RGBZ Pixel Unit Cell Shared Capacitor Design
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Solution Overview
Problem
In image sensor design, there is a challenge in expanding the surface area of photodiodes for enhanced optical sensitivity while accommodating the necessary transistors, and balancing the size of storage capacitors for visible light and infrared detection pixels to minimize noise and maximize detection capacity.
Innovation Solution
The implementation of an RGBZ pixel unit cell design where visible light pixels share a common storage capacitor, and the infrared pixel has its own larger storage capacitor, allowing for sequential readouts and optimized transistor placement to enhance sensitivity and detection capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the surface area of photodiodes is expanded to enhance optical sensitivity, then optical sensitivity is improved, but the space available for transistors and capacitors is reduced
Solution Approach 1:
The patent merges the storage capacitors for visible light pixels (C1) and infrared pixels (C2) into a shared capacitor structure. This consolidation reduces the total area required for capacitors, thereby providing more space for photodiodes to expand their surface area and improve optical sensitivity while maintaining all necessary transistor and capacitor functions.
Solution Approach 2:
The shared capacitor structure serves multiple functions: it stores charge from both visible light photodiodes and infrared photodiodes, and supports both standard imaging mode and time-of-flight mode operations. This multi-functionality eliminates the need for separate dedicated capacitors for each pixel type, optimizing the use of available pixel area.
2Quantity of substance
If separate storage capacitors are provided for visible light pixels and infrared pixels, then charge storage capacity is improved, but device complexity and area are increased
Solution Approach 1:
The patent combines multiple storage functions into a unified capacitor structure where C1 and C2 share common circuit elements and physical space. This merging maintains the ability to store charge from different photodiode types while reducing the overall complexity and area compared to completely separate capacitor structures.
Solution Approach 2:
The capacitor structure is segmented into distinct regions (C1 for visible light, C2 for infrared) that can be independently controlled through transfer gates. This segmentation allows each region to maintain its charge storage capacity while the overall structure remains compact and integrated, reducing total device complexity.
3Area of stationary object
If a single storage capacitor is shared among all pixels, then area is reduced, but noise increases and detection capacity decreases
Solution Approach 1:
The shared capacitor structure is divided into separate charge storage regions (C1 for visible light, C2 for infrared) that can be independently managed. This segmentation prevents noise from one pixel type from affecting the other, as each region has its own transfer gate control, while still benefiting from the reduced total area of a shared structure.
Solution Approach 2:
Transfer gate transistors act as intermediaries between the photodiodes and the shared capacitor regions. These intermediaries enable selective charge transfer from specific photodiodes to specific capacitor regions, isolating noise sources and preventing cross-contamination while maintaining efficient charge storage and readout capabilities.
4Quantity of substance
If larger storage capacitors are used for infrared pixels to increase detection capacity, then infrared detection capacity is improved, but the area available for other components is reduced
Solution Approach 1:
The patent merges the infrared storage capacitor (C2) with the visible light storage capacitor (C1) into a shared structure. This allows the infrared capacitor to have sufficient capacity for time-of-flight detection while sharing physical space and circuit resources with the visible light capacitor, thereby maintaining adequate detection capacity without proportionally increasing total area.
Solution Approach 2:
The capacitor structure is designed to be dynamically configurable through transfer gate control, allowing the system to adapt charge storage allocation between visible and infrared modes as needed. This dynamic control enables the infrared detection capacity to be optimized when required while minimizing the impact on other components during standard imaging operation.
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
This design improves optical sensitivity and reduces readout noise for visible light pixels while increasing infrared detection capacity, enabling efficient simultaneous operation of RGB and Z pixel values.
Implementation Method 1
The pixel array has a unit cell that includes visible light photodiodes and an infra-red photodiode
Data Source
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AI summary
An image sensor is described having a pixel array. The pixel array has a unit cell that includes visible light photodiodes and an infra-red photodiode. The visible light photodiodes and the infra-red photodiode are coupled to a particular column of the pixel array. The unit cell has a first capacitor coupled to the visible light photodiodes to store charge from each of the visible-light photodiodes. The unit cell has a readout circuit to provide the first capacitor's voltage on the particular column. The unit cell has a second capacitor that is coupled to the infra-red photodiode through a first transfer gate transistor to receive charge from the infra-red photodiode during a time-of-flight exposure. The first capacitor is coupled to the infra-red photodiode through a second transfer gate transistor to receive charge from the infra-red photodiode during the time-of-flight exposure.