Optical plethysmography sensor and semiconductor device comprising the same

Abstract

A photoplethysmography sensor is provided. The photoplethysmography sensor includes a photoelectric conversion element including a first terminal and a second terminal, and configured to receive light reflected from a blood vessel and generate a current corresponding to the received light; a current-voltage converter configured to receive the generated current through a first input terminal and a second input terminal, and configured to generate an output voltage corresponding to the received current; and a switch configured to connect the photoelectric conversion element to the current-voltage converter according to a control signal, wherein, in response to the control signal of a first level, the switch connects the first terminal of the photoelectric conversion element to the first input terminal of the current-voltage converter and connects the second terminal of the photoelectric conversion element to the second input terminal of the current-voltage converter, and wherein, in response to the control signal of a second level different from the first level, the switch connects the first terminal of the photoelectric conversion element to the second input terminal of the current-voltage converter and connects the second terminal of the photoelectric conversion element to the first input terminal of the current-voltage converter.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0085492, filed on July 10, 2020, with the Korean Intellectual Property Office, and all rights arising from that patent application, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to photoplethysmography (PPG) sensors and semiconductor devices including PPG sensors. Background Technology

[0004] A pulse wave sensor is a sensor that measures the photoplethysmography signal (hereinafter referred to as the PPG signal or pulse wave signal) from an object by using light pulses.

[0005] When sensing a pulse wave signal, noise (such as external light interference, sound, vibration, or motion) can be simultaneously input to the sensor input unit along with the pulse wave signal. If the noise component is significantly larger than the pulse wave signal, the measurement sensitivity may degrade. Therefore, more efficient methods for removing this noise are needed. Summary of the Invention

[0006] This disclosure provides a photoplethysmography sensor capable of efficiently removing noise when measuring pulse wave signals.

[0007] This disclosure also provides a semiconductor device capable of efficiently removing noise when measuring pulse wave signals.

[0008] According to some aspects of the present invention, a photoplethysmography sensor is provided, comprising: a photoelectric conversion element including a first terminal and a second terminal, and configured to receive light reflected from a blood vessel and generate a current corresponding to the received light; a current-to-voltage converter configured to receive the generated current through the first input terminal and the second input terminal, and configured to generate an output voltage corresponding to the received current; and a switch configured to connect the photoelectric conversion element to the current-to-voltage converter according to a control signal, wherein, in response to a control signal of a first level, the switch connects the first terminal of the photoelectric conversion element to a first input terminal of the current-to-voltage converter and connects a second terminal of the photoelectric conversion element to a second input terminal of the current-to-voltage converter, and wherein, in response to a control signal of a second level different from the first level, the switch connects the first terminal of the photoelectric conversion element to the second input terminal of the current-to-voltage converter and connects the second terminal of the photoelectric conversion element to the first input terminal of the current-to-voltage converter.

[0009] According to some aspects of the inventive concepts, there is provided a semiconductor device including: a light source configured to output light during a first time section and configured to not output light during a second time section after the first time section; and a detector configured to receive light output from the light source and reflected from a blood vessel and configured to generate a first output voltage corresponding to the light received during the first time section and the second time section, wherein the detector includes a photoelectric conversion element configured to generate a charge corresponding to the received light, and a storage unit configured to store the generated charge and generate the output voltage, and wherein an amount of the charge in the storage unit increases corresponding to the charge generated by the photoelectric conversion element during the first time section and decreases corresponding to the charge generated by the photoelectric conversion element during the second time section.

[0010] According to some aspects of the inventive concepts, there is provided a semiconductor device including: a light source configured to output light according to a first control signal having a first period and to modulate and output the light according to a second control signal having a second period shorter than the first period; a photoelectric conversion element configured to receive light output from the light source and reflected from a blood vessel and to generate a current corresponding to the received light; a current-voltage converter configured to generate an output voltage corresponding to the current generated from the photoelectric conversion element; and a switch configured to perform a first connection between the photoelectric conversion element and the current-voltage converter in response to the second control signal of a first level and to perform a second connection different from the first connection between the photoelectric conversion element and the current-voltage converter in response to the second control signal of a second level different from the first level.

[0011] However, aspects of the present disclosure are not limited to those set forth herein. The above and other aspects of the present disclosure will become more apparent by reference to the following detailed description of the present disclosure given for describing some example embodiments thereof. BRIEF DESCRIPTION OF DRAWINGS

[0012] The above and other aspects and features of the present disclosure will become more apparent by describing in detail example embodiments thereof with reference to the attached drawings, in which:

[0013] Figure 1 is a block diagram of a semiconductor device according to some example embodiments;

[0014] Figure 2 is a diagram illustrating an application example of a processor according to some example embodiments;

[0015] Figure 3 is Figure 1 a circuit diagram of a pulse wave sensor of

[0016] Figure 4 and Figure 5 is a timing diagram describing an operation of a pulse wave sensor according to some example embodiments;

[0017] Figures 6 to 8 is a graph describing an operation of a pulse wave sensor according to some example embodiments;

[0018] Figures 9 to 11 is a graph describing an operation of a pulse wave sensor in a frequency domain according to some example embodiments;

[0019] Figure 12 is a circuit diagram of a pulse wave sensor according to some example embodiments;

[0020] Figure 13 is a conceptual diagram of a pulse wave sensor according to some example embodiments;

[0021] Figure 14 is a timing diagram describing an operation of a pulse wave sensor of Figure 13 ; and

[0022] Figure 15 is a block diagram of an electronic device according to some example embodiments. DETAILED DESCRIPTION

[0023] Hereinafter, example embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0024] Figure 1 is a block diagram of a semiconductor device according to some example embodiments. Figure 2 is a graph illustrating an application example of a processor according to some example embodiments.

[0025] Referring to Figure 1 , the semiconductor device 1 can include a pulse wave sensor 110 (or a PPG sensor) and a processor 120.

[0026] In some example embodiments, the semiconductor device 1 can be, for example, a pulse wave measuring device. The semiconductor device 1 can be mounted on an electronic device such as a smart phone, a tablet PC, a desktop PC, or a laptop PC, or can be mounted on a medical device of a professional medical institution. Alternatively, the semiconductor device 1 can be manufactured in a standalone form such as a wearable device (such as a wrist watch type, a bracelet type, a wristband type, a ring type, glasses type, or a hairband type) wearable on a subject.

[0027] The pulse wave sensor 110 can sense a pulse wave signal (or a PPG signal) from the object OBJ by using light pulses output from the light source 112. The pulse wave sensor 110 can include the light source 112 that irradiates light L to the object OBJ, and the detector 114 that detects reflected light RL when the light L irradiated by the light source 112 is reflected from biological tissue such as a surface of the skin SK or a blood vessel BV.

[0028] The PPG signal is a waveform that reflects a change in blood vessel volume depending on a heartbeat in a peripheral region. When the heart contracts, blood ejected from the left ventricle of the heart flows to the peripheral tissue, thereby increasing arterial blood volume. Also, when the heart contracts, red blood cells carry more oxyhemoglobin to the peripheral tissue. When the heart relaxes, the heart receives part of the blood flow from the peripheral tissue. When light L is irradiated to the peripheral blood vessel, the irradiated light L is absorbed by the peripheral tissue. The absorbance depends on the hematocrit and the blood volume. The absorbance can have a maximum value when the heart contracts, and can have a minimum value when the heart relaxes.

[0029] The pulse wave signal reflects the maximum value of the absorbance when the heart contracts, and reflects the minimum value of the absorbance when the heart relaxes. Also, the pulse wave signal vibrates according to a heartbeat cycle. Thus, since the pulse wave signal reflects a blood pressure change depending on a heartbeat, it can be used for, for example, blood pressure measurement.

[0030] The light source 112 can irradiate one or more different wavelengths of light. For example, the different wavelengths can include blue, green, red, and infrared wavelengths, but example embodiments are not limited thereto.

[0031] For example, the light source 112 can be composed of a light emitting diode (LED), a laser diode (LD), a phosphor, etc., but is not limited thereto.

[0032] In some example embodiments, the light source 112 includes a plurality of light sources, and the plurality of light sources can be arranged at different distances from the detector 114.

[0033] The detector 114 can include one or more pixels that detect the reflected light RL reflected from the biological tissue of the object OBJ and convert the reflected light RL into an electrical signal. The one or more pixels can include a photodiode, a phototransistor (PTr), an image sensor (e.g., a CMOS image sensor), etc., but example embodiments are not limited thereto.

[0034] The processor 120 can receive a pulse wave signal from the pulse wave sensor 110 and perform various signal processing using the received pulse wave signal. For example, the processor 120 can extract various features for estimating blood glucose from the received pulse wave signal. Also, for example, as shown in Figure 2 the processor 120 can extract a pulse rate variability (PRV), a heart rate variability (HRV), a heart rate, a pulse rate, a vascular stiffness, a blood pressure, a perfusion index, a stroke volume, etc. from the received pulse wave signal.

[0035] In the drawing, the pulse wave sensor 110 and the processor 120 are shown as being separately configured, but the example embodiments are not limited thereto, and according to the example embodiments, the processor 120 can be implemented to be integrated in the pulse wave sensor 110.

[0036] Hereinafter, a more detailed configuration of the pulse wave sensor according to some example embodiments will be described with reference to Figure 3

[0037] Figure 3 is a circuit diagram of the pulse wave sensor of Figure 1

[0038] Referring to Figure 3 , the light source 112 can include a light emitting element LS and switches SW1 and SW2.

[0039] The light emitting element LS can generate light L in proportion to an applied current or voltage. Although the drawing shows a light emitting diode as an example of the light emitting element LS, the example embodiments are not limited thereto.

[0040] The switch SW1 can be turned on / off by a control signal CON. The switch SW2 can be turned on / off by a control signal CM.

[0041] For example, in response to the control signal CON of a first level (e.g., a logic high level (hereinafter referred to as an H level)), the switch SW1 can be turned on to connect the light emitting element LS to the current source. Also, in response to the control signal CON of a second level (e.g., a logic low level (hereinafter referred to as an L level)), the switch SW1 can be turned off to disconnect the light emitting element LS from the current source.

[0042] In response to the control signal CM of the H level, the switch SW2 can be turned on to connect the light emitting element LS to the current source. In response to the control signal CM of the L level, the switch SW2 can be turned off to disconnect the light emitting element LS from the current source.

[0043] Here, the control signal CON can be an emission control signal of the light emitting element LS, and the control signal CM can be a modulation control signal.

[0044] ​​That is, while the control signal CON remains at the H level, the control signal CM can repeatedly transition between the H level and the L level to allow the light L output from the light source 112 to become a light pulse having a certain period. That is, the switch SW2 can function as a kind of modulator.

[0045] On the other hand, when the control signal CON remains at the L level, the light L is not output from the light source 112 regardless of the level of the control signal CM.

[0046] In the figure, the switch SW1 controlled by the control signal CON as an emission control signal and the switch SW2 controlled by the control signal CM as a modulation control signal are shown separately, but the example embodiments are not limited thereto. The light source 112 can also be configured with only one switch by using a control signal obtained by an AND operation of the control signal CON and the control signal CM.

[0047] Further, in some other example embodiments, the light source 112 can also be configured without the illustrated switches. For example, when a control current and a control voltage for controlling the light emitting element LS are applied as a waveform obtained by an AND operation of the control signal CON and the control signal CM, the light source 112 can be configured without the switches. Further, even when a logic similar to the above is implemented in software that controls the light emitting element LS, the light source 112 can be configured without the switches.

[0048] The detector 114 can include a photoelectric conversion element RS, switches SW3, SW4, SW5, and SW6, and / or a current-voltage converter IVC.

[0049] The photoelectric conversion element RS can generate a charge (or a current) corresponding to received light. Although a photodiode is illustrated as an example in the figure, the example embodiments are not limited thereto. When the photoelectric conversion element RS is a photodiode, the photoelectric conversion element RS can include an anode terminal and a cathode terminal.

[0050] Among the light received by the photoelectric conversion element RS, not only the reflected light RL irradiated from the light source 112 and reflected from the object OBJ, but also light (e.g., noise) provided from an external environment exist. Therefore, it is advantageous to remove such noise from the light received by the photoelectric conversion element RS to obtain an accurate pulse wave signal (or a PPG signal) from the reflected light RL.

[0051] The current-voltage converter IVC can generate an output voltage VOUT corresponding to the charge (or the current) generated from the photoelectric conversion element RS. For example, the output voltage VOUT can be output through an output terminal OUT1 and an output terminal OUT2.

[0052] The current-voltage converter IVC can include a trans-impedance amplifier (hereinafter referred to as a TIA), storage elements C1 and C2, and / or switches SW7 and SW8.

[0053] For example, the TIA can include a first input terminal (+) and a second input terminal (-). The storage element C1 can be connected between the first input terminal (+) and an output terminal OUT1. The storage element C2 can be connected between the second input terminal (-) and an output terminal OUT2.

[0054] The switch SW7 can be connected between the first input terminal (+) and the output terminal OUT1. The switch SW8 can be connected between the second input terminal (-) and the output terminal OUT2. The switches SW7 and SW8 can be controlled to be turned on / off by a reset control signal RST.

[0055] For example, the switch SW7 can be turned on by the H-level reset control signal RST to reset the storage element C1. For example, the charge in the storage element C1 can be removed. For example, the switch SW8 can be turned on by the H-level reset control signal RST to reset the storage element C2. For example, the charge in the storage element C2 can be removed.

[0056] In some example embodiments, the charge capacity of the storage element C1 and the charge capacity of the storage element C2 can be the same. However, example embodiments are not limited thereto, and the charge capacities of the storage elements C1 and C2 can be modified and implemented differently if necessary.

[0057] The switches SW3, SW4, SW5, and SW6 can switch the connection relationship between the photoelectric conversion element RS and the current-voltage converter IVC. For example, the switches SW3, SW4, SW5, and SW6 can be turned on / off by a control signal CM to switch the connection relationship between the photoelectric conversion element RS and the current-voltage converter IVC.

[0058] For example, the switches SW3 and SW6 can be turned on / off by the control signal CM, and the switches SW4 and SW5 can be turned on / off by a control signal CMB obtained by inverting the control signal CM. Accordingly, when the switches SW3 and SW6 are turned on, the switches SW4 and SW5 are turned off, and when the switches SW3 and SW6 are turned off, the switches SW4 and SW5 are turned on.

[0059] When the switches SW3 and SW6 are turned on and the switches SW4 and SW5 are turned off, the cathode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC. Therefore, the current generated from the photoelectric conversion element RS charges the storage elements Cl and C2 with electric charges. That is, the amount of electric charges in the storage elements Cl and C2 increases. Therefore, the output voltage VOUT increases.

[0060] Conversely, when the switches SW3 and SW6 are turned off and the switches SW4 and SW5 are turned on, the cathode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC. Therefore, the current generated from the photoelectric conversion element RS discharges the electric charges stored in the storage elements Cl and C2. That is, the amount of electric charges in the storage elements Cl and C2 decreases. Therefore, the output voltage VOUT decreases. This will be described in more detail later.

[0061] Although the drawing shows an example in which four switches SW3, SW4, SW5, and SW6 are used to switch the connection relationship between the photoelectric conversion element RS and the current-voltage converter IVC, the example embodiments are not limited to this. If necessary, the connection relationship between the photoelectric conversion element RS and the current-voltage converter IVC can also be switched by using other methods.

[0062] In the following, reference will be made to Figures 3 to 8 the operation of the pulse wave sensor in the time domain will be described.

[0063] Figure 4 and Figure 5 is a timing chart describing the operation of the pulse wave sensor according to some example embodiments. Figures 6 to 8 is a graph describing the operation of the pulse wave sensor according to some example embodiments.

[0064] First, reference will be made to Figure 4 In the first period Tl, the control signal CON transitions between the H level and the L level. Further, the control signal CM transitions between the H level and the L level in the second period T2 which is shorter than the first period Tl.

[0065] Since the control signal CM which is a modulation control signal repeats every second period T2, the light source 112 outputs light pulses modulated at a frequency fl. Here, fl = 1 / T2 holds.

[0066] In some example embodiments, the period T3 during which the control signal CM remains at the H level can be half of the second period T2. Since the light source 112 outputs the light L during the period during which the control signal CM remains at the H level, and does not output the light L during the period during which the control signal CM remains at the L level, the duty ratio of the light pulse output from the light source 112 can be substantially 0.5. However, example embodiments are not limited to this, and the duty ratio of the light pulse can be modified differently as needed.

[0067] As described above, during the period during which the control signal CM is at the L level, the light source 112 does not output the light L.

[0068] First, the reset control signal RST remains at the H level during an initial period t0. Thus, as shown in FIG. 7, the switches SW7 and SW8 are turned on, and the storage elements C1 and C2 are initialized. Due to the initialization of the storage elements C1 and C2, the output voltage VOUT is also initialized (e.g., becomes zero). Figure 6

[0069] Next, during a first period tl, the reset control signal RST becomes the L level, and the switches SW7 and SW8 are turned off. In addition, the control signal CON and the control signal CM become the H level, and the light L is output from the light source 112.

[0070] The light L output from the light source 112 is provided to the photoelectric conversion element RS in the form of the reflected light RL. Referring to FIG. 8, the reflected light RL received by the photoelectric conversion element RS has a greater intensity than the intensity of the light L output from the light source 112 due to the noise N. For example, the light source 112 can output the light L having only the signal component S, but the reflected light RL received by the photoelectric conversion element RS can include the signal component S and the noise N. Figure 5

[0071] Referring to FIG. 9, due to the control signal CM being at the H level, the switches SW3 and SW6 are turned on, and the switches SW4 and SW5 are turned off. Thus, the cathode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC. Figure 7 Thus, the current IPD generated from the photoelectric conversion element RS flows in the direction shown in FIG. 9. Since the reflected light RL received by the photoelectric conversion element RS includes the signal component S and the noise N, the current IPD includes the signal current ISIG and the noise current IN.

[0072]

[0073] ​​​The current IPD generated from the photoelectric conversion element RS charges the storage elements Cl and C2 with charges. Therefore, the amount of charges in the storage elements Cl and C2 increases in correspondence with the signal current ISIG and the noise current IN (or, charges generated from the photoelectric conversion element RS). As the amount of charges in the storage elements Cl and C2 increases, the output voltage V1N including the signal component and the noise component is output to the output terminals OUT1 and OUT2.

[0074] In some example embodiments, for example, the output voltage V1N can be calculated by the following equation.

[0075] V1N = ((ISIG + IN) x t1) / (capacitance of C2, Cl)... Equation 1

[0076] Referring again to Figure 4 , the control signal CON remains at the H level during a second time period t2 after the first time period t1, but the control signal CM becomes the L level, and thus the light L is not output from the light source 112.

[0077] Referring to Figure 5 , since the light L is not output from the light source 112, the reflected light RL received by the photoelectric conversion element RS can include only the noise N.

[0078] Referring to Figure 8 , since the control signal CM is at the L level, the switches SW3 and SW6 are turned off, and the switches SW4 and SW5 are turned on. Therefore, the cathode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC.

[0079] Therefore, the current IPD generated from the photoelectric conversion element RS flows in the direction indicated by the arrow. Since the reflected light RL received by the photoelectric conversion element RS includes only the noise N, the current IPD includes only the noise current IN.

[0080] The current IPD generated from the photoelectric conversion element RS discharges charges from the storage elements Cl and C2. Therefore, the amount of charges in the storage elements Cl and C2 decreases in correspondence with the noise current IN (or, charges generated from the photoelectric conversion element RS). As the amount of charges in the storage elements Cl and C2 decreases, the output voltage V1 obtained by subtracting the noise component from the output voltage V1N is output to the output terminals OUT1 and OUT2.

[0081] At a time point at which the second time period t2 has elapsed, for example, the output voltage V1 can be calculated by the following equation.

[0082] V1 = (ISIG x t1) / (C2, C1 capacitance)... Equation 2

[0083] At the point in time at which the second time period t2 has elapsed, since the amount of charge corresponding to the signal component has been stored in the storage elements C1 and C2, the amount of charge that decreases in the storage elements C1 and C2 during the second time period t2 is smaller than the amount of charge that increases in the storage elements C1 and C2 during the first time period t1.

[0084] Accordingly, the output voltage V1 is smaller than the output voltage V1N, but is larger than the initial voltage (e.g., zero).

[0085] Referring again to Figure 4 During a third time period t3 after the second time period t2, the control signal CM again becomes the H level, and the light L is output from the light source 112.

[0086] The light L output from the light source 112 is provided to the photoelectric conversion element RS in the form of the reflected light RL. In some example embodiments, the reflected light RL received by the photoelectric conversion element RS can include the signal component S and the noise N.

[0087] Referring again to Figure 7 Since the control signal CM is at the H level, the switches SW3 and SW6 are turned on, and the switches SW4 and SW5 are turned off. Accordingly, the cathode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC.

[0088] Accordingly, the current IPD generated from the photoelectric conversion element RS flows in the direction indicated by the arrow. Since the reflected light RL received by the photoelectric conversion element RS includes the signal component S and the noise N, the current IPD includes the signal current ISIG and the noise current IN.

[0089] The current IPD generated from the photoelectric conversion element RS charges the storage elements C1 and C2 with charges. Accordingly, the amount of charge in the storage elements C1 and C2 increases from the amount of charge that has been stored in the storage elements C1 and C2 at the point in time at which the second time period t2 has elapsed, corresponding to the signal current ISIG and the noise current IN (or, the charges generated by the photoelectric conversion element RS). As the amount of charge in the storage elements C1 and C2 increases, the output voltage V2N including the signal component and the noise component is output to the output terminals OUT1 and OUT2.

[0090] Referring again to Figure 4, the control signal CON remains at the H level during a fourth time period t4 after the third time period t3, but the control signal CM becomes the L level, and thus the light L is not output from the light source 112. In some example embodiments, the reflected light RL received by the photoelectric conversion element RS can include only the noise N.

[0091] Reference will now be made to Figure 8 Since the control signal CM is at the L level, the switches SW3 and SW6 are turned off, and the switches SW4 and SW5 are turned on. Thus, the cathode terminal of the photoelectric conversion element RS is connected to the second input terminal (-) of the current-voltage converter IVC, and the anode terminal of the photoelectric conversion element RS is connected to the first input terminal (+) of the current-voltage converter IVC.

[0092] Thus, the current IPD generated from the photoelectric conversion element RS flows in the direction indicated by the arrow. Since the reflected light RL received by the photoelectric conversion element RS includes only the noise N, the current IPD includes only the noise current IN.

[0093] The current IPD generated from the photoelectric conversion element RS discharges the charges from the storage elements Cl and C2. Thus, the amount of the charges in the storage elements Cl and C2 is reduced from the amount of the charges that has been stored in the storage elements Cl and C2 at the point of time when the third time period t3 has elapsed, corresponding to the noise current IN (or, the charges generated by the photoelectric conversion element RS). As the amount of the charges in the storage elements Cl and C2 is reduced, the output voltage V2 obtained by subtracting the noise component from the output voltage V2N is output to the output terminals OUT1 and OUT2.

[0094] At the point of time when the fourth time period t4 has elapsed, since the amount of the charges corresponding to the signal component has been stored in the storage elements Cl and C2, the amount of the charges reduced in the storage elements Cl and C2 during the fourth time period t4 is smaller than the amount of the charges increased in the storage elements Cl and C2 during the third time period t3.

[0095] Thus, the output voltage V2 is smaller than the output voltage V2N, but larger than the output voltage V1.

[0096] If the above operation is repeated M times (M is a natural number), the current-voltage converter IVC can output the output voltage VM corresponding to the light L output from the light source 112 while the control signal CON remains at the H level. Since the noise component received by the photoelectric conversion element RS has been removed step by step in turn as described above, the output voltage VM corresponds only to the signal component of the light L output from the light source 112.

[0097] Hereinafter, the operation of the above-described pulse wave sensor in the frequency domain will be described with reference to Figure 3 and Figures 9 to 11 the frequency domain.

[0098] Figures 9 to 11 is a graph describing the operation of the pulse wave sensor in the frequency domain according to some example embodiments.

[0099] Referring to Figure 3 and Figure 9 As described above, the light source 112 of the pulse wave sensor according to the present example embodiment modulates the light L at a frequency of 1 / T2and outputs the light L. Therefore, the light L output from the light source 112 has a frequency of 1 / T2in the frequency domain.

[0100] Next, referring to Figure 3 and Figure 10 As described above, the reflected light RL received by the photoelectric conversion element RS has a signal component and a noise component. Further, the photoelectric conversion element RS generates a current ISIG corresponding to the signal component and a current IN corresponding to the noise component.

[0101] The signal component of the reflected light RL has a frequency of 1 / T2, but since the noise component is not modulated at a specific frequency, the current ISIG and the current IN can be separated in the frequency domain as shown in the graph.

[0102] Next, referring to Figure 3 and Figure 11 By the operation of the above-described switches SW3, SW4, SW5, and SW6, the current ISIG can be demodulated, and the current IN can be modulated. That is, the switches SW3, SW4, SW5, and SW6 can function as a modulator that demodulates the current ISIG and modulates the current IN. That is, in the present example embodiment, a modulator can be arranged in each of the light source 112 and the detector 114.

[0103] Depending on the operation of the switches SW3, SW4, SW5, and SW6, the positions of the current ISIG and the current IN can be switched in the frequency domain. That is, the signal component does not have a frequency, and the noise component has a frequency of 1 / T2.

[0104] The above-described current-voltage converter IVG can function as a filter. For example, the current IN having a frequency of 1 / T2may be filtered by the bandwidth FTIA of the TIA of the current-voltage converter IVG.

[0105] Therefore, the output voltage VOUT corresponding to the light L output from the light source 112 can be output to the output terminals OUT1 and OUT2 of the current-voltage converter IVG.

[0106] In the pulse wave sensor according to the present example embodiment, since the noise component is removed from the received light in this way, noise can be efficiently removed regardless of the signal sensitivity of the light L output from the light source 112 when the modulation operation of the light source 112 is properly adjusted. Further, since a separate sampling circuit (for example, a sample and hold circuit) is not required to remove noise, the pulse wave sensor is advantageous in terms of miniaturization.

[0107] Figure 12 is a circuit diagram of a pulse wave sensor according to some example embodiments. Hereinafter, the description overlapping with the above-described example embodiments will be omitted, and the difference will be mainly described.

[0108] Reference Figure 12 , the detector (for example, the detector 114 of

[0109] In the present example embodiment, the switches SW3, SW4, SW5, and SW6, the TIA, the analog-digital converter 115a, and the digital-analog converter 115b can function as a sigma-delta modulator.

[0110] For example, when the switches SW3, SW4, SW5, and SW6 and the TIA functioning as a modulator operate as an integrator to output a signal, the output signal can be converted into a digital signal DOUT according to the resolution of the analog-digital converter 115a, and the digital signal DOUT can be output. The output digital signal DOUT can be input to the digital-analog converter 115b and converted into an analog signal, and the analog signal can be provided again to the analog-digital converter 115a through the integrator.

[0111] According to some example embodiments, the illustrated pulse wave sensor 115 can further include an extraction filter, and when the pulse wave sensor 115 is configured in this way, a pulse wave signal can be directly converted into a digital signal without requiring an additional analog-digital conversion operation in a separate external readout circuit.

[0112] Figure 13 is a conceptual diagram of a pulse wave sensor according to some example embodiments. Hereinafter, the difference from the above-described example embodiments will be mainly described.

[0113] Reference Figure 13 , the detector (for example, the detector 114 of Figure 1 The detector 114 of

[0114] Although the drawing shows a plurality of photoelectric conversion elements RS1 to RS16 arranged in a 4 x 4 arrangement, the example embodiments are not limited thereto. If necessary, the arrangement of the plurality of photoelectric conversion elements RS1 to RS16 can be modified differently.

[0115] The photoelectric conversion elements arranged in the same row (e.g., R1) (e.g., RS1, RS2, RS3, and RS4) can be connected to different columns, and the photoelectric conversion elements arranged in the same column (e.g., C1) (e.g., RS1, RS5, RS9, and RS13) can share the same column line.

[0116] The optical filters F1 to F16 can be arranged in the respective rows R1 to R4 and the respective columns C1 to C4. The optical filters F1 to F16 can filter and / or transmit the light received by the pulse wave sensor 116, and provide the filtered and / or transmitted light to the plurality of photoelectric conversion elements RS1 to RS16.

[0117] In some example embodiments, the optical filters F1 to F16 can have different optical characteristics. Thus, the light received by the photoelectric conversion elements RS1, RS4, RS13, and RS16 can all have different optical characteristics.

[0118] Further, in some example embodiments, the optical filters F1 to F16 can be arranged to have the same optical characteristics for each row, or can be arranged to have the same optical characteristics for each column.

[0119] When the optical filters F1 to F16 are arranged to have the same optical characteristics for each row, the photoelectric conversion elements RS1 and RS4 can receive light having the same optical characteristics, but the photoelectric conversion element RS13 can receive light having optical characteristics different from those of the light received by the photoelectric conversion elements RS1 and RS4.

[0120] Further, when the optical filters F1 to F16 are arranged to have the same optical characteristics for each column, the photoelectric conversion elements RS1 and RS13 can receive light having the same optical characteristics, but the photoelectric conversion element RS2 can receive light having optical characteristics different from those of the light received by the photoelectric conversion elements RS1 and RS13.

[0121] Each of the column lines CL1, CL2, CL3, and CL4 can be shared among the photoelectric conversion elements RS1 to RS16 arranged in the same column. That is, the column line CL1 can connect the photoelectric conversion elements RS1, RS5, RS9, and RS13 to the current-voltage converter IVC1, and the column line CL2 can connect the photoelectric conversion elements RS2, RS6, RS10, and RS14 to the current-voltage converter IVC2, the column line CL3 can connect the photoelectric conversion elements RS3, RS7, RS11, and RS15 to the current-voltage converter IVC3, and the column line CL4 can connect the photoelectric conversion elements RS4, RS8, RS12, and RS16 to the current-voltage converter IVC4.

[0122] Figure 14 is a timing chart describing the operation of the pulse wave sensor. Figure 13

[0123] Referring to Figure 14 , the rows R1 to R4 can be selected in turn when the control signal CM transitions between the H level and the L level.

[0124] For example, the row R1 can be selected and then not selected while the control signal CM transitions between the H level and the L level twice (e.g., while the light pulse output from the light source is received twice). The row R2 can be selected after the row R1 is not selected and can be selected and then not selected while the control signal CM transitions between the H level and the L level twice. The rows R3 and R4 can also be selected in turn in the same manner.

[0125] Although the drawing illustrates an example in which each of R1 to R4 is selected in a cycle in which the light pulse output from the light source is received twice, the example embodiments are not limited thereto. If necessary, the cycle can be variously modified and implemented.

[0126] Further, in some example embodiments, the rows R1 and R3 can be selected at the same time, and the rows R2 and R4 can be selected at the same time.

[0127] In the case of sensing a pulse wave signal based on light having different optical characteristics as described above, the processor (e.g., the processor 120 of Figure 1 ) can perform more different processing.

[0128] Figure 15 is a block diagram of an electronic device according to some example embodiments.

[0129] Referring to Figure 15 , the electronic device 2 can include a pulse wave sensor 110, a processor 120, an output unit 130, a storage unit 140, and / or a communication unit 150. ​

[0130] As for the pulse wave sensor 110, the pulse wave sensor 110 according to the various example embodiments described above can be employed.

[0131] The processor 120 can perform the same or substantially the same operations as the processor 120 described earlier with reference to FIG. 1. Figure 1

[0132] The output unit 130 can output the processing result of the processor 120 to the user. For example, the output unit 130 can visually output the heart rate, the pulse rate, the blood pressure, the blood sugar estimation value, etc. through a display module. Alternatively, the output unit 130 can output the same content in a non-visual manner such as a voice, a vibration, or a tactile sensation through a speaker module, a haptic module, etc.

[0133] The output unit 130 can divide a display area into two or more parts according to a setting, and can output the biometric information extracted by the processor 120 for each part.

[0134] The storage unit 140 can store the processing result of the processor 120 therein. In addition, the storage unit 140 can store reference information required for the signal processing of the processor 120. For example, the reference information can include user characteristic information such as the age, the gender, and the health condition of the user.

[0135] The storage unit 140 can include a storage medium such as a flash memory type storage, a hard disk type storage, a multimedia card micro type storage, and a card type storage (e.g., a secure digital (SD) or an extreme digital (XD) memory), a random access memory (RAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic storage, a magnetic disk, or an optical disk, but the example embodiments are not limited thereto.

[0136] The communication unit 150 can communicate with the external device 160 using wired / wireless communication technology under the control of the processor 120 to transmit and receive various types of data. For example, the communication unit 150 can transmit the biometric information to the external device 160. In addition, the communication unit 150 can receive various signals required to estimate the biometric information from the external device 160.

[0137] The external device 160 can include an information processing device such as a wearable device, a smart phone, a tablet PC, a desktop PC, or a notebook PC.

[0138] ​According to some example embodiments, the communication technology can include Bluetooth communication, Bluetooth Low Energy (BLE) communication, Near Field Communication (NFC), WLAN communication, Zigbee communication, Infrared Data Association (IrDA) communication, Wi-Fi Direct (WFD) communication, Ultra Wide Band (UWB) communication, Ant+ communication, Wi-Fi communication, Radio Frequency Identification (RFID) communication, 3G communication, 4G communication, and 5G communication, etc., but example embodiments are not limited thereto.

[0139] Any of the above-disclosed elements can include or be implemented in processing circuitry, such as hardware including logic circuitry, a hardware / software combination such as a processor executing software, or combinations thereof. For example, more specifically, processing circuitry can include, but is not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a system on a chip (SoC), a programmable logic unit, a microprocessor, an application-specific integrated circuit (ASIC), or the like.

[0140] In summarizing the detailed description, those skilled in the art will appreciate that numerous changes and modifications can be made to the preferred example embodiments without departing from the principles of the inventive concepts. Therefore, the disclosed preferred example embodiments of the inventive concepts are used only for illustrative and descriptive purposes, and are not used for purposes of limitation.

Claims

1. A photoplethysmography sensor, comprising: a photodiode comprising a cathode terminal and an anode terminal, the photodiode being configured to receive light reflected from a blood vessel and to generate a current corresponding to the received light; a current-voltage converter comprising a first input terminal and a second input terminal, the current-voltage converter being configured to receive the generated current through the first input terminal and the second input terminal as a received current, and the current-voltage converter being configured to generate an output voltage corresponding to the received current; and a switch configured to connect the photodiode to the current-voltage converter in accordance with a control signal, wherein, in response to the control signal being at a first level, the switch directly connects the cathode terminal of the photodiode to the first input terminal of the current-voltage converter and directly connects the anode terminal of the photodiode to the second input terminal of the current-voltage converter, and wherein, in response to the control signal being at a second level different from the first level, the switch directly connects the cathode terminal of the photodiode to the second input terminal of the current-voltage converter and directly connects the anode terminal of the photodiode to the first input terminal of the current-voltage converter. the current-voltage converter comprises:

2. The photoplethysmography sensor of claim 1, wherein, a transimpedance amplifier (TIA) comprising the first input terminal and the second input terminal; and a storage unit connected to at least one of the first input terminal of the TIA or the second input terminal of the TIA and an output terminal of the TIA, the storage unit being configured to store the output voltage. the storage unit comprises a first storage element and a second storage element, 3. The photoplethysmography sensor of claim 2, wherein, the output terminal of the TIA comprises a first output terminal and a second output terminal, the first storage element is connected to the first input terminal of the TIA and the first output terminal of the TIA, and the second storage element is connected to the second input terminal of the TIA and the second output terminal of the TIA. while the control signal is at the first level, an amount of charge in the storage unit increases corresponding to the current generated from the photodiode, and 4. The photoplethysmography sensor of claim 2, wherein, when the control signal is at the second level, the amount of charge in the storage unit decreases corresponding to the current generated from the photodiode.

5. The photoplethysmography sensor according to claim 4, further comprising a light source configured to output the light in response to the control signal being at the first level and configured to not output the light in response to the control signal being at the second level. the control signal comprises a first control signal and a second control signal, 6. The photoplethysmography sensor of claim 5, wherein, the switch connects the photodiode to the current-voltage converter in accordance with the second control signal, and the light source outputs the light in response to the first control signal being at the first level and the second control signal being at the first level. the switch comprises:

7. The photoplethysmography sensor of claim 1, wherein, ​ a first switch configured to connect the cathode terminal of the photodiode to the first input terminal of the current-voltage converter in response to the control signal at the first level; a second switch configured to connect the cathode terminal of the photodiode to the second input terminal of the current-voltage converter in response to the control signal at the second level; a third switch configured to connect the anode terminal of the photodiode to the first input terminal of the current-voltage converter in response to the control signal at the second level; and a fourth switch configured to connect the anode terminal of the photodiode to the second input terminal of the current-voltage converter in response to the control signal at the first level.

8. The photoplethysmography sensor of claim 7, further comprising a light source configured to output the light in response to the control signal at the first level and configured to not output the light in response to the control signal at the second level, wherein, the control signal comprising: a first control signal having a first period; and a second control signal having a second period shorter than the first period, and wherein the first switch through the fourth switch are configured to connect the photodiode to the current-voltage converter in accordance with the second control signal, and the light source outputs the light in response to the first control signal at the first level and the second control signal at the first level.

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