Light Sensor Temperature Compensation via Shielded Well
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Solution Overview
Problem
Conventional ambient light sensors are sensitive to temperature variations, affecting their accuracy in detecting ambient light spectral content, as they are mounted on components that can have higher temperatures than the ambient environment, leading to inaccuracies in photopic response.
Innovation Solution
A light sensor arrangement with unshielded and shielded wells in a substrate, where the unshielded well is exposed to incident light and the shielded well generates a sensor signal through indirect pathways, combined with a temperature sensor and processing unit for temperature compensation, allowing for accurate spectral content determination and improved photopic response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional ambient light sensors are mounted on PCB and flex cables, then the sensor can be integrated into display devices, but the sensor temperature becomes higher than ambient environment temperature leading to reduced measurement precision
Solution Approach 1:
The patent introduces a shielded well as an intermediary element that indirectly measures temperature effects on the photodiode. The shielded well blocks direct light but allows thermal effects to manifest as photo-currents, serving as a mediator to separate temperature measurement from direct light detection.
Solution Approach 2:
The patent changes the operational parameters by measuring photo-currents from both shielded and unshielded wells at different temperature conditions. By varying temperature and recording corresponding photo-current changes, the system establishes temperature compensation parameters that correct spectral content measurements.
2Volume of moving object
If photodiodes are closely spaced to detect ambient light, then the sensor structure is compact, but the sensors become very sensitive to pn-junction temperature variations
Solution Approach 1:
The patent segments the photodiode structure into unshielded and shielded portions within the same substrate. This segmentation allows the unshielded portion to detect light while the shielded portion measures temperature effects, separating the detection functions while maintaining compact integration.
Solution Approach 2:
The patent converts the harmful temperature sensitivity into a useful measurement tool. By using the shielded well to capture temperature-induced photo-currents, the previously problematic temperature sensitivity becomes a source of temperature information that can be used for compensation of the unshielded well measurements.
3Measurement precision
If temperature compensation is implemented using shielded and unshielded wells, then spectral content detection accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent makes the photodiode substrate multi-functional by using it for both light detection (unshielded well) and temperature measurement (shielded well). The same substrate and photodiode structure serve dual purposes, eliminating the need for separate temperature sensors and reducing overall device complexity.
Solution Approach 2:
The patent merges the temperature sensing function with the light detection function by integrating the shielded well directly into the photodiode substrate. This combination allows simultaneous measurement of light and temperature using a single integrated structure, simplifying the overall device architecture.
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 provides higher accuracy in ambient light detection, enabling the light sensor arrangement to function effectively over a wider temperature range and expanding its application markets.
Implementation Method 1
Under exposure to the incident light the first unshielded well generates a first sensor signal as a function of the incident light. This first sensor signal is generated by absorption of light photons in the material of the first well.
Implementation Method 2
The origin of this second sensor signal is from indirect pathways to the well structure via the substrate. For example, infrared photons may penetrate into the substrate and are absorbed underneath the shielded well. By way of diffusion, minority carriers which are generated in the course of the absorption may diffuse towards the shielded well and lead to the generation of the second sensor signal.
Data Source
AI summary
A light sensor arrangement according to the proposed principle comprises at least one first unshielded well (D0) and at least one second shielded well (D1) in a substrate (P). The at least one first unshielded well (D0) is being exposed to incident light (λ) and configured to generate a first sensor signal (Ch0) as a function of the incident light (λ). The at least one second shielded well (D1) in the substrate (p) being shielded from the incident light (λ) and configured to generate a second sensor signal (Ch1) as a function of the incident light (λ). The light sensor arrangement further comprises means for temperature compensation providing the first and second sensor signals (Ch0, Ch1) as temperature compensated sensor signals as a function of substrate temperature. Means to determine spectral content of the incident light (λ) are provided to determine the spectral content as a function of the temperature compensated first and second sensor signals (Ch0, Ch1).