Tri-gate Charge Transfer Block for TOF Pixel Power Reduction
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Solution Overview
Problem
Time of flight cameras face challenges in balancing performance parameters with physical size and power constraints, particularly due to high power requirements and complex charge transfer processes in existing photogate indirect time of flight (iTOF) pixel structures, which limit miniaturization and increase power consumption.
Innovation Solution
The implementation of tri-gate charge transfer block structures with central collection photodiodes in time of flight pixel structures, which reduce power consumption and enhance charge transfer speeds without increasing pixel size, by utilizing a tri-gate charge transfer block structure that includes a transfer gate, shutter gate, and switch gate sharing a single shared channel region to efficiently transfer image charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional photogate indirect time of flight pixel structures are used, then charge transfer can be achieved, but power consumption is high and device size is large
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photodiode region for charge generation, a tri-gate charge transfer block structure for efficient charge transfer, and a readout circuit region. This segmentation allows each region to be optimized independently, reducing overall power consumption while maintaining charge transfer performance
Solution Approach 2:
The patent introduces a vertical tri-gate structure that extends into the substrate, utilizing the third dimension (depth) to create charge transfer pathways. This vertical configuration reduces the lateral footprint of the pixel while providing efficient charge transfer routes, thereby reducing device size without compromising charge transfer speed
2Speed
If high performance time of flight systems operate at very high frequencies, then charge transfer speed is improved, but power requirements become considerably high
Solution Approach 1:
The tri-gate charge transfer block structure utilizes periodic gating signals to transfer charges in discrete steps. This periodic action allows the system to achieve high effective charge transfer speeds while consuming power only during the active transfer phases, rather than continuously, thereby reducing overall power requirements
Solution Approach 2:
The tri-gate structure acts as an intermediary mechanism between the photodiode and readout circuits. It provides a controlled pathway for charge transfer that can be activated only when needed, mediating the charge flow to achieve high transfer speeds while minimizing power consumption during idle periods
3Volume of moving object
If miniaturization of time of flight sensors is pursued, then device size is reduced, but charge transfer efficiency and performance may deteriorate
Solution Approach 1:
By transitioning from a planar two-dimensional charge transfer architecture to a vertical three-dimensional tri-gate structure, the patent achieves efficient charge transfer within a minimized lateral footprint. The vertical gates extend into the substrate to create compact yet effective charge transfer pathways, enabling miniaturization without sacrificing charge transfer efficiency
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 solution achieves reduced power consumption and improved charge transfer speeds, enabling more efficient and miniaturized time of flight image sensors that can operate effectively in smaller devices with lower power usage.
Implementation Method 1
a sensor that detects the light that is reflected from the object
Data Source
AI summary
A pixel circuit includes a photodiode in semiconductor material to accumulate image charge in response to incident light. A tri-gate charge transfer block coupled includes a single shared channel region the semiconductor material. A transfer gate, shutter gate, and switch gate are disposed proximate to the single shared channel region. The transfer gate transfers image charge accumulated in the photodiode to the single shared channel region in response to a transfer signal. The shutter gate transfers the image charge in the single shared channel region to a floating diffusion in the semiconductor material in response to a shutter signal. The switch gate is configured to couple the single shared channel region to a charge storage structure in the semiconductor material in response to a switch signal.