DC component for the external light, so that reliable data can be obtained. 
     A device for processing biometric signals for external light calibration may be a wearable electronic device. The wearable electronic device may include a housing and/or a bezel. The rear surface of the housing, i.e., the rear surface of the wearable electronic device, may contact a body portion (e.g., wrist), and the rear surface may be formed of metal. Sensors for measuring biometric signals may be arranged around the center portion of the rear surface. The arrangement of the sensors is described below with reference to  FIG.  4   . 
     A method for processing biometric signals for external light calibration and embodiments of a wearable electronic device are described below in detail with reference to the drawings. 
       FIG.  3    is a block diagram  300  schematically illustrating a biometric signal processing device for external light calibration according to certain embodiments. 
       FIG.  3    is a block diagram illustrating an internal configuration of a biometric signal processing device according to an embodiment. The biometric signal processing device may be a wearable electronic device. The biometric signal processing device may be equipped, in the form of a hardware or software module, in an electronic device, such as a wearable electronic device. The biometric signal processing device may be implemented as a stand-alone hardware device in which case it may be used to obtain and analyze various kinds of biometric signals. However, without limitations thereto, various modifications may be made thereto depending on the purposes of utilizing the instant technology. 
     The biometric light detector  310  receives reflected light as well as external light and outputs an electrical corresponding to the reflected light and external light. The external light calibration circuit  315  detects light from a light receiving unit during when a light emitting unit is not emitting light. As a result, the signal provided by the light receiving unit is an electrical signal corresponding to the external light. The external light calibration circuit  315  can then apply the current with the magnitude corresponding to the extracted external light signal to the input terminal of at least one light receiving unit. 
     Referring to  FIG.  3   , a biometric signal processing device  301  may include a biometric signal detector  310 , an external light calibration circuit  315 , a processor  320 , a memory  330 , and a display  360 . Here, the biometric signal processing device  301  may be a wearable electronic device (e.g., the electronic device  101  of  FIG.  1 A  or the electronic device  101   b  of  FIGS.  1 B to  1 D ). 
     The biometric signal detector  310  may include a plurality of sensors and receive signals for obtaining biometric signals through the plurality of sensors. For example, the plurality of sensors may include biometric sensors, such as an electrocardiogram sensor (hereinafter, ECG sensor), a photoplethysmography sensor (hereinafter, PPG sensor), a heart rate sensor, and a body temperature sensor and, as necessary, may include optionally other various sensors for measuring necessary biometric signals, such as an acceleration sensor but embodiments of the disclosure are not limited thereto. 
     Among the plurality of sensors, the PPG sensor is a sensor for estimating various biological states based on the characteristics of the body or the blood flow in the body using the characteristics of absorption, scattering, or reflection by the skin tissues of the user’s body, obtained by radiating light to the user’s body (or user’s skin). 
     It is possible to obtain various biometric information based on heart rate information including the heart rate by using the PPG sensor. For example, if the PPG sensor is used, various wavelengths of light may be radiated and received, so that it is possible to measure the blood saturation of percutaneous oxygen (SpO2), with a plurality of wavelengths of light signals. 
     If a plurality of sensors including the PPG sensor are used, upon measuring an ECG signal, the acceleration, PPG, and SpO2 may be measured as well. The blood pressure may be measured using the ECG and PPG signals, and sleep apnea may be measured using the acceleration and SpO2 signal. For example, the measurement value from the acceleration sensor may measure the change in the height of the chest during breathing and the user’s toss-and-turn. In particular, the SpO2 measurement value is a measurement of the blood oxygen concentration and sleep apnea may be detected by determining whether the SpO2 measurement value reduces. 
     The biometric signal detector  310  may include at least one light emitting unit (or light emitting element) and at least one light receiving unit (or light receiving element). The sensor including the at least one light emitting unit and the at least one light receiving unit may be referred to as a PPG sensor. 
     The biometric signal detector  310  may radiate a specific wavelength of light to the user’s body through the at least one light emitting unit The at least one light emitting unit may radiate light with a predetermined intensity to the user’s body. The wavelength of the radiated light may be varied depending on the object of the measurement or the type of the target component to be analyzed. The at least one light emitting unit may include a light emitting diode (LED) or a laser diode (LD). For example, the at least one light emitting unit may use various wavelength bands, such as green light, red light, blue light, or infrared light, to reduce influence of motion artifacts and may emit light in a manner to simultaneously turn on or alternate several wavelengths. 
     Further, the biometric signal detector  310  may detect the light reflected or transmitted from the user’s body corresponding to the radiated light, through the at least one light receiving unit. The biometric signal detector  310  may output the biometric signal corresponding to the light returning from the user’s body through the at least one light receiving unit. 
     The at least one light receiving unit of the biometric signal detector  310  may receive the light radiated and returning and generate at least one biometric information using the electrical signal into which the light has been converted. The signal may be a PPG signal. The at least one light receiving unit may include a photodiode (PD), a photo transistor, or a charge-coupled device (CCD). As long as it is an element capable of converting a light signal into an electrical signal, the type of the device may not be limited thereto. The structure of at least one light receiving unit may be a reflective-type or a transmissive-type. 
     The biometric signal detector  310  may receive the current corresponding to the measured PPG signal, convert the measured PPG signal into a digital signal, and transfer the digital signal to the processor  320 . The biometric signal detector  310  may perform current-voltage conversion for processing the PPG signal and, before transferring to the processor  320 , digitize the output analog voltage signal and transfer the result to the processor  320 . 
     Accordingly, the processor  320  may analyze the biometric signal based on the biometric signal from the biometric signal detector  310 . The processor  320  may be the processor  120  of  FIG.  1   . Or, the processor  320  may be a sensor processor implemented separately from the processor  120  of  FIG.  1   . For example, the processor  320  may measure an intravascular blood flow that is increased or decreased due to a heartbeat based on the biometric signal collected through at least one light receiving unit and may measure the user’s pulse wave based on the measured blood flow. For example, it is possible to obtain information about the user’s heart rate and monitor the health condition based on the received heart rate information. 
     Meanwhile, according to an embodiment, at least one light receiving unit of the biometric signal detector  310  may collect light and convert it into current. If external light is introduced, the signal including the external light together with the reflection light by the internal light source (which may also be referred to as light output (or scattered) from the body (or the skin of the body)) may be output. For example, when the signal output from the biometric signal detector  310  includes the external light signal, the external light calibration circuit  315  may perform a calibration operation for removing the external light signal to obtain only the biometric signal. 
     The external light calibration circuit  315  may extract or remove a the external light signal from the signal output from the biometric signal detector  310 . The external light calibration circuit  315  can then apply the current with the magnitude corresponding to the extracted external light signal to the input terminal of at least one light receiving unit. As a result, the external light calibration unit  315  removes the external light signal. 
     The external light calibration circuit  315  may use the on/off characteristics of at least one light emitting unit as a method for extracting only the external light signal from the signal output from the biometric signal detector  310 . 
     The processor  320  may remove the external light signal from the biometric signal with the external light calibration circuit  315 . 
     The processor  320  may be electrically connected with the external light calibration circuit  315  and the biometric signal detector  310  and control to radiate light to the user’s body (or the user’s skin) through the at least one light emitting unit of the biometric signal detector  310 . 
     The at least one light emitting unit can have a first period where the at least one light emitting unit radiates light and a second period where the at least one light emitting unit does not radiate light. In certain embodiments, the first period and second period can be repeated, such that a cycle includes the first period followed by the second period. 
     The processor  320  may detect the external light signal output through the at least one light receiving unit during a second period, using the external light calibration circuit  315 . Accordingly, when the at least one light emitting unit radiates light, the processor can remove the external light signal from the biometric signal provided by the at least one light receiving unit. The first period during which the light is radiated may be a period during which the at least one light emitting unit, e.g., an LED, is on, and the second period during which the light is not radiated may be a period during which the LED is off. 
     As described above, the signal detected during the period when the LED is off may be regarded as the external light signal since there would be no light reflected by the user’s skin. The signal applied at this time may be applied to the external light calibration circuit  315  to extract only the external light signal. The external light signal may be removed from the biometric signal detected during the period when the LED is on, based on the extracted external light signal. For example, during the LED-off period, the output terminal from the biometric signal detector  310  may be switched to connect to the input terminal of the external light calibration circuit  315  and, during the LED-on period, the output terminal from the biometric signal detector  310  may be switched to connect to the input terminal of the processor  320  (or the output terminal from the biometric signal detector  310  does not connect to the input terminal of the external light calibration circuit  315 ). According to an embodiment, during the LED-on period, the output signal (or calibrated biometric signal) from the biometric signal detector  310  may be converted into a digital signal and be transferred to the processor  320 . To that end, analog-digital (AD) conversion may be performed. 
     The light input at an LED off timing through at least one light receiving unit corresponds to external light, so that if only external light is selectively extracted by performing sampling only at the LED-off timing, it may be known how much external light signal is included in the biometric signal. Here, sampling during the LED-off timing represents an operation for storing the potential for the external light and may differ from sampling to convert the voltage signal into a digital signal. Accordingly, if as large a signal magnitude as the magnitude corresponding to the external light is subtracted, it is possible to obtain only the biometric signal by the internal light source, i.e., the at least one light emitting unit. 
     The external light calibration circuit  315  may perform the operation of removing external light every LED-off interval but, even at the LED-on timing, perform external light calibration operation in realtime (or continuously). 
     The external light calibration circuit  315  may extract the external light signal every LED-off timing and, every LED-on timing, perform the external light calibration operation (i.e., the operation of removing the external light signal/component from the biometric signal) using the external light signal extracted at the LED-off timing without extracting the external light signal. 
     The processor  320  may detect, predict, or analyze the user’s health condition based on the biometric signal from the biometric signal detector  310 . 
     The processor  320  may measure the heart rate using the PPG sensor of the biometric signal detector  310 . The heart rate is an observation of the number of pumps in the heart for one minute and be used to determine the health condition on ordinary days or exercise state. The processor  320  may determine the stress or tension level by using heart rate variability (HRV) based on the heart rate interval information. 
     As described above, the processor  320  may analyze the biometric signal and store it in the memory  330  to provide at least one piece of biometric information. Here, the at least one piece of biometric information may be information, such as heart rate, blood pressure, or sleep apnea. Such biometric information may be utilized as basic data for analyzing the user’s physical strength or health condition. 
     The processor  320  may obtain more complex and medical information through a combination with the user’s personal information or history information, artificial intelligence (AI), and bigdata. For example, medical information that may be fatal to the user, such as blood pressure, blood glucose, atrial fibrillation, and arrhythmia may also be measured. The information may be measured by a single PPG sensor or may be combined with another sensor or several additional pieces of information to be corrected into more accurate, reliable information. Further, the processor  320  may detect sleep and respiration and may also detect an abnormality, such as sleep apnea, or a gesture based on a change in blood flow according to a hand gesture. Various symptoms, such as blood pressure and sleep apnea, as well as simple heart checkup, may be measured by using various sensors together with the PPG sensor of the biometric signal detector  310 , thereby providing a complex health-care function. 
     According to certain embodiments, the processor  320  may provide a biometric signal in the form of the original signal, where noise, e.g., external light, has been removed, and provide high-accuracy biometric information based on the biometric signal. 
     The memory  330  may store data (e.g., biometric information) from the biometric signal processing device (or wearable electronic device)  301 . The memory  330  may be implemented in substantially the same or similar manner to the memory  130  described above in connection with  FIG.  1 A . The memory  330  may be implemented as a non-volatile memory. 
     According to certain embodiments, the display  360  may be implemented in substantially the same or similar manner to the display module  160  described in connection with  FIG.  1 A . The display  360  may receive at least one piece of biometric information from the processor  320  and visually display the same. For example, the display  360  may display a user interface based on the biometric signal measured upon executing an application for biometric signal measurement (e.g., an ECG application or a health-care application). The display  360  may output a guide screen or abnormal state upon measuring a biometric signal under the control of the processor  320 . 
       FIG.  4    is a view  400  illustrating an example of placement of a PPG sensor of a wearable electronic device according to certain embodiments.  FIG.  4    illustrates the front surface  401   a  and the rear surface  401   b  of the wearable electronic device  401  (e.g., the electronic device  101  of  FIG.  1 A , the electronic device  101   b  of  FIGS.  1 B to  1 D , or the biometric signal processing device  301  or wearable electronic device  301  of  FIG.  3   ). 
     As shown in  FIG.  4   , a PPG sensor includes at least one light emitting unit  410  and at least one light receiving unit  415 . The light emitting unit  410  and the light receiving unit  415  measure the optical biometric signal and may be disposed on the rear surface  401   b  of the wearable electronic device  401 . The at least one light receiving unit  415  may be disposed on the same surface as the at least one light emitting unit  410 . 
     As shown in  FIG.  4   , the at least one light emitting unit  410  may be positioned in the middle of the rear surface  401   b  and be constituted of a single element or a plurality of elements. The single element emits the same wavelength band of light. The plurality of elements can emit different wavelength bands of light. Further, although  FIG.  4    shows an example in which the at least one light emitting unit  410  is positioned in the middle, it may be disposed outside the light receiving unit  415  considering the positional relationship with the light receiving unit  415 . Alternatively, the light emitting unit  410  may be disposed in a position where the influence by the external light is as low as possible, e.g., as inside as possible, considering the situation in which sleep is disturbed in the middle of the night by the nature of the PPG sensor that performs monitoring 24 hours. 
     Meanwhile, in  FIG.  4   , the rear surface  401   b  where the PPG sensor is disposed may be a flat surface or may be formed in a dome shape which is curved to be brought in tight contact with the user’s skin (e.g., wrist). For example, since it is advantageous in performance measurement that the at least one light receiving unit  415  collects the light emitted from the at least one light emitting unit  410  as much as possible, more and broader light receiving units  415  may be advantageous.  FIG.  4    illustrates a case in which eight light receiving units  415  surround at least one light emitting unit  410  on the rear surface  401   b . 
     Meanwhile, more external light may be introduced when the light receiving units increase in number or area or when formed in a curved shape than flat. According to certain embodiments, since the external light may be removed, it is possible to diversify the design regardless of how much external light is introduced, thus expanding the design development range for wearable electronic devices. Further, although an example in which the rear surface  401   b  is flat or convex has been described in connection with  FIG.  4   , the shape may not be limited thereto. 
       FIG.  5    is a view illustrating a structure  500  of a PPG sensor according to certain embodiments. 
     Referring to  FIG.  5   , a plurality of sensors are included on the rear surface of a wearable electronic device (e.g., the biometric signal processing device  301  of  FIG.  3   ). Among the plurality of sensors is a PPG sensor, which is an optical sensor. The optical sensor may be used to measure PPG signals (or data). 
       FIG.  5    describes the rear surface  570  of the wearable electronic device  301  and the vertically cross-section  560  of the PPG sensor-side end of the wearable electronic device  301 . As shown in  FIG.  5   , a structure divided by a barrier rib  520  may be formed according to the position  515  of at least one light receiving unit of the PPG sensor of the wearable electronic device and the position  510  of at least one light emitting unit, and the barrier rib  520  structure may be used as a passage for measuring the PPG signal. 
     According to certain embodiments, other various sensors than the PPG sensor may be disposed on the rear surface of the wearable electronic device  301 . At least one electrode  505  may be included on the rear surface of the wearable electronic device  301 . Further, according to certain embodiments, at least one light emitting unit (e.g., LED) and at least one light receiving unit (e.g., PD) may be disposed in the main body (e.g., on the PCB) of the wearable electronic device  301 . On the rear surface  570  of the wearable electronic device  301 , a first position (e.g., light emitting unit position)  510  corresponding to at least one light emitting unit (e.g., LED) which is hidden and invisible and a second position (e.g., light receiving unit position)  515  corresponding to at least one light receiving unit (e.g., PD) may be marked. For example, in practice, the light emitting unit position  510  and the light receiving unit position  515  may be portions of the glass, and at least one light emitting unit and at least one light receiving unit may be formed inside the wearable electronic device of the light emitting unit position  510  and the light receiving unit position  515 . The glass may be colored in ink so that the at least one light emitting unit and at least one light receiving unit disposed in the wearable electronic device  301  are invisible. 
     The at least one light emitting unit may be disposed inside, in the position corresponding to the light emitting unit position  510 , and the at least one light receiving unit may be disposed inside, in the position corresponding to the light receiving unit position  515 . An opaque optical shield (or barrier rib)  520  may be formed to surround the side portion extending from the at least one light emitting unit and at least one light receiving unit to the surface exposed to the outside of the rear surface of the wearable electronic device  301  Such opaque optical shield may be referred to as a barrier rib. The barrier rib structure may have a structure that prevents the light emitted from the at least one light emitting unit from entering the at least one light receiving unit after being diffracted or reflected by the internal structure. The barrier rib structure may be not only a passage for guiding the light emission path of the at least one light emitting unit but also a passage for receiving the light reflected from the user’s skin. 
     According to certain embodiments, the wearable electronic device  301  may collect the PPG sensor through the middle hole divided by the barrier rib  520  while simultaneously measuring the ECG signal through at least one electrode  505 . According to certain embodiments, if measurement commences, the light from the at least one light emitting unit (LED)  510  may be oriented to the user’s body, e.g., the user’s skin  530 , and the reflected light may have a state modulated by the blood flow under the skin  530 . The reflected light may be collected ( 550 ) by at least one light receiving unit (PD)  515  via the passage formed by the barrier structure. 
       FIG.  6    is a view  600  illustrating an example of a biometric signal processing circuit for external light calibration in a wearable electronic device according to certain embodiments. 
       FIG.  6    illustrates a detailed structure of the biometric signal detector  310  and the external light calibration circuit  315  for biometric signal processing of  FIG.  3   . For ease of description, an example is described below in which the biometric signal processing device is a wearable electronic device. 
     The light emitting unit  610   b  has a first period when the light emitting unit  610   b  emits light, and a second period when the light emitting unit  610   b  does not emit light. In certain embodiments, the first period and second period can be repeating, thereby resulting in alternating periods of light, and no light. When the light emitting unit  610   b  does not emit light, the light receiving unit  610   a  receives only the external light  605   c . The light receiving unit  610   a  converts the external light  605   c  to an external light signal. The external light signal can be provided as an input to the external light calibration unit  615 . The external light calibration unit  615  provides an input to the light receiving unit  610   a  during a subsequent period when the light emitting unit  610   b  emits light. 
     When the light emitting unit  610   b  emits light, the light is reflected (reflected light  605   b ) by the user’s skin. However, the light receiving unit  610   a  receives both the reflected light  605   b , and external light  605   c . The light receiving unit  610   a  can use the input to provide an electronic signal that only corresponds to the light that is reflected. 
     A controller  640  controls a switch that connects the output of the light receiving unit  610   a  to the external light calibration circuit  615 , during the second period (when light is not emitted), but connects to and ADC  660  during the first period (light is emitted). 
     As shown in  FIG.  6   , the wearable electronic device  301  may include a PPG sensor  610 , an amplification circuit  650 , an external light calibration circuit  615 , and an analog-to-digital converter (ADC)  660 . The biometric signal detector  310  of  FIG.  3    may include the PPG sensor  610  and the amplification circuit  650 . The output from the biometric signal detector  310  may be converted into a digital signal through the ADC  660  before transferred to the processor  320  and be output to the processor  320 . In other words, the output from the ADC  660  may be input to the processor  320 . The ADC  660  may further be included in the biometric signal detector  310  so that the output from the biometric signal detector  310  is transferred to the processor  320  or be alternatively implemented separately between the biometric signal detector  310  and the processor  320 . 
     Meanwhile, as shown in  FIG.  6   , the PPG sensor  610  may include at least one light receiving unit  610   a  and at least one light emitting unit  610   b . Described below is an example in which the at least one light receiving unit  610   a  is a PPD, and the at least one light emitting unit  610   b  is an LED. 
     As shown in  FIG.  6   , the wearable electronic device  301  may further include a controller  640  to control the on/off operation of the at least one light emitting unit  610   b . Alternatively, the on/off operation of the at least one light emitting unit  610   b  may be controlled under the control of a processor (e.g., the processor  320  of  FIG.  3   ). At the on-time of the at least one light emitting unit  610   b , the output terminal of the amplification circuit  650  may be connected to the input terminal of the ADC  660  under the control of the controller  640  (or the output terminal of the amplification circuit  650  may not be connected to the input terminal of the external light calibration circuit  615 ). Accordingly, the reflected light  605   b  by the light  605   a  in the on state of the at least one light emitting unit  610   b  may be received through at least one light receiving unit  610   a , converted into a voltage through the amplification circuit  650 , and output to the ADC  660 . 
     The amplification circuit  650  may include a transimpedance amplifier (TIA). The amplification circuit  650  may convert the current signal corresponding to the reflected light output from the at least one light receiving unit  610   a  into a voltage signal. The current signal transferred to the amplification circuit  650  may be a current signal generated by an optical signal (e.g., reflected light  605   b ) input to the at least one light receiving unit  610   a . 
     Meanwhile, when light is received through the at least one light receiving unit  610   a  in the off state of the at least one light emitting unit  610   b , the light is not the reflected light  605   b  by the light radiated by the at least one light emitting unit  610   b  but may correspond to the external light  605   c . Accordingly, in the off state of the at least one light emitting unit  610   b , the current component output through the at least one light receiving unit  610   a  may correspond to external light, so that only the external light component may be extracted, and the external light calibration operation may be performed. 
     To that end, at the off time of the at least one light emitting unit  610   b , the output terminal of the amplification circuit  650  of the biometric signal detector  310  may be connected to the external light calibration circuit  615  under the control of the controller  640 . Accordingly, the component corresponding to the external light output through the at least one light receiving unit  610   a  may be input to the external light calibration circuit  615 , and the calibration operation may be performed to remove the component corresponding to the external light from the component output through the at least one light receiving unit  610   a . 
     As described above, the output terminal of the amplification circuit  650  of the biometric signal detector  310  may be connected to the input terminal of the ADC  660  or be selectively connected to the input terminal of the external light calibration circuit  615  according to the on/off time of the at least one light emitting unit  610   b . For example, the selective connection may be implemented in a switching manner. 
     The external light calibration circuit  615  may include a filter  665 , a proportion integral derivation (hereinafter ‘PID’) controller  670 , an inverter  675 , or a current pump  680 . 
     The external light calibration circuit  615  may be configured to have a feedback structure in which the output terminal of the external light calibration circuit  615  is connected to the input terminal of the at least one light receiving unit  610   a , playing a role to remove the current signal corresponding to the external light. The external light calibration circuit  615  may monitor changes in the output terminal of the amplification circuit  650 , e.g., changes in voltage and feed back to the input terminal of the at least one light receiving unit  610   a  according to the monitoring result, removing the current component corresponding to the external light signal from the light signal coming from the at least one light receiving unit  610   a . 
     The output terminal of the external light calibration circuit  615 , e.g., the output terminal of the current pump  680 , may be connected with the input terminal of the at least one light receiving unit  610   a . As described above, as the external light calibration circuit  615  is disposed with a feedback structure which includes the current pump  680  serving to remove the current signal corresponding to the external light at the input terminal of the at least one light receiving unit  610   a , realtime monitoring is possible, so that realtime calibration is possible. 
     For example, it is possible to initially remove the external light component through external light calibration so that no voltage change is made due to influence of the external light over time upon realtime biometric signal measurement. Here, when a voltage change is initially caused due to the external light, processing for obtaining the biometric signal may temporarily be not performed on the signal output through the amplification circuit  650  while external light calibration is performed. Such temporary period may be referred to as a blanking region. If some signals obtained in a certain initial period are disregarded, only biometric signals in the input dynamic range may be obtained although there is sudden introduction of external light, rendering it possible to stably obtain biometric signals. For example, as shown in  FIG.  2   , only the partial signal  240  corresponding to the blanking region is not processed, so that loss of biometric signal may be minimized, and biometric signals may stably be obtained. 
     As described above, when the current signal output from the at least one light receiving unit  610   a  is input to the amplification circuit  650  so that there is a voltage signal output through the amplification circuit  650  in the off period of the at least one light emitting unit  610   b  during the repeated on/off operation of the at least one light emitting unit  610   b , the external light calibration operation may be performed with the voltage signal regarded as the voltage signal corresponding to the external light. In this case, since the voltage output through the amplification circuit  650  is a voltage coming in the off period of the at least one light emitting unit  610   b  although the magnitude of the voltage falls within, e.g., the input dynamic range  220 , the external light calibration operation may be performed. As described above, the external light calibration operation may be performed by removing the current component in the at least one light receiving unit  610   a , which is generated while the at least one light emitting unit  610   b  emits no light. 
     In contrast, if the voltage signal output through the amplification circuit  650  falls outside the input dynamic range upon realtime monitoring, signals after falling outside the input dynamic range may not be measured and, thus, it is not known which biometric signal it is, causing performance deterioration upon biometric signal measurement. Thus, according to an embodiment, if the voltage signal output through the amplification circuit  650  upon realtime monitoring falls outside the input dynamic range, the external light calibration operation may be performed immediately regardless of whether the at least one light emitting unit  610   b  is in the off state. 
     To calibrate the external light in realtime, the wearable electronic device  301  may detect the external light component input together with the light component corresponding to the biometric signal and control to output only the biometric signal where the detected external light component has been removed. 
     To that end, the filter  665  of the external light calibration circuit  615  may be a filter for extracting the external light component. The filter  665  may perform filtering to extract the external light component every off period of the at least one light emitting unit  610   b . The filter  665  may include at least one frequency band filter to filter at least one frequency band different from the actual biometric signal band to extract the external light. For example, for high-frequency band external light, only the external light component may be extracted using a high pass filter (HPF) having a band different from the biometric signal band. According to an embodiment, when the external light has a specific frequency pattern, the filter  665  may include a frequency band filter capable of extracting the specific frequency pattern. 
     The PID controller  670  may serve as a component to quickly estimate variations in the input signal, reflect it to the signal input to the at least one light receiving unit  610   a  to actively deal with signal variations due to the actual external light input. 
     The PID controller  670  may be an analog processor for removing the external light output from the filter  665  and generate a control value for the current pump  680  to make the magnitude of the external light zero. For example, the control signal from the PID controller  670  may be a voltage generated based on the output from the filter  665 . 
     The inverter  675  may serve to operate the sink and source of the current pump  680  which is used to remove the DC component in the at least one light receiving unit  610   a , e.g., photodiode, in a floating state. Here, the floating state may mean that the operation direction of the current pump  680  is not towards the ground GND. For example, the at least one light receiving unit  610   a  is connected to the amplification circuit (TIA)  650 . Thus, to selectively adjust only the current of the at least one light receiving unit  610   a , a current source and sink are needed. As two current pumps  680  are operated with the current direction changed by the inverter  675  to supply the same magnitude of current in different directions, the at least one light receiving unit  610   a  may become the floating state. 
     The current pumps  680  may include a first current pump operating as the source and a second current pump operating as the sink. The current pumps may be connected to the output terminal and input terminal, respectively, of the inverter  675 , receive voltage signals from the output terminal and input terminal of the inverter  675 , and output the current corresponding to the applied voltage signal to the input terminal of the at least one light receiving unit  610   a . For example, when the input voltage of the inverter  675  is operated as the sink (or source), the output voltage of the inverter  675  may be connected with the input terminal of the current pump  680  to be the source (or sink). 
     The output terminal of the current pump  680  may be connected to the input terminal of the at least one light receiving unit  610   a , so that the current pump  680  may input current to the at least one light receiving unit  610   a , corresponding to the control signal, i.e., voltage signal, from the PID controller  670 . As such, as the above-described operation is repeated, the signal output from the at least one light receiving unit  610   a  may be a signal where as much current component as the external light signal output from the at least one light receiving unit  610   a  has been removed, and only the biometric signal may pass through the amplification circuit  650  to the ADC  660 , so that the biometric signal measurement may be obtained. According to an embodiment, use of such a feedback structure makes it possible to remove external light in realtime and thus measure only the reliable biometric signal. 
     The external light calibration circuit  615  may extract the external light signal using the filter  665  every off timing of the at least one light emitting unit  610   b  and perform the external light calibration operation (i.e., the operation of removing the external light signal/component from the biometric signal) through current input to the at least one light receiving unit  610   a  by the current pump  680 , based on the external light signal extracted at the off timing of the at least one light emitting unit  610   b , without extracting the external light signal every on timing of the at least one light emitting unit  610   b . For example, the filter  665  or the current pump  680  may be configured to maintain the output at the off timing of the at least one light emitting unit  610   b , even at the on timing of the at least one light emitting unit  610   b . 
     According to certain embodiments, a wearable electronic device  301  may comprise a biometric signal detector (e.g.,  310  of  FIG.  3   ) including at least one light receiving unit  610   a  and at least one light emitting unit  610   b , an external light calibration circuit  315 , and a processor (e.g.,  320  of  FIG.  3   ) electrically connected with the biometric signal detector and the external light calibration circuit. The processor  320  may be configured to radiate light to a user’s skin through the at least one light emitting unit  610   b , detect an external light signal output through the at least one light receiving unit  610   a  during a second period among a first period during which the light is radiated through the at least one light emitting unit  610   b  and the second period during which the light is not radiated and remove the external light signal from a biometric signal corresponding to light reflected from the user’s skin output through the at least one light receiving unit  610   a , using the external light calibration circuit  315 . 
     According to certain embodiments, the at least one light emitting unit  610   b  may include a light emitting diode (LED). The first period during which the light is radiated may be a period during which the LED is on, and the second period during which the light is not radiated may be a period during which the LED is off. 
     According to certain embodiments, the external light calibration circuit  315  may include a filter  665  configured to filter the external light signal, a proportional integral deviate (PID) controller  670  configured to generate a control signal for removing the external light signal output from the filter  665 , an inverter  675  configured to apply a voltage signal corresponding to the control signal, and a current pump  680  configured to apply a current signal corresponding to the voltage signal from the inverter to the at least one light receiving unit  610   a . 
     According to certain embodiments, the control signal for removing the external light signal may include a control signal for making a magnitude of the external light signal zero. 
     According to certain embodiments, the current pump  680  may include a first current pump  680   a  connected with an output terminal of the inverter  675  and a second current pump  680   b  connected to an input terminal of the inverter  675 . 
     According to certain embodiments, the external light calibration circuit  315  may be configured to detect the external light signal by sampling every second period during which the light is not radiated. 
     According to certain embodiments, the external light calibration circuit  315  may remove the external light signal every first period during which the light is radiated. 
     According to certain embodiments, the wearable electronic device  301  may further comprise an amplification circuit  650  configured to convert a current signal output from the at least one light receiving unit  610   a  into a voltage signal and an analog-to-digital converter (ADC)  660  configured to convert the voltage signal into a digital signal. 
     According to certain embodiments, an output terminal of the amplification circuit  650  may be selectively connected with an input terminal of the external light calibration circuit  315  or an input terminal of the ADC  660  based on a first period during which the light is radiated and a second period during which the light is not radiated. 
     According to certain embodiments, a voltage signal output from the amplification circuit  650  during the second period during which the light is not radiated may be input to the filter  665 . 
     According to certain embodiments, as a current by the current pump  680  is applied to the at least one light receiving unit  610   a , a voltage signal output from the amplification circuit  650  during the first period during which the light is radiated may be input to the ADC  660 . 
     According to certain embodiments, the voltage signal output from the amplification circuit  650  during the first period during which the light is radiated may include a signal where the external light signal is removed. 
       FIG.  7    describes the operation of the electronic device when the external light  730  changes. The light emitting unit repeats between a first period  715  for radiating light, and second period  720  for not radiating light. A sampling interval  705  includes a first period  715  and a second period  720 . 
     After each period when the light is radiates, t(1) ... t(n), the light is not radiated. When light is not radiated, light detected by the light receiving unit is used to remove a portion of the light that is detected during the subsequent period when light is emitted. That is, the light received by the light receiving unit after t(k) is used to remove light from the light that is detected during t(k+1). When the external light  730  changes during t(4), during  755 , the light receiving unit detects the changed external light. At t(5), the changed external light measured during  755  is used to remove external light. As a result, calibration occurs in real time, resulting in minimal data loss. 
       FIG.  7    is a view  700  illustrating a method for selectively extracting external light in a filter of an external light calibration circuit according to certain embodiments. 
     Referring to  FIG.  7   , when a sampling interval  705  includes the on time of the LED and the off time of the LED, the wearable electronic device  301  (e.g., the processor  320 ) may control the on/off operation of the LED to perform the operation of extracting and removing the external light in each sampling interval unit. As shown in  FIG.  7   , when the first LED on  710  time is t(1), the PPG signal and the external light signal  715  together enter the filter  665  during the t(1)  710  time, and the signal entering the filter  665  during the LED off time between t(1) and t(2) may be a signal  720  corresponding to external light. In other words, during the LED off time, only signals corresponding to the external light may be introduced. In this case, the signal entering the filter  665  may be a voltage signal converted into through the amplification circuit  650 . Accordingly, the processor  320  may selectively extract and obtain only the signal corresponding to the external light when signals are sampled every LED off time. Accordingly, the PID controller  670  may know the magnitude (or intensity) of the external light output from the filter  665 , so that although the PPG signal and the external light signal together are introduced, the magnitude of external light may be removed to leave only the PPG signal. 
     For example, when external light  730  with a high magnitude is introduced at t(4), the processor  320  may, at t(5), perform the calibration operation by subtracting the magnitude of the signal  755  corresponding to the external light between t(4) and t(5) from the signal at t(4). Further, the processor  320  may continuously perform the calibration operation every LED on timing, removing applied external light. For example, although a high magnitude of external light  730  is introduced after t(4), the processor  320  may continuously perform calibration as much as the external light  750  obtained in realtime every LED on timing, thus obtaining only the PPG signal  740  which is constantly introduced, without influence by noise, e.g., external light, and thus allowing for stable biometric measurement. 
       FIG.  8    is a flowchart  800  illustrating an operation for performing an external light calibration method in a wearable electronic device according to certain embodiments. Referring to  FIG.  8   , the operation method may include operations  801  to  803 . Each step/operation of the operation method of  FIG.  8    may be performed by at least one of a wearable electronic device (e.g., the electronic device  101  of  FIG.  1    or the biometric signal processing device  301  of  FIG.  3   ) or at least one processor (e.g., the processor  120  of  FIG.  1    or the processor  320  of  FIG.  3   ) of the wearable electronic device. 
     The wearable electronic device  301  (e.g., the processor  320 ) may start measuring a biometric signal. According to an embodiment, when a wearing of the wearable electronic device on the user’s body is detected, a signal of the detection may be determined to be an ‘input or request for measurement.’ For example, when the wearable electronic device is attached to the user’s body, if the signal input through at least one sensor included in the wearable electronic device is first received, the wearable electronic device may determine that the first signal is an ‘input or request for measurement.’ According to an embodiment, when its wearing is detected, the wearable electronic device  301  may switch to an operation mode for biometric signal measurement and start measurement. According to an embodiment, measurement of the biometric signal in the wearable electronic device  301  may be allowed to start and end by the user’s manipulation on the wearable electronic device  301  or an electronic device (e.g., smartphone) interworking with the wearable electronic device  301 . According to an embodiment, measurement may be allowed to start using the on/off function. 
     As described above, if biometric signal measurement starts, light may be radiated to the user’s skin through at least one light emitting unit. Accordingly, in operation  801 , the wearable electronic device  301  may detect the external light signal output through at least one light receiving unit during a second period among a first period during which light is radiated to the user’s body through the at least one light emitting unit and the second period during which the light is not radiated. The first period during which the light is radiated may be a period during which the light emitting unit is on, and the second period during which the light is not radiated may be a period during which the light emitting unit is off. 
     In operation  803 , the wearable electronic device  301  may remove the external light signal from the biometric signal corresponding to the light reflected from the user’s skin, output through the at least one light receiving unit. 
     According to certain embodiments, the external light calibration method may include filtering the external light signal, generating a control signal for removing the external light signal output through the filtering, applying a voltage signal corresponding to the control signal, and applying a current signal corresponding to the voltage signal to the at least one light receiving unit. 
     According to certain embodiments, detecting the external light signal may include detecting the external light signal by sampling every second period during which the light is not radiated. 
     According to certain embodiments, removing the external light signal may include removing the external light signal every first period during which the light is radiated. 
     According to certain embodiments, the external light calibration method may further include converting the current signal output from the at least one light receiving unit into a voltage signal and converting the voltage signal into a digital signal. 
     According to certain embodiments, as a current signal corresponding to the voltage signal is applied to the at least one light receiving unit, a current signal output from the at least one light receiving unit during a first period during which the light is radiated may include a signal where the external light signal is removed. 
       FIG.  9    is a view  900  illustrating a signal upon initial external light calibration according to certain embodiments. 
     The wearable electronic device  301  (e.g., the processor  320 ) may receive a biometric signal  910  using at least one light emitting unit  610   b  and at least one light receiving unit  610   a . 
     Referring to  FIG.  9   , the reflected light  605   b  by the light  605   a  radiated in the on state of the at least one light emitting unit  610   b  may be received through the at least one light receiving unit  610   a  and, at this time, external light  605   c  may be received together. For example, when the biometric signal  910  of the reflected light  605   b  by the light  605   a  radiated to the user’s body, along with the external light signal  905 , is introduced to the at least one light receiving unit  610   a , a signal  920  with current magnitude A may be output through the at least one light receiving unit  610   a  upon input  915  to the light receiving unit. In other words, a signal whose current magnitude has suddenly been increased by A may be output. Accordingly, the amplification circuit  650  may output a voltage signal  930  with magnitude V from the current signal with magnitude A, through voltage conversion and amplification  925 . 
     According to an embodiment, when a signal falling outside the input dynamic range is output from the amplification circuit  650  while the signal from the amplification circuit  650  is sampled in realtime every constant sampling interval, the processor  320  may perform the operation  935  of extracting the external light by the filter  665 , extracting the voltage signal with magnitude A. Here, the voltage signal with magnitude A may be a voltage signal extracted at the LED off timing. Alternatively, the voltage signal with magnitude A may be a voltage signal extracted by the filter  665  for extracting only external light with a band different from that of the biometric signal. 
     In proportion to the voltage signal output from the filter  665 , the PID controller  670  may generate ( 945 ) a PID signal for making the voltage signal zero. Accordingly, the current pump  680  may output the current signal  950  corresponding to the voltage signal by the PID controller  670  and be applied to the input terminal of the at least one light receiving unit  610   a . 
     Here, the processor  320  may temporarily stop processing for obtaining the biometric signal on the signal output through the amplification circuit  650  while the external light calibration operation is performed as a voltage change is initially caused due to external light. Accordingly, the signal output through the amplification circuit  650  is not transferred to the ADC  660  not to be used as a biometric signal measurement and may be treated as loss. Since the blanking region where it is treated as loss corresponds to a very small region, it may have no influence on the biometric signal measurement. 
     The external light calibration operation is performed with the above-described feedback structure, which is described in detail with reference to  FIG.  10   . 
       FIG.  10    is a view  1000  illustrating a signal after external light calibration according to certain embodiments. 
     As shown in  FIG.  10   , when external light is first detected upon realtime biometric signal measurement, the wearable electronic device  301  (e.g., the processor  320 ) may remove the external light component through the external light calibration operation from the next sampling period so that no voltage change due to external light influence occurs over time. The operation  1010  of at least one light receiving unit  610   a  and the current pump  680  for removing the external light component is described below. 
     For example, although the signal of the reflected light  605   b  by the light  605   a  radiated to the user’s body, together with the external light signal  1005 , is introduced to the at least one light receiving unit  610   a , the current signal  1050  from the current pump  680  is applied to the input terminal of the at least one light receiving unit  610   a , so that a signal  1080  offset as much as the external light may be output. As such, in the case of an input change  1060  in the at least one light receiving unit  610   a , a signal whose current magnitude is increased by, e.g., A, in response to sudden introduction of the external light temporarily appears and then only a signal corresponding to the biometric signal  1080  where it has been removed may be input to the amplification circuit  650 . 
     As described above, the processor  320  may disregard some signal  1070  obtained in a certain initial period and, in such a case, although there is sudden external light input, it is possible to obtain only the biometric signal  1080  within the input dynamic range, rendering it possible to stably obtain the biometric signal. 
       FIG.  11    is a detailed circuit diagram  1100  for external light calibration according to certain embodiments. 
     As shown in  FIG.  11   , the first current pump  680   a  operating as the source and the second current pump  680   b  operating as the sink may apply current to the photodiode  610   a  in response to the control signal of the PID controller  670 . The amplification circuit  650  may include a differential amplification circuit and, when the output signal of the amplification circuit  650  includes the external light signal and the biometric signal both, filter only the external light signal using the filter  665 . If only the external light signal is extracted using the filter  665 , the PID controller  670  may output a control signal (or voltage signal) for making the input corresponding to the external light signal zero through the inverter  675 . 
       FIG.  12    is a view  1200  illustrating comparison the respective outputs of the components (e.g., the current pumps  680   a  and  680   b , the photodiode  610   a , and the inverter  675 ) after external light calibration according to certain embodiments. 
     As shown in  FIG.  12   , when the current generated from the photodiode  610   a  is IG1  1220 , if AM2  1210  and AM3  1215  which are output currents of the current pumps  680   a  and  680   b  for removing the current generated from the photodiode  610   a  in response to VM2  1225  which is the input current of the inverter  675  are applied, it may be seen that, for AM1  1205  indicating the current input to TIA which is the amplification circuit  650 , a mere temporary blanking region occurs every sampling period, and AM1  1205  with a constant magnitude is output. 
     As shown in  FIG.  12   , despite a sudden DC variation in IG1  1220 , e.g., although it is varied with a large width, such as 0-&gt;2-&gt;0..., AM1  1205  corresponding to the calibrated result may be output with a constant magnitude as the DC component is calibrated. In this case, it may be seen that a signal, i.e., AM2  1210 , which is opposite to IG1  1220  which is the current generated from the photodiode  610   a  is applied to the external light calibration circuit  615  for calibration. As described above, it may be identified that for an abrupt external light condition, e.g., a step input of IG1  1220 , the calibration circuit (AM2  1210  or AM3  1215 ) is quickly operated to output AM1  1205  and is thus not influenced by the DC value of IG1  1220 . 
     Here, it may be seen that temporary noise  1250  is caused in AM1  1205  which is the result of calibration for sudden application of the external light, and this may be noise generated when the PID controller  670  is operated. The noise region may be referred to as a blanking region, which is described in detail with reference to  FIG.  13   . 
       FIG.  13    is a view  1300  illustrating comparison between the respective outputs of components upon initial external light calibration according to certain embodiments. In particular,  FIG.  13    is an example enlarged view of the region  1250  instantaneously caused by the PID controller  670  at the time of application of the external light of  FIG.  12   . 
     As shown in  FIG.  13   , it may be seen that if the region  1250  of  FIG.  12    is enlarged, an oscillation  1350  is generated. The generation period and magnitude of the oscillation  1350  may be finely tuned by changing the value of the element constituting the PID controller  670 .  FIG.  13    shows an example of one option to allow the PID controller  670  to operate as over damping to quickly adjust to the baseline. The value of the element constituting the PID controller  670  may be modified to further shorten the region of oscillation  1350 , and data loss may be minimized by decreasing the region of the oscillation  1350 . As described above, according to certain embodiments, it is possible to quickly remove noise through analog signal processing through realtime feedback structure. Thus, internal computation for discretely adjusting the DC current is not required, and it is needless to adjust the intensity of the internal light source to reduce influence of external light. Thus, SNR may be maintained. 
     According to certain embodiments, a wearable electronic device, comprises: at least one light receiving unit; at least one light emitting unit; an external light calibration circuit; and a processor electrically connected with the at least one light receiving unit, at least one light emitting unit, and the external light calibration circuit, wherein the processor is configured to: control the at least one light emitting unit to radiate light during first periods, and not emit light during second periods, and detect light through the at least one light receiving unit during the second periods, and controlling the external light calibration circuit to provide an input to the at least one light receiving unit during first periods, based on the light detected during the second periods; and wherein during the first periods the at least one light receiving unit provides an output based on light received, and the input from the external light calibration circuit. 
     According to certain embodiments, the at least one light emitting unit includes a light emitting diode (LED), and during the first periods the LED is on, and during the second periods the LED is off. 
     According the certain embodiments, the external light calibration circuit includes: a filter configured to filter a light signal corresponding to detected light, thereby resulting in a filtered light signal; a proportional integral deviate (PID) controller configured to generate a control signal for removing the filtered light signal output from the filter; an inverter configured to apply a voltage signal corresponding to the control signal; and a current pump configured to apply a current signal corresponding to the voltage signal from the inverter to the at least one light receiving unit. 
     According to certain embodiments, the control signal for removing the filtered light signal includes a control signal for making a magnitude of the filtered light signal zero. 
     According to certain embodiments, the current pump includes a first current pump connected with an output terminal of the inverter and a second current pump connected to an input terminal of the inverter. 
     According to certain embodiments, the external light calibration circuit is configured receive the light signal by sampling every second period. 
     According to certain embodiments, the wearable electronic device further comprises: an amplification circuit configured to convert a current signal output from the at least one light receiving unit into a voltage signal; and an analog-to-digital converter (ADC) configured to convert the voltage signal into a digital signal. 
     According to certain embodiments, an output terminal of the amplification circuit is selectively connected with an input terminal of the external light calibration circuit or an input terminal of the ADC based on the first periods or second periods, and wherein a voltage signal output from the amplification circuit during the second periods is not radiated is input to the filter. 
     According to certain embodiments, a current by the current pump is applied to the at least one light receiving unit, a voltage signal output from the amplification circuit during the first periods is input to the ADC, and wherein the voltage signal output from the amplification circuit during the first periods includes a signal where a portion of the signal corresponding to external light is removed. 
     According to certain embodiments, the at least one light receiving unit comprises a photodiode. 
     According to certain embodiments, a method for calibrating external light for biometric signal measurement in a wearable electronic device, comprises: radiating light with at least one light emitting unit during first periods and not radiating light during second periods; detecting a light signal output by at least one light receiving unit during the second periods; and providing an input to the at least one light receiving unit during the first periods by an external light calibration circuit, wherein the input is based on the detected light signal; provides an output during the first periods based on light received and the input by the at least one light emitting unit. 
     According to certain embodiments, the at least one light emitting unit includes a light emitting diode (LED), and wherein during the first periods the LED is on, and during the second periods the LED is off. 
     According to certain embodiments, providing the input comprises: filtering the light signal, thereby resulting in a filtered light signal; generating a control signal for removing the filtered light signal; applying a voltage signal corresponding to the control signal with an inverter; and applying a current signal corresponding to the voltage signal to the at least one light receiving unit with a current pump. 
     According to certain embodiments, the control signal for removing the filtered light signal includes a control signal for making a magnitude of the filtered light signal zero. 
     According to certain embodiments, the current pump includes a first current pump connected with an output terminal of the inverter and a second current pump connected to an input terminal of the inverter. 
     According to certain embodiments, detecting the light signal includes detecting the light signal by sampling every second period. 
     According to certain embodiments, the method further comprises converting a current signal output from the at least one light receiving unit into a voltage signal with an amplifier; and converting the voltage signal into a digital signal with an analog-to-digital converter (ADC). 
     According to certain embodiments, the method further comprises: connecting an output terminal of the amplifier to an input terminal of the ADC during first periods; and connecting the output terminal of the amplifier to an input terminal of the external light calibration circuit during second periods. 
     According to certain embodiments, as a current signal corresponding to the voltage signal is applied to the at least one light receiving unit, a current signal output from the at least one light receiving unit during a first period includes a signal where a portion of the signal corresponding to external light signal is removed. 
     According to certain embodiments, the at least one light receiving unit comprises a photodiode. 
     The electronic device according to certain embodiments may be one of various types of electronic devices. The electronic devices may include, for example, a portable communication device (e.g., a smartphone), a computer device, a portable multimedia device, a portable medical device, a camera, a wearable device, or a home appliance. According to an embodiment of the disclosure, the electronic devices are not limited to those described above. 
     It should be appreciated that certain embodiments of the present disclosure and the terms used therein are not intended to limit the technological features set forth herein to particular embodiments and include various changes, equivalents, or replacements for a corresponding embodiment. With regard to the description of the drawings, similar reference numerals may be used to refer to similar or related elements. It is to be understood that a singular form of a noun corresponding to an item may include one or more of the things, unless the relevant context clearly indicates otherwise. As used herein, each of such phrases as “A or B,” “at least one of A and B,” “at least one of A or B,” “A, B, or C,” “at least one of A, B, and C,” and “at least one of A, B, or C,” may include all possible combinations of the items enumerated together in a corresponding one of the phrases. As used herein, such terms as “1st” and “2nd,” or “first” and “second” may be used to simply distinguish a corresponding component from another, and does not limit the components in other aspect (e.g., importance or order). It is to be understood that if an element (e.g., a first element) is referred to, with or without the term “operatively” or “communicatively”, as “coupled with,” “coupled to,” “connected with,” or “connected to” another element (e.g., a second element), it means that the element may be coupled with the other element directly (e.g., wiredly), wirelessly, or via a third element. 
     As used herein, the term “module” may include a unit implemented in hardware, software, or firmware, and may interchangeably be used with other terms, for example, “logic,” “logic block,” “part,” or “circuitry”. A module may be a single integral component, or a minimum unit or part thereof, adapted to perform one or more functions. For example, The module may be implemented in a form of an application-specific integrated circuit (ASIC). 
     Certain embodiments as set forth herein may be implemented as software (e.g., the program  140 ) including one or more instructions that are stored in a storage medium (e.g., internal memory  136  or external memory  138 ) that is readable by a machine (e.g., the electronic device  101 ). For example, a processor (e.g., the processor  120 ) of the machine (e.g., the electronic device  101 ) may invoke at least one of the one or more instructions stored in the storage medium, and execute it, with or without using one or more other components under the control of the processor. This allows the machine to be operated to perform at least one function according to the at least one instruction invoked. The one or more instructions may include a code generated by a complier or a code executable by an interpreter. The machine-readable storage medium may be provided in the form of a non-transitory storage medium. Wherein, the term “non-transitory” simply means that the storage medium is a tangible device, and does not include a signal (e.g., an electromagnetic wave), but this term does not differentiate between where data is semi-permanently stored in the storage medium and where the data is temporarily stored in the storage medium. 
     According to an embodiment, a method according to certain embodiments of the disclosure may be included and provided in a computer program product. The computer program products may be traded as commodities between sellers and buyers. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read only memory (CD-ROM)), or be distributed (e.g., downloaded or uploaded) online via an application store (e.g., Play StoreTM), or between two user devices (e.g., smart phones) directly. If distributed online, at least part of the computer program product may be temporarily generated or at least temporarily stored in the machine-readable storage medium, such as memory of the manufacturer’s server, a server of the application store, or a relay server. 
     According to certain embodiments, each component (e.g., a module or a program) of the above-described components may include a single entity or multiple entities. Some of the plurality of entities may be separately disposed in different components. According to certain embodiments, one or more of the above-described components may be omitted, or one or more other components may be added. Alternatively or additionally, a plurality of components (e.g., modules or programs) may be integrated into a single component. In such a case, according to certain embodiments, the integrated component may still perform one or more functions of each of the plurality of components in the same or similar manner as they are performed by a corresponding one of the plurality of components before the integration. According to certain embodiments, operations performed by the module, the program, or another component may be carried out sequentially, in parallel, repeatedly, or heuristically, or one or more of the operations may be executed in a different order or omitted, or one or more other operations may be added. 
     There may be provided a storage medium storing instructions configured to, when executed by at least one processor, enable the at least one processor to perform at least one operation which may comprise radiating light to a user’s skin through at least one light emitting unit, detecting an external light signal output through at least one light receiving unit during a second period among a first period during which the light is radiated through the at least one light emitting unit and the second period during which the light is not radiated, and removing the external light signal from a biometric signal corresponding to light reflected from the user’s skin output through the at least one light receiving unit. 
     The embodiments herein are provided merely for better understanding of the present invention, and the present invention should not be limited thereto or thereby. It should be appreciated by one of ordinary skill in the art that various changes in form or detail may be made to the embodiments without departing from the scope of the present invention defined by the following claims.