Anti-blooming Pixel Row Drivers for CMOS Imager Charge Control
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Solution Overview
Problem
Existing anti-blooming protection methods for CMOS imagers are inadequate in skipping and windowing modes, as they fail to provide effective charge draining in skipped rows, leading to contamination of neighboring pixels, and are insufficient when applied only locally in rolling shutter mechanisms.
Innovation Solution
Implementing a global anti-blooming operation that turns on transfer and reset transistors during non-integration periods to drain excess charges, using negative transfer low voltage and non-boosted reset control signals to maintain low floating diffusion region voltage, and varying output voltages based on row selection and integration status through latch circuits in row drivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If anti-blooming protection is applied only locally in rolling shutter mechanisms, then power consumption is reduced, but skipped rows are not protected and contaminate neighboring pixels
Solution Approach 1:
The patent applies different anti-blooming strategies to different row types: integrating rows receive continuous protection while skipped rows receive protection only during non-integration periods. This localized differentiation protects skipped rows from contaminating neighboring pixels while minimizing unnecessary power consumption in rows that are actively integrating.
Solution Approach 2:
For skipped rows, anti-blooming protection is applied periodically during non-integration periods rather than continuously. The transfer and reset transistors are activated only when needed (during shutter phase and non-integration periods), reducing power consumption while still preventing blooming contamination when the pixel array is not in full integration mode.
2Object-affected harmful factors
If transfer and reset transistors are turned on during non-integration periods, then skipped rows are protected from blooming, but power consumption increases
Solution Approach 1:
The patent activates transfer and reset transistors during non-integration periods before skipped rows could potentially accumulate excess charge that would contaminate neighboring pixels. By performing this charge draining action in advance during the shutter phase and non-integration periods, the system prevents blooming contamination while limiting power consumption to specific time windows rather than continuous operation.
3Productivity
If control signals are boosted continuously, then charge transfer efficiency is maximized, but booster load and power consumption increase
Solution Approach 1:
The patent applies boosted control signals only during critical phases: the shutter phase (when rows are transitioning between integration states) and non-integration periods (when skipped rows need charge draining). During full integration mode, continuous boosting is not applied, reducing booster load and power consumption while maintaining sufficient charge transfer efficiency when needed most.
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 approach provides comprehensive anti-blooming protection for all rows, including skipped ones, reduces hot pixel and dark current issues, and minimizes power consumption and booster load by boosting control signals only during sampling and shutter phases, ensuring effective charge transfer and reduced contamination.
Implementation Method 1
A CMOS imager includes a focal plane array of pixels, each one of the pixels including a photosensor, for example, a photogate, photoconductor or a photodiode overlying a substrate for accumulating photo-generated charge
Data Source
AI summary
Circuits and methods of generating control signals for transistors in a pixel row of a pixel array are disclosed. The circuits include a transfer transistor control signal row driver that includes a plurality of output branches and a reset transistor control signal row driver that includes a plurality of output branches. The row drivers output positive boosted control signals to selected pixel rows during a photosensor-to-floating diffusion region charge transfer phase and during a floating diffusion region reset phase and to unselected pixel rows during an initial part of an integration phase. The row drivers output positive non-boosted control signals to unselected non-integrating pixel rows.