Image Sensor AD Conversion Using Switched Comparison Signals
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Solution Overview
Problem
Existing image capturing apparatuses face challenges in reducing circuit noise without significantly extending the analog-to-digital (AD) conversion period, especially when performing AD conversion multiple times for higher signal levels.
Innovation Solution
The apparatus employs a pixel array with a signal generator that produces a comparison signal with changing electric potential, and a converter that counts inversions of the magnitude relationship between the pixel signal and the comparison signal, allowing for multiple AD conversions within the same period by switching reference signals used for comparison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AD conversion is performed multiple times for higher signal levels, then circuit noise is reduced, but the AD conversion period largely extends
Solution Approach 1:
The patent applies preliminary action by performing AD conversion multiple times for low luminance signals (low signal levels) where circuit noise is more prominent, while performing AD conversion only once for high luminance signals (high signal levels) where circuit noise is less observable. This selective approach reduces the overall AD conversion period while still achieving noise reduction where it is most beneficial.
Solution Approach 2:
The patent applies local quality by differentiating the AD conversion strategy based on signal level characteristics. Low luminance signals receive multiple AD conversions with averaging to reduce circuit noise, while high luminance signals receive single AD conversion. This localized approach optimizes noise reduction effectiveness while minimizing the extension of the AD conversion period.
2Loss of time
If AD conversion is performed once for high luminance signal, then the AD conversion period is short, but circuit noise cannot be effectively reduced
Solution Approach 1:
The patent performs AD conversion multiple times in advance for low luminance signals and averages the conversion results, thereby reducing circuit noise before final signal processing. This preliminary multi-time conversion approach ensures that noise reduction is achieved proactively where it is most needed, rather than attempting to reduce noise after conversion.
Solution Approach 2:
The patent applies different AD conversion strategies to different signal levels: multiple conversions for low luminance signals to reduce circuit noise, and single conversion for high luminance signals. This localized differentiation ensures that noise reduction efforts are concentrated where circuit noise is most observable and impactful.
Data Source
AI summary
An image capturing apparatus is provided. The apparatus comprises a pixel array, a signal generator that generates a comparison signal whose electric potential changes with time and a converter that converts a pixel signal into a digital signal. The comparison signal starts to change from a first electric potential in accordance with a start of the conversion of the pixel signal by the converter, and changes again, in accordance with inversion of a magnitude relationship between the pixel signal and the comparison signal, from a third electric potential between the first electric potential and a second electric potential at which the magnitude relationship is inverted. The converter includes a counter that holds, as a signal value, a count value obtained by counting from the start of the conversion of the pixel signal until the inversion of the magnitude relationship.