Solid-State Imaging Device Nonlinear AD Conversion
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in achieving a high gray scale and constant resolution when combining outputs from large and small photodiodes with different light receiving sensitivities, leading to coarse gray scales and inadequate performance in applications requiring precise illumination levels.
Innovation Solution
The implementation of a solid-state imaging device with a pixel array unit and an analog-to-digital (AD) conversion unit that compares electric signals from low-light sensitivity photoelectric conversion units with nonlinear or linear reference signals to enhance gray scale and resolution, using a comparator and counter to output a count value based on the time required for signal matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the output of the small PD is multiplied by a digital gain of 240 times to extend dynamic range, then the dynamic range is improved, but the gray scale becomes coarse
Solution Approach 1:
The patent changes the parameter of the reference signal from linear to nonlinear (specifically, a power function with exponent 0.4545) to match the compression effect of digital gain. This allows the AD conversion to naturally produce finer gray scales in the combined output region without requiring multiplication by a large digital gain, thereby resolving the contradiction between extended dynamic range and maintained gray scale precision
Solution Approach 2:
The patent introduces a nonlinear reference signal as an intermediary element in the AD conversion process. This nonlinear reference signal acts as a mediator that transforms the linear relationship between charge amount and digital output into a nonlinear relationship that naturally compresses the dynamic range while preserving gray scale precision, eliminating the need for post-processing digital gain multiplication
2Device complexity
If a linear reference signal is used for AD conversion, then the conversion process is simple, but the gray scale precision deteriorates when combining outputs of PDs with different sensitivities
Solution Approach 1:
The patent modifies the parameter of the reference signal from a linear function to a power function (nonlinear). This parameter change transforms the AD conversion characteristic so that the output digital signal naturally compresses the dynamic range with appropriate gray scale distribution, achieving both high precision and simplicity without complex post-processing
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 gray scale and achieves constant resolution of 1% or less, improving the dynamic range and signal-to-noise ratio while suppressing motion artifacts and achieving a wide dynamic range.
Implementation Method 1
a pixel including a plurality of photoelectric conversion units having different light receiving sensitivities
Data Source
AI summary
The present technology relates to a solid-state imaging device, a driving method, and an electronic device that are able to enhance a gray scale of a combined pixel value obtained from a pixel including a plurality of photoelectric conversion units having different light receiving sensitivities.In a pixel array unit, a pixel including a plurality of photoelectric conversion units having different light receiving sensitivities is disposed. An analog to digital (AD) conversion unit that compares an electric signal corresponding to a charge of the photoelectric conversion unit having a low light receiving sensitivity among the plurality of photoelectric conversion units included in the pixel of the pixel array unit with a nonlinear reference signal that changes nonlinearly to perform AD conversion on the electric signal. The present technology is able to be applied to, for example, a complementary metal-oxide semiconductor (CMOS) image sensor.