Patent Publication Number: US-11658749-B2

Title: Sensor device and mobile device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to Korean Patent Application No. 10-2021-0015316, filed on Feb. 3, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Embodiments relate to a sensor device and a mobile device including the same. 
     2. Description of the Related Art 
     Recently, a sensor device such as a biosensor, capable of collecting biometric information to provide useful services to users, tends to be mounted in wearable devices as well as mobile devices. A sensor device for collecting biometric information may include photodiodes generating electrical charges in response to light, and may perform signal processing on electrical charges, generated by the photodiodes, to determine biometric information. 
     SUMMARY 
     Embodiments are directed to a sensor device, including: a sensor array including a plurality of photodiodes configured to generate current signals in response to light; an encoder configured to encode the current signals to generate a plurality of analog signals and output the plurality of analog signals sequentially; a signal processing module configured to process the analog signals, received from the encoder, to generate digital signals; and a decoder configured to decode the digital signals, received from the signal processing module, to generate a plurality of data signals corresponding to the current signals. 
     Embodiments are also directed to a sensor device, including: a plurality of photodiodes configured to generate current signals in response to light; an encoder connected to the photodiodes through a plurality of analog channels, including a multiplier and an adder operating based on a predetermined orthogonal code, and configured to sequentially output a plurality of analog signals, obtained by encoding the current signals, to a single input channel; a signal processing module including an input terminal connected to the input channel and configured to successively output a plurality of digital signals corresponding to the analog signals, to an output terminal; a decoder connected to the output terminal and configured to output a plurality of data signals, obtained by decoding the digital signals according to an inverse matrix of an orthogonal matrix corresponding to the orthogonal code, to a plurality of digital channels; and a processor configured to generate information corresponding to the current signals using the data signals. 
     Embodiments are also directed to a mobile device including: a substrate; a plurality of photodiodes mounted on the substrate and configured to generate current signals in response to light incident from an object; a signal processing device mounted on the substrate and configured to convert the current signals into a plurality of data signals; and a processor configured to obtain biometric information using the data signals. The signal processing device is configured to convert a plurality of analog signals, generated using the current signals received through a plurality of input channels, into a plurality of digital signals sequentially, and generate the data signals using the digital signals. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Features will become apparent to those of skill in the art by describing in detail example embodiments with reference to the attached drawings in which: 
         FIGS.  1  and  2    are schematic diagrams of mobile devices according to example embodiments, respectively. 
         FIG.  3    is a schematic diagram of a sensor device according to an example embodiment. 
         FIG.  4    is a diagram illustrating an operation of a sensor device according to an example embodiment. 
         FIG.  5    is a schematic diagram of a sensor device according to an example embodiment. 
         FIG.  6    is a schematic block diagram of a mobile device according to an example embodiment. 
         FIG.  7    is a schematic block diagram of a sensor device according to an example embodiment. 
         FIG.  8    is a schematic diagram of a signal processing module included in a sensor device according to an example embodiment. 
         FIG.  9    is a schematic diagram of a sensor device according to an example embodiment. 
         FIG.  10    is a timing diagram illustrating an operation of a sensor device according to an example embodiment. 
         FIGS.  11 A and  11 B  are diagrams illustrating an operation of a sensor device according to an example embodiment. 
         FIGS.  12 A and  12 B  are diagrams illustrating an operation of a sensor device according to an example embodiment. 
         FIG.  13    is a graph illustrating an operation of a sensor device according to an example embodiment. 
         FIG.  14    is a schematic diagram of a sensor device according to an example embodiment. 
         FIGS.  15  to  17    are diagrams illustrating a comparative example of a sensor device. 
         FIG.  18    is a schematic block diagram of a mobile device according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1  and  2    are schematic diagrams of mobile devices according to example embodiments, respectively. 
     Referring to  FIG.  1   , a mobile device  10  may be implemented as a watch-type wearable device. The mobile device  10  may include a housing or main body  11  and a strap  12  to fix the mobile device  10  to a user&#39;s body such as a wrist, and the like. A display, outputting a display image, may be provided on a front surface of the main body  11 . Various application images, including time information, received message information, and the like, may be displayed on the display. According to an example embodiment, at least one of the front and side surfaces of the main body  11  may be provided with an input device  13  for receiving and processing a user input. The input device  13  may include a mechanical button or key, a touch panel, or the like. 
     A sensor device  14  may be disposed on a rear surface of the main body  11  facing the user&#39;s body. The sensor device  14  may include a light source emitting light to a user&#39;s body (such as a user wrist, to which the main body  11  may be fixed by the strap  12 ), at least one photodiode generating a current signal in response to light reflected from the user (e.g., the user&#39;s wrist), a signal processing module for processing the current signal, and the like. As an example, the mobile device  10  may determine biometric information, such as user heart rate, blood oxygen saturation, blood pressure, and the like, using a data signal output by the sensor device  14 . 
     Referring to  FIG.  2   , a mobile device  20  may also be implemented as an ear-wearable device. The mobile device  20  may include an ear strap  21  or other fixed portion fixed to a user&#39;s body, and the user may hang the ear strap  21  on an auricle to wear the mobile device  20 . In the state in which the user wears the mobile device  20 , a main body of the mobile device  20  may be inserted into a user&#39;s external auditory meatus. 
     A sensor device may be mounted on the main body or the ear strap  21  of the mobile device  20 . As an example, the sensor device may be provided on the ear strap  21  in contact with a user&#39;s skin to output light to the user&#39;s body and to detect light reflected from the user&#39;s body to output a digital signal. The mobile device  20  may determine user&#39;s biometric information using the digital signal, and may provide various applications using the biometric information. 
       FIG.  3    is a schematic diagram of a sensor device according to an example embodiment. 
     Referring to  FIG.  3   , a sensor device  30  according to an example embodiment may operate in a form proximate to a user&#39;s body  40 , and may include a light emitting unit  31  and a sensor array  32 . The sensor array  32  may include a plurality of sensing elements  33 . As an example, each of the plurality of sensing elements may include a photodiode. As an example, the sensor device  30  may be a multi-channel optical sensor including a plurality of photodiodes, and may be a photoplethysmography (PPG) sensor or a spectrometer. 
     Referring to  FIG.  3   , the light emitting unit  31  may emit light toward the user&#39;s body  40 . The light emitting unit  31  may include at least one light source. According to an example embodiment, the light source may emit light of a specific wavelength band. For example, a wavelength band of light emitted by the light source may vary depending on biometric information to be determined using the sensor device  30 . 
     For example, when a heart rate is intended to be determined from the user&#39;s body  40 , a light source outputting light of a green wavelength band may be included in the light emitting unit  31 . In another example, when blood oxygen saturation is intended to be determined from the user&#39;s body  40 , light sources outputting portions of light of a red wavelength band and an infrared wavelength band may be included in the light emitting unit  31 . A plurality of light sources, emitting portions of light of different wavelength bands, may constitute the light emitting unit  31 . The light emitting unit  31  may operate at least one of the plurality of light sources based on biometric information to be determined, and may obtain a signal from the sensor array  32 . 
     In an example embodiment, the sensor array  32  may include a plurality of sensing elements  33  arranged in a matrix form. However, the arrangement form of the sensing elements  33  may vary according to an example embodiment. Each of the sensing elements  33  may include a photodiode which may generate a current signal in response to light. A signal processing module, included in the sensor device  30 , may process a current signal to generate a digital signal. A processor of a mobile device, in which the sensor device  30  is mounted, may determine biometric information using the digital signal. 
       FIG.  4    is a diagram illustrating an operation of a sensor device according to an example embodiment. 
     Referring to  FIG.  4   , a sensor array  50  of a sensor device according to an example embodiment may include a filter layer  51  and a photodiode layer  52 . The filter layer  51  may include a plurality of color filters, and the photodiode layer  52  may include a plurality of photodiodes. 
     Light, emitted by a light emitting unit and reflected from a user&#39;s body, e.g., a blood vessel  41  in the user&#39;s body (see  FIG.  3   ), may appear in all wavelength bands as illustrated in a first graph  60  of  FIG.  4   . However, as described above, light of a specific wavelength band may be selectively used depending on type of biometric information to be determined using a sensor device. To this end, the sensor array  50  may include a filter layer  51 . The filter layer  51  may allow light of a specific wavelength band to selectively pass therethrough and may transmit the light to the photodiode layer  52 , as illustrated in a second graph  70 . Thus, the sensor device including the sensor array  50  according to an example embodiment illustrated in  FIG.  4    may operate as a multi-wavelength PPG sensor. 
     Accordingly, sensitivity of the sensor device may be improved, light sources emitting portions of light of all wavelength bands may constitute a light emitting unit, and light of a required wavelength band may be selectively incident on a photodiode through the filter layer  51  to implement a sensor device which may determine various types of biometric information with a single light source. To this end, at least some of a plurality of color filters may allow portions of light of different wavelength bands to pass therethrough. 
     As an example, among the plurality of color filters, a first color filter  51 A may allow only light of a green wavelength band to pass therethrough. The first color filter  51 A may have a structure in which an infrared cutoff filter and a green color filter, allowing only light of a green wavelength band to pass therethrough, are stacked. Accordingly, among portions of light emitted from the light sources of the light emitting unit and reflected from a blood vessel, only the light of the green wavelength band may be incident on the first photodiode  52 A below the first color filter  51 A. The processor of the mobile device, in which the sensor device is mounted, may determine user&#39;s heart rate and pulse rate using a current signal output from the first photodiode  52 A. 
     Among the plurality of color filters, a second color filter  51 B may allow only light of a red wavelength band to pass therethrough, and a third color filter  51 C may allow only light of an infrared wavelength band to pass therethrough. Therefore, among the portions of light emitted from the light source of the light emitting unit and reflected from the blood vessel, the light of the red wavelength band may be incident on the second photodiode  52 B below the second color filter  51 B, and the light of the infrared wavelength band may be incident on the lower third photodiode  52 C below the third color filter  51 C. The processor of the mobile device, in which the sensor device is mounted, may determine user&#39;s blood oxygen saturation using current signals output from the second photodiode  52 B and the third photodiode  52 C. 
     In order for a single sensor device to determine various types of biometric information, the sensor array  50  may include a filter layer  51  and a photodiode layer  52 , as described with reference to  FIG.  4   . Photodiodes included in the photodiode layer  52  may be connected to a signal processing module, for processing a current signal, through a plurality of channels such that a current signal output by the sensor array  50  according to an example embodiment may be processed to determine desired biometric information. The signal processing module may be configured to independently process a current signal, received through a plurality of channels, to generate a digital signal. However, in this case, an area occupied by the signal processing module and power consumption of the signal processing module may be increased. 
     In an example embodiment, a sensor device may process current signals, generated by the sensor array  50 , with one signal processing module. A sensor device according to an example embodiment may include an encoder, connected between an input terminal of a signal processing module and the sensor array  50 , and a decoder connected to an output terminal of the signal processing module. The encoder may encode current signals, received through a plurality of channels, to generate analog signals, and may sequentially input the analog signals to the signal processing module. When the signal processing module sequentially processes analog signals to output digital signals, the decoder may generate data signals corresponding to the plurality of channels using the digital signals. Accordingly, the current signals received through the plurality of channels may be processed with a single signal processing module, and an area and power consumption of the sensor device may be reduced. In addition, an influence of noise generated in a process, in which the signal processing module converts a current signal into a data signal, may be reduced. This and other aspects of example embodiments are described in further detail below. 
       FIG.  5    is a schematic diagram of a sensor device according to an example embodiment. 
     Referring to  FIG.  5   , a sensor device  100  according to an example embodiment may include a substrate  101 , a light source  110  mounted on a first surface of the substrate  101 , a plurality of photodiodes  120  mounted on the first surface together with the light source  110 , a signal processing device  130 , and the like. According to an example embodiment, the signal processing device  130  may be mounted on a second surface, facing away from the first surface, of the substrate  101 . The substrate  101  may include a connector  140 . A processor of a mobile device, in which the sensor device  100  is mounted, and the sensor device  100  may be electrically connected to each other through the connector  140 . 
     Referring to  FIG.  5   , the photodiodes  120  may be disposed to be distributed around the light source  110 . However, this is only an example embodiment, and the number and location of the photodiodes  120  may vary. As described above, a color filter allowing light of a specific wavelength band to selectively pass therethrough may be further disposed above the photodiodes  120 . 
     Referring to  FIG.  5   , the sensor device  100  may include four photodiodes  120 , and the signal processing device  130  may receive current signals from the photodiodes  120  through four channels. 
     According to the present example embodiment, the signal processing device  130  may include an encoder receiving the current signals through the four channels, a signal processing module processing analog signals output by the encoder to output digital signals, a decoder restoring data signals corresponding to four channels using the digital signals output by the signal processing module, and the like. 
       FIG.  6    is a schematic block diagram of a mobile device according to an example embodiment. 
     Referring to  FIG.  6   , a mobile device  200  according to an example embodiment may include a sensor device  210  and a processor  220 . The processor  220  may be a semiconductor device controlling all operations of the mobile device  200 , and may determine information related to an object OBJ using a digital signal output by the sensor device  210 . As an example, when an object OBJ is a human body, the processor may determine information such as heart rate, blood oxygen saturation, blood pressure, and the like, and may execute various applications based on the information. 
     The sensor device  210  may include a light source  211 , a light source driver  212 , a sensor array  213 , a signal processing device  214 , and the like. 
     The light source  211  may emit light toward the object OBJ in response to a light control signal output from the light source driver  212 . As an example, the light control signal output to the light source  211  by the light source driver  212  may be a pulse width modulation (PWM) signal. Accordingly, the light source  211  may be repeatedly turned on and off while the sensor device  210  is enabled to operate. 
     The sensor array  213  may include a plurality of photodiodes PD. According to an example embodiment, the sensor array  213  may further include a color filter allowing light of a predetermined wavelength band to be selectively incident on the photodiodes PD. The photodiodes PD may generate current signals in response to light emitted by the light source  211  and reflected from the object OBJ. According to an example embodiment, the light source  211  may be omitted. In this case, the photodiodes PD may generate current signals in response to light incident from the object OBJ, or the like. 
     The signal processing device  214  may convert current signals into digital signals and may output the digital signal to the processor  220 . Since the light source  211  may be repeatedly turned on and off at a predetermined frequency while the sensor device  210  is enabled to operate, the signal processing device  214  may be synchronized with the light source driver  212  to obtain current signals from the photodiodes PD for a time for which the light source  211  is turned on. The signal processing device  214  may include an encoder receiving the current signals from the photodiodes PD of the sensor array  213  through respective channels, a signal processing module processing analog signals output by the encoder to output digital signals, a decoder restoring data signals corresponding to respective channels using the digital signals output by the signal processing module, and the like. 
       FIG.  7    is a schematic block diagram of a sensor device according to an example embodiment. 
     Referring to  FIG.  7   , a sensor device  300  according to an example embodiment may include a plurality of photodiodes PD 1  to PD 4 , a signal processing module  310 , an encoder  320 , a decoder  330 , and the like. 
     The photodiodes PD 1  to PD 4  may generate current signals I 1  to I 4  in response to external incident light. As an example, the photodiodes PD 1  to PD 4  may have incident thereon light that is emitted from an additional light source to generate the current signals I 1  to I 4  in response to light reflected from an object, and the object may be a part of a user&#39;s body. The current signals I 1  to I 4  may be input to the encoder  320  through a plurality of analog channels ACH 1  to ACH 4 . 
     The encoder  320  may be connected to the photodiodes PD 1  to PD 4  through the analog channels ACH 1  to ACH 4 , and may be connected to an input terminal of the signal processing module  310  through a single input channel ICH. The encoder  320  may encode current signals I 1  to I 4  to generate analog signals, and may sequentially input the analog signals to the signal processing module  310  through an input channel ICH. Accordingly, the signal processing module  310  may sequentially receive the analog signals through the input channel ICH. Each of the analog signals, encoded by the encoder  320 , may be a signal including the current signals I 1  to I 4  and may be a signal obtained by encoding the current signals I 1  to I 4  based on a predetermined orthogonal code. 
     The signal processing module  310  may process the sequentially input analog signals to generate digital signals. As an example, the encoder  320  may generate four analog signals using the four current signals I 1  to I 4 , and the signal processing module  310  may convert the four analog signals into a digital domain to output four digital signals. The signal processing module  310  may sequentially output the four digital signals to the decoder  330  through a single output channel OCH connected to the output terminal. 
     The decoder  330  may generate data signals DATA 1  to DATA 4  using digital signals. The data signals DATA 1  to DATA 4  may be output through the plurality of digital channels DCH 1  to DCH 4 , respectively. Each of the data signals DATA 1  to DATA 4  may be obtained by converting each of the current signals I 1  to I 4  into a digital domain. For example, the first data signal DATA 1  may be obtained by converting the first current signal I 1  into a digital domain, and the second data signal DATA 2  may obtained by converting the second current signal I 2  into a digital domain. 
     The decoder  330  may generate the data signals DATA 1  to DATA 4  based on an orthogonal code used when the encoder  320  encodes the current signals I 1  to I 4  to generate the analog signals. As an example, the decoder  330  may restore the data signals DATA 1  to DATA 4  from digital signals using an inverse matrix of an orthogonal matrix corresponding to the orthogonal code. 
     The signal processing module  310  may be an analog-front end (AFE) module. The signal processing module  310  may include a current-to-voltage converter converting analog signals generated from the current signals I 1  to I 4  into a voltage, an amplifier amplifying analog signals, an analog-to-digital converter (ADC), and the like. Hereinafter, the signal processing module  310  will be described in more detail with reference to  FIG.  8   . 
       FIG.  8    is a schematic diagram of a signal processing module included in a sensor device according to an example embodiment. 
     Referring to  FIG.  8   , the signal processing module  310  according to an example embodiment may include a current-to-voltage converter  311 , an amplifier  312 , an analog-to-digital converter  313 , and the like. The current-to-voltage converter  311  may be a circuit converting analog signals, sequentially received through the input channel ICH, into a voltage and may include, e.g., an operational amplifier, a feedback resistor, and the like. A voltage signal output by the current-to-voltage converter  311  may be transmitted to the amplifier  312 , and the amplifier  312  may include a programmable gain amplifier. 
     The analog-to-digital converter  313  may convert the voltage signal, output by the amplifier  312 , into a digital domain to generate a digital signal, and may output the digital signal through the output channel OCH. In an operation of the signal processing module  310 , analog signals may be sequentially input by an encoder connected to an input terminal of the signal processing module  310 , and the analog-to-digital converter  313  may sequentially output digital signals corresponding to the analog signals. 
       FIG.  9    is a schematic diagram of a sensor device according to an example embodiment. 
     Referring to  FIG.  9   , a sensor device  400  according to an example embodiment may include a signal processing module  410 , an encoder  420 , a decoder  430 , and the like. The encoder  420  may be connected to a plurality of photodiodes PD 1  to PD 4 , and may encode current signals I 1  to I 4  to generate analog signals AIN. The analog signals AIN may be sequentially input to the signal processing module  410 . 
     The signal processing module  410  may digitally convert analog signals AIN to generate digital signals DOUT. The digital signals DOUT may be input to the decoder  430 , and the decoder  430  may generate data signals DATA 1  to DATA 4  using the digital signals DOUT. As an example, the data signals DATA 1  to DATA 4  may correspond to current signals I 1  to I 4  generated by the photodiodes PD 1  to PD 4 , respectively. 
     In the example embodiment illustrated in  FIG.  9   , the encoder  420  may include a plurality of multipliers  421  to  424  and an adder  425 . The multipliers  421  to  424  may respectively receive encoding coefficients ENC 1  to ENC 4 , and may output signals obtained by multiplying the current signals I 1  to I 4  by the encoding coefficients ENC 1  to ENC 4 . The encoding coefficients ENC 1  to ENC 4  may not be zero. The adder  425  may sum the multiplied signals (i.e., the signals resulting from the multiplication of the encoding coefficients ENC 1  to ENC 4  with the current signals I 1  to I 4 ) to generate the analog signals AIN. 
     The encoding coefficients ENC 1  to ENC 4  may be determined by an orthogonal code used when the encoder  420  encodes the current signals I 1  to I 4  to generate the analog signals AIN. As an example, values of the encoding coefficients ENC 1  to ENC 4  may be changed while the plurality of photodiodes PD 1  to PD 4  output the current signals I 1  to I 4 . When the number of the photodiodes PD 1  to PD 4  is four, the encoder  420  may divide output time of the current signals I 1  to I 4  into four unit times (the unit times may have a duration corresponding to a time in which the signal processing module converts each of the analog signals into a digital domain), and at least one of the encoding coefficients ENC 1  to ENC 4  may be set to different values in the unit times (the encoding coefficients ENC 1  to ENC 4  and an operation of the encoder  420  depending thereon will be described below with reference to  FIG.  10   ). 
     Still referring to  FIG.  9   , the decoder  430  may include a plurality of multipliers  431  to  434  and a plurality of accumulators  435  to  438 . For example, one of the multipliers  431  to  434  and one of the accumulators  435  to  438  may be assigned to each of the digital channels outputting the data signals DATA 1  to DATA 4 . 
     The multipliers  431  to  434  may respectively receive decoding coefficients DEC 1  to DEC 4 , and may multiply each of the sequentially output digital signals DOUT by the decoding coefficients DEC 1  to DEC 4 . The accumulators  435  to  438  may sequentially accumulate and sum the digital signals DOUT, obtained by multiplying the decoding coefficients DEC 1  to DEC 4 , to generate data signals DATA 1  to DATA 4 . 
     The decoding coefficients DEC 1  to DEC 4  may be determined by an inverse matrix of an orthogonal code used by the encoder  420 . In an example embodiment, an absolute value of each of the decoding coefficients DEC 1  to DEC 4  may be smaller than an absolute value of each of the encoding coefficients ENC 1  to ENC 4 . 
     Hereinafter, an example operation of the sensor device  400  will be described in detail with reference to  FIGS.  10 ,  11 A, and  11 B . 
       FIG.  10    is a timing diagram illustrating an operation of a sensor device according to an example embodiment, and  FIGS.  11 A and  11 B  are diagrams illustrating an operation of a sensor device according to an example embodiment. 
     Referring to  FIG.  10   , the photodiodes PD 1  to PD 4  may output current signals I 1  to I 4  during a light emitting time TON during which a light source is turned on by a light control signal. The sensor device  400  may divide the light emitting time TON into a plurality of unit times T 1  to T 4 , and the encoder  420  may adjust the encoding coefficients ENC 1  to ENC 4  at each of the unit times T 1  to T 4  to generate analog signals AIN. 
     As an example, during the first unit time T 1 , the encoding coefficients ENC 1  to ENC 4  may be determined as [+1, −1, −1, −1]. Thus, during the first unit time T 1 , a first analog signal AIN 1  input to the signal processing module  410  may be determined as [I 1 −I 2 −I 3 −I 4 ]. During the next second unit time T 2 , the encoding coefficients ENC 1  to ENC 4  may be determined as [− 1 , +1, −1, −1], and thus the signal processing module  410  may receive a second analog signal AIN 2  defined as [−I 1 +I 2 −I 3 −I 4 ]. Similarly, during the third unit time T 3 , a third analog signal AIN 3  input to the signal processing module  410  may be represented by [−I 1 −I 2 +I 3 −I 4 ], and a fourth analog signal AIN 4  input to the signal processing module  410  may be represented by [−I 1 −I 2 −I 3 +I 4 ]. 
     The signal processing module  410  may sequentially convert the first to fourth analog signals AIN 1  to AIN 4  to digital domains to output first to fourth digital signals DOUT 1  to DOUT 4 . Output timings of the first to fourth digital signals DOUT 1  to DOUT 4  may be determined as illustrated in  FIG.  10    by time required for the signal processing module  410  to convert each of the first to fourth analog signals AIN 1  to AIN 4  into a digital domain. A delay time (i.e., a difference between an input time of the first to fourth analog signals AIN 1  to AIN 4  and an output time of the first to fourth digital signals DOUT 1  to DOUT 4 ) may vary depending on the configuration of the signal processing module  410 . 
     The encoding code, used when the encoder  420  encode the current signals I 1  to I 4  to generate the analog signals AIN, may be a code generated based on an orthogonal code and may be represented by an orthogonal matrix, e.g., an N-by-N matrix where N is a number of photodiodes (where N is a positive integer of 2 or more). As an example, in the example embodiment described with reference to  FIG.  10   , the encoding code may be represented by Equation 1 below. Rows of the encoding code may respectively correspond to unit times T 1  to T 4 , and columns may respectively correspond to encoding coefficients ENC 1  to ENC 4 . As illustrated in Equation 1, the encoding coefficients ENC 1  to ENC 4  may not be zero. 
     
       
         
           
             
               
                 
                   
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     Additionally, the decoding coefficients DEC 1  to DEC 4 , used by the decoder  430  to restore the data signals DATA 1  to DATA 4  from the digital signals DOUT, may be determined by a decoding code represented by an inverse matrix of an orthogonal matrix. As an example, a decoding code corresponding to the encoding code expressed in Equation 1 may be represented by Equation 2 below. In the decoding code, columns may correspond to decoding coefficients DEC 1  to DEC 4 , respectively. As illustrated in Equations 1 and 2, an absolute value of each of the decoding coefficients DEC 1  to DEC 4  may be smaller than an absolute value of each of the encoding coefficients ENC 1  to ENC 4 . 
     
       
         
           
             
               
                 
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                                 + 
                                 1 
                               
                             
                           
                         
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                   Equation 
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                   2 
                 
               
             
           
         
       
     
     Hereinafter, operations of the encoder  420  and the decoder  430  will be described in more detail with reference to  FIGS.  11 A and  11 B . 
       FIG.  11 A  is a diagram for describing an operation of the encoder  420 . 
     Referring to  FIG.  11 A , current signals I 1  to I 4  generated by photodiodes PD 1  to PD 4  may be represented by a matrix, and first to fourth analog signals AIN 1  to AIN 4  may be generated as a result of an operation of an encoding code on the current signals I 1  to I 4 . 
     For example, the first to fourth analog signals AIN 1  to AIN 4  may be sequentially input to the signal processing module  410 , and the signal processing module  410  may digitally convert each of the first to fourth analog signals AIN 1  to AIN 4  to sequentially output first to fourth digital signals DOUT 1  to DOUT 4 . Correspondingly, noise may be generated during the operation in which the signal processing module  410  digitally converts the first to fourth analog signals AIN 1 . Accordingly, each of the first to fourth digital signals DOUT 1  to DOUT 4  may include a predetermined noise component V N  (in  FIG.  11 A , the first to fourth digital signals DOUT 1  to DOUT 4  are illustrated as including noise components V N  having the same size, but at least some of the signals DOUT 1  to DOUT 4  may include noise components VN having different sizes). 
       FIG.  11 B  is a diagram for describing an operation of the decoder  430 . 
     Referring to  FIG.  11 B , the operation of the decoder  430  may be represented by a decoding code. While the signal processing module  410  outputs the first digital signal DOUT 1 , digital coefficients DEC 1  to DEC 4  may be defined as [+¼, −¼, −¼, −¼]. Thus, +¼*DOUT 1  may be input to the first accumulator  435 , and −¼*DOUT 1  may be input to each of the second to fourth accumulators  436  to  438 . Next, while the signal processing module  410  outputs the second digital signal DOUT 2 , the digital coefficients DEC 1  to DEC 4  may be determined as [−¼, +¼, −¼, −¼], and thus +¼*DOUT 2  may be input to the second accumulator  436 , and −¼*DOUT 2  may be input to each of the first, third, and fourth accumulators  435 ,  437 , and  438 . While the signal processing module  410  outputs the third digital signal DOUT 3 , the digital coefficients DEC 1  to DEC 4  may be determined as [−¼, −¼, +¼, −¼], and thus +¼*DOUT 3  may be input to the third accumulator  437 , and −¼*DOUT 3  may be input to each of the first, second, and fourth accumulators  435 ,  436 , and  438 . Finally, while the signal processing module  410  outputs the fourth digital signal DOUT 4 , the digital coefficients DEC 1  to DEC 4  may be determined as [−¼, −¼, −¼, +¼], and thus +¼*DOUT 4  may be input to the fourth accumulator  438 , and −¼*DOUT 4  may be input to each of the first to third accumulators  435  to  437 . 
     As described above, after the signal processing module  410  outputs to the fourth digital signal DOUT 4 , signals that are accumulated and summed in each of the accumulators  435  to  438  may be represented by Equation 3 below.
 
1 st  Accumulator=¼*(DOUT1−DOUT2−DOUT3−DOUT4)
 
2 nd  Accumulator=¼*(−DOUT1+DOUT2−DOUT3−DOUT4)
 
3 rd  Accumulator=¼*(−DOUT1−DOUT2+DOUT3−DOUT4)
 
4 th  Accumulator=¼*(−DOUT1−DOUT2−DOUT3+DOUT4)  Equation 3
 
     The digital signals DOUT 1  to DOUT 4 , output from the signal processing module  410 , may include the noise component V N  and may be defined as described above with reference to  FIG.  11 A . When the digital signals DOUT 1  to DOUT 4  described with reference to  FIG.  11 A  are applied to Equation 3, the data signals DATA 1  to DATA 4  output from the accumulators  435  to  438  may be defined as illustrated in  FIG.  11 B . I can. In other words, each of the data signals DATA 1  to DATA 4  may include data, obtained by converting each of the current signals I 1  to I 4  into a digital domain, and a noise component 0.5V N  that is averaged to be reduced by the operation of the decoder  430 . 
     In an example embodiment, the encoder  420  and the decoder  430  may be respectively connected to an input terminal and an output terminal of the signal processing module  410 , and the encoder  420  may input the current signals I 1  to I 4 , received through a plurality of analog channels, to the signal processing module  410 . The signal processing module  410  may convert analog signals AIN into digital signals DOUT, and then may sequentially output the digital signals DOUT to the decoder  430 . In this case, a predetermined noise component V N  may be reflected in each of the digital signals DOUT. The noise component V N  may be canceled and/or reduced while the decoder  430  restores the data signals DATA 1  to DATA 4  corresponding to the current signals I 1  to I 4  using the digital signals DOUT. Accordingly, the sensor device  400  may be implemented having improved signal-to-noise ratio (SNR) characteristics. 
     The configurations of the encoding code and the decoding code for the operations of the encoder  420  and the decoder  430  are not limited to those described with reference to  FIGS.  10 ,  11 A, and  11 B . The encoding coefficients ENC 1  to ENC 4  and the decoding coefficients DEC 1  to DEC 4 , respectively defining the encoding code and the decoding code, may be freely selected under conditions satisfying the characteristics of an orthogonal code. A size of a matrix, representing the encoding code and the decoding code, may be determined depending on a number of sensing elements, e.g., a number of photodiodes PD connected to the signal processing module  410 . 
       FIGS.  12 A and  12 B  are diagrams illustrating an operation of a sensor device according to an example embodiment. 
     Referring to  FIGS.  12 A and  12 B , a sensor device may include eight sensing components. Therefore, as illustrated in  FIG.  12 A , an encoding code may be represented by an 8-by-8 matrix. In the embodiment illustrated in  FIG.  12 A , all diagonal components of the encoding code may be +1, and all other components may be −1. However, this is only an example embodiment, and components of the encoding code may vary under conditions satisfying characteristics of the orthogonal code. 
     The sensor device may divide a light emitting time, during which a light source emits light, into eight unit times T 1  to T 8 . At least some of encoding coefficients ENC 1  to ENC 8  may have different values in each of the unit times T 1  to T 8 , and a signal processing module may sequentially receive eight analog signals AIN 1  to AIN 8  generated by the encoder during the emission time. 
       FIG.  12 B  is a diagram for describing an operation of a decoder. 
     Referring to  FIG.  12 B , a decoding code may be an inverse matrix of the encoding code, and may be represented by an 8-by-8 matrix. Digital signals DOUT 1  to DOUT 8 , respectively obtained by digitally converting analog signals AIN 1  to AIN 8  by the signal processing module, may be restored to data signals DATA 1  to DATA 8  by the decoding code. As an example, each of the data signals DATA 1  to DATA 8  may include data, obtained by converting each of the current signals I 1  to I 8  into a digital domain, and a noise component 0.75V N  averaged to be reduced by the decoder. 
     Accordingly, noise characteristic of the sensor device may be improved, as compared with the case in which the encoder and the decoder are not applied. In addition, a single signal processing module may process current signals output from a plurality of sensing elements, so that the degree of integration of the sensor device may be increased and power consumption may be reduced. 
       FIG.  13    is a graph illustrating an operation of a sensor device according to an example embodiment. 
     Referring to  FIG.  13   , as the number of photodiodes included in a sensor device increases, a signal-to-noise ratio (SNR) of the sensor device may increase. For example, an SNR when a current signal generated by four photodiodes is used (96 dB) may be improved by about 6 dB, as compared with an SNR when a signal processing module generates a data signal using a current signal generated by a single photodiode (90 dB). In addition, when a data signal is generated using a current signal generated by eight photodiodes, an SNR (99 dB) may be improved by about 9 dB relative to the single photodiode (90 dB). As a result, the SNR may be improved and performance of the sensor device may be improved by increasing the number of photodiodes emitting light and generating a current signal in response to light reflected from a user&#39;s body or the like. 
     However, as the number of photodiodes increases, the number of channels connecting the signal processing module and the photodiodes may also increase, and power consumption of the signal processing module and a circuit area occupied by the signal processing module may increase. In an example embodiment, this issue may be addressed by respectively connecting an encoder and a decoder to an input terminal and an output terminal of a signal processing module. Then, current signals, generated by photodiodes, may be sequentially input to a signal processing module after being encoded into analog signals by an encoder, and the signal processing module may sequentially output digital signals. The decoder may restore data signals using the sequentially output digital signals. Accordingly, only one signal processing module may process current signals of photodiodes connected to a plurality of channels, so that power consumption and circuit area of the sensor device may be reduced and manufacturing costs of the sensor device may be reduced. 
     In another example embodiment, the sensor device may include two or more signal processing modules. For example, when N photodiodes are connected through N channels, the N photodiode may be divided by half and then N/2 photodiodes may be distributed and connected to each of the two signal processing modules. In this case, the number of photodiodes connected to each of the signal processing modules and the number of current signals to be processed by each of the signal processing modules accordingly may be decreased to improve an operation speed of the sensor device. 
       FIG.  14    is a schematic diagram of a sensor device according to an example embodiment. 
     In the example embodiment illustrated in  FIG.  14   , a sensor device  500  may include a plurality of photodiodes PD 1  to PD 4 , a signal processing module  510 , an encoder  520 , a decoder  530 , and the like. As described above, the number of photodiodes PD 1  to PD 4  may vary. 
     The encoder  520  may include a plurality of pairs of switches SW 1  and SW 2 , e.g., a positive switch and a negative switch, respectively. Each of the photodiodes PD 1  to PD 4  may be connected to one of the pairs of switches SW 1  and SW 2 . 
     Activation, e.g., a turn-on/off, of the pair of switches SW 1  and SW 2  may be determined by encoding coefficients ENC 1  to ENC 4 . 
     As an example, the pair of switches SW 1  and SW 2  may not both be turned on at the same time. For example, when the first switch SW 1  of the pair of switches SW 1  and SW 2  is turned on, the second switch SW 2  may be turned off. Meanwhile, when the second switch SW 2  is turned on, the first switch SW 1  may be turned off. 
     Referring to  FIG.  14   , the signal processing module  510  may receive analog signals in a differential signal manner through a positive input terminal  511  and a negative input terminal  512 . The first switch SW 1  may be connected to the positive input terminal  511 , and the second switch SW 2  may be connected to the negative input terminal  512 . 
     The operation of the encoder  520  may be similar to that described with reference to  FIGS.  10  and  11 A . For example, the first switch SW 1  connected to the first photodiode PD 1  may be turned on by the first encoding coefficient ENC 1  for a first unit time, and the second switch SW 2  connected to the second to fourth photodiodes PD 2  to PD 4  by the second to fourth encoding coefficients ENC 2  to ENC 4  may be turned on. Accordingly, the analog signal AIN input to the signal processing module  510  for the first unit time may be defined as [I 1 −I 2 −I 3 −I 4 ]. Similarly, for the second unit time, the second switch SW 2  connected to the second photodiode PD 2  may be turned on, and the first switch SW 1  connected to the first, third, and fourth photodiodes PD 1 , PD 3 , and PD 4  may be turned on. Accordingly, the encoder  520  may operate in a similar manner as described with reference to  FIGS.  10  and  11 A . The operation of the decoder  530  may also be similar to the operation described with reference to  FIG.  11 B . 
       FIGS.  15  to  17    are diagrams illustrating a comparative example of a sensor device. 
     Referring to  FIG.  15   , in a sensor device  600  according to a comparative example, a signal processing module  610  may convert an analog signal AIN into a digital signal DOUT. A plurality of photodiodes PD 1  to PD 4  may be connected to an input terminal of the signal processing module  610  through a plurality of switches SW 1  to SW 4 . 
       FIG.  16    is a timing diagram for describing an operation of the sensor device  600 . 
     Referring to  FIG.  16   , first to fourth switches SW 1  to SW 4  may be sequentially turned on at first to fourth timings T 1  to T 4 , respectively. Accordingly, the first to fourth current signals I 1  to I 4  may be sequentially input to the signal processing module  610 , and the signal processing module  610  may sequentially output digital signals DOUT 1  to DOUT 4  corresponding to the first to fourth current signals I 1  to I 4 . 
     The operation of the sensor device  600  may be represented as a matrix illustrated in  FIG.  17   . 
     Referring to  FIG.  17   , the operations of the first to fourth switches SW 1  to SW 4  during the first to fourth timings T 1  to T 4  may be represented by a matrix in which all diagonal components are 1 and the other components are 0. During the first timing T 1 , only the first switch SW 1  may be turned on to input the first current signal I 1  to the signal processing module  610 , and the signal processing module  610  may digitally convert the first current signal I 1  to generate a first digital signal DOUT 1 . Operations, similar to the above operations, may be performed in each of the second to fourth timings T 2  to T 4 . 
     Accordingly, a noise component V N  generated in the operation of the signal processing module  610  may be reflected in the first to fourth digital signals DOUT 1  to DOUT 4  as it is. In the comparative example (in which an encoder and a decoder are not connected to an input terminal and an output terminal of the signal processing module  610 , unlike the above-described example embodiments), it is not expected that the noise component V N  generated in the operation of the signal processing module  610  will be averaged to be reduced. Relative to the comparative example, referring to  FIGS.  11 A and  11 B  illustrating an example embodiment including four photodiodes PD 1  to PD 4 , the noise component V N  may be averaged by a decoder to be reduced by half as compared with the comparative example. Accordingly, a sensor device having an improved signal-to-noise ratio (SNR) and improved noise characteristics may be implemented according to example embodiments. 
       FIG.  18    is a schematic block diagram of a mobile device according to an example embodiment. 
     Referring to  FIG.  18   , a mobile device  1000  may include a camera  1100 , a display  1200 , an audio processing unit  1300 , a modem  1400 , DRAMs  1500   a  and  1500   b , flash memory devices  1600   a  and  1600   b , input/output (I/O) devices  1700   a  and  1700   b , a sensor device  1800 , and an application processor (hereinafter referred to as “AP”)  1900 . 
     The mobile device  1000  may be implemented as, e.g., a laptop computer, a portable terminal, a smartphone, a tablet personal computer (table PC), a wearable device, a healthcare device, or an Internet-of-Things (IoT) device. Also, the mobile device  1000  may be implemented as a server or a PC. 
     Various components included in the mobile device  1000  may operate in synchronization with a predetermined clock. For example, the display  1200  may display an image according to a predetermined scanning rate, and the DRAMs  1500   a  and  1500   b  and the flash memory devices  1600   a  and  1600   b  may store and read data at a predetermined speed or may operate according to a predetermined clock to exchange the data with external other devices. The I/O devices  1700   a  and  1700   b  and the application processor  1900  may also operate according to the predetermined clock. 
     The camera  1100  may capture a still image or a video under the user&#39;s control. The mobile device  1000  may obtain specific information using a still image/video captured by the camera  1100 , or may convert and store the still image/video into other types of data such as text. The camera  1100  may include a plurality of cameras having different fields of view, stop values, or the like. The camera  1100  may further include a camera generating a depth image using depth information of a subject and/or a background, in addition to a camera imaging the subject to generate an actual image. 
     The display  1200  may provide a touchscreen function to be used as an input device of the mobile device  1000 . In addition, the display  1200  may be integrated with a fingerprint sensor, or the like, to provide a security function of the mobile device  1000 . The audio processing unit  1300  may process audio data, stored in the flash memory devices  1600   a  and  1600   b , or audio data included in contents received from an external device through the modem  1400  or the I/O devices  1700   a  and  1700   b.    
     The modem  1400  may modulate a signal and transmit the modulated signal to transmit and receive wired/wireless data, and may demodulate an externally received signal to restore an original signal. The I/O devices  1700   a  and  1700   b  may provide digital input and output, and may include an input device, such as a port connectable to an external recording medium, a touchscreen, or a mechanical button key, and an output device, capable of outputting a vibration in a haptic manner. 
     The sensor device  1800  may include a plurality of sensors collecting various types of external information. In an example embodiment, the sensor device  1800  may include an illuminance sensor detecting brightness of light, a gyro sensor detecting a movement of the mobile device  1000 , a multi-channel optical sensor for obtaining biometric information from a user&#39;s body in contact with and/or proximate to the mobile device  1000 , or the like. As an example, the multi-channel optical sensor may include a photoplethysmography (PPG) sensor and/or a spectrometer. The multi-channel optical sensor, included in the sensor device  1800 , may include a light source, a sensor array, and a signal processing module processing a signal generated by the sensor array. As an example, the multi-channel optical sensor may be implemented according to the example embodiments described above with reference to  FIGS.  3  to  14   . 
     The AP  1900  may measure biometric information on a user&#39;s body, e.g., a pulse rate, a heart rate, blood oxygen saturation, a blood pressure, and the like, using data signals output by the multi-channel optical sensor, and may execute applications based on the biometric information. 
     The AP  1900  may control all operations of the mobile device  1000 . For example, the AP  1900  may control the display  1200  to display a portion of the contents, stored in the flash memory devices  1600   a  and  1600   b , on the screen. In addition, when receiving a user input through the I/O devices  1700   a  and  1700   b , the AP  1900  may perform a control operation corresponding to the user input. 
     In an example embodiment, the AP  1900  may include an accelerator block  1920 . According to another example embodiment, a separate accelerator chip may be provided separate from the AP  1900 , and a DRAM  1500   b  may be additionally connected to the accelerator block  1920  or an accelerator chip. The accelerator block  1920  may be a functional block specialized in performing specific functions of the AP  1900 , and may include a graphics processing unit (GPU) serving as a functional block specialized in processing graphics data, a neural processing unit (NPU) serving as a functional block specialized in performing AI computation and interference, a data processing unit (DPU) serving as a functional block specialized in transmitting data, or the like. 
     As described above, in an example embodiment, current signals output by a plurality of photodiodes may be encoded and then input to a single signal processing module, and a signal output by the signal processing module may be decoded to generate data signals corresponding to the current signals. Accordingly, noise reflected in a data signal in a process of converting the current signal into the data signal may be reduced to improve noise characteristics such as a signal-to-noise ratio (SNR). 
     As described above, example embodiments may provide a sensor device and a mobile device including the same which may improve noise characteristics. Example embodiments may encode current signals generated by a plurality of photodiodes, process the current signals by a single signal processing module, and decode an output of the signal processing module into data signals corresponding to the current signals. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.