Image Sensor Gain Switching for Precise Wide-Dynamic-Range ADC
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Solution Overview
Problem
Current image sensor technologies face challenges in achieving high AD conversion precision due to reset noise in comparators, particularly in correcting gain differences across different signal levels, which affects dynamic range and signal-to-noise ratio.
Innovation Solution
An imaging apparatus with a pixel, an amplifier circuit, and an AD converting unit that compares output signals with a time-variable reference signal to adjust gain settings and correct resolution differences, using a correcting unit to output digital values and perform bit shifting for improved precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If different gain processes are performed on pixel signals to widen dynamic range, then the dynamic range is expanded, but the AD conversion precision deteriorates due to reset noise of the comparator
Solution Approach 1:
The patent segments the AD conversion process into multiple gain stages (first gain and second gain larger than the first gain). The amplifier circuit switches between different gain settings based on signal level, allowing the system to process both small and large signals with appropriate precision for each range, thereby resolving the contradiction between dynamic range and conversion precision.
Solution Approach 2:
The patent changes the gain parameter of the amplifier circuit based on the signal level. When the output signal from the amplifier circuit is larger than a threshold, the gain is set to a first gain; when smaller than the threshold, the gain is set to a second gain larger than the first gain. This dynamic parameter adjustment allows optimal precision across the full dynamic range.
2Reliability
If the gain of the amplifier circuit is increased to improve signal-to-noise ratio, then the signal-to-noise ratio is improved, but the dynamic range is reduced
Solution Approach 1:
The patent implements dynamic gain switching in the amplifier circuit. The gain is not fixed but changes based on the signal level: a higher second gain is used for small signals to improve signal-to-noise ratio, while a lower first gain is used for large signals to prevent saturation and maintain dynamic range. This dynamic adaptation resolves the contradiction between signal-to-noise ratio and dynamic range.
3Reliability
If high gain is used for small signals, then the signal-to-noise ratio is improved, but the resolution of AD data differs requiring correction
Solution Approach 1:
The patent incorporates a correcting unit that receives both first AD data (from reset noise measurement) and second AD data (from pixel signal). The correcting unit compares the resolutions of these data and performs correction when they differ. This feedback mechanism ensures consistent resolution across different gain settings while maintaining the signal-to-noise ratio benefits of high gain for small signals.
Solution Approach 2:
The patent performs preliminary measurement of reset noise using the same amplifier circuit and AD converter before processing pixel signals. This preliminary action (measuring reset noise at the same gain setting) provides reference data that enables subsequent correction of resolution differences, ensuring consistent precision across different gain modes.
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 AD conversion precision, reduces quantization errors, and allows for high-speed imaging by adjusting gain settings based on signal levels, thereby improving the signal-to-noise ratio and expanding the dynamic range.
Implementation Method 1
a pixel configured to generate a signal by photoelectric conversion
Data Source
AI summary
An AD converting unit compares an output signal from an amplifier circuit after reset of a pixel with a reference signal of time-variable, outputs a first digital value, when the output signal from the amplifier circuit in a non-reset state of the pixel is larger than a threshold, sets a gain of the amplifier circuit to a first gain, when the output signal is smaller than the threshold, sets the gain of the amplifier circuit to a second gain larger than the first gain, further after the gain of the amplifier circuit was set to the first or second gain, compares the output signal from the amplifier circuit in the non-reset state of the pixel with the reference signal of time-variable, and outputs a second digital value. When resolutions of the first and second digital values differ, a correcting unit corrects a difference between the resolutions.