Pixel Cell With Multiple Photodiodes For Collocated 2D And 3D Sensing
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Solution Overview
Problem
Existing image sensors face challenges in performing collocated 2D and 3D sensing due to spatial resolution limitations and increased power consumption when using separate pixel cells for different wavelength ranges, leading to complications in mapping and merging 2D and 3D image data, especially in wearable devices.
Innovation Solution
An image sensor design featuring a pixel cell with a first photodiode for infra-red light and a second photodiode for visible light, both integrated in a semiconductor substrate with a barrier layer to prevent charge flow, allowing for simultaneous 2D and 3D sensing using indirect time-of-flight measurement, which simplifies image mapping and reduces hardware requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate pixel cells are used for different wavelength ranges (2D and 3D sensing), then spatial resolution can be maintained, but device complexity and power consumption increase
Solution Approach 1:
The patent combines multiple photodiodes (first photodiode for 3D sensing, second photodiode for 2D sensing) within a single pixel cell structure, allowing both 2D and 3D sensing functions to be integrated in one location rather than requiring separate pixel cells for each function
Solution Approach 2:
The pixel cell is designed to perform multiple functions simultaneously - the first photodiode enables indirect time-of-flight measurement for 3D depth sensing while the second photodiode performs 2D image sensing, making the same pixel cell universal for both sensing types
2Adaptability or versatility
If separate pixel cells are used for different wavelength ranges, then functional separation is achieved, but power consumption increases
Solution Approach 1:
Multiple photodiodes are merged within a single pixel cell to share common infrastructure including readout circuits, signal processing pathways, and control logic, thereby reducing the total power consumption compared to operating separate pixel cells independently
3Device complexity
If multiple photodiodes are integrated in one pixel cell, then device complexity is reduced, but charge crosstalk between photodiodes occurs
Solution Approach 1:
A barrier layer is introduced as an intermediary structure between the first photodiode and second photodiode to prevent charge carriers generated in one photodiode from diffusing or drifting into the other photodiode, thereby eliminating crosstalk while maintaining the integrated structure
Solution Approach 2:
The pixel cell is segmented into distinct regions with the barrier layer creating electrical isolation between the first photodiode region and second photodiode region, allowing each photodiode to operate independently without charge interference from the other
4Ease of operation
If collocated 2D and 3D sensing is implemented, then image mapping is simplified, but manufacturing precision requirements increase
Solution Approach 1:
The first photodiode and second photodiode are merged in a stacked configuration within the same pixel cell location, ensuring automatic spatial correspondence between 2D and 3D sensing data without requiring complex post-processing alignment or calibration
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 enables robust, high-performance collocated 2D and 3D imaging with improved spatial resolution and reduced power consumption, enhancing applications in virtual, augmented, and mixed reality systems.
Implementation Method 1
A first photodiode, a second photodiode... The first photodiode is configured to generate a first charge in response to infra-red light
Implementation Method 2
The second photodiode is configured to generate a second charge in response to visible light
Implementation Method 3
a barrier layer to prevent charge flow
Data Source
AI summary
In one example, a method comprises: transmitting a first signal to transfer a first portion of a first charge from a first photodiode to a first charge sensing unit to obtain a first measurement result and transmitting a second signal to transfer a second portion of the first charge from the first photodiode to a second charge sensing unit to obtain a second measurement result. The timing of transmission of the first signal and the second signal are based on the indirect time-of-flight measurement operation. The method further comprises performing the indirect time-of-flight measurement operation based on the first measurement result and the second measurement result; transmitting a third signal to transfer a second charge from a second photodiode to the second charge sensing unit via the first photodiode to obtain a third measurement result; and performing a D sensing operation based on the third measurement result.