MEMS Line Scanner and Silicon Photomultiplier Camera for Eye Imaging
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Solution Overview
Problem
Virtual reality and mixed reality display systems face challenges in eye imaging due to limited power budgets and dynamic range requirements, particularly when imaging human eyes in varying lighting conditions, which conventional imaging systems struggle to address effectively.
Innovation Solution
A light-sensing circuit incorporating a solid-state silicon photomultiplier and a switchable array with capacitors or resistors, allowing for dynamic range expansion and reduced quantization error, synchronized with high-frequency emissions from an IR laser, enabling efficient eye tracking and imaging in photon-sparse environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional imaging systems are used for eye imaging in varying lighting conditions, then the system structure is simple, but the dynamic range is limited and quantization error increases
Solution Approach 1:
The patent implements dynamic range expansion by making the capacitor array switchable and reconfigurable during operation. Different capacitor combinations can be selected based on lighting conditions, allowing the circuit to adapt its gain and dynamic range characteristics dynamically rather than being fixed
Solution Approach 2:
The patent divides the capacitor array into multiple switchable capacitors (C1, C2, C3, C4) that can be independently connected or disconnected. This segmentation allows selective combination of different capacitance values to achieve various gain levels and dynamic range settings, resolving the contradiction between reliability and complexity
2Productivity
If high-frame-rate eye tracking is implemented, then productivity is improved, but power consumption increases
Solution Approach 1:
The patent employs periodic pulsed IR laser illumination synchronized with the eye tracking frame rate. The silicon photomultiplier detects reflected light during these periodic pulses, enabling high-frame-rate operation without continuous power consumption from the light source
Solution Approach 2:
The silicon photomultiplier inherently provides high gain and low noise amplification without requiring external power management circuits, allowing the system to achieve high frame rates while maintaining efficient power usage through the detector's intrinsic properties
3Measurement precision
If imaging in photon-sparse environments is performed, then measurement precision is improved, but the system becomes more sensitive to quantization error
Solution Approach 1:
The patent changes the capacitance parameter dynamically by switching between different capacitor combinations in the array. In photon-sparse conditions, larger capacitance values are selected to increase the signal amplitude, thereby improving measurement precision while reducing the relative impact of quantization error
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 solution enhances the dynamic range and reduces quantization error, allowing for high-frame-rate eye tracking and imaging while operating within limited power budgets, effectively handling the intensity variations encountered in eye imaging applications.
Implementation Method 1
detecting photons reflected off the object using a solid state silicon photomultiplier
Data Source
AI summary
A light sensing circuit includes a photomultiplier in electrical communication with an array of capacitors or resistors. Each capacitor or resistor in the array having an associated switch and having a capacitance or resistance different from every other capacitor or resistor in the array. Each switch has an open state and a closed state, thus enabling each capacitor or resistor to be placed in electrical communication with the photomultiplier or be isolated from the photomultiplier. The switchable array may be in electrical communication with an analog to digital converter (ADC) or a transimpedance amplifier (TIA). The switchable array allows the ADC or TIA to be sensitive to low value signals and operate at a large dynamic range and operate at a fast rate.