Transimpedance Amplifier Gaze Detection for Eye-Mountable Devices
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Solution Overview
Problem
As individuals age, the effectiveness of the ciliary muscle degrades, leading to presbyopia, a progressive loss of accommodative strength, making it difficult to focus on objects at near distances, and existing eye-mountable devices face challenges in efficiently utilizing power and resources.
Innovation Solution
A photodetection-capable eye-mountable device with embedded light sensor circuitry and an accommodation actuator that determines the direction of gaze to adjust focal distance, incorporating a transimpedance amplifier circuit with a differential amplifier and photodiode, and a capacitor to mitigate power consumption, and an energy harvesting system for sustainable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If photodetection circuitry is added to determine gaze direction for accommodation control, then the functionality and adaptability of the eye-mountable device is improved, but the power consumption and device complexity increase
Solution Approach 1:
The photodetection circuitry operates in periodic sampling mode rather than continuous operation. The controller periodically activates the photodetector to capture light intensity values at specific time intervals, processes these samples to determine gaze direction, and then enters a low-power state until the next sampling cycle is needed. This periodic operation maintains the accommodation control functionality while significantly reducing average power consumption compared to continuous monitoring.
Solution Approach 2:
The system utilizes naturally occurring light from the environment as the detection source, eliminating the need for additional light-emitting components that would consume power. The photodetector passively captures ambient light reflected from or emitted by objects in the user's field of view, allowing the device to derive gaze direction information without requiring active illumination, thereby reducing power requirements.
2Measurement precision
If photodetection circuitry with continuous operation is used to accurately detect gaze direction, then the measurement precision is improved, but the power consumption increases
Solution Approach 1:
The system implements periodic sampling of light intensity values at strategically chosen time intervals that capture sufficient information about gaze direction changes. By sampling at appropriate frequencies and using temporal analysis of multiple samples, the system achieves accurate gaze detection without requiring continuous photodetector operation, thereby maintaining measurement precision while reducing power consumption through intermittent measurement cycles.
Solution Approach 2:
The controller continuously processes incoming light intensity data streams from the photodetector to maintain real-time gaze direction determination. Even though the photodetector operates periodically, the controller maintains continuous computational activity to analyze the data stream, detect patterns indicating gaze direction, and update accommodation control accordingly, ensuring uninterrupted useful action despite intermittent sensing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device efficiently provides real-time auto-accommodation or user-controlled accommodation, reducing power consumption and enhancing usability for individuals with presbyopia by accurately adjusting focal distance based on gaze direction, thereby improving visual focus without significant resource depletion.
Implementation Method 1
a transimpedance amplifier circuit including a differential amplifier and a photodiode
Data Source
AI summary
Techniques and mechanisms to perform photodetection with an eye-mountable device. In an embodiment, the eye-mountable device includes an enclosure material and light sensor circuitry formed therein, the enclosure material to be disposed in or on an eye of a user. The light sensor circuitry comprises a transimpedance amplifier circuit including a differential amplifier, one or more feedback paths coupled across the differential amplifier, a photodiode and a capacitor coupled between the photodiode and an input terminal of the differential amplifier. Incidence of light upon the photodiode results in some charging of the capacitor, where an amplified signal is provided at an output terminal of differential amplifier based on such charging. The capacitor mitigates static power consumption by the photodiode. In another embodiment, the amplified signal is evaluated based on at least two threshold values to detect a direction of gaze by the user.