PATENT DOCUMENT

Publication Number: US-11940293-B2
Application Number: US-202117465594-A
Country: US
Kind Code: B2

Title: Finger devices with self-mixing interferometric proximity sensors

Abstract:
A system may include one or more finger devices that gather input from a user&#39;s fingers. A finger device may include one or more self-mixing interferometric proximity sensors that measure a distance to the user&#39;s finger. The proximity sensor may measure changes in distance between the proximity sensor and a flexible membrane that rests against a side portion of the user&#39;s finger. The self-mixing interferometric proximity sensor may include a laser and a photodiode. In some arrangements, a single laser driver may drive the lasers of multiple self-mixing proximity sensors using time-multiplexing. The self-mixing proximity sensor may operate according to a duty cycle. Interpolation and stitching may be used to determine the total displacement of the user&#39;s finger including both the on periods and off periods of the self-mixing proximity sensor.

Claims:
What is claimed is: 
     
       1. A finger device configured to be worn on a finger of a user, comprising:
 a housing configured to be coupled to the finger; 
 a self-mixing interferometric proximity sensor coupled to the housing that measures changes in a distance between the self-mixing interferometric proximity sensor and a side of the finger; and 
 control circuitry configured to determine a force of a touch input by the finger using the self-mixing interferometric proximity sensor, wherein the control circuitry is configured to operate the self-mixing interferometric proximity sensor according to a duty cycle where the self-mixing interferometric proximity sensor alternates between an on state in which the changes in the distance are measured and an off state in which the changes in the distance are not measured and wherein the control circuitry is configured to use interpolation to estimate changes in the distance between the self-mixing interferometric proximity sensor and the side of the finger during the off states. 
 
     
     
       2. The finger device defined in  claim 1 , wherein the housing is configured to be coupled to the finger without covering a lower finger pad surface of the finger and wherein determining the force of the touch input by the finger comprises determining the force of the touch input by the lower finger pad surface. 
     
     
       3. The finger device defined in  claim 1 , wherein the self-mixing interferometric proximity sensor comprises a vertical cavity surface emitting laser. 
     
     
       4. The finger device defined in  claim 3 , wherein the self-mixing interferometric proximity sensor comprises a photodiode and wherein the control circuitry includes a drive circuit configured to modulate the vertical cavity surface emitting laser and includes a sense circuit configured to use the photodiode to measure corresponding self-mixing fluctuations in output light intensity from the vertical cavity surface emitting laser. 
     
     
       5. The finger device defined in  claim 1 , further comprising a flexible membrane that conforms to the side of the finger. 
     
     
       6. The finger device defined in  claim 5 , wherein the flexible membrane comprises silicone. 
     
     
       7. The finger device defined in  claim 5 , wherein the flexible membrane comprises a flexible layer that is coupled to a reflective layer and wherein the self-mixing interferometric proximity sensor comprises a light source that directs light towards the reflective layer. 
     
     
       8. The finger device defined in  claim 5 , wherein the self-mixing interferometric proximity sensor comprises a light source and a transparent cap formed over the light source and wherein the transparent cap is interposed between the light source and the flexible membrane. 
     
     
       9. The finger device defined in  claim 8 , wherein the self-mixing interferometric proximity sensor comprises a lens formed on the transparent cap. 
     
     
       10. The finger device defined in  claim 5 , further comprising a substrate, wherein the flexible membrane has a first portion that is parallel to the substrate, and wherein, when no force is applied by the finger to the flexible membrane, the flexible membrane has three bends between the first portion and the substrate. 
     
     
       11. The finger device defined in  claim 1 , wherein the self-mixing interferometric proximity sensor comprises a vertical cavity surface emitting laser and a photodiode, wherein the control circuitry includes sensing circuitry that is configured to determine the changes in the distance between the self-mixing interferometric proximity sensor and the side of the finger, and wherein the sensing circuitry comprises:
 a transimpedance amplifier coupled to the photodiode; 
 an analog-to-digital converter coupled to an output of the transimpedance amplifier; 
 demodulation and offset circuitry coupled to an output of the analog-to-digital converter, wherein the demodulation and offset circuitry outputs an I signal and a Q signal; and 
 processing circuitry configured to determine displacement based on the I signal and the Q signal. 
 
     
     
       12. The finger device defined in  claim 11 , wherein the demodulation and offset circuitry includes offset generation circuitry that is configured to output a stored offset value. 
     
     
       13. The finger device defined in  claim 11 , wherein the sensing circuitry further comprises:
 amplitude analysis circuitry that is configured to adjust the vertical cavity surface emitting laser based on a ratio between amplitudes of the I signal and the Q signal. 
 
     
     
       14. A finger device configured to be worn on a finger of a user, comprising:
 a housing configured to be coupled to the finger; 
 a self-mixing interferometric proximity sensor module coupled to the housing, wherein the self-mixing interferometric proximity sensor module comprises a substrate, a self-mixing interferometric proximity sensor on the substrate, a rigid structure, and at least one flexible sidewall that couples the rigid structure to the substrate; and 
 control circuitry configured to determine a force of a touch input by the finger using the self-mixing interferometric proximity sensor. 
 
     
     
       15. The finger device defined in  claim 14 , wherein the housing is configured to be coupled to the finger without covering a lower finger pad surface of the finger and wherein determining the force of the touch input by the finger comprises determining the force of the touch input by the lower finger pad surface. 
     
     
       16. The finger device defined in  claim 14 , wherein the self-mixing interferometric proximity sensor comprises a vertical cavity surface emitting laser. 
     
     
       17. The finger device defined in  claim 16 , wherein the self-mixing interferometric proximity sensor comprises a photodiode and wherein the control circuitry includes a drive circuit configured to modulate the vertical cavity surface emitting laser and includes a sense circuit configured to use the photodiode to measure corresponding self-mixing fluctuations in output light intensity from the vertical cavity surface emitting laser. 
     
     
       18. A finger device configured to be worn on a finger of a user, comprising:
 a housing configured to be coupled to the finger; 
 a self-mixing interferometric proximity sensor coupled to the housing that measures changes in a distance between the self-mixing interferometric proximity sensor and a side of the finger, wherein the self-mixing interferometric proximity sensor comprises a vertical cavity surface emitting laser and a photodiode; and 
 control circuitry configured to determine a force of a touch input by the finger using the self-mixing interferometric proximity sensor, wherein the control circuitry is configured to obtain an I signal and a Q signal using output from the photodiode and wherein the vertical cavity surface emitting laser is updated based on a ratio between amplitudes of the I signal and the Q signal. 
 
     
     
       19. The finger device defined in  claim 18 , wherein the housing is configured to be coupled to the finger without covering a lower finger pad surface of the finger and wherein determining the force of the touch input by the finger comprises determining the force of the touch input by the lower finger pad surface.

Description:
FIELD 
     This relates generally to electronic devices, and, more particularly, to sensors for finger-mounted electronic devices. 
     BACKGROUND 
     Electronic devices such as computers can be controlled using computer mice and other input accessories. In virtual reality systems, force-feedback gloves can be used to control virtual objects. Cellular telephones may have touch screen displays and vibrators that are used to create haptic feedback in response to touch input. 
     Devices such as these may not be convenient for a user, may be cumbersome or uncomfortable, or may provide inadequate feedback. 
     SUMMARY 
     A system may include one or more finger devices that gather input from a user&#39;s fingers. The system may include control circuitry that sends control signals to an electronic device based on the input gathered with the finger devices. 
     A finger device may include one or more proximity sensors that measure a distance to the user&#39;s finger. The proximity sensor may be an optical proximity sensor such as a self-mixing interferometric optical proximity sensor having a laser and photodiode. The proximity sensor may have submicron resolution and may be configured to detect very small movements of the user&#39;s finger. The proximity sensor may measure changes in distance between the proximity sensor and a flexible membrane that rests against a side portion of the user&#39;s finger. 
     A self-mixing proximity sensor may have a coherent or partially coherent source of electromagnetic radiation. The source of radiation may, for example, be a coherent light source such as an infrared vertical cavity surface-emitting laser, a quantum cascade laser, or other laser. The self-mixing proximity sensor may also have a light detector such as a photodiode and/or other electromagnetic-radiation-sensitive element. The photodiode may be stacked with the laser and/or may be an intra-cavity photodiode that is located within the laser cavity. In some arrangements, a single laser driver may drive the lasers of multiple self-mixing proximity sensors using time-multiplexing. 
     The self-mixing proximity sensor may operate according to a duty cycle. Interpolation and stitching may be used to determine the total displacement of the user&#39;s finger including both the on periods and off periods of the self-mixing proximity sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an illustrative system with a finger device in accordance with an embodiment. 
         FIG.  2    is a top view of an illustrative finger of a user on which a finger device has been placed in accordance with an embodiment. 
         FIG.  3    is a cross-sectional side view of an illustrative finger device on the finger of a user in accordance with an embodiment. 
         FIGS.  4 A and  4 B  are cross-sectional side views of an illustrative finger device with a self-mixing interferometric proximity sensor on the side of the finger of a user in accordance with an embodiment. 
         FIG.  5    is a graph of force as a function of displacement for the side of the finger of a user in accordance with an embodiment. 
         FIG.  6 A  is a cross-sectional side view of an illustrative self-mixing interferometric proximity sensor that includes a flexible membrane attached to rigid sidewalls in accordance with an embodiment. 
         FIG.  6 B  is a cross-sectional side view of an illustrative self-mixing interferometric proximity sensor that includes a continuous flexible membrane in accordance with an embodiment. 
         FIG.  6 C  is a cross-sectional side view of an illustrative self-mixing interferometric proximity sensor that includes a rigid structure attached to flexible sidewalls in accordance with an embodiment. 
         FIG.  6 D  is a cross-sectional side view of an illustrative self-mixing interferometric proximity sensor that includes a semi-rigid, cantilever structure in accordance with an embodiment. 
         FIGS.  7 A- 7 D  are cross-sectional side views of illustrative self-mixing interferometric proximity sensors that includes continuous flexible membranes of various shapes in accordance with an embodiment. 
         FIG.  8    is a cross-sectional side view of an illustrative self-mixing interferometric proximity sensor that includes a vertical cavity surface-emitting laser, a photodiode, and a transparent cap in accordance with an embodiment. 
         FIG.  9    is a schematic diagram of illustrative sensing circuitry that may be used to determine displacement using the self-mixing interferometric proximity sensor in accordance with an embodiment. 
         FIG.  10    is a schematic diagram of illustrative DC subtraction logic such as the DC subtraction logic in  FIG.  9    that may be used to determine an offset value in accordance with an embodiment. 
         FIG.  11    is a series of graphs showing how an illustrative self-mixing interferometric proximity sensor may operate with a duty cycle and use interpolation and stitching to calculate a total displacement in accordance with an embodiment. 
         FIG.  12 A  is a graph of velocity as a function of time showing how velocity interpolation may be used by the sensing circuitry in accordance with an embodiment. 
         FIG.  12 B  is a graph of calculated displacement as a function of time showing how the interpolated velocity from  FIG.  12 A  may be integrated to calculate displacement during an off period in accordance with an embodiment. 
         FIG.  13    is a schematic diagram showing how a single laser driver may operate multiple self-mixing interferometric proximity sensors using time-multiplexing in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices that are configured to be mounted on the body of a user may be used to gather user input and to provide a user with output. For example, electronic devices that are configured to be worn on one or more of a user&#39;s fingers, which are sometimes referred to as finger devices or finger-mounted devices, may be used to gather user input and to supply output. A finger device may, as an example, include an inertial measurement unit with an accelerometer for gathering information on finger motions such as finger taps or free-space finger gestures, may include proximity sensors such as self-mixing interferometric optical proximity sensors for measuring small changes in distance to the finger surface as the finger moves, may include force sensors for gathering information on normal and shear forces in the finger device and the user&#39;s finger, and may include other sensors for gathering information on the interactions between the finger device (and the user&#39;s finger on which the device is mounted) and the surrounding environment. The finger device may include a haptic output device to provide the user&#39;s finger with haptic output and may include other output components. 
     One or more finger devices may gather user input from a user. The user may use finger devices in operating a virtual reality or mixed reality device (e.g., head-mounted equipment such as glasses, goggles, a helmet, or other device with a display) and/or in operating other equipment such as desktop computers, laptop computers, tablet computers, and other electronic devices. During operation, the finger devices may gather user input such as information on interactions between the finger device(s) and the surrounding environment (e.g., interactions between a user&#39;s fingers and the environment, including finger motions and other interactions associated with virtual content displayed for a user). The user input may be used in controlling visual output on the display. Corresponding haptic output may be provided to the user&#39;s fingers using the finger devices. Haptic output may be used, for example, to provide the fingers of a user with a desired texture sensation as a user is touching a real object or as a user is touching a virtual object. Haptic output can also be used to create detents and other haptic effects. 
     Finger devices can be worn on any or all of a user&#39;s fingers (e.g., the index finger, the index finger and thumb, three of a user&#39;s fingers on one of the user&#39;s hands, some or all fingers on both hands, etc.). To enhance the sensitivity of a user&#39;s touch as the user interacts with surrounding objects, finger devices may have inverted U shapes or other configurations that allow the finger devices to be worn over the top and sides of a user&#39;s fingertips while leaving the user&#39;s finger pads exposed. In other words, the fiber device does not cover the user&#39;s finger pad surface. This allows a user to touch objects with the finger pad portions of the user&#39;s fingers during use. If desired, finger devices may be worn over knuckles on a user&#39;s finger, between knuckles, and/or on other portions of a user&#39;s finger. The use of finger devices on a user&#39;s fingertips is sometimes described herein as an example. 
     Users can use the finger devices to interact with any suitable electronic equipment. For example, a user may use one or more finger devices to interact with a virtual reality or mixed reality system (e.g., a head-mounted device with a display), to supply input to a desktop computer, tablet computer, cellular telephone, watch, ear buds, or other accessory, or to interact with other electronic equipment. 
       FIG.  1    is a schematic diagram of an illustrative system of the type that may include one or more finger devices. As shown in  FIG.  1   , system  8  may include electronic device(s) such as finger device(s)  10  and other electronic device(s)  24 . Each finger device  10  may be worn on a finger of a user&#39;s hand. Additional electronic devices in system  8  such as devices  24  may include devices such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a desktop computer (e.g., a display on a stand with an integrated computer processor and other computer circuitry), a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wristwatch device, a pendant device, a headphone or earpiece device, a head-mounted device such as glasses, goggles, a helmet, or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a remote control, a navigation device, an embedded system such as a system in which equipment is mounted in a kiosk, in an automobile, airplane, or other vehicle, a removable external case for electronic equipment, a strap, a wrist band or head band, a removable cover for a device, a case or bag that has straps or that has other structures to receive and carry electronic equipment and other items, a necklace or arm band, a wallet, sleeve, pocket, or other structure into which electronic equipment or other items may be inserted, part of a chair, sofa, or other seating (e.g., cushions or other seating structures), part of an item of clothing or other wearable item (e.g., a hat, belt, wrist band, headband, sock, glove, shirt, pants, etc.), or equipment that implements the functionality of two or more of these devices. 
     With one illustrative configuration, which may sometimes be described herein as an example, device  10  is a finger-mounted device having a finger-mounted housing with a U-shaped body that grasps a user&#39;s finger or a finger-mounted housing with other shapes configured to rest against a user&#39;s finger and device(s)  24  is a cellular telephone, tablet computer, laptop computer, wristwatch device, head-mounted device, a device with a speaker, or other electronic device (e.g., a device with a display, audio components, and/or other output components). A finger device with a U-shaped housing may have opposing left and right sides that are configured to receive a user&#39;s finger and a top housing portion that couples the left and right sides and that overlaps the user&#39;s fingernail. 
     Devices  10  and  24  may include control circuitry  12  and  26 . Control circuitry  12  and  26  may include storage and processing circuitry for supporting the operation of system  8 . The storage and processing circuitry may include storage such as nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  12  and  26  may be used to gather input from sensors and other input devices and may be used to control output devices. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors and other wireless communications circuits, power management units, audio chips, application specific integrated circuits, etc. 
     To support communications between devices  10  and  24  and/or to support communications between equipment in system  8  and external electronic equipment, control circuitry  12  may communicate using communications circuitry  14  and/or control circuitry  26  may communicate using communications circuitry  28 . Circuitry  14  and/or  28  may include antennas, radio-frequency transceiver circuitry, and other wireless communications circuitry and/or wired communications circuitry. Circuitry  14  and/or  26 , which may sometimes be referred to as control circuitry and/or control and communications circuitry, may, for example, support bidirectional wireless communications between devices  10  and  24  over wireless link  38  (e.g., a wireless local area network link, a near-field communications link, or other suitable wired or wireless communications link (e.g., a Bluetooth® link, a WiFi® link, a 60 GHz link or other millimeter wave link, etc.). Devices  10  and  24  may also include power circuits for transmitting and/or receiving wired and/or wireless power and may include batteries. In configurations in which wireless power transfer is supported between devices  10  and  24 , in-band wireless communications may be supported using inductive power transfer coils (as an example). 
     Devices  10  and  24  may include input-output devices such as devices  16  and  30 . Input-output devices  16  and/or  30  may be used in gathering user input, in gathering information on the environment surrounding the user, and/or in providing a user with output. Devices  16  may include sensors  18  and devices  24  may include sensors  32 . Sensors  18  and/or  32  may include proximity sensors (e.g., self-mixing optical proximity sensors), force sensors (e.g., strain gauges, capacitive force sensors, resistive force sensors, etc.), audio sensors such as microphones, touch and/or proximity sensors such as capacitive sensors, optical sensors such as optical sensors that emit and detect light, ultrasonic sensors (e.g., ultrasonic sensors for tracking device orientation and location and/or for detecting user input such as finger input), and/or other touch sensors and/or proximity sensors, monochromatic and color ambient light sensors, image sensors, sensors for detecting position, orientation, and/or motion (e.g., accelerometers, magnetic sensors such as compass sensors, gyroscopes, and/or inertial measurement units that contain some or all of these sensors), muscle activity sensors (EMG) for detecting finger actions, radio-frequency sensors, depth sensors (e.g., structured light sensors and/or depth sensors based on stereo imaging devices), optical sensors such as self-mixing sensors and light detection and ranging (lidar) sensors that gather time-of-flight measurements, optical sensors such as visual odometry sensors that gather position and/or orientation information using images gathered with digital image sensors in cameras, gaze tracking sensors, visible light and/or infrared cameras having digital image sensors, humidity sensors, moisture sensors, and/or other sensors. In some arrangements, devices  10  and/or  24  may use sensors  18  and/or  32  and/or other input-output devices  16  and/or  30  to gather user input (e.g., buttons may be used to gather button press input, touch sensors overlapping displays can be used for gathering user touch screen input, touch pads may be used in gathering touch input, microphones may be used for gathering audio input, accelerometers may be used in monitoring when a finger contacts an input surface and may therefore be used to gather finger press input, etc.). If desired, device  10  and/or device  24  may include rotating buttons (e.g., a crown mechanism on a watch or finger device or other suitable rotary button that rotates and that optionally can be depressed to select items of interest). Alphanumeric keys and/or other buttons may be included in devices  16  and/or  30 . In some configurations, sensors  18  may include joysticks, roller balls, optical sensors (e.g., lasers that emit light and image sensors that track motion by monitoring and analyzing changings in the speckle patterns and other information associated with surfaces illuminated with the emitted light as device  10  is moved relative to those surfaces), fingerprint sensors, and/or other sensing circuitry. Radio-frequency tracking devices may be included in sensors  18  to detect location, orientation, and/or range. Beacons (e.g., radio-frequency beacons) may be used to emit radio-frequency signals at different locations in a user&#39;s environment (e.g., at one or more registered locations in a user&#39;s home or office). Radio-frequency beacon signals can be analyzed by devices  10  and/or  24  to help determine the location and position of devices  10  and/or  24  relative to the beacons. If desired, devices  10  and/or  24  may include beacons. Frequency strength (received signal strength information), beacon orientation, time-of-flight information, and/or other radio-frequency information may be used in determining orientation and position information. At some frequencies (e.g., lower frequencies such as frequencies below 10 GHz), signal strength information may be used, whereas at other frequencies (e.g., higher frequencies such as frequencies above 10 GHz), indoor radar schemes may be used. If desired, light-based beacons, ultrasonic beacons, and/or other beacon devices may be used in system  8  in addition to or instead of using radio-frequency beacons and/or radio-frequency radar technology. 
     Devices  16  and/or  30  may include haptic output devices  20  and/or  34 . Haptic output devices  20  and/or  34  can produce motion that is sensed by the user (e.g., through the user&#39;s fingertips). Haptic output devices  20  and/or  34  may include actuators such as electromagnetic actuators, motors, piezoelectric actuators, electroactive polymer actuators, vibrators, linear actuators (e.g., linear resonant actuators), rotational actuators, actuators that bend bendable members, actuator devices that create and/or control repulsive and/or attractive forces between devices  10  and/or  24  (e.g., components for creating electrostatic repulsion and/or attraction such as electrodes, components for producing ultrasonic output such as ultrasonic transducers, components for producing magnetic interactions such as electromagnets for producing direct-current and/or alternating-current magnetic fields, permanent magnets, magnetic materials such as iron or ferrite, and/or other circuitry for producing repulsive and/or attractive forces between devices  10  and/or  24 ). In some situations, actuators for creating forces in device  10  may be used in squeezing a user&#39;s finger and/or otherwise directly interacting with a user&#39;s finger pulp. In other situations, these components may be used to interact with each other (e.g., by creating a dynamically adjustable electromagnetic repulsion and/or attraction force between a pair of devices  10  and/or between device(s)  10  and device(s)  24  using electromagnets). 
     If desired, input-output devices  16  and/or  30  may include other devices  22  and/or  36  such as displays (e.g., in device  24  to display images for a user), status indicator lights (e.g., a light-emitting diode in device  10  and/or  24  that serves as a power indicator, and other light-based output devices), speakers and other audio output devices, electromagnets, permanent magnets, structures formed from magnetic material (e.g., iron bars or other ferromagnetic members that are attracted to magnets such as electromagnets and/or permanent magnets), batteries, etc. Devices  10  and/or  24  may also include power transmitting and/or receiving circuits configured to transmit and/or receive wired and/or wireless power signals. 
       FIG.  2    is a top view of a user&#39;s finger (finger  40 ) and an illustrative finger-mounted device  10 . As shown in  FIG.  2   , device  10  may be formed from a finger-mounted unit that is mounted on or near the tip of finger  40  (e.g., partly or completely overlapping fingernail  42 ). If desired, device  10  may be worn elsewhere on a user&#39;s fingers such as over a knuckle, between knuckles, etc. Configurations in which a device such as device  10  is worn between fingers  40  may also be used. 
     A user may wear one or more of devices  10  simultaneously. For example, a user may wear a single one of devices  10  on the user&#39;s ring finger or index finger. As another example, a user may wear a first device  10  on the user&#39;s thumb, a second device  10  on the user&#39;s index finger, and an optional third device  10  on the user&#39;s middle finger. Arrangements in which devices  10  are worn on other fingers and/or all fingers of one or both hands of a user may also be used. 
     Control circuitry  12  (and, if desired, communications circuitry  14  and/or input-output devices  16 ) may be contained entirely within device  10  (e.g., in a housing for a fingertip-mounted unit) and/or may include circuitry that is coupled to a fingertip structure (e.g., by wires from an associated wrist band, glove, fingerless glove, etc.). Configurations in which devices  10  have bodies that are mounted on individual user fingertips are sometimes described herein as an example. 
       FIG.  3    is a cross-sectional side view of an illustrative finger device (finger-mounted device)  10  showing illustrative mounting locations  46  for electrical components (e.g., control circuitry  12 , communications circuitry  14 , and/or input-output devices  16  such as sensors  18 , haptic output devices  20 , and/or other devices  22 ) within and/or on the surface(s) of finger device housing  44 . These components may, if desired, be incorporated into other portions of housing  44 . 
     As shown in  FIG.  3   , housing  44  may have a U shape (e.g., housing  44  may be a U-shaped housing structure that faces downwardly and covers the upper surface of the tip of user finger  40  and fingernail  42 ). During operation, a user may press against structures such as structure  50 . As the bottom of finger  40  (e.g., finger pulp  40 P) presses against surface  48  of structure  50 , the user&#39;s finger may compress and force portions of the finger outwardly against the sidewall portions of housing  44  (e.g., for sensing by force sensors or other sensors mounted to the side portions of housing  44 ). Lateral movement of finger  40  in the X-Y plane may also be sensed using force sensors or other sensors on the sidewalls of housing  44  or other portions of housing  44  (e.g., because lateral movement will tend to press portions of finger  40  against some sensors more than others and/or will create shear forces that are measured by force sensors that are configured to sense shear forces). 
     The sensors in device  10  may, for example, measure how forcefully a user is moving device  10  (and finger  40 ) against surface  48  (e.g., in a direction parallel to the surface normal n of surface  48  such as the −Z direction of  FIG.  3   ) and/or how forcefully a user is moving device  10  (and finger  40 ) within the X-Y plane, tangential to surface  48 . The direction of movement of device  10  in the X-Y plane and/or in the Z direction can also be measured by the force sensors and/or other sensors  18  at locations  46 . 
     Structure  50  may be a portion of a housing of device  24 , may be a portion of another device  10  (e.g., another housing  44 ), may be a portion of a user&#39;s finger  40  or other body part, may be a surface of a real-world object such as a table, a movable real-world object such as a bottle or pen, or other inanimate object external to device  10 , and/or may be any other structure that the user can contact with finger  40  while moving finger  40  in a desired direction with a desired force. Because motions such as these can be sensed by device  10 , device(s)  10  can be used to gather pointing input (e.g., input moving a cursor or other virtual object on a display such as a display in devices  36 ), can be used to gather tap input, swipe input, pinch-to-zoom input (e.g., when a pair of devices  10  is used), or other gesture input (e.g., finger gestures, hand gestures, arm motions, etc.), and/or can be used to gather other user input. 
       FIGS.  4 A and  4 B  show in greater detail how a sensor in device  10  may measure how forcefully a user is moving device  10  (and finger  40 ) against surface  48  (e.g., the −Z direction of  FIG.  4   ). As shown in  FIG.  4 A , sensor module  60  (sometimes referred to as a sensor  60 ) is positioned on a side of finger  40 . Sensor module  60  includes a flexible membrane  62 , a rigid housing portion  64 , and a self-mixing interferometric (SMI) proximity sensor  66  (sometimes referred to as self-mixing proximity sensor  66 , self-mixing sensor  66 , self-mixing optical proximity sensor  66 , etc.). 
     Self-mixing proximity sensor  66  may have a coherent or partially coherent source of electromagnetic radiation. The source of radiation may, for example, be a coherent light source such as an infrared vertical cavity surface-emitting laser (VCSEL), a quantum cascade laser, or other laser. The self-mixing proximity sensor may also have a light detector such as a photodiode and/or other electromagnetic-radiation-sensitive element. 
     Self-mixing proximity sensors may have submicron resolution and may be configured to detect very small changes in distance. This allows sensor  66  to detect very small movements of finger  40  (sometimes referred to as microgestures or nanogestures). 
     In  FIG.  4 A , finger  40  is lightly contacting (or not contacting) surface  48 . With this amount of force applied in the negative Z-direction, membrane  62  is positioned a distance  68  from the self-mixing proximity sensor. In  FIG.  4 B , finger  40  presses harder on surface  48  than in  FIG.  4 A . Applying this increased force in the negative Z-direction (relative to as in  FIG.  4 A ) causes the edge of finger  40  to expand in the X-direction (as reflected by displacement  72 ). This in turn causes flexible membrane  62  to be pushed closer to self-mixing proximity sensor  66 . In  FIG.  4 B , membrane  62  is positioned a distance  70  from the self-mixing proximity sensor. Distance  70  in  FIG.  4 B  is less than distance  68  in  FIG.  4 A . Self-mixing proximity sensor  66  has sufficiently high resolution to detect the change in distance to the flexible membrane between  FIG.  4 A  and  FIG.  4 B . 
     Flexible membrane  62  may conform to the side of finger  40 . In this way, changes in the shape/position of finger  40  caused by finger  40  applying force to surface  48  may be translated to displacement in flexible membrane  62  that is in turn detected by self-mixing proximity sensor  66 .  FIG.  5    is a graph of force (applied by the finger in the negative Z-direction) as a function of displacement of the flexible membrane (in the positive X-direction). As shown, the displacement increases with increasing force applied by the finger. Therefore, the displacement measured by the self-mixing proximity sensor may be used to determine the force applied by the finger. 
     Rigid housing portion  64  may optionally be formed integrally with finger device housing  44 . In other words, housing  44  has a portion that forms the housing for sensor module  60 . Alternatively, rigid housing portion  64  for sensor module  60  may be formed separately from finger device housing  44  and attached to finger device housing  44 . 
     There are many possible arrangements for rigid and flexible components within sensor module  60 .  FIG.  6 A  shows an arrangement where self-mixing proximity sensor  66  is positioned on a substrate  74 . Substrate  74  may be a rigid printed circuit board, a flexible printed circuit board, or another desired substrate. In some cases, substrate  74  may itself be a rigid housing structure (e.g., structure  64  in  FIG.  4 A ). Module  60  also includes rigid housing structures  64 . In  FIG.  6 A , the rigid housing structures  64  form sidewalls for the sensor module. Flexible membrane  62  is attached to the rigid sidewalls and forms the finger-interfacing portion of the sensor. In other words, flexible membrane  62  is configured to directly contact finger  40  during operation of sensor module  60 . Flexible membrane  62  may be formed from silicone or another desired material. The flexible membrane is sufficiently flexible to move towards self-mixing proximity sensor  66  when biased (e.g., when the finger touches a surface) as discussed in connection with  FIGS.  4 A and  4 B . 
     The example of  FIG.  6 A  is merely illustrative. In another possible arrangement, shown in  FIG.  6 B , flexible membrane  62  forms the sidewalls of the sensor module in addition to the finger-interfacing portion. Flexible membrane  62  may be formed from silicone or another desired material. In the arrangement of  FIG.  6 B , flexible membrane  62  may be three-dimensional (3D) printed to have the desired shape for the sensor module. The flexible membrane  62  is attached directly to substrate  74 . The flexible membrane has sufficient structural integrity to maintain the shape shown in  FIG.  6 B  when no bias force is applied to the flexible membrane. However, the flexible membrane is sufficiently flexible to move towards self-mixing proximity sensor  66  when biased (e.g., when the finger touches a surface) as discussed in connection with  FIGS.  4 A and  4 B . 
     In another arrangement, shown in  FIG.  6 C , rigid structure  64  is configured to contact finger  40  during operation of device  10 . Rigid structure  64  is connected to substrate  74  by flexible sidewalls  62 . The flexible sidewalls are sufficiently flexible to allow rigid structure  64  to move towards self-mixing proximity sensor  66  when biased (e.g., when the finger touches a surface). 
     In yet another possible arrangement, shown in  FIG.  6 D , a semi-rigid structure  76  with a sidewall portion and a finger-interfacing portion is attached to substrate  74 . The semi-rigid structure  76  has a cantilever arrangement. Opposite the semi-rigid sidewall portion is a flexible sidewall  62  that allows for the semi-rigid structure  76  to move towards self-mixing proximity sensor  66  when biased (e.g., when the finger touches a surface). 
     The aforementioned flexible membranes  62  may have a Young&#39;s modulus of less than 1 GPa, less than 0.5 GPa, less than 0.1 GPa, less than 0.01 GPa, greater than 0.01 GPa, between 0.01 GPa and 0.5 GPa, etc. The semi-rigid structure  76  may have a higher Young&#39;s modulus than flexible membrane  62 . Rigid structures  64  may have a higher Young&#39;s modulus than semi-rigid structure  76  and flexible membrane  62 . 
     In  FIGS.  6 A- 6 D , the sensor module includes various flexible and rigid components that define a cavity. In some arrangements, the cavity is filled with air (and may be referred to as an air-filled cavity). If desired, the cavity may instead be filled with an optically clear filler material  78 . The optically clear filler material may have a refractive index that is greater than 1.3, greater than 1.4, greater than 1.5, greater than 1.6, less than 1.6, between 1.4 and 1.6, etc. The optically clear filler material may help prevent contaminants from interfering with operation of self-mixing proximity sensor  66 . 
       FIG.  6 B  shows one example where a unitary flexible membrane defines the sidewalls and finger-interfacing portion of the sensor module. In  FIG.  6 B , the flexible membrane has planar sidewalls, a planar finger-interfacing portion (that is configured to conform to and/or contact the side of the user&#39;s finger when the finger device is worn by the user), and rounded corners (e.g., 1 bend) between the planar sidewalls and planar finger-interfacing portion. This example is merely illustrative.  FIGS.  7 A- 7 D  show alternative shapes that may be used for a unitary flexible membrane that defines the sidewalls and finger-interfacing portion of the sensor module. 
     In  FIG.  7 A , flexible membrane  62  includes a sidewall portion  80  and a finger-interfacing portion  86 . Sidewall portion  80  has an angled portion  82  and a base  84  that is wider than angled portion  82 . Angled portion  82  is at a non-orthogonal angle relative to substrate  74 . Finger-interfacing portion  86  is planar and is connected to angled portion  82 . Finger-interfacing portion  86  is parallel to substrate  74 . 
     In  FIG.  7 B , flexible membrane  62  includes a sidewall portion  80  and a finger-interfacing portion  86 . Sidewall portion  80  has a rounded corner portion  88  and a base portion  90  that is orthogonal to substrate  74 . Rounded corner portion  88  connects planar base portion  90  to planar finger-interfacing portion  86 . Finger-interfacing portion  86  is parallel to substrate  74 . Planar base portion  90  is orthogonal to substrate  74 . 
     In  FIG.  7 C , flexible membrane  62  includes a sidewall portion  80  with three bends ( 92 ,  94 , and  96 ) between the substrate  74  and a planar finger-interfacing portion  86 . Finger-interfacing portion  86  is parallel to substrate  74 . A first portion of the flexible membrane between bend  96  and substrate  74  is at an orthogonal angle relative to the substrate. A second portion of the flexible membrane between bends  94  and  96  is parallel to the substrate. A third portion of the flexible membrane between bends  92  and  94  is orthogonal to the substrate. 
     In  FIG.  7 D , flexible membrane  62  again includes a sidewall portion  80  with three bends ( 92 ,  94 , and  96 ) between the substrate  74  and a planar finger-interfacing portion  86 . A first portion of the flexible membrane between bend  96  and substrate  74  is at an orthogonal angle relative to the substrate. A second portion of the flexible membrane between bends  94  and  96  doubles back towards the substrate  74  and is at a non-orthogonal angle relative to the substrate. A third portion of the flexible membrane between bends  92  and  94  is orthogonal to the substrate. 
     The flexible membrane shapes of  FIGS.  7 A- 7 D  provide different resistance forces as a function of finger deformation. A flexible membrane shape may be selected that provides a desired resistance force at finger deformations of interest. The flexible membrane shapes of  FIGS.  7 A- 7 D  may also help ensure that deformation is concentrated at the center of the flexible membrane towards the self-mixing proximity sensor  66  (as opposed to deformation occurring at off-center portions of the membrane that are more difficult to detect with sensor  66 ). 
       FIG.  8    is a cross-sectional side view of sensor module  60 . Sensor module  60  includes a self-mixing proximity sensor  66  that detects the proximity of a flexible membrane  62  (as opposed to a rigid structure as in  FIG.  6 C , for example). In  FIG.  8   , the self-mixing proximity sensor includes an infrared light source such as a vertical cavity surface-emitting laser (VCSEL)  102 . The VCSEL  102  serves as a coherent source of electromagnetic radiation for the sensor. The self-mixing proximity sensor also has a photodiode  104  that is used to sense the light transmitted by VCSEL  102 . 
     In  FIG.  8   , the photodiode  104  is stacked with the laser  102 . The photodiode may have a photosensitive area that forms a ring around VCSEL  102  (when viewed from above). This example is merely illustrative. In another possible arrangement, the photodiode  104  may be an intra-cavity photodiode that is located within the laser cavity of laser  102 . 
     Laser  102  may emit light towards the target (flexible membrane  62  with optional reflective coating  106 ). The light reflects off of the target towards laser  102  and photodiode  104 . Terminals of photodiode  104  may be coupled to sensing circuitry in control circuitry  12 . This circuitry gathers photodiode output signals that are produced in response to reception of light that is reflected off the flexible membrane. In addition to using a photodiode, self-mixing can be detected using laser junction voltage measurements (e.g., if the laser is driven at a constant bias current) or laser bias current (e.g., if the laser is driven at a constant voltage). 
     Some of the light that is reflected or backscattered from the flexible membrane (target) reenters the laser cavity of laser  102  and perturbs the electric field coherently, which also reflects as a perturbation to the carrier density in laser  102 . These perturbations in laser  102  cause coherent self-mixing fluctuations in the power of light emitted by the laser and associated operating characteristics of laser  102  such as laser junction voltage and/or laser bias current. These fluctuations may be monitored. For example, the fluctuations in the power of light from laser  102  may be monitored using photodiode  104 . 
     Control circuitry in device  10  can modulate the laser bias current signal for laser  102  to produce a target distance measurement corresponding to a distance between the self-mixing proximity sensor and the flexible membrane that rests against the user&#39;s finger. This modulation can enable the detection of the relative displacement of the user&#39;s finger. Sensor  66  may have submicron resolution, allowing for small displacements of the user&#39;s finger to be accurately measured. 
     The stacked photodiode  104  and laser  102  may be covered by a transparent cap  98 . Transparent cap  98  may be formed from transparent glass, plastic, or another desired material. If desired, the transparent cap may optionally have an integrated lens  100  formed over the stacked photodiode  104  and laser  102 . The lens may be formed integrally with the transparent cap or may be formed from a separate material that is attached to the transparent cap. The lens may increase the signal-to-noise ratio of the sensor as well as reduce the overall target area of the sensor (allowing for flexible membrane  62  to have a reduced size). 
     Optically clear filler material  78  may optionally be included in sensor  66  (between transparent cap  98  and the stacked photodiode  104  and laser  102 ) and/or in sensor module  60  (between flexible membrane  62  and sensor  66 ). 
     The target used by the self-mixing proximity sensor  66  may impact the performance of the sensor. Detecting the displacement of flexible membrane  62  (instead of a user&#39;s finger directly without an intervening flexible membrane) may have the advantage of providing a uniform target having optimized optical properties. 
     To optimize the properties of the self-mixing proximity sensor target, a reflective coating  106  may be attached to an interior surface of flexible membrane  62 . Said another way, the flexible membrane may include a flexible layer (e.g., formed from silicone) that is coupled to a reflective coating/tape. In this type of arrangement, flexible membrane  62  has optimized physical properties (e.g., optimized flexibility) and reflective coating  106  has optimized optical properties for the self-mixing proximity sensor  66 . Coating  106  may be a metallic mirror-like coating (or tape) that has high specular reflection on the light emitted by laser  102 . Alternatively, the coating  106  may be a retro-reflector coating (or tape) that reflects incident light at an angle equal to the incidence angle. This causes a diverging beam (from the laser) to be focused back into the laser aperture. In another possible arrangement, coating  106  may be omitted and flexible membrane  62  itself serves as the target for sensor  66 . 
       FIG.  9    is a schematic diagram of sensing circuitry  110  that may be used to detect displacement of flexible membrane  62  using proximity sensor  66 . Sensing circuitry  110  may be considered part of control circuitry  12  in  FIG.  1    and may sometimes be referred to as control circuitry  110 . 
       FIG.  9    shows laser  102  including light-emitting diode  112  and laser driver  114 . Laser driver  114  modulates the laser bias current signal for laser  102  (e.g., using a sine wave, triangular wave, square wave, trapezoid wave, etc.). Photodiode  104  may be used to detect self-mixing fluctuations in the output power of laser  102 . Sensing circuitry  110  is coupled to photodiode  104 . 
     Sensing circuitry  110  includes a transimpedance amplifier (TIA)  116  that converts the photodiode current into a representative voltage. The voltage output by the transimpedance amplifier is then converted into a digital signal by analog-to-digital convertor (ADC)  120 . The output of ADC  120  is therefore a digital value that represents the photodiode current (I PD ). Sensing circuitry  110  may perform further processing on the detected photodiode current to determine the total displacement of the flexible membrane. Bias subtraction circuitry  118  may optionally be included to remove a bias before converting the photodiode current to a voltage using transimpedance amplifier  116 . 
     First, as shown in  FIG.  9   , the I PD  value is demodulated using a demodulation scheme similar to I/Q demodulation. The photodiode current signal is provided to a first mixer  122  and a second mixer  124 . The first mixer  122  multiplies the photodiode current signal by sin(ω m t) to extract the Q component (where om is the driving frequency of the laser and t is time). The second mixer  124  multiplies the photodiode current signal by cos(2ω m t) to extract the I component. 
     Subtraction circuits  126  and  128  may be used to subtract a direct current (DC) offset that is provided by DC subtraction logic  134  and  136 , respectively, as will be discussed later in greater detail. DC subtraction logic  134  and  136  may sometimes be referred to as offset generation circuits  134  and  136 . The DC subtraction may remove noise from the signal. After the offset correction by subtraction circuits  126  and  128 , a low-pass filter  130  may filter the Q signal and a low-pass filter  132  may filter the I signal. Performing the demodulation (using mixers  122  and  124 ) converts the signals from high frequency into low frequency, sometimes referred to as down-mixing. The low-pass filters  130 / 132  are then applied to the signals to remove noise outside the desired bandwidth. After the low-pass filters are applied, the filtered I/Q signals are output to processing circuitry  140 . Mixers  122  and  124 , subtraction circuits  126  and  128 , low-pass filters  130  and  132 , and DC subtraction logic  134  and  136  may sometimes collectively be referred to as demodulation and offset circuitry or I/Q demodulation and offset circuitry. 
     Processing circuitry  140  may process the Q and I signals to determine a displacement of the target (e.g., the flexible membrane) for the self-mixing proximity sensor. The processing circuitry may calculate λ/(4π)*tan −1 (Q/I) to determine a displacement (ΔL) of the flexible membrane (where λ is the wavelength of operation of the laser). In some cases, the self-mixing proximity sensor may be operated according to a duty cycle. In these scenarios, interpolation and stitching circuitry  142  may use interpolation to determine displacement during off periods and stitch together the measured displacements (from on periods) with interpolated displacements (from off periods) to determine total overall displacement, as will be discussed later in more detail. 
     To accurately measure displacement, the amplitudes of the Q signal and the I signal need to be balanced (e.g., the amplitude of I should be equal to the amplitude of Q). The I/Q balance may be adjusted using the current modulation depth of laser  102 . Laser driver  114  drives the diode  112  between maximum and minimum current magnitudes at a driving frequency (e.g., 350 kHz, between 300 kHz and 400 kHz, or any other desired frequency). The difference between the maximum and minimum current values used by the laser driver may be referred to as the current modulation depth of laser  102 . Adjusting the current modulation depth may adjust the I/Q ratio. 
     Sensing circuitry  110  may include amplitude analysis circuitry  138 . The amplitude analysis circuitry  138  may receive the offset and filtered Q and I values from low-pass filters  130  and  132 , respectively. Amplitude analysis circuitry  138  may then characterize the amplitudes of Q and I (e.g., using a standard deviation, root mean squares analysis, fast Fourier transform (FFT), etc.). If the determined amplitudes of Q and I are equal (e.g., within 5%, within 3%, within 1%, within 0.1%, etc.), the current modulation depth may remain unchanged. If the determined amplitude of Q is greater than the determined amplitude of I (e.g., by greater than 5%, greater than 3%, greater than 1%, greater than 0.1%, etc.), the current modulation depth may be increased. If the determined amplitude of I is greater than the determined amplitude of Q (e.g., by greater than 5%, greater than 3%, greater than 1%, greater than 0.1%, etc.), the current modulation depth may be decreased. Amplitude analysis circuitry  138  may provide a control signal to laser driver  114  that updates the current modulation depth based on the comparison between the amplitudes of Q and I. 
       FIG.  10    is a schematic diagram of DC subtraction logic  134 . DC subtraction logic  134  may be used to determine a DC offset that is subtracted from the Q signal by subtraction circuit  126 . The DC offset may be determined for the I/Q values over a given time frame (e.g., a period/frame of the duty cycle when the sensor is on). 
     When the velocity of displacement of the flexible membrane is high, the I/Q signals will have a relatively high frequency. When the velocity of displacement of the flexible membrane is low, the I/Q signals will have a relatively low frequency. At a high frequency, the average of the I/Q signal may be taken as the DC offset. In other words, the offset value for Q is equal to mean(Q) over T ON  and the offset value for I is equal to mean(I) over T ON  (e.g., an on period of the duty cycle). At low frequency, however, less than 1 period may be present during the time period T ON . This means that the average value is not an accurate representation of the DC offset. Accordingly, if the frequency is low and less than 1 period is present during the time period T ON , a previously determined offset (from a high frequency T ON ) may be used. This concept is represented by the schematic diagram of  FIG.  10   . 
     As shown, the DC subtraction logic may receive an input signal. In this case, Q will be discussed, but it should be understood that I could be substituted for Q for DC subtraction logic  136 . A first block  144  (sometimes referred to as mean calculating circuitry  144 ) may determine the average of the input signal (Q MEAN ) whereas a second block  146  (sometimes referred to as standard deviation calculating circuitry  146 ) may determine the standard deviation of the input signal (Q STD ). Block  148  (sometimes referred to as comparison circuitry  148 ) is used to determine if the standard deviation is higher than a predetermined threshold. If the standard deviation is higher than the predetermined threshold (STD THRESHOLD ), it can be assumed that the input signal has a sufficiently high frequency to provide an accurate offset value. A control signal from block  148  may be provided to switch  152 . When Q STD  is higher than STD THRESHOLD , switch  152  may be closed and Q MEAN  is provided to offset history block  150 . The offset from offset history block  150  is then provided as Q OFFSET  to subtraction circuit  126  (as in  FIG.  9   ). 
     If, at block  148 , the standard deviation is lower than the predetermined threshold (STD THRESHOLD ), it can be assumed that the input signal has a low frequency that is insufficient to provide an accurate offset value. When Q STD  is lower than STD THRESHOLD , switch  152  may be opened and Q MEAN  is not provided to offset history block  150 . The previously stored offset from the most recent frame in which Q STD &gt;STD THRESHOLD  is then provided as Q OFFSET  to subtraction circuit  126  (as in  FIG.  9   ). 
     Offset generation circuitry  136  for the I signal may have the same arrangement as offset generation circuitry  134  of  FIG.  10    for the Q signal. 
     In one possible arrangement for self-mixing proximity sensor  66 , the self-mixing proximity sensor  66  may operate with a 100% duty cycle. In other words, the self-mixing proximity sensor may always be monitoring for changes in displacement in flexible membrane  62  while the finger device is on. Although an ‘always on’ approach obtains a maximum amount of data to inform the sensor on displacement, operating at a 100% duty cycle may consume more power than desired. Accordingly, the self-mixing proximity sensor may operate with a duty cycle that is less than 100%. Interpolation and stitching circuitry  142  in  FIG.  9    may be used to determine the total displacement of the flexible membrane when the duty cycle is less than 100%. 
       FIG.  11    is a series of graphs showing how the self-mixing proximity sensor may operate with a duty cycle and still determine total displacement. Graph  162  shows the actual displacement of the flexible membrane (e.g., the SMI proximity sensor target) over time. Graph  164  shows the duty cycle of the self-mixing proximity sensor. Graph  166  shows the displacement measured by the self-mixing proximity sensor over time. Graph  168  shows the total calculated displacement determined by interpolation and stitching circuitry  142  over time. 
     As shown by graph  164 , the self-mixing proximity sensor operates at a duty cycle with on periods and off periods. In  FIG.  11   , the sensor is on from t 0  to t 1 , from t 2  to t 3 , and from t 4  to t 5 . The sensor is off from t 1  to t 2  and from t 3  to t 4 . As shown by graph  166 , displacement from the starting point ‘0’ is measured during each on period (T ON ). Therefore, displacement measurements are obtained between t 0  and t 1 , between t 2  and t 3 , and between t 4  and t 5 . The shapes of the curves of graph  166  match the shapes of the actual displacement curve of graph  162  during these time periods. However, no displacement measurements are obtained between t 1  and t 2  and between t 3  and t 4 . Accordingly, the measured displacement during these times in graph  166  are blank or unknown. 
     To determine the total displacement, the displacement during the off periods (T OFF ) may be estimated using interpolation. Specifically, linear interpolation may be used to estimate a velocity of the target during the off period.  FIG.  12 A  shows an example of this type for the off period between t 1  and t 2 . The measured displacement data from t 0  to t 1  may be used to determine the instantaneous velocity V 1  of the target at t 1  (when the data gathering ceases). Similarly, measured displacement data from t 2  to t 3  may be used to determine the instantaneous velocity V 2  of the target at t 2 . An assumption is made that the velocity varies linearly between t 1  and t 2 .  FIG.  12 A  shows the interpolated velocity during the off period between t 1  and t 2 . 
     As shown in  FIG.  12 B , the interpolated velocity from  FIG.  12 A  is integrated (e.g., by circuitry  142 ) to determine a calculated (estimated) displacement between t 1  and t 2 . The estimated displacement between t 1  and t 2  is then stitched (added) to the measured displacement between t 0  and t 1 . The measured displacement between t 2  and t 3  is stitched (added) to the estimated displacement between t 1  and t 2 . This process may be repeated for each off period to fill in the displacement during the off periods. The resulting total calculated displacement is shown in graph  168  of  FIG.  11   . The total calculated displacement (determined by the interpolation and stitching circuitry  142 ) may be used by control circuitry  12  to estimate the force applied by the finger when touching a surface. 
     The duration of each on period (T ON ) may be greater than 0.5 milliseconds, greater than 1 millisecond, greater than 2 milliseconds, greater than 5 milliseconds, greater than 8 milliseconds, greater than 20 milliseconds, less than 0.5 milliseconds, less than 1 millisecond, less than 2 milliseconds, less than 5 milliseconds, less than 8 milliseconds, less than 20 milliseconds, between 1 millisecond and 10 milliseconds, etc. The duration of each off period (T OFF ) may be greater than 0.5 milliseconds, greater than 1 millisecond, greater than 2 milliseconds, greater than 5 milliseconds, greater than 8 milliseconds, greater than 20 milliseconds, greater than 50 milliseconds, greater than 100 milliseconds, less than 0.5 milliseconds, less than 1 millisecond, less than 2 milliseconds, less than 5 milliseconds, less than 8 milliseconds, less than 20 milliseconds, less than 50 milliseconds, less than 100 milliseconds, between 5 milliseconds and 100 milliseconds, etc. 
     The duty cycle of sensor  66  may be less than 100%, less than 75%, less than 50%, less than 30%, less than 20%, less than 10%, greater than 75%, greater than 50%, greater than 30%, greater than 20%, greater than 10%, greater than 5%, between 5% and 50%, between 20% and 30%, between 40% and 60%, etc. 
     If desired, a single laser driver  114  may be shared between the laser diodes of multiple SMI proximity sensors (e.g., at different locations within finger device  10 ).  FIG.  13    is a schematic diagram of a group of sensors of this type. As shown, driver  114  drives self-mixing interferometric proximity sensors 1, 2, 3, and 4. Switching circuitry  170  (e.g., one or more switches) may be coupled between driver  114  and sensors 1, 2, 3, and 4. The sensors may be positioned at different locations within device  10  (e.g., any of the illustrative locations  46  from  FIG.  3   ). Driver  114  may drive sensors 1, 2, 3, and 4 using a time-multiplexing scheme. In other words, driver  114  may drive sensor 1 for a first length of time, then drive sensor 2 for a second length of time, then drive sensor 3 for a third length of time, then drive sensor 4 for a fourth length of time. This cycle may be continuously repeated. The lengths of time each sensor is driven may be equal, such that each sensor has a 25% duty cycle. 
     The example of  FIG.  13    is merely illustrative. In general, a driver  114  may control any desired number of sensors. Those sensors may have equal duty cycles (e.g., 4 sensors at 25% duty cycle) or different duty cycles (e.g., 1 sensor at 50% duty cycle and 2 sensors at 25% duty cycles). 
     As described above, one aspect of the present technology is the gathering and use of information such as information from input-output devices. The present disclosure contemplates that in some instances, data may be gathered that includes personal information data that uniquely identifies or can be used to contact or locate a specific person. Such personal information data can include demographic data, location-based data, telephone numbers, email addresses, twitter ID&#39;s, home addresses, data or records relating to a user&#39;s health or level of fitness (e.g., vital signs measurements, medication information, exercise information), date of birth, username, password, biometric information, or any other identifying or personal information. 
     The present disclosure recognizes that the use of such personal information, in the present technology, can be used to the benefit of users. For example, the personal information data can be used to deliver targeted content that is of greater interest to the user. Accordingly, use of such personal information data enables users to have control of the delivered content. Further, other uses for personal information data that benefit the user are also contemplated by the present disclosure. For instance, health and fitness data may be used to provide insights into a user&#39;s general wellness, or may be used as positive feedback to individuals using technology to pursue wellness goals. 
     The present disclosure contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users, and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the United States, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA), whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different personal data types in each country. 
     Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In another example, users can select not to provide certain types of user data. In yet another example, users can select to limit the length of time user-specific data is maintained. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an application (“app”) that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app. 
     Moreover, it is the intent of the present disclosure that personal information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user&#39;s privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of data stored (e.g., collecting location data at a city level rather than at an address level), controlling how data is stored (e.g., aggregating data across users), and/or other methods. 
     Therefore, although the present disclosure broadly covers use of information that may include personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Table of  
                   
                   
                   
               
               
                 Reference 
                   
                   
                   
               
               
                 Numerals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 8 
                 System 
                 10 
                 Finger device 
               
               
                 12, 26 
                 Control circuitry 
                 14, 28 
                 Communications  
               
               
                   
                   
                   
                 circuitry 
               
               
                 16, 30 
                 Input-output 
                 18, 32 
                 Sensors 
               
               
                   
                 devices 
                   
                   
               
               
                 20, 34 
                 Haptic Output 
                 22, 36 
                 Other devices 
               
               
                   
                 Devices 
                   
                   
               
               
                 24 
                 Electronic device 
                 38 
                 Wireless link 
               
               
                 40 
                 Finger 
                 40P 
                 Finger pulp 
               
               
                 42 
                 Fingernail 
                 44 
                 Housing 
               
               
                 46 
                 Location 
                 48 
                 Surface 
               
               
                 n 
                 Surface normal 
                 50 
                 Structure 
               
               
                 60 
                 Sensor module 
                 62 
                 Flexible membrane 
               
               
                 64 
                 Rigid housing 
                 66 
                 Self-mixing  
               
               
                   
                 structure 
                   
                 proximity sensor 
               
               
                 68, 70 
                 Distances 
                 72 
                 Displacement 
               
               
                 74 
                 Substrate 
                 76 
                 Semi-rigid structure 
               
               
                 78 
                 Optically clear 
                 80 
                 Sidewall portion 
               
               
                   
                 filler material 
                   
                   
               
               
                 82 
                 Angled portion 
                 84 
                 Base 
               
               
                 86 
                 Finger-interfacing 
                 88 
                 Rounded corner  
               
               
                   
                 portion 
                   
                 portion 
               
               
                 90 
                 Planar base portion 
                 92, 94, 96 
                 Bends 
               
               
                 98 
                 Transparent cap 
                 100 
                 Lens 
               
               
                 102 
                 Laser 
                 104 
                 Photodiode 
               
               
                 106 
                 Reflective coating 
                 110 
                 Sensing circuitry 
               
               
                 112 
                 Light-emitting 
                 114 
                 Laser driver 
               
               
                   
                 diode 
                   
                   
               
               
                 116 
                 Transimpedance 
                 118 
                 Bias subtraction  
               
               
                   
                 amplifier 
                   
                 circuitry 
               
               
                 120 
                 Analog-to-digital 
                 122, 124 
                 Mixers 
               
               
                   
                 converter 
                   
                   
               
               
                 126, 128 
                 Subtraction 
                 130, 132 
                 Low-pass filters 
               
               
                   
                 circuits 
                   
                   
               
               
                 134, 136 
                 DC subtraction 
                 138 
                 Amplitude analysis  
               
               
                   
                 logic 
                   
                 circuitry 
               
               
                 140 
                 Processing 
                 142 
                 Interpolation and  
               
               
                   
                 circuitry 
                   
                 stitching circuitry 
               
               
                 144 
                 Mean calculating 
                 146 
                 Standard deviation  
               
               
                   
                 circuitry 
                   
                 calculating circuitry 
               
               
                 148 
                 Comparison 
                 150 
                 Offset history block 
               
               
                   
                 circuitry 
                   
                   
               
               
                 152 
                 Switch 
                 162, 164, 
                 Graphs 
               
               
                   
                   
                 166, 168 
                   
               
               
                 170 
                 Switching 
                   
                   
               
               
                   
                 circuitry

Metadata:
Filing Date: 20210902
Publication Date: 20240326
Grant Date: 20240326
Priority Date: 20210902
Inventors: HUANG, MENGSHU
CIHAN, AHMET FATIH
HARB, ADRIAN Z.
Dey, Stephen E.
PAN, Yuhao
Mutlu, Mehmet
Assignee: APPLE INC
CPC Classifications: [{"code": "G01C3/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01B9/02092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/014", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B9/02097", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/017", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/0331", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01C3/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/014", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/014", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/0331", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/017", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01B9/02092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B9/02097", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 85386654