Hearing device with optical sensor

Abstract

A hearing device with an optical sensor includes: a light source (212, 300, 304, 308, 402) configured to emit light; a photodetector (214, 404) configured to detect light emitted by the light source after it has passed through tissue of a subject; an audio receiver (116, 202) configured to transmit sound to the subject; and a dome structure (120, 206) configured to conform to the shape of the ear canal when the hearing device is in the subject's ear canal. The output of the light source (212, 300, 304, 308, 402) and the input of the photodetector (214, 404) are separated by the dome structure (120, 206), and the dome structure (120, 206) absorbs and / or reflects at least a portion of the light emitted by the light source.

Description

Technical Field

[0001] This disclosure relates to a hearing device that includes a light source and a light detector. Background Technology

[0002] Hearing devices can be used, for example, to improve a user's hearing or communication abilities by compensating for hearing loss. In this case, hearing devices are often referred to as hearing instruments, such as hearing aids or hearing prostheses. Hearing devices can also be used to generate sounds in a user's ear canal based on audio signals that can be transmitted to the hearing device via wires or wirelessly. Hearing devices can also be used to reproduce sounds in a user's ear canal detected by a microphone. The reproduced sound can be amplified to account for hearing loss, as in hearing instruments, or can be output without accounting for hearing loss, for example, to provide a faithful reproduction of detected ambient sounds and / or to add augmented reality sound features to the reproduced ambient sounds, as in wearable hearing devices. Different types of hearing devices designed to be inserted at least partially into the ear canal include earplugs, headphones, wearable hearing devices, and hearing instruments such as receiver-in-the-canal (RIC) hearing aids, in-the-ear (ITE) hearing aids, invisible-in-the-canal (IIC) hearing aids, and completely-in-the-canal (CIC) hearing aids. Hearing devices typically include an audio receiver that is configured to transmit sound to an object that wears the hearing device.

[0003] Optical sensors use a light source to emit light into the environment and a photodetector to detect the light from the environment in order to obtain information about it. For example, this type of optical sensor is often used to project light onto the tissue of an object (e.g., skin) and measure the reflected or transmitted light characteristics of the projected light. The detected light intensity varies according to the blood flow projected through the blood vessels through which the light passes. Therefore, the measured intensity signal over time represents a photoplethysmography (PPG) signal, which can be processed to determine heart rate, blood pressure, and other physiological properties.

[0004] While data can be collected in many locations on the body (e.g., where blood vessel density and tissue type and thickness are optimal for best transmission and reflection), some locations are more susceptible to the effects of movement and noise from ambient light. Additional factors that can affect the quality of PPG signals include measurement location, the wavelength of light emitted by the light source, body movement, ambient light, and the subject's skin color. Furthermore, PPG sensors made of different materials that are transparent to and / or reflective of light emitted by the light source (including infrared and other types of (non-)visible wavelengths) can cause interference with the obtained sensor data. With this in mind, many PPG sensor shape factors utilize contact optics in which the light source and detector are in contact with the skin. This helps prevent leakage of light emitted by the light source and light from the environment into the detector, thus reducing noise caused by ambient light.

[0005] Some PPG sensors are designed to take measurements at the subject's ear. Therefore, the PPG sensor can be part of a standard hearing device that is not tailored to the shape of an individual's ear, such as a standard RIC hearing device module (a module with a housing not tailored to the shape of the subject's ear canal) or headphones or wearable devices. The PPG sensor can then be implemented such that it does not (completely) contact the walls of the ear canal. As a result, there may not be sufficient optical isolation between the photodetector and the light source, which can lead to a short circuit between the light source and the photodetector. Therefore, users of standard hearing devices may suffer from unreliable measurement results from PPG sensors.

[0006] The greater the distance between the light source and the photodetector, the greater the probability that the detection light has traversed the vascular system in the tissue, and therefore the greater the probability that an acceptable physiological signal can be extracted from the detection light signal. However, such a long path significantly attenuates the light emitted by the light source. As a result, powerful and power-consuming light sources and / or complex amplification circuitry are required to extract an acceptable physiological signal. Such power is greater than that typically used in hearing devices, and the necessary electrical components for power control and amplification increase the complexity of the PPG sensor system and can generate electrical interference in small packages, such as those associated with hearing devices. The complexity of the sensor also increases when multiple light sources with potentially different wavelengths are used by the PPG sensor.

[0007] The purpose of this disclosure is to avoid at least one of the disadvantages mentioned above and to improve the detection reliability of optical sensors included in hearing devices and / or reduce the complexity and / or power consumption of optical detection circuitry. Summary of the Invention

[0008] According to an example of this disclosure, a hearing device includes: a light source configured to emit light; a photodetector configured to detect light emitted by the light source after interaction with tissue of a subject; an audio receiver configured to transmit sound to the subject; and a dome structure configured to conform to the shape of the ear canal when the hearing device is in the ear canal of the subject, wherein the dome structure absorbs and / or reflects at least a portion of the light emitted by the light source, and wherein the output of the light source and the input of the photodetector are separated by the dome structure. In some instances, the reliability of the measurement results of the hearing device can be improved by separating the output of the light source and the input of the photodetector by the dome structure. In some instances, separating the output of the light source and the input of the photodetector by the dome structure can be used to implement optical detection circuitry with reduced complexity and / or power consumption.

[0009] In some embodiments, the light source is configured to emit directional light toward the walls of the ear canal. In some embodiments, the light source is configured to emit diffuse light within the ear canal. In some embodiments, the light source includes at least one light-emitting diode.

[0010] In some embodiments, the hearing device includes a sound conduit, wherein the audio receiver is configured to transmit sound to the object through the sound conduit. The sound conduit may be provided at the front end of the hearing device, the front end facing the tympanic membrane within the ear canal when the hearing device is inserted into the ear canal. The sound conduit may be a member defining a volume through which sound can be conducted, specifically, between two opposite ends of the volume. The defined volume may be tubular. In particular, the sound conduit may be configured to provide acoustic coupling between the audio receiver and the ear canal when the hearing device is inserted into the ear canal. The sound conduit may include an opening through which sound can be released into the ear canal when the hearing device is inserted into the ear canal. The sound conduit may include, for example, a bore provided in the dome structure and / or a nozzle. The nozzle may be, for example, a tubular member. The nozzle may be positioned in front of the audio receiver such that, when the hearing device is inserted into the ear canal, the nozzle is positioned between the audio receiver and the tympanic membrane within the ear canal.

[0011] The output of the light source can be located at the dome structure, for example, on one side of the dome structure facing the tympanic membrane and / or inside the cavity, and the input of the photodetector can be located at the audio receiver.

[0012] The output of the light source can be positioned at the nozzle, and the output of the photodetector can be positioned at the audio receiver. The nozzle is transparent to the wavelength of light emitted by the light source. The nozzle may include a light guide connected to the input of the photodetector. The light guide may include a waveguide configured to guide light having the wavelength of light emitted by the light source.

[0013] The output section of the light source can be located at a separate position from the light source, and the output section of the light source is connected to the light source via a light guide. The input section of the photodetector can be located at a separate position from the photodetector, and the input section of the photodetector is connected to the photodetector via a light guide.

[0014] The output of the light source can be located at a separate position from the light source, and the output of the light source is connected to the light source via a first light guide. The input of the photodetector can be located at a separate position from the photodetector, and the input of the photodetector is connected to the photodetector via a second light guide. In some examples, the output of the light source can be positioned at the nozzle, and the output of the photodetector can be positioned at the audio receiver.

[0015] The dome structure may be opaque to ambient light. In some instances, the output of the light source may be located at the audio receiver, and the output of the photodetector may be located at the nozzle.

[0016] The optical sensor may also include a shield that is opaque to ambient and / or visible light wavelengths, and is configured to shield the photodetector from ambient and / or visible light wavelengths.

[0017] When viewed in a parasagittal section of the ear canal, the output portion of the light source and the input portion of the photodetector are preferably at an angle of at least 45°. This angle can be an acute angle facing the posterior wall of the ear canal. The light source can be configured to emit light with a wavelength in the near-infrared region. For example, the light source can be configured to emit light with wavelengths of 800 nm and / or 850 nm and / or 880 nm and / or 904 nm and / or 910 nm and / or 940 nm and / or 950 nm. The wavelength in the near-infrared region can be a first wavelength, and the light source can be configured to emit light with a second wavelength of approximately 660 nm.

[0018] The dome structure can be configured to contact the tissue of the ear canal.

[0019] The dome structure may be configured to absorb and / or reflect at least a portion of the light emitted by the light source, such that the intensity of light emitted by the light source having a wavelength passing through the dome structure is less than the intensity of light emitted by the light source having a wavelength passing through the tissue. In some instances, the dome structure may absorb and / or reflect at least a portion of the light emitted by the light source, such that the intensity of light emitted by the light source passing through the dome structure is less than the intensity of light emitted by the light source passing through the tissue. In some instances, the dome structure may be opaque to the wavelength of light emitted by the light source. In some instances, the dome structure may be opaque to the light emitted by the light source.

[0020] The photodetector may include a forward-biased photodiode.

[0021] The optical sensor device can be configured to determine the intensity of light detected by the photodetector by measuring the time delay between the start of the forward voltage of the photodetector and the start of the forward current of the photodetector. In some instances, the light source is configured to emit light with a light intensity such that the time delay is at least 200 ns. Attached Figure Description

[0022] Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings. In the drawings:

[0023] Figure 1 The illustration shows an example of an in-ear receiver (RIC) hearing device;

[0024] Figure 2 The illustration shows an example of the sound delivery system (SDS) portion of a RIC hearing device with a PPG sensor in the ear canal;

[0025] Figures 3A-3E The illustration shows an example light source output from the ITE section of a hearing aid;

[0026] Figure 4-6 Another example of an SDS section with a PPG sensor in the ear canal is illustrated.

[0027] Figure 7 The illustration shows a cross-section of the right ear canal at an angle to the light source and photodetector of the PPG sensor in the hearing device.

[0028] Figures 8A-8C The diagram illustrates the operating characteristics of a forward-biased photodiode.

[0029] Figure 9 The diagram illustrates a simplified circuit for detecting the light intensity at a forward-biased photodiode. Detailed Implementation

[0030] Considering the foregoing, this disclosure relates to hearing devices having optical sensors that overcome the deficiencies described above. Such hearing devices may be in-ear receiver (RIC) devices comprising: a "behind-the-ear" portion (or "BTE" portion) configured to be worn behind the ear; and a sound transmission system (SDS) portion configured to be worn at least partially in the ear (ITE). Hearing devices may also be either ITE hearing devices configured to be worn at least partially in the ear canal or fully in-ear (CIC) hearing devices configured to be worn completely in the ear canal, each provided without the BTE portion. Hearing devices may also be headphones or wearable devices including the SDS portion.

[0031] Figure 1An example RIC hearing device 100 is illustrated. The RIC device 100 includes a BTE section 102 and an SDS section 104 connected by a cable 106. The cable 106 can be a power cable or an air-conducting cable. The BTE section 102 includes a housing 108 for a battery 110, a processor 112, and a microphone 114. The SDS section includes an audio receiver 116, a sound conduit 118, and a dome structure 120. In the illustrated example, the second conduit 118 is a nozzle positioned at the front end of the audio receiver 116. In other examples, the second conduit 118 may be provided as a cavity in the dome structure 120, specifically extending through a through-hole in the dome structure 120. The dome structure 120 may then be positioned such that the cavity is provided at the front end of the audio receiver 116.

[0032] BTE section 102 is configured to collect sound from microphone 114, process the collected sound using processor 112, and transmit the processed sound via cable 106 to audio receiver 116 of SDS section 104. Audio receiver 116 may include a speaker configured to generate an audible version of the processed sound, and a printed circuit board (PCB) thereon providing electronic components for sound generation. Nozzle 118 may be specifically configured to output sound from the speaker toward the tympanic membrane within the ear canal through a tubular shape having an opening facing the eardrum. Dome structure 120 may be flexible, etc., such that it is configured to shape adjust into the ear canal to support audio receiver 116 within the ear canal. For example, dome structure 120 may be mushroom-shaped and / or umbrella-shaped.

[0033] In other embodiments, the speaker may be part of the BTE section 102. In these cases, the cable 106 may be an air-conducting cable configured to deliver output sound to the nozzle. In other embodiments, the microphone 114, processor 112, and battery 110 may all be included within the SDS section 104, as with ITE-only and CIC hearing devices, thus eliminating the need for the BTE section 102.

[0034] Go to Figure 2 The illustration depicts the general operation of a PPG sensor with an SDS portion of a hearing device. As shown, an exemplary SDS portion 200 (having an audio receiver 202, a nozzle 204, and a dome structure 206) is positioned in the ear canal 208 with the nozzle end of the SDS portion 200 closest to the tympanic membrane 202. Here, the SDS portion 200 can be described as being composed of a middle half (closest to the tympanic membrane 202) and a transverse half (closest to the opening of the ear canal). Although the illustration shows the SDS portion entirely within the ear canal 208, it should be noted that this disclosure also applies to hearing devices that are only partially inserted into the ear canal.

[0035] according to Figure 2 In one illustrated embodiment, a light source (e.g., an LED or OLED) 212 is provided in the middle half of the SDS portion 200 (shown at the nozzle 204), and a photodetector 214 is provided in the lateral half of the SDS portion 200 (shown at the audio receiver 202). The light source 212 is configured to emit light 216 through the walls of the ear canal 208, where it passes through the vasculature; and the photodetector 214 is configured to detect the light 216 emitted by the light source 212 re-entering the ear canal 208. The light source 212 can emit light of any wavelength, such as green, red, or infrared. In one embodiment, the wavelength can be in the near-infrared spectrum, which may include wavelengths between 780 nm and 2500 nm. Such wavelengths may be less common in many ambient light sources such as sunlight. In some instances, at least one wavelength of the light emitted by light source 212 is 800 nm and / or 850 nm and / or 880 nm and / or 904 nm and / or 910 nm and / or 940 nm and / or 950 nm. In some instances, at least one wavelength of the light emitted by light source 212 is in the red spectrum, for example, 660 nm. In some instances, at least one wavelength of the light emitted by light source 212 is in the green spectrum, for example, 520 nm.

[0036] The light source 212 can also be configured to emit light having at least two different wavelengths. For example, the light source 212 may include at least two light emitters, each configured to emit light having a corresponding wavelength and / or multiple wavelengths. In some instances, the first wavelength of the light emitted by the light source 212 is in the near-infrared spectrum, for example, at least one of 800 nm and / or 850 nm and / or 880 nm and / or 904 nm and / or 910 nm and / or 940 nm and / or 950 nm, and the second wavelength of the light emitted by the light source 212 is 660 nm. For example, such a combination of wavelengths can be advantageously used to determine the oxygen saturation value of peripheral capillaries in tissues.

[0037] The dome structure 206 is preferably predominantly opaque to at least one wavelength of light emitted by the light source 212 and / or the wavelength of visible ambient light, wherein predominantly means that the light intensity at said wavelength passing through the dome structure is significantly less than the light intensity at said wavelength passing through the tissue to the photodetector. By blocking the wavelength of light emitted by the light source 212, the dome structure 206 thus optically isolates the light source 212 and the photodetector 214, thereby preventing light 216 emitted by the light source 212 from traveling directly to the photodetector 214 without first passing through the tissue surrounding the ear canal 208. For this purpose, the dome structure 206 may have any suitable material and / or may contain one or more layers and / or coatings to achieve the desired opacity.

[0038] Position the light source 212 and the photodetector 214 as follows: Figure 2 The different locations of the SDS section 200 shown mitigate interference that can lead to low-quality data measurement results. This contrasts with current designs where the light emitter and photodetector are provided on a single PCB in the audio receiver 202. Furthermore, the separation allows the light 216 emitted by the light source 212 to travel further through human skin, thus maximizing its chances of penetrating vascular structures and providing relevant information. At least a portion of the light 216 emitted by the light source 212 is scattered and / or reflected multiple times within the tissue. Another portion of the light 216 emitted by the light source 212 may be absorbed by the tissue. After interacting with the tissue, at least a portion of the light 216 emitted by the light source 212 can be detected by the photodetector 214.

[0039] like Figure 2 As shown, the light source 212 is a single LED or OLED directly mounted in the nozzle 204. However, the light source 212 can be implemented in any manner to achieve the desired output characteristics. For example, the light source 212 can be directly mounted in the nozzle 204 (e.g., emitting light through a window, opening, etc. of the nozzle 204), or externally mounted on the nozzle 204. In other examples, the light source can be located at a distance from the end of the nozzle 204, such that any light emitted by the light source 212 is guided to the output position at the nozzle 204 via a light guide (such as an optical fiber). Similarly, the light source 212 can instead be integrated into the body of the speaker and emit light through the speaker's sound outlet. The light source 212 can be configured to output light directionally toward the eardrum or toward the wall of the ear canal; or it can be configured to emit diffuse light that illuminates the ear canal as wide as possible.

[0040] Figures 3A-3E Examples of various light outputs and light source configurations are illustrated. More specifically, Figure 3A The illustration shows light directionally emitted from a light source 300 located at the end of the nozzle toward the eardrum. The light source 300 can take the form of... Figure 3A The shape of the nozzle (ring) shown can be either a ring or one or more discrete point light sources located at the end of the nozzle. Similarly, Figure 3B The illustration shows the directional output of light toward the eardrum through an opening 302 in the nozzle, through which the speaker output is provided. In such an example, the light source may be within the opening, or, as described above, integrated with the speaker. Similar to... Figure 3A , Figure 3C The illustration shows diffused light emitted by the annular light source 304 at the end of the nozzle. Furthermore, the light source can also be implemented as a single or multiple discrete point light sources. Figure 3D The illustration shows diffused light emitted from the opening of nozzle 306, wherein the light source can be as shown in the diagram. Figure 3B The described implementation. Finally. Figure 3EThe illustration shows a directional light source 308 (as a single light source or one or more discrete point light sources) implemented in a ring around one side of the nozzle. According to this configuration, light is directionally emitted towards the walls of the ear canal. This configuration of the light source can also emit diffuse light around the nozzle towards the walls of the ear canal.

[0041] Similar to the above description of the light source, the photodetector 214 can be configured to directionally receive light from the ear canal wall or detect scattered light from any direction. The photodetector 214 can also be positioned within the audio receiver 202 and thus detect light 216 emitted by the light source 212 passing through windows, openings, etc., in the audio receiver 202, or it can be externally mounted to the audio receiver 202. Still in other embodiments, the photodetector 214 can be located within the audio receiver 202, away from its housing, or at any other part of the hearing device. In such a configuration, the light 216 emitted by the light source 212 can be collected at a separate input location from the light source 212 and guided to the photodetector 212 via a light guide. In any of these variations, a shield opaque to ambient and visible light wavelengths (e.g., implemented as a window) can cover the input portion of the photodetector 214. Such shielding reduces the ambient light detected by the photodetector 214, thereby reducing the required intensity of light emitted by the light source 212 and the required power for the light source 212. The shield can also be a narrowband filter, allowing only a narrow wavelength of light from the LED source without any other visible or invisible light. Furthermore, the complex circuitry used to remove noise caused by detected ambient light can be minimized, thus simplifying the device. This can also increase the quality of measurements from the photodetector 214.

[0042] According to another embodiment, such as Figure 4 As illustrated, the positions of the light source 212 and the photodetector 214 can be reversed, such that the photodetector 214 is positioned in the middle half of the SDS section 200, for example, at the nozzle 204; and the light source 212 is positioned in the lateral half of the SDS section 200, for example, at the audio receiver 202. In this case, the dome structure 206 can thus again be used to limit the direct detection of light emitted by the light source 212 at the photodetector 214. As mentioned above, since the deeper parts of the ear canal are darker, especially when the dome structure 206 is present, the measurement quality from the photodetector 214 can be improved by reducing the detected ambient light. Therefore, again, a lower intensity light source requiring less operating power can be utilized.

[0043] According to other embodiments, such as Figure 5 and 6As illustrated, a photodetector 214 is positioned within an audio receiver 202. For example, the audio receiver 202 may include a housing 216, and the photodetector 214 is positioned within an internal volume surrounded by the housing 216 of the audio receiver 202. The input of the photodetector 214 may be in optical communication with the nozzle 204. For example, the input of the photodetector 214 may be connected to the nozzle 204. In some instances, such as... Figure 5 As illustrated, the input portion of the photodetector 214 can be positioned at a lateral end of a nozzle 204 leading to an internal volume surrounded by the housing 216 of the audio receiver 202. The nozzle 204 can be transparent to at least one wavelength of light emitted by the light source 212. Specifically, the nozzle 204 may include a portion of a light guide configured to allow light 216 emitted by the light source 212 to travel between the outer surface of the nozzle 204 (e.g., the surface at the middle end of the nozzle 204) and the lateral end of the nozzle 204. In some instances, such as... Figure 6 As illustrated, the nozzle 204 may include a light guide 215 extending through a portion of an internal volume surrounded by the housing 216 of the audio receiver 202. For example, the light guide 215 may extend between a central end of the nozzle 214 and the input portion of the photodetector 214. The light guide 215 may include a waveguide, such as an optical fiber and / or a dielectric waveguide that is transparent to at least one wavelength of light emitted by the light source 212. Therefore, the light 216 emitted by the light source 212 can be detected by the photodetector 214 within the audio receiver 202.

[0044] In another example, the light source can be provided at the BTE section of the hearing device. In such a variation, light can be guided to and emitted from any location within the SDS section via a light guide.

[0045] Regardless of the relative positions of the light source and the photodetector, when viewed in a parasagittal section of the ear canal, the output portion of the light source and the input portion of the photodetector in the ear canal (or its walls) are preferably at an angle of at least 45°, and more preferably at an angle greater than 90° and up to and including 180°. An example section of the right ear canal is shown in... Figure 7 The diagram illustrates this concept. As seen therein, the light source 402 and the photodetector 404 in the ear canal 400 are at an angle of approximately 120°. This angle helps to maximize the distance traveled by the light 406 emitted by the light source 402 before detection at the photodetector 404. It is also possible to maximize the distance traveled by the light 406 by maximizing the linear distance between the light source 402 and the photodetector 404. For example, placing the light source 402 at the center of the SDS section and the photodetector 404 at the most lateral position of the ITE section provides a greater travel distance for the light 406 than when the light source 402 and the photodetector 404 are placed relatively close to each other.

[0046] Furthermore, when the movement of the ear canal wall due to mandibular movement is dominant on the anterior wall, the optical path 406 is preferably tailored to the posterior ear canal wall, such as... Figure 7 As shown, this is to mitigate mandibular movement artifacts. Compared to the posterior wall of the ear canal, the anterior wall of the ear canal can be defined as the portion of the ear canal located closer to the front of the subject's head (particularly closer to the subject's face). In other words, the angle between the light source 402 and the photodetector 404 is an acute angle facing the posterior wall of the ear canal. However, if mandibular movement is intended to be detected, then the optical path 406 can be customized to primarily pass through the posterior wall. Customization of the optical path 406 can be accomplished by directional light output from the light source 402 as discussed, directional detection of light from the photodetector 404 as discussed above, and / or by adjusting the angle between the light source 402 and the photodetector 404. In other embodiments, different light sources or photodetectors may be combined to cover different optical paths, one intentionally sensitive to mandibular movement and another non-dominantly sensitive.

[0047] In some embodiments, the photodetector may be a reverse-biased photodiode, wherein incident light induces a current proportional to the intensity of the incident light. Therefore, the measured current of the photodiode can indicate the intensity of the detected light. However, other embodiments may utilize a forward-biased photodiode by measuring the time delay between the applied forward voltage and the corresponding change in the forward current of the photodiode, which depends on the intensity of the incident light.

[0048] like Figure 8A As shown in -C, this time depends on the intensity of the incident light at the photodiode, where the change in forward current takes longer for lower light intensities than for higher light intensities. More specifically, Figure 8A The diagram illustrates the IV curve for an example forward-biased photodiode. I F and V F These correspond to forward current and voltage, respectively; and I R and V R These correspond to reverse current and voltage, respectively. Compare. Figure 8B and Figure 8C It should be noted that if a positive voltage is applied at time zero... V F Then the current will not increase to the forward current. I F until time t That time t It is inversely proportional to the intensity of light, where lower intensity light corresponds to a longer duration.

[0049] Therefore, the intensity of incident light at the photodiode can be detected by measuring the forward voltage. V F The measurement is based on the time delay between the measured current and the measured current. Figure 9 The diagram illustrates an example circuit for performing this detection. As seen therein, oscillator 600 feeds counter 602. A voltage applied to photodiode 604 later induces a current at a specific time t, which is measured as the voltage across the resistor, and subsequently stops counter 602. Therefore, counter 602 receives a start / reset signal along with the change in voltage across photodiode 604, resulting in another voltage step that stops the counter again. Based on the frequency of oscillator 600, the counter can then determine the time. t The counter 602 continues until it receives a stop signal in the form of a forward current measured via the voltage across a resistor from the photodiode 604. The counter 602 outputs the detection time. t Or corresponding to the detection time t The signal represents the intensity of the incident light that can be processed by the microprocessor 606 or similar circuitry. The microprocessor 606 can analyze the detection time. t The incident light intensity is identified, and the resulting PPG signal is further analyzed to determine physiological parameters. Because the determination of the incident light intensity utilizes only a counter 602 instead of analyzing the small current caused by the greatly attenuated incident light, the corresponding circuitry for the forward bias photodiode has lower peak current, energy consumption, and system complexity than conventional PPG sensor systems that require high-power light sources and amplifier circuits.

[0050] Furthermore, if the light intensity at the photodetector is intentionally kept low (e.g., by using a lower-power light source), then the time delay is long enough (e.g., μs to ms) that the counter 602 does not require a special high-frequency oscillator 600 as a time base. Instead, a relatively low-frequency oscillator 600 (e.g., only tens of MHz) already used in hearing devices is sufficient to achieve a sufficiently high photodiode measurement resolution. Such a lower-frequency oscillator and its corresponding circuitry also limit power consumption and system complexity compared to higher-frequency oscillators and associated circuitry. Moreover, a weaker power light source providing less light can be used with a sufficiently long optical path to achieve an acceptable signal-to-noise ratio.

[0051] For example, the brightest light intensity at the photodetector may cause a 1 μs delay between the switching of the photodiode to its forward voltage and the forward current flow. Therefore, using a 20 MHz oscillator, counter 602 can determine a delay with 20 least significant bits (LSBs) and 5% resolution. For darker conditions, when more blood blocks the light path, a longer delay occurs and therefore a higher value is output by counter 602. Preferably, the intensity of the light emitted by the light source is weak enough to cause a time delay of at least 200 ns, and even more preferably, the delay is at least 1 μs. Therefore, it is possible that the power-consuming high-frequency oscillator 600 is not required, and the total power for the PPG sensor can be further reduced. Power can be further reduced by operating the light source, oscillator, and / or other related circuitry according to the duty cycle.

[0052] For non-operational or even brighter conditions, such as when the hearing device and PPG sensor are removed from the ear canal, the particularly short time delay detectable by the low-frequency oscillator and counter described above may not be necessary. While such detection may not be suitable for determining the PPG signal, the short delay can be used instead to detect that the hearing device has been or is being removed from the ear, since the situation is non-operational. Such detection may cause the hearing device to, for example, automatically power off, or hear an alarm warning the user of potential errors, or trigger any other suitable measures. In a further embodiment, the PPG sensor and hearing device may also include a motion sensor, such as an accelerometer. Such a motion sensor can be used to detect artifact sources, which can then be removed from any resulting PPG signal during processing.

[0053] While various features have been presented above, it should be understood that these features can be used individually or in any combination thereof. Furthermore, it should be understood that variations and modifications will occur to those skilled in the art to which the claimed paradigm belongs. Therefore, the above description is merely illustrative and not intended to be restrictive.

Claims

1. A hearing device, comprising: a light source (212, 300, 304, 308, 402) configured to emit light; a light detector (214, 404) configured to detect light emitted by the light source after interaction with tissue of a subject; an audio receiver (116, 202) configured to deliver sound to the subject; and a dome structure (120, 206) configured to conform to a shape of an ear canal of a subject when the hearing device is in the ear canal of the subject, characterized in that the dome structure (120, 206) absorbs and / or reflects at least part of the light emitted by the light source such that an intensity of the light emitted by the light source at a wavelength that passes through the dome structure is less than an intensity of the light emitted by the light source at a wavelength that passes through the tissue, wherein an output of the light source (212, 300, 304, 308, 402) and an input of the light detector (214, 404) are separated by the dome structure (120, 206). the light source (212, 300, 304, 308, 402) is configured to emit directed light towards a wall of the ear canal.

2. The hearing device of claim 1, wherein, the light source (212, 300, 304, 308, 402) is configured to emit diffuse light within the ear canal.

3. The hearing device according to claim 1 or 2, wherein, the hearing device further comprises a nozzle (118, 204), the audio receiver (116, 202) being configured to deliver the sound to the subject through the nozzle (118, 204).

4. The hearing device according to claim 1 or 2, wherein, the output of the light source (212, 300, 304, 308, 402) is positioned at the nozzle (118, 204) and the input of the light detector (214, 404) is positioned at the audio receiver (116, 202).

5. The hearing device of claim 4, wherein, the output of the light source (212, 300, 304, 308, 402) is positioned at the audio receiver (116, 202) and the input of the light detector (214, 404) is positioned at the nozzle (118, 204).

6. The hearing device of claim 4, wherein, the nozzle (118, 204) is transparent to a wavelength of light emitted by the light source.

7. The hearing device of claim 4, wherein, the nozzle (118, 204) comprises a light guide connected to the input of the light detector (214, 404).

8. The hearing device of claim 7, wherein, the output of the light source (212, 300, 304, 308, 402) is at a discrete location from the light source, the output of the light source being connected to the light source via a light guide (215).

9. The hearing device according to any of claims 1-2 and 5-8, wherein, the input of the light detector (214, 404) is at a discrete location from the light detector, the input of the light detector being connected to the light detector via a light guide (215).

10. The hearing device according to any of claims 1-2 and 5-8, wherein, the dome structure (120, 206) is opaque to ambient light.

11. The hearing device according to any of claims 1-2 and 5-8, wherein, ​ 12. The hearing device according to any one of claims 1-2 and 5-8, wherein, The output of the light source (212, 300, 304, 308, 402) and the input of the light detector (214, 404) are at an angle of at least 45° when viewed in a para-sagittal section of the ear canal.

13. The hearing device of claim 12, wherein, The angle is an acute angle facing the back wall of the ear canal.

14. The hearing device according to any of the claims 1-2, 5-8 and 13, wherein The light detector (214, 404) is a forward biased photodiode, and wherein the hearing device is configured to determine the intensity of the light detected by the light detector (214, 404) by measuring a time delay between the onset of the forward voltage of the light detector and the onset of the forward current of the light detector.

15. The hearing device of claim 14, wherein, The light source (212, 300, 304, 308, 402) is configured to emit light with an intensity such that the time delay is at least 200 ns.

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