Range Imaging Pixel Layout for Uniform Charge Transfer
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Solution Overview
Problem
Conventional range imaging devices face accuracy issues in distance measurement due to variations in transfer characteristics of transfer gates between photoelectric conversion devices and charge storages, leading to inconsistent transfer efficiency of charge carriers.
Innovation Solution
A range imaging device with a semiconductor substrate and pixel circuit configuration, including symmetrically arranged transfer MOS transistors and charge drainage MOS transistors, ensures uniform transfer characteristics across all transfer paths, allowing for consistent and efficient transfer of charge carriers to charge storages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transfer gates are provided between photoelectric conversion device and charge storages, then charge carriers can be transferred from photoelectric conversion device to charge storages, but transfer characteristics vary due to layout causing different transfer efficiency
Solution Approach 1:
The patent applies asymmetry by intentionally introducing dummy transfer gates to create symmetric layouts. The dummy transfer gates are added to balance the number of transfer gates between different charge storages, ensuring that all transfer paths have equal numbers of gates despite the inherent asymmetric positions of charge storages relative to the photoelectric conversion device. This symmetry compensation resolves the transfer characteristic variation caused by layout differences.
Solution Approach 2:
The patent achieves homogeneity by making all transfer gates (including dummy transfer gates) have identical structures, sizes, and electrical characteristics. By ensuring that dummy transfer gates are substantially the same as real transfer gates in terms of gate length, width, and positioning, the patent creates uniform transfer paths that provide consistent transfer efficiency across all charge storages, eliminating the heterogeneity caused by layout variations.
2Measurement precision
If multiple charge storages are provided for different predetermined cycles, then delay time can be calculated accurately, but transfer gate layout variation causes inconsistent charge carrier transfer
Solution Approach 1:
The patent segments the transfer function by dividing it into real transfer gates and dummy transfer gates. Each charge storage has its own dedicated real transfer gate, while dummy transfer gates are strategically placed to balance the total number of gates in each transfer path. This segmentation allows the system to maintain multiple charge storages for accurate delay time measurement while ensuring uniform transfer efficiency through the dummy gate compensation mechanism.
Solution Approach 2:
The patent creates copies of transfer gates in the form of dummy transfer gates that replicate the structure and characteristics of real transfer gates. These dummy copies are added to specific transfer paths to match the gate counts of other paths, ensuring that all transfer paths have equivalent transfer characteristics. This copying approach enables consistent charge carrier transfer efficiency across all charge storages without affecting the functionality of real transfer gates.
3Measurement precision
If transfer gates have different transfer characteristics, then charge carriers are transferred with different efficiency, but adding more transfer gates increases device complexity
Solution Approach 1:
The patent merges the functionality of real and dummy transfer gates into a unified transfer system. Both real and dummy transfer gates are integrated into the same pixel circuit structure and operate under the same control mechanisms. This merging approach allows the system to achieve uniform transfer characteristics without creating separate complex circuits, as the dummy gates are seamlessly incorporated into the existing transfer gate architecture and controlled alongside real gates.
Solution Approach 2:
The patent creates equipotential transfer paths by ensuring that all transfer paths have the same number of transfer gates with identical characteristics. By balancing the gate counts and making dummy gates substantially the same as real gates, the patent equalizes the electrical potential and transfer conditions across all paths from the photoelectric conversion device to different charge storages. This equipotential approach simplifies the overall system design by eliminating the need for complex compensation circuits or variable gain amplifiers.
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 ensures that charge carriers are transferred with the same efficiency, resulting in more accurate distance measurements by maintaining consistent transfer characteristics across all transfer paths.
Implementation Method 1
the amount of incident light is converted into charge carriers by a photoelectric conversion device
Data Source
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AI summary
The present invention is a range imaging device including a pixel circuit at a surface of a semiconductor substrate. The pixel circuit includes a photoelectric conversion device that generates charge carriers based on incident light, charge storages that store the charge carriers, a transfer MOS transistor (hereinafter TR) that transfers the charge carriers to the charge storages, and a charge drainage TR that discharges the charge carriers from the photoelectric conversion device. The photoelectric conversion device has a rectangular shape. The pixel circuit includes 2M transfer TRs (M is an integer, M ≥ 2), and 2N charge drainage TRs (N is an integer, N ≥ 1). M transfer TRs are arranged on each of long sides of the photoelectric conversion device symmetrically with respect to an x-axis parallel to the long sides and passing through a center of the photoelectric conversion device. The M transfer TRs on one of the long sides face the M transfer TRs on the other of the long sides. The charge drainage TRs are provided on respective short sides of the photoelectric conversion device.