CMOS Image Sensor ADC Reference Signal Thresholding
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Solution Overview
Problem
Existing CMOS image sensors with analog-to-digital converters face challenges in achieving fast and accurate conversion due to the time required to set a threshold reference signal, which can lead to insufficient accuracy when the slope of the reference signal is increased for faster operation.
Innovation Solution
A solid state imaging device with a reference signal generation unit that generates a reference signal changing at a predetermined rate over time, allowing for comparison with pixel signals to convert them into digital signals efficiently, and an analog-to-digital converter unit that performs conversions in multiple periods with varying gains based on comparison results, ensuring accurate threshold setting without changing the direction of the reference signal's change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the slope of the reference signal is increased to achieve faster operation, then the conversion speed is improved, but the accuracy of threshold setting becomes insufficient
Solution Approach 1:
The patent applies preliminary action by performing a determination period before the actual AD conversion. During this determination period, the reference signal is advanced to a predetermined threshold level in advance, allowing the system to pre-establish the threshold setting before the pixel signal comparison begins. This preliminary preparation eliminates the need to change the reference signal direction during conversion, thereby maintaining both high speed and high accuracy.
2Measurement precision
If time is allocated to generate the threshold reference signal, then the accuracy is improved, but the conversion speed decreases
Solution Approach 1:
The patent implements continuity of useful action by ensuring the reference signal changes continuously in one direction without pausing to reverse direction. The reference signal generation unit maintains continuous monotonic change throughout the conversion process, eliminating idle time for direction changes. This continuous operation allows the system to maintain high productivity while achieving accurate threshold setting through the predetermined threshold level established in the determination period.
3Measurement precision
If the reference signal direction is changed to set the threshold, then the threshold accuracy is improved, but the time required increases
Solution Approach 1:
The patent applies preliminary action by establishing the predetermined threshold level during the determination period before the actual conversion begins. This advance preparation allows the reference signal to reach the accurate threshold position in advance, eliminating the need for time-consuming direction changes during the conversion process itself.
Solution Approach 2:
The patent inverts the conventional approach by not changing the reference signal direction to set the threshold. Instead, it uses a determination period to advance the reference signal to the predetermined threshold level in advance, then maintains continuous unidirectional change during conversion. This inverted approach eliminates direction changes entirely, reducing time loss while maintaining threshold accuracy.
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 reduces the time needed to set a threshold, enables fast operation without sacrificing accuracy, and improves the framerate of the imaging device by maintaining high accuracy in analog-to-digital conversion.
Implementation Method 1
a pixel including at least one photoelectric conversion unit
Data Source
AI summary
In a solid state imaging device as an embodiment, an analog-to-digital converter unit converts, in a first period, a first pixel signal into a digital signal, performs, in a determination period after the first period, the comparison of a second pixel signal with the reference signal set to a predetermined threshold, and converts, in a second period after the determination period, the second pixel signal at a gain in accordance with a result of the comparison performed in the determination period into a digital signal. Until the reference signal reaches the threshold from the first period, the reference signal generation unit changes the reference signal without changing a direction of change of the reference signal with respect to the lapse of time.