Patent Description:
This disclosure relates generally to ophthalmic devices, and in particular but not exclusively, relates to accommodation control for accommodative contact lenses.

Accommodation is a process by which the eye adjusts its focal distance to maintain focus on objects of varying distance. Accommodation is a reflex action, but can be consciously manipulated. Accommodation is controlled by contractions of the ciliary muscle. The ciliary muscle encircles the eye's elastic lens and applies a force on the elastic lens during muscle contractions that change the focal point of the elastic lens.

As an individual ages, increased stiffness of the eyes' lenses tend to decrease the effectiveness of the ciliary muscles in providing accommodation. Presbyopia is a progressive age-related loss of accommodative or focusing strength of the eye, which results in increased blur at near distances. This loss of accommodative strength with age has been well studied and is relatively consistent and predictable. Presbyopia affects nearly <NUM> billion people worldwide (<NUM> million in the United States alone) and that number is expected to substantially rise as the world's population ages.

Recent technologies have begun to provide for various devices that operate in or on a human eye to aid the visual focus of a user. For some types of these devices, an accommodating lens includes one or more elements and circuitry to apply an electrical signal to change a focusing/optical power of the one or more elements. Determining when to change such focusing power may be based on a direction of a gaze by a user of the optical device. As the capabilities of accommodation-capable optical devices continue to increase, there is expected to be an increased demand for such optical devices to provide accurate tracking of the direction of gaze by a user. The closest prior art includes the documents <CIT> and <CIT> describing standard ophthalmic devices, comprising an antenna electrode; an impedance sensor coupled to the antenna electrode, and the impedance sensor forming an oscillator with the antenna electrode.

Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Not all instances of an element are necessarily labeled so as not to clutter the drawings where appropriate. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described.

Embodiments of an apparatus, system and method of operation for an ophthalmic device that shares a single antenna electrode between an impedance sensor for gaze/blink detection and other circuitry for communications and/or power charging are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

The operation of an accommodating ophthalmic device (e.g., contact lens, intraocular lens, or other eyewear) requires a control mechanism for determining when and how much accommodation (optical power adjustment) is needed at a given moment. This accommodation control may be manual, fully automatic, or a hybrid of the two schemes. In some cases, the amount of accommodative optical power needed may be inferred from determining a user's direction of gaze. For example, if both user's eyes pivot inward or down, it may be inferred that the user is using their near-distance vision. Correspondingly, if the user's eyes are looking straight forward or up, it may be inferred that they are using their far-distance vision. A determination of an amount that a user's eyelids overlap the ophthalmic device may be used as a proxy for determining their gaze direction from which an accommodation setting may be correlated and used for feedback control to an accommodation actuator (i.e., variable power dynamic lens). The determination of eyelid overlap may also be used to identify blinks.

In some designs for eye-mountable devices (e.g., contact lens, IOL, etc.), the sensing of eyelid overlap is performed by photodetection to determine whether light is being prevented from reaching a photodiode that is disposed in an eye-mountable device (EMD). This use of light-based sensing has certain drawbacks - e.g., due to the wide dynamic range of ambient light in many typical environments. As an alternative to photodetector sensing, other EMD designs rely on a type of capacitive sensing, similar to that used in touchscreen technologies, to detect a capacitance of an eyelid. However, this type of capacitive sensing tends to have problems distinguishing a user's eyelid from the presence of a film of tear fluid (or "tear film") over the user's eye. It is believed that the conductivity of a tear film tends to block, or severely limit, the impact that a capacitance of a user's eyelid may otherwise have on dielectric and/or electric field properties of a fully-encapsulated capacitance sensor within an EMD. The tear film is believed to be a source of error in detecting eyelid capacitance.

Accordingly, embodiments described herein use an oscillator circuit that correlates an oscillation condition influenced by an impedance of an inductive antenna electrode to an amount of eyelid overlap, which in turn correlates to an accommodation setting for controlling an accommodation actuator. The impedance sensing used by the oscillator is capable of efficiently distinguishing between a tear film and eyelid overlap. Some embodiments detect a resistivity (and/or a change thereof) that is due to a combination of resistances each provided by a different respective one of a tear film and a user's eyelid.

Embodiments described herein have been refined to timeshare the antenna electrode used by the impedance sensor with one or both of charging circuitry for wireless power harvesting and communication circuitry for RF wireless communications with devices external to the EMD. By intelligently and effectively arbitrating access to the shared antenna electrode, the use of multiple antenna electrodes is avoided, which reduces the rigid surface area of the EMD. A more flexible EMD provides greater comfort to the wearer. A timeshared single antenna electrode consumes less real estate to allow for a larger dynamic optic area. Less surface area dedicated to an antenna electrode, means less metallic area to reflect ambient light, thereby providing an improved cosmetic appearance. Finally, the intelligent arbitration and timesharing between charging circuitry, communication circuitry, and the gaze/blink detection circuitry (i.e., impedance sensor), enables each one of these components to more efficiently use the shared antenna electrode without negatively impacting, triggering, or loading the operation of the other components.

The impedance sensor incorporated into the gaze/blink detection circuitry described herein functions as an oscillator when coupled with the shared antenna electrode. The oscillator, including the shared antenna electrode and impedance sensor, commences oscillation based upon particular bias settings and an electromagnetic interaction between the shared antenna electrode and the tear film and a portion of the eyelid that overlaps the EMD (if at all). For example, a frequency of resonance by the oscillator may be based at least in part on inductive structures and capacitive structures of the ophthalmic device and such couplings to the structures of the eye. By evaluating operational characteristics of the oscillator, the various impedances of such inductive structures and capacitive structures may be accounted for, thus enabling detection of a resistive (real domain) component of impedance that is attributable to a tear film and any overlapping eyelid portion. Variation of such a resistive component may be proportional to an amount that the eyelid overlaps at least some portion of the sensor mechanism. The onset of an oscillation condition for the oscillator formed by the impedance sensor and the shared antenna electrode may, at a given time, be characterized by a minimum amount of current needed (at least at that time) to enable signal oscillation with that circuit. The required minimum amount of current may change over time with changes to the external environment adjoining the ophthalmic device - e.g., in proportion to a varying resistance that is provided by the tear film and any overlapping eyelid portion.

<FIG> is a functional block diagram of an ophthalmic device <NUM>, such as a smart contact lens, including circuitry to detect whether at least a portion of ophthalmic device <NUM> is being overlapped by an eyelid of a user. Detection of this type of overlap (for brevity, referred to herein simply as "eyelid overlap") may be used, for example, for feedback control of an accommodation actuator.

The illustrated embodiment of ophthalmic device <NUM> includes a controller <NUM>, an accommodation actuator <NUM>, a shared electrode antenna <NUM>, and a power source <NUM> all sealed within an enclosure <NUM>. The illustrated embodiment of controller <NUM> includes control circuitry/logic <NUM>, communication circuitry <NUM>, charging circuitry <NUM>, and gaze detection circuitry <NUM>. In some embodiment, gaze detection circuitry <NUM> may be used (alternatively or additionally) to perform blink detection. It should be appreciated that <FIG> is a functional diagram and the illustrated components and circuitry may be implemented in hardware, software, or a combination of both. Furthermore, the physical components that implement the illustrated functions may be centralized as illustrated, or distributed. In one embodiment, controller <NUM> is implemented within a custom application specific integrated circuit (ASIC) that is mounted on an annular substrate within enclosure <NUM>.

The enclosure material, represented by enclosure <NUM>, may function as a light transmissive lensing material and may form, at least in part, a sealed enclosure in which is disposed circuitry of ophthalmic device <NUM>. The dielectric enclosure material may be fabricated of a variety of materials compatible for direct contact with a human eye, such as a polymeric material, a hydrogel, PMMA, silicone based polymers (e.g., fluoro-silicon acrylate), or otherwise. Enclosure material <NUM> may be in the form of a round lens with a concave curvature configured to mount to a corneal surface of an eye. The electronics may be disposed upon a substrate embedded within the one or more enclosure materials near a periphery of ophthalmic device <NUM> to avoid interference with incident light received closer to the central region of the cornea.

Control circuitry/logic <NUM> represents miscellaneous components for orchestrating the operation of ophthalmic device <NUM>. For example, control circuitry/logic <NUM> may be implemented with a microcontroller, on-board memory storing various software instructions, and may also include hardware logic configured to perform specific functions. Communication circuitry <NUM> may include RF electronics to receive, and in some embodiments also transmit, wireless data over shared antenna electrode <NUM>. In one embodiment, communication circuitry <NUM> is a RF identification tag that uses backscatter communications. Charging circuitry <NUM> may include RF power rectification circuitry to harvest power from an RF carrier wave incident upon shared antenna electrode <NUM> and charge power source <NUM> (e.g., on-board battery, storage capacitor, etc.). Gaze detection circuitry <NUM> includes embodiments of the impedance sensor described herein, which selectively forms an oscillator with shared antenna electrode <NUM> to sense an amount of eyelid overlap and provide feedback control to accommodation actuator <NUM>. Accommodation actuator <NUM> is a dynamic lens, such as a liquid crystal (LC) cell, a multi-layer LC diffractive lensing structure, an electrowetting lens, or otherwise.

<FIG> are illustrations of a contact lens system <NUM> including a dynamic diffractive liquid crystal lens, in addition to a gaze detection circuit that utilizes eyelid overlap sensing according to an embodiment of the disclosure. System <NUM> is one possible implementation of ophthalmic device <NUM> illustrated in <FIG>. The illustrated embodiment of contact lens system <NUM> includes an annular substrate <NUM>, a dynamic lens <NUM>, an enclosure <NUM>, a controller <NUM>, a power source <NUM>, and a ring-shaped antenna electrode <NUM>. Enclosure <NUM> has a size and shape that mounts over the cornea of an eye. In the illustrated embodiment, enclosure <NUM> includes an anterior side <NUM> having a convex shape and a posterior side <NUM> having a concave shape. Of course, contact lens system <NUM> may assume other shapes and geometries including a piggyback configuration that attaches to a surface of an eye-mountable carrier substrate having an overall shape that resembles a conventional contact lens. Ring-shaped antenna electrode <NUM> is one possible implementation of shared antenna electrode <NUM>. As illustrated, ring-shaped antenna electrode <NUM> encircles dynamic lens <NUM> and is coupled at either end to controller <NUM>. In one embodiment, ring-shaped antenna electrode <NUM> is a single-ended antenna electrode structure in that one end is tied to a fixed potential (e.g., ground) while the other end is a tied to a shared terminal that is accessed by communication circuitry, charging circuitry, and an impedance sensor for gaze detection. The communication circuitry, charging circuitry, and gaze detection circuitry all timeshare ring-shaped antenna electrode <NUM>, and in one embodiment, access between the communication circuitry and gaze detection circuitry is arbitrated.

<FIG> shows cross-sectional views - during respective states <NUM>, <NUM> - of a user's eye while that user is wearing an ophthalmic device <NUM> (e.g., ophthalmic device <NUM>, contact lens system <NUM>) according to an embodiment. Gaze detection circuitry including an impedance sensor may be fully encapsulated within an encapsulation material <NUM> of the ophthalmic device <NUM>. Such encapsulation may aid in preventing moisture ingress during the operating lifetime of ophthalmic device <NUM>. Operation of the impedance sensor, which forms an oscillator when connected with ring-shaped antenna electrode <NUM>, may exploit the formation of a capacitive link which extends between a fully encapsulated electrode of the sensor circuit and the surface of a tear film. For brevity, this type of capacitive link is referred to herein as "lens capacitance.

A tear film may be conductive of a current that is induced by the oscillator. The effect of such conductivity on operational characteristics of the oscillator may change over time with the changing external environment - e.g., due to any additional conductance of a biological material (such as the eyelid) that comes in contact with the tear film. The extent to which an eyelid overlaps the sensor circuit may affect a resistivity of a current path that is in parallel with the tear film. In order to efficiently measure bio-conductance/bio-resistance of a tear film (in combination with that resulting from any eyelid overlap), some embodiments variously provide an inductive element L1 that, for example, is coupled in parallel with an in-series combination of lens capacitance Cp and two parallel resistances from the tear film RT and eyelid RE (see <FIG>). During a resonance state of the oscillator, such an inductance element may cancel out or otherwise significantly offset an impedance provided with the lens capacitance Cp. Therefore, at the resonance state of the sensor circuit, the frequency of oscillation may be automatically determined as a resonance for a combination of the inductor L1 and the lens capacitance Cp, effectively exposing a total amount of resistance provided by the tear film RT and eyelid RE, if present, - e.g., where sensing of such resistance is not obscured by the impedance of the lens capacitance Cp. This resistance may directly correlate with, and be sensed by determining, a bias setting (e.g., a minimum amount of current) needed to startup oscillation of the oscillator. Accordingly, the impedance sensors described herein sense or measure the impedances RT and RE by determining a bias setting (e.g., setting of a current source) of an oscillator circuit at the onset of an oscillation condition.

An inductance element L1 may be formed, for example, with a ring-like configuration for the antenna electrode <NUM> that also contributes to lens capacitance. As mentioned, the impedance sensor of the gaze detection circuitry forms an oscillator circuit (e.g., Collpits oscillator structure) when selectively coupled to ring-shaped antenna electrode <NUM> that is configured to induce oscillation (resonance) with the antenna electrode that contributes to the lens capacitance. An amount of current required to achieve oscillation startup (e.g., onset of an oscillation condition) may be proportional to the amount of resistance across at least a portion of the tear film. Accordingly, a measurement of the startup current necessary to induce the oscillation condition is a proxy or measurement of the impedance across ring-shaped antenna electrode <NUM>. At a time when an eyelid overlaps at least a portion of the ring-shaped antenna electrode <NUM>, the resistance across an underlying portion of tear film may be relatively low, as compared to when there is relatively less (or no) eyelid overlap. A level of such bio-resistance may be measured in some embodiments by determining a threshold amount of current required to start oscillator of sensor circuitry.

During states <NUM> and <NUM>, ophthalmic device <NUM> is disposed on a cornea <NUM> of the user's eye, wherein a tear film <NUM> extends between a cornea <NUM> of the eye and enclosure material <NUM> of ophthalmic device <NUM>. Another tear film <NUM> may extend across an upper surface of enclosure material <NUM>. State <NUM> represents a time when, as compared to state <NUM>, an eye of the user is relatively more open. During state <NUM>, an eyelid <NUM> of the user overlaps a surface area of enclosure material <NUM> that is larger than any area of enclosure material <NUM> that might be overlapped by eyelid <NUM> during state <NUM>.

<FIG> is a hybrid circuit diagram and functional block diagram illustrating the charging, communication, and gaze detection components of ophthalmic device <NUM>, in accordance with an embodiment of the disclosure. Charging circuitry <NUM>, communication circuitry <NUM>, and gaze detection circuitry <NUM> all timeshare access to shared antenna electrode L1 through shared terminal N1. In one embodiment, the timeshared access is arbitrated by arbiter <NUM>. The illustrated embodiment of charging circuitry <NUM> includes switching circuit <NUM> and RF power rectifier <NUM>. The illustrated embodiment of switching circuit <NUM> includes a power switch controller <NUM> and a power switch SW5. The illustrated embodiment of communication circuitry <NUM> includes RF communication rectifier <NUM>, demodulator <NUM>, and RF detector <NUM>. The illustrated embodiment of gaze detection circuitry <NUM> includes impedance sensor <NUM> and evaluation logic <NUM>. Gaze detection circuitry <NUM> provides feedback control in the form of an accommodation setting to accommodation controller <NUM>, which in turn drives accommodation actuator <NUM>. Alternatively (or additionally), it should be appreciated that impedance sensor <NUM> may be used to perform blink detection. It should be appreciated that the illustrated components may be implemented in hardware circuits/logic, in software instructions/logic, or a combination of both hardware and software.

During operation power rectifier <NUM> serves to harvest power from a wireless signal, such as a radio frequency (RF) signal, to charge power source <NUM> and provide power to the other circuit components. Power rectifier <NUM> is coupled to shared antenna electrode L1 to harvest power from the wireless signal incident thereon. Switching circuit <NUM> is coupled to power rectifier <NUM> and shared terminal N1 to selectively couple a load of power rectifier <NUM> to shared antenna electrode L1 during power harvesting and in response to sensing a presence of the wireless signal on shared antenna electrode L1. Switching circuit <NUM> also decouples the load of power rectifier <NUM> when impedance sensor <NUM> is operating to measure the impedance of shared antenna electrode L1 so as to not unduly load or otherwise adversely affect the gaze detection circuitry.

In the illustrated embodiment, switching circuity <NUM> includes a power switch SW5 coupled between shared terminal N1 and power rectifier <NUM> along with power switch controller <NUM> to control the switching operation of power switch SW5. Power switch controller <NUM> is coupled to shared terminal N1 to sense the presence or absence of an incident wireless signal for charging, and in turn controls power switch SW5 accordingly. In one embodiment, power switch SW5 is a transistor having its gate control terminal coupled to the output of power switch controller <NUM>.

In one embodiment, power switch controller <NUM> operates as a low pass filter (LPF) voltage rectifier. When a voltage signal of sufficient amplitude is present on shared antenna electrode L1 due to an incident wireless signal, power switch controller <NUM> close circuits power switch SW5 when the time persistence of the wireless signal is sufficiently long. The amount of time persistence is physically set by the low pass filter corner frequency that is after the wireless signal rectifier (e.g., RF voltage rectifier <NUM>). The target time persistence is determined by the wireless standard and required operating time of impedance sensor <NUM>. Otherwise, power switch SW5 is open circuited to allow the other circuit components (e.g., impedance sensor <NUM>) to access shared antenna electrode L1. Circuit <NUM> represents one possible implementation of power switch controller <NUM>. As illustrated, the output of an RF voltage rectifier <NUM> is filtered by LPF <NUM>, which generates an enable signal ENB1 for controlling a control terminal of power switch SW5. In one embodiment, the cutoff frequency of LPF <NUM> falls between a carrier frequency of the wireless signal used for wireless inductive charging via shared antenna electrode L1 and an oscillation frequency of impedance sensor <NUM> when operating for gaze detection. The low pass filtering prevents oscillations induced on shared antenna electrode L1 by impedance sensor <NUM> from triggering power switch SW5 and placing the load of power rectifier <NUM> on impedance sensor <NUM>.

In yet another embodiment, power switch controller <NUM> may also be coupled to be responsive to arbiter <NUM>, data detect signal <NUM>, and/or active signal ACT output from impedance sensor <NUM>. For example, power switch controller <NUM> may include logic to ensure that power switch SW5 is not closed circuited during an operational period of impedance sensor <NUM>. In one embodiment, power switch controller <NUM> closes power switch SW5 when a wireless signal persists for longer than a preset time (e.g., <NUM>).

Communication circuitry <NUM> is coupled to shared terminal N1 to receive wireless data via shared antenna electrode L1. RF communication rectifier <NUM> rectifies the analog signal and generates a baseband signal for demodulator <NUM>. The baseband signal may be a simple form of amplitude-shift keying, such as on-off keying (OOK), which is then demodulated by modulator <NUM> to regenerate the data in digital form. RF detector <NUM> is coupled to receive the rectified signal and generate a data detect signal <NUM> indicating a presence of wireless data on shared antenna electrode L1. RF detector <NUM> may look for a pattern indicative of a rectified data signal.

Arbiter <NUM> is coupled to receive the data detect signal <NUM> from RF detector <NUM>. If data detect signal <NUM> is high indicating the presence of RF data on shared antenna electrode L1, then arbiter <NUM> de-asserts enable signal ENB2 to impedance sensor <NUM> blocking its operation. On the other hand, if impedance sensor <NUM> is already operating, as indicated by an assertion of the active signal ACT from impedance sensor <NUM>, then arbiter <NUM> will mask the assertion of the data detect signal <NUM> until impedance sensor <NUM> is complete and the active signal ACT is de-asserted. This masking prevents operation of impedance sensor <NUM> from being prematurely interrupted by arbiter <NUM> by new in-bound RF data.

Impedance sensor <NUM> is periodically enabled and coupled to shared terminal N1 in response to an assertion of the enable signal ENB2 from arbiter <NUM>. Once impedance sensor <NUM> commences a gaze detection cycle, impedance sensor <NUM> asserts the active signal ACT to indicate to arbiter <NUM> that it is actively using shared antenna electrode L1. In one embodiment, impedance sensor <NUM> has a duty cycle of approximately <NUM>%, or a period T1 = <NUM> to <NUM> and an evaluation period T2 = <NUM>-<NUM> us (see <FIG>).

Upon activating impedance sensor <NUM>, it is coupled to shared antenna electrode L1 and forms an oscillator therewith. As previously mentioned, shared antenna electrode L1 has an impedance that varies based upon an amount an eyelid overlaps shared antenna electrode L1, which in turn is related to the user's gaze direction. This impedance forms part of an RLC oscillator circuit with impedance sensors <NUM>, and as such, the user's gaze direction influences an oscillation condition of the oscillator. During each evaluation period, impedance sensor <NUM> iteratively resets the oscillator, re-biases the oscillator, perturbs the oscillator, and then monitors for the onset of an oscillation condition. The bias level of the oscillator at the point where the oscillator commences oscillation when perturbed is correlated by evaluation logic <NUM> to a gaze direction, and by extension, to an accommodation setting. A binary search algorithm may be executed to quickly identify the bias conditions that result in the onset of an oscillation condition. In one embodiment, evaluation logic <NUM> uses a lookup table to correlate bias settings to an accommodation setting. The lookup table may be pre-calibrated, calibrated per user, or even periodically calibrated by a given user. The accommodation setting is then used by accommodation controller <NUM> to adjust the optical power of accommodation actuator <NUM>.

<FIG> is a functional block diagram illustrating functional components of an impedance sensor <NUM>, in accordance with an embodiment of the disclosure. Impedance sensor <NUM> is one possible implementation of impedance sensor <NUM>. The illustrated embodiment of impedance senor <NUM> includes oscillator circuitry components <NUM>, an initialization controller <NUM>, and an oscillation detector <NUM>.

In response to the enable signal ENB2 being asserted by arbiter <NUM>, initialization controller <NUM> configures oscillator circuitry components <NUM> to establish an oscillator <NUM> with shared antenna electrode L1. While ENB2 is asserted, initialization controller <NUM> iteratively resets oscillator <NUM>, re-biases one or more oscillator circuitry components <NUM>, and perturbs oscillator <NUM>. Concurrently, oscillation detector <NUM> monitors oscillator <NUM> for the onset of an oscillation condition. For example, oscillation detector <NUM> may be coupled to monitor shared terminal N1 for a characteristic oscillation signal (e.g., repetition of a specified amplitude and/or frequency). Accordingly, in one embodiment, oscillation detector <NUM> may include an amplitude and/or frequency comparator along with a counter that is reset with each initialization iteration by initialization controller <NUM>. The bias level of the oscillator circuitry components <NUM> at the point where the oscillator commences oscillation when perturbed is then provided to evaluation logic <NUM> for correlation to an accommodation setting. Initialization controller <NUM> may execute a binary search algorithm to quickly and efficiently identify the onset of the oscillation condition.

Oscillation detector <NUM> may couple to any number of circuit nodes within oscillator circuitry components <NUM> (or <NUM>) to monitor for an oscillation condition. In one embodiment, oscillation detector <NUM> is coupled to shared node N1 (see <FIG>), which may also be considered an interconnecting node of oscillator circuitry components <NUM>. The double arrowed connection illustrated in <FIG> connecting oscillation detector <NUM> to initialization controller <NUM> symbolizes that these two components may be coupled to communication with each other. For example, oscillation detector <NUM> may inform initialization controller <NUM> that a given iteration of biasing current source CS1 did or didn't trigger an oscillation condition. Correspondingly, initialization controller <NUM> may be coupled to oscillation detector <NUM> to enable or disable its operation.

<FIG> is a circuit diagram illustrating oscillator circuitry components <NUM> that couple with shared antenna electrode L1 to form an oscillator (e.g., oscillator <NUM>), in accordance with an embodiment of the disclosure. Oscillator circuitry components <NUM> are one possible implementation of oscillator circuitry components <NUM> in <FIG>.

The illustrated embodiment of oscillator circuitry components <NUM> includes current source CS1, transistor T1, capacitors C1 and C2 along with switches SW1, SW2, SW3, and SW4. Transistor T1 has a channel coupled in series with current source CS1 between high voltage rail VDD and low voltage rail VSS (e.g., ground). The pair of capacitors C1 and C2 are coupled in series between VDD and shared terminal N1. A gate of transistor T1 is coupled to shared terminal N1. Circuit node N2 between transistor T1 and current source CS1 is coupled to circuit node N3 between capacitors C1 and C2. Switch SW1 is coupled in series between VDD and capacitor C1. Switch SW2 is coupled in series between VSS and the channel of transistor T1. Switch SW3 is coupled in series between VDD and current source CS1.

When switches SW1, SW2, and SW3 are closed, the oscillator circuitry components <NUM> establish an RLC oscillator (e.g., oscillator <NUM>) with shared antenna electrode L1. When switches SW1, SW2, SW3, and SW4 are open, the oscillator is disabled and shared antenna electrode L1 is available for use by communication circuitry <NUM> or charging circuitry <NUM> without undue interference from impedance sensor <NUM>. Switch SW4 is a reset switch that operates to reset the voltage at shared terminal N1 between each iteration of initializing (e.g., adjusting the startup current output from current source CS1 via control signal S5) and perturbing oscillator <NUM> during operation of impedance sensor <NUM> for gaze detection.

Switches SW1, SW2, SW3, and SW4 may be implemented as transistors (e.g., NMOS transistors) while transistor T1 may be implemented as a PMOS transistor. In the illustrated embodiment, current source SC1 is a variable current source that varies its output current in response to a control signal S5. In the illustrated embodiment, switches SW1, SW2, SW3, and SW4 along with current source CS1 operate under the influence of control signals S1-S5 output from initialization controller <NUM>.

In the illustrated embodiment, oscillator circuitry components <NUM> form a single-ended oscillator, such as a Colpitts oscillator, with shared antenna electrode L1, which represents the inductive element of the RLC oscillator. The resistive elements of the RLC oscillator arise from RE and RT (only illustrated in <FIG>). Although <FIG> illustrates oscillator circuitry components <NUM> as forming a Colpitts oscillator, it should be appreciated that other oscillator configurations may be implemented. For example, oscillator circuitry components <NUM> may form a Harley oscillator, an Armstrong oscillator, or other variations of single-ended oscillators.

In the illustrated embodiment, the oscillator formed by oscillator circuitry components <NUM> and shared antenna electrode L1 is a single-end oscillator (as opposed to a differential oscillator) and shared antenna electrode L1 is configured as a single-ended inductive element having its opposite terminal tied to a fixed potential (e.g., grounded) while its single ended output terminal (i.e., shared terminal N1) is coupled to the single input of oscillator <NUM>. It should be appreciated that other configurations than just a single-ended oscillator may also be implemented.

Oscillation detector <NUM> is coupled to oscillator <NUM> to monitor oscillator <NUM> for the onset of an oscillation condition. In the illustrated embodiment, oscillation detector <NUM> is coupled to shared terminal N1, although it may be coupled to other circuit nodes that express an oscillating signal when oscillator <NUM> is operating in an oscillation regime.

<FIG> illustrates a timing diagram for the operation of the oscillator circuit illustrated in <FIG>. Trace <NUM> illustrates the operation of control signals S1, S2, and S3, which have an evaluation period T2 of approximately <NUM>-<NUM> us and a duty cycle of approximately <NUM>% (e.g., T1 = <NUM> to <NUM>). Trace <NUM> illustrates control signal S4 used to reset shared terminal N1. Control signal S4 is asserted at the beginning of each evaluation period T2 for a portion (e.g., T3 = <NUM>*T2) of the evaluation time. T3 may be thought of as a reset period. Of course, T1, T2, and T3 may be implemented with other durations and duty cycles. Trace <NUM> illustrates that initialization controller <NUM> activates oscillator <NUM> by closing switches SW1, SW2, and SW3 in response to arbiter asserting the enable signal ENB2.

<FIG> is a flow chart illustrating a process <NUM> for operation of power switch controller <NUM> illustrated in <FIG>, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process <NUM> should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

As mentioned above, power switch controller <NUM> operates to selectively couple and decouple the load of power rectifier <NUM> to/from shared terminal N1 and shared antenna electrode L1. In a process block <NUM>, power switch controller <NUM> monitors shared terminal N1 for a wireless signal having power to harvest. If a wireless signal having power to harvest is determined to be present on shared antenna electrode L1 (decision block <NUM>), then enable signal ENB1 is asserted and shared antenna electrode L1 is loaded by power rectifier <NUM> (process block <NUM>). If a wireless signal having power to harvest is determined not present on shared antenna electrode L1 (decision block <NUM>), then enable signal ENB1 is de-asserted and the load of power rectifier <NUM> is isolated from shared antenna electrode L1. In one embodiment, power switch controller <NUM> includes a voltage rectifier and low pass filter that permits the lower carrier frequency of the wireless power signal to pass through the low pass filter after rectification to enable switch SW5. In contrast, the oscillation frequency of impedance sensor <NUM> (and oscillator <NUM>) are too high to pass through LPF <NUM>. Accordingly, power switch controller <NUM> operates to ensure the higher frequency operation of impedance sensor <NUM> does not trigger power harvesting thereby loading impedance sensor <NUM> with power rectifier <NUM>. In an embodiment implemented with RF voltage rectifier <NUM>, the rectification circuitry of RF voltage rectifier <NUM> may be voltage matched such that the amplitude of oscillations on shared antenna electrode L1 due to impedance sensor <NUM> are too small for threshold voltage rectification by RF voltage rectifier <NUM> and thus will not active switch SW5. Other control logic may be used to implement the above described functionality of power switch controller <NUM>.

<FIG> is a flow chart illustrating a process <NUM> for arbitrating access to shared antenna electrode L1, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process <NUM> should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

In a process block <NUM>, RF communication rectifier <NUM> and RF detector <NUM> monitor shared terminal N1 for the presence of wireless data on shared antenna electrode L1. If data is determined not present (decision block <NUM>), then data detect signal <NUM> is de-asserted and arbiter <NUM> in turn asserts the enable signal ENB2 to impedance sensor <NUM> indicating that impedance sensor <NUM> is granted access to shared antenna electrode L1 for gaze detection. However, if wireless data is determined present (decision block <NUM>), then data detect signal <NUM> is asserted and arbiter <NUM> reads the active signal ACT from impedance sensor <NUM> to see if impedance sensor <NUM> is currently using shared antenna electrode L1. If the active signal ACT is not currently asserted by impedance sensor <NUM> (decision block <NUM>), then in response, arbiter <NUM> de-asserts the enable signal ENB2 to impedance sensor <NUM>, thereby blocking impedance sensor <NUM> from operating on shared antenna electrode L1 while wireless data is received. However, if the active signal ACT is currently asserted (decision block <NUM>) indicating that impedance sensor <NUM> is currently using shared antenna electrode L1, then arbiter <NUM> masks data detect signal <NUM> to permit impedance sensor <NUM> to complete its gaze detection operation, thereby temporarily delaying de-assertion of the enable signal ENB2 until the active signal ACT is de-asserted and impedance sensor <NUM> has indicated its completion.

<FIG> is a flow chart illustrating a process <NUM> for operation of gaze detection circuitry <NUM> to provide accommodation feedback control to accommodation actuator <NUM>, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process <NUM> should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

In a decision block <NUM>, initialization controller <NUM> monitors the enable signal ENB2 from arbiter <NUM>. If the ENB2 is unasserted, then arbiter <NUM> has not granted impedance sensor <NUM> access to shared antenna electrode L1 and therefore impedance sensor <NUM> remains disabled. In one embodiment, disabling impedance sensor <NUM> includes open circuiting switches SW1, SW2, SW3, and SW4 to disable oscillator <NUM>. However, if ENB2 is asserted by arbiter <NUM>, then process <NUM> continues to a process block <NUM>.

In process block <NUM>, impedance sensor <NUM> (or <NUM>) is enabled and oscillator <NUM> is established between oscillation circuitry components <NUM> and shared antenna electrode L1. In one embodiment, establishing oscillator <NUM> includes close circuiting switches SW1, SW2, and SW3. Initially, switch SW4 is close circuited to reset the voltage at shared terminal N1 to a default voltage (e.g., VSS or ground). In response to accessing shared antenna electrode L1, initialization controller <NUM> asserts the active signal ACT to indicate to arbiter <NUM> that impedance sensor <NUM> is actively using shared terminal N1 and shared antenna electrode L1 for gaze detection (process block <NUM>).

In a process block <NUM>, impedance sensor <NUM> commences measuring the impedance of shared antenna electrode L1 by iteratively adjusting one or more bias settings (e.g., startup current of current source CS1), perturbing oscillator <NUM>, and monitoring for the onset of an oscillation condition. Between iterations, initialization controller <NUM> resets the voltage at shared terminal N1 by close circuiting reset switch SW4. Oscillator <NUM> is perturbed after readjusting the bias setting of current source CS1. The perturbation is instigated by opening switch SW4 after the reset period T3 expires. Oscillation self-starts due to inherent circuit noise and the action of releasing switch SW4 (that will have some parasitic capacitance to "kick" oscillator <NUM>), as well as having a sufficient bias setting for current source CS1. Oscillation detector <NUM> monitors a circuit node (e.g., shared terminal N1) within oscillator <NUM> for a characteristic oscillation signal (e.g., repetition of a specified amplitude and/or frequency). If oscillation does not occur, then the next iteration is commenced by resetting the voltage at shared terminal N1 with switch SW4, adjusting the bias setting of current source CS1, and perturbing oscillator <NUM> again. This iterative process continues until the onset of the oscillation condition is detected by oscillation detector <NUM>. In one embodiment, initialization controller <NUM> uses a binary search algorithm to quickly identify the bias setting for current source CS1 that just results in the onset of the oscillation condition.

In a process block <NUM>, evaluation logic <NUM> correlates the onset of the oscillation condition to an accommodation setting. This correlation may reference a lookup table, be the product of a machine learning algorithm, or otherwise. In one embodiment, the lookup table is calibrated by asking the user to follow a series of gaze calibration instructions (e.g., look up, look down, read a book, etc.) while impedance sensor <NUM> measures the impedance of shared antenna electrode L1. Finally, in a process block <NUM>, accommodation controller <NUM> uses the selected accommodation setting output from evaluation logic <NUM> to manipulate the optical power of accommodation actuator <NUM>. In one embodiment, accommodation actuator <NUM> is a dynamic LC lens, which changes its optical power in response to changes in a bias voltage applied across the LC material of the dynamic LC lens.

A tangible machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a non-transitory form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable/non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

Claim 1:
A contact lens system (<NUM>), comprising:
a shared antenna electrode (<NUM>);
an accommodation actuator to provide variable optical power; and
a controller (<NUM>, <NUM>) coupled to the accommodation actuator and the shared antenna electrode (<NUM>), the controller (<NUM>, <NUM>) including logic that when executed by the controller (<NUM>, <NUM>) causes the contact lens system (<NUM>) to perform operations comprising:
arbitrating access to the shared antenna electrode (<NUM>) between an impedance sensor (<NUM>, <NUM>) and a communication circuit;
selectively establishing an oscillator with the impedance sensor (<NUM>, <NUM>) and the shared antenna electrode (<NUM>), wherein an impedance across the shared antenna electrode (<NUM>) varies based upon an amount an eyelid overlaps the contact lens system (<NUM>) when the contact lens system (<NUM>) is worn on an eye;
correlating an oscillation condition of the oscillator to an accommodation setting; and
adjusting the variable optical power of the accommodation actuator based upon the accommodation setting.