Dual Holding Unit Image Sensor for Residual Charge Noise Reduction
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Solution Overview
Problem
Existing image pickup apparatuses face challenges in achieving high image quality due to residual charge noise and the need for improved global electronic shutter performance, particularly in configurations with separate charge holding units and floating diffusion structures.
Innovation Solution
The image pickup apparatus incorporates a dual holding unit configuration where a first holding unit holds charge generated by the photoelectric conversion unit, and a second holding unit holds charge transferred from the first holding unit, with a dedicated discharge path for the first holding unit, allowing for efficient charge transfer and reduction of residual noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single holding unit is used to hold charge from the photoelectric conversion unit, then the device complexity is reduced, but residual charge noise increases and global electronic shutter performance deteriorates
Solution Approach 1:
The holding function is segmented into two separate units: a first holding unit that receives charge from the photoelectric conversion unit, and a second holding unit that receives charge from the first holding unit. This segmentation allows independent control and discharge of charges at different stages, effectively reducing residual charge noise while maintaining manageable device complexity through systematic charge management.
2Device complexity
If charge is discharged from the first holding unit through the same path used for charge transfer, then the discharge path is simplified, but charge transfer efficiency decreases and noise increases
Solution Approach 1:
The charge management paths are segmented into two distinct routes: a first path for transferring charge from the photoelectric conversion unit to the first holding unit, and a second path for discharging charge from the first holding unit to the second holding unit. This path segmentation enables simultaneous charge transfer and discharge operations without interference, maintaining high charge transfer efficiency while simplifying the discharge path configuration.
3Productivity
If all pixels discharge charge simultaneously, then the global electronic shutter performance is improved, but residual charge noise increases due to synchronized discharge interference
Solution Approach 1:
The discharge operation is segmented into two sequential stages: first, charge is discharged from the photoelectric conversion unit to the first holding unit; second, charge is discharged from the first holding unit to the second holding unit. This staged discharge approach maintains synchronized global shutter performance across all pixels while reducing noise by separating the discharge events in time and space.
Solution Approach 2:
The first holding unit serves as an intermediate buffer that performs preliminary charge discharge before the second holding unit discharges. This preliminary action allows the system to maintain global electronic shutter functionality while reducing the noise impact of synchronized discharge by spreading it across multiple stages and units.
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 enhances image quality by reducing noise due to residual charge and enables synchronized global electronic shutter operation across all pixels, ensuring consistent exposure periods and improved image capture performance.
Implementation Method 1
a photoelectric conversion unit; configured to hold a charge generated by the photoelectric conversion unit
Data Source
AI summary
Each of multiple pixels includes a photoelectric conversion unit. A first holding unit is configured to hold a charge generated by the photoelectric conversion unit, at a location different from location of the photoelectric conversion unit. A second holding unit is configured to hold a charge held by the first holding unit at a location different from locations of both of the first holding unit and the photoelectric conversion unit. An amplifying unit includes an input node different from the second holding unit and is configured to output a signal based on a charge transferred to the input node from the second holding unit. A first discharge unit includes a charge draining node which is electrically connected to a line where a predetermined voltage is supplied. The first discharge unit discharges a charge held by the first holding unit to the charge draining node.