CMOS Imaging Sensor Array Parasitic Photodiode Dynamic Range
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Solution Overview
Problem
Current CMOS image sensors face limitations in dynamic range due to noise sources, particularly shot noise, which restrict their ability to accurately measure both low and high light intensities without saturating or requiring larger pixel sensors.
Innovation Solution
Incorporating a parasitic photodiode with significant detection efficiency within each pixel sensor, along with a dual gain amplifier and column calibration circuits, to extend the dynamic range without increasing pixel size, and using signal injectors for noise correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single photodiode is used per pixel sensor, then the pixel sensor size remains small, but the dynamic range is limited and cannot accurately measure both low and high light intensities
Solution Approach 1:
The patent merges a main photodiode and a parasitic photodiode within a single pixel sensor structure. The main photodiode has high detection efficiency for low light signals, while the parasitic photodiode has lower detection efficiency suitable for high light signals. By combining these two photodiodes and their respective readout circuits, the system achieves extended dynamic range without requiring separate pixel sensors for different light conditions.
Solution Approach 2:
The patent changes the detection efficiency parameter by utilizing two photodiodes with different efficiencies within the same pixel sensor. The main photodiode is designed with high detection efficiency (first parameter value) for low light detection, while the parasitic photodiode has lower detection efficiency (second parameter value) for high light detection. This parameter variation enables the system to measure across a wider dynamic range.
2Measurement precision
If exposure is set to detect low level light signals, then low light regions are captured accurately, but bright regions become saturated and lose information
Solution Approach 1:
The patent combines readout paths for both the main photodiode (high sensitivity) and parasitic photodiode (low sensitivity) within the same pixel sensor. During exposure, the main photodiode captures low light signals with high accuracy, while the parasitic photodiode simultaneously captures high light signals that would otherwise saturate the main photodiode. The system merges these two measurements to reconstruct the full dynamic range image without information loss.
Solution Approach 2:
The parasitic photodiode acts as an intermediary for high light intensity measurement. When the main photodiode would saturate in bright regions, the parasitic photodiode provides an alternative measurement path with lower sensitivity that remains in the linear response range, thereby preserving information about bright regions that would otherwise be lost to saturation.
3Measurement precision
If a second photodiode with lower sensitivity is added to extend high intensity response, then dynamic range increases, but noise sources limit the ability to image low light regions
Solution Approach 1:
The patent segments the dynamic range measurement function into two separate photodiodes: the main photodiode dedicated to low light region detection with high sensitivity and low noise floor, and the parasitic photodiode dedicated to high light region detection with lower sensitivity. This segmentation allows each photodiode to be optimized for its specific function, with the main photodiode maintaining low noise characteristics for accurate low light imaging while the parasitic photodiode handles high intensity signals.
Solution Approach 2:
The patent applies local quality by giving each photodiode different detection efficiency characteristics suited to its intended measurement range. The main photodiode has high detection efficiency optimized for low light signals, while the parasitic photodiode has lower detection efficiency optimized for high light signals. This localized optimization of detection efficiency in different parts of the pixel sensor enables simultaneous accurate measurement across the full dynamic range without compromising noise performance in low light regions.
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 enhances the dynamic range of CMOS image sensors to 10^6, allowing for accurate measurement of a wide range of light intensities with reduced noise, particularly shot noise, and maintains image quality across varying light conditions.
Implementation Method 1
Each photodetector converts the light received during an exposure period into an electrical signal
Data Source
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AI summary
An apparatus having a rectangular imaging array characterized by a plurality of pixel sensors and a plurality of readout lines is disclosed. The apparatus has a plurality of column processing circuits, each column processing circuit being connected to a corresponding one of the readout lines and a plurality of signal injectors, one signal injector being connected to each of the readout lines. Each signal injector causes one of a predetermined number of voltages to be coupled to that readout line. An exposure for each of the pixel sensors is determined during image recording periods. The signal injectors inject a plurality of calibration voltages into the readout lines during calibration periods, and determines a gain function of an amplifier in one of the column processing circuits by measuring an output of the amplifier for the plurality of calibration voltages, the calibration period is between the imaging recording periods.