TDI Linear Image Sensor Gate Segmentation for MTF and Sensitivity
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Solution Overview
Problem
TDI-type linear image sensors with VPCCD structures face a trade-off between sensitivity and Modulation Transfer Function (MTF) in the TDI transfer direction due to light being gathered onto electrodes with microlenses, leading to reduced resolution and image blurring.
Innovation Solution
The implementation of a TDI-type linear image sensor with CCDs of n phases, where each phase has a gate opening portion and a gate non-opening portion forming a TDI transfer channel, and microlenses are formed within one pixel pitch to gather light onto the gate opening portion of each transfer gate, ensuring optimal light collection without compromising MTF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If microlenses are formed to gather light onto electrodes in a TDI-type linear image sensor with VPCCD structure, then sensitivity is improved, but MTF in the TDI transfer direction deteriorates causing image blurring
Solution Approach 1:
The image sensor is divided into multiple TDI transfer gates (first, second, third, and fourth transfer gates) arranged in the TDI transfer direction. Each transfer gate is further segmented into gate opening portions and gate non-opening portions. This segmentation allows light to be gathered onto specific gate opening portions of different phases, improving sensitivity while maintaining MTF by distributing light collection across multiple segmented regions rather than concentrating it on a single electrode structure.
Solution Approach 2:
Different regions of the transfer gates are assigned different functions: gate opening portions are optimized for light gathering to improve sensitivity, while gate non-opening portions maintain the electrode structure to preserve MTF. The microlenses are strategically positioned to focus light onto the gate opening portions of specific phases, creating local quality optimization where each region serves its intended purpose without compromising the other.
2Measurement precision
If pixel pitch is minimized to improve resolution, then area of photodetectors decreases, but S/N ratio deteriorates
Solution Approach 1:
The invention utilizes the TDI transfer direction (vertical dimension) to compensate for the reduced light-gathering area in the horizontal dimension. By transferring charges through multiple phases in the vertical direction and integrating signals over time, the system achieves high resolution in the horizontal direction while maintaining good S/N ratio through temporal integration in the vertical dimension.
Solution Approach 2:
Signal charges are transferred through multiple TDI phases before final readout, allowing preliminary accumulation and integration of signals from multiple passes. This preliminary action in the vertical transfer direction compensates for the reduced photodetector area, maintaining S/N ratio despite minimized pixel pitch for high resolution.
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 simultaneously enhances sensitivity and maintains high MTF, preventing image blurring and improving overall image quality in TDI-type linear image sensors.
Implementation Method 1
each of n microlenses is formed within one pixel pitch in a TDI transfer direction so that light is gathered onto the gate opening portion formed at the transfer gate of each phase
Implementation Method 2
Incident light is photoelectrically converted within a silicon substrate and produces signal charges
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a TDI-type linear image sensor in which pixels are constituted of CCDs (Charge Coupled Devices) of n phases (n being an integer not smaller than 3), a gate opening portion and a gate non-opening portion functioning as a TDI transfer channel (15) are formed in all of the transfer gates of the CCDs of n phases constituting the pixels. Within one pixel pitch in a TDI transfer direction, n microlenses (18) are formed such that light is concentrated at the gate non-opening portion formed at the transfer gate of each phase.