Depth Pixel Compensation for Ambient Light Interference
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Solution Overview
Problem
Three-dimensional image sensors face challenges in accurately measuring distance information due to performance degradation caused by strong ambient light, as existing technologies struggle to effectively compensate for ambient light components in depth pixel operations.
Innovation Solution
The proposed solution involves a depth pixel design with a compensation unit that generates charges different from those based on ambient light components, which are injected into a floating diffusion area, allowing for accurate distance measurement even under strong ambient light conditions. This design includes a first photo gate, photo detection area, transmission gate, floating diffusion area, and a compensation unit with an ambient light detection area and injection gate, configured to operate within a semiconductor substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional depth pixel design is used, then the device structure is simple, but measurement precision deteriorates under strong ambient light conditions
Solution Approach 1:
The pixel is divided into two separate photo detection areas: a first photo detection area for generating first charges from reflected light, and a second photo detection area for generating second charges from ambient light. This segmentation allows independent measurement and compensation of ambient light effects, improving distance measurement accuracy without requiring complex external compensation systems.
Solution Approach 2:
A compensation unit is introduced as an intermediary mechanism that uses the second charges from the second photo detection area to compensate for ambient light interference in the first photo detection area. The compensation unit includes a compensation photo gate and compensation transistor that transfer and subtract ambient light charges from the measurement signal, enabling accurate depth measurement under varying ambient light conditions.
2Measurement precision
If photo detection area size is increased to improve light sensitivity, then measurement precision improves, but ambient light interference increases
Solution Approach 1:
The photo detection function is segmented into two parallel pathways: one for measuring reflected light (first photo detection area) and one for measuring ambient light (second photo detection area). Both areas can be optimized for sensitivity, and the ambient light measurement is used to compensate the reflected light measurement, allowing large photo detection areas without proportional increase in harmful ambient light interference.
Solution Approach 2:
The second photo detection area provides real-time feedback about ambient light conditions, which is processed by the compensation unit to generate compensation charges. This feedback mechanism dynamically adjusts for ambient light variations, allowing the photo detection areas to maintain high sensitivity while automatically compensating for the corresponding increase in ambient light interference.
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 enables accurate distance measurement in three-dimensional image sensors without performance degradation, even when ambient light is strong, by effectively compensating for ambient light components through the injection of charges generated by the compensation unit into the floating diffusion area.
Implementation Method 1
a first photo detection area configured to generate first charges based on a received light reflected from a subject
Implementation Method 2
The first ambient light detection area may generate the second charges based on the ambient light components
Data Source
AI summary
A depth pixel of a three-dimensional image sensor includes a first photo gate which is turned on/off in response to a first photo control signal, a first photo detection area configured to generate first charges based on a received light reflected from a subject when the first photo gate is turned on, a first transmission gate which is turned on/off in response to a first transmission control signal, a first floating diffusion area configured to accumulate the first charges generated from the first photo detection area when the first transmission gate is turned on, and a first compensation unit configured to generate second charges which are different from the first charges based on ambient light components included in the received light to supply the second charges to the first floating diffusion area.