Lateral Overflow Drain for Image Sensor Dark Current Flushing
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Solution Overview
Problem
Current digital-still cameras face increased shutter latency and power consumption due to the need for high-speed clocking to flush out residual dark current in CCD image sensors, especially as the number of pixels increases, which is undesirable for photographers.
Innovation Solution
An image sensor structure featuring a substrate with pixels, lateral overflow drains, and additional gate electrodes for efficient dark current removal, allowing quick disposal of dark charges without additional pixel area and minimizing power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-speed clocking is used to flush out residual dark current in CCD image sensors, then dark current removal efficiency is improved, but power consumption increases
Solution Approach 1:
The patent divides the charge storage function into multiple regions (first charge-storage region and second charge-storage region) with separate overflow paths. The first lateral overflow gate handles dark current flushing while the second lateral gate handles blooming control, allowing independent optimization of each function's timing and voltage requirements, thereby reducing overall power consumption.
Solution Approach 2:
The patent introduces a lateral overflow drain as an intermediary structure that receives charges from both charge-storage regions. This mediator enables efficient dark current removal by providing a dedicated drainage path that operates at lower voltages and speeds compared to traditional full-CCD flushing methods.
2Reliability
If high-speed clocking is used to flush out residual dark current in CCD image sensors, then dark current removal efficiency is improved, but shutter latency increases
Solution Approach 1:
The patent segments the charge handling functions by creating separate overflow paths for different purposes. The first lateral overflow gate is dedicated to dark current flushing and can operate independently and simultaneously with image capture preparation, enabling parallel processing that reduces overall shutter latency.
Solution Approach 2:
The patent implements preliminary dark current flushing through the first lateral overflow gate before the actual image capture begins. By pre-clearing dark current charges during the shutter latency period, the system prepares the sensor for immediate image capture without requiring additional high-speed flushing operations afterward.
3Measurement precision
If more pixels are added to the sensor, then image resolution is improved, but shutter latency increases
Solution Approach 1:
The patent introduces a lateral overflow drain structure that can be integrated into existing pixel arrays without requiring additional pixel area. This segmentation of the overflow function from the pixel structure allows high-resolution sensors to maintain efficient dark current removal capabilities regardless of pixel count.
Solution Approach 2:
By implementing preliminary flushing capability through the lateral overflow gate structure, the patent enables sensors with any pixel density to clear dark current charges before image capture. This preliminary action occurs during the shutter latency period, ensuring that even high-resolution sensors with many pixels can prepare for capture without proportionally increased latency.
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 reduces shutter latency, dark current in images, and power consumption by efficiently flushing dark charges through the lateral overflow drain, maintaining image quality while minimizing power dissipation.
Implementation Method 1
a first lateral overflow gate adjacent the first charge-storage regions that passes substantially all charges from the first charge-storage region to the lateral overflow drain
Implementation Method 2
The photosites, or pixels as they are commonly referred to in the art, collect incoming photons and convert them to electron-hole pairs (EHPs)
Data Source
AI summary
An image sensor includes a substrate; a plurality of pixels on the substrate, one or more of the pixels comprises (i) first and second charge-storage regions having at least one photosensitive area; (ii) a lateral overflow drain; (iii) a first lateral overflow gate adjacent the first charge-storage regions that passes substantially all charges from the first charge-storage region to the lateral overflow drain; and (iv) a second lateral gate adjacent the second charge-storage region that passes excess photo-generated charge into the lateral overflow drain for blooming control.