ToF Light Receiving Pixel Layout for Low-Voltage Charge Transfer
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Solution Overview
Problem
The indirect Time of Flight (ToF) method faces a trade-off between reducing the on-voltage of transfer transistors to improve distance measurement accuracy and preventing transfer failures.
Innovation Solution
A light receiving element with a matrix of pixels, each equipped with photoelectric conversion units, charge storage units, transfer transistors, amplification transistors, and connection wirings that extend in a row direction in a first wiring layer, along with discharge, reset, and boost wirings, to manage charge transfer and storage efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the on-voltage of the transfer transistor is reduced to improve distance measurement accuracy, then measurement precision is improved, but transfer reliability deteriorates due to transfer failures
Solution Approach 1:
The patent applies different voltage levels to different regions of the pixel array. Specifically, pixels in different rows are assigned different on-voltage levels to their transfer transistors. This local differentiation allows the system to optimize for both low voltage (to improve measurement precision) and sufficient voltage (to prevent transfer failures) by distributing operations across multiple voltage levels rather than using a single uniform voltage for all pixels.
2Use of energy by moving object
If the on-voltage of the transfer transistor is reduced to lower power consumption, then energy use is reduced, but transfer failures increase
Solution Approach 1:
The patent implements a multi-level voltage strategy where different rows of pixels operate at different on-voltage levels. This allows the system to reduce overall power consumption by using lower voltages for some pixel rows while maintaining higher voltages for other rows that require them for reliable charge transfer, thus balancing energy efficiency with transfer reliability across the entire array.
3Measurement precision
If the on-voltage of the transfer transistor is reduced to improve measurement accuracy, then measurement precision is improved, but the number of transfer failures increases
Solution Approach 1:
The patent divides the pixel array into multiple rows, each operating at different on-voltage levels. This local quality differentiation enables the system to minimize transfer failures by assigning appropriate voltage levels to specific rows based on their requirements, while still achieving improved measurement precision overall through the reduced voltage operation in suitable rows.
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 configuration suppresses transfer failures while maintaining low on-voltage, enhancing the accuracy and reliability of distance measurements.
Implementation Method 1
a photoelectric conversion unit; first and second charge storage units that store charges generated by the photoelectric conversion unit
Data Source
AI summary
Provided is a light receiving element capable of lowering the on-voltage of a transfer transistor and suppressing transfer failures at a low on-voltage. The light receiving element includes a plurality of pixels arranged in a matrix, each of the plurality of pixels including: a photoelectric conversion unit; first and second charge storage units that store charges generated by the photoelectric conversion unit; first and second transfer transistors that transfer the charges from the photoelectric conversion unit to the first and second charge storage units, respectively; first and second amplification transistors that amplify potentials of the first and second charge storage units, respectively; and a connection wiring that electrically connects the first charge storage unit and the first amplification transistor, wherein a first transfer control wiring electrically connected to a gate of the first transfer transistor of each of the pixels in the same row extends in a row direction in a first wiring layer, and the connection wiring extends to the first wiring layer.