Pixel Readout Circuit Dynamic Integration for High Dynamic Range
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Solution Overview
Problem
Digital image sensors, particularly biosensors, face challenges in achieving a high dynamic range due to varying light levels across pixels, leading to saturation issues where some pixels saturate quickly while others take longer, necessitating improved readout circuitry to analyze signals effectively.
Innovation Solution
A pixel readout circuit that repeatedly samples pixel output levels during integration, stores samples in multiple memory locations with timestamps, and ceases sampling when a threshold is reached, allowing for correlated sampling using initial and penultimate sample values, enabling efficient handling of varying integration times and light levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single integration period is used for all pixels, then the readout circuit is simple to operate, but pixels with different light levels cannot be simultaneously captured without saturation
Solution Approach 1:
The patent implements dynamic integration periods for different pixels based on their light levels. The readout circuit determines integration time dynamically - shorter integration periods for bright pixels to prevent saturation, and longer integration periods for dim pixels to capture sufficient signal. This dynamic adaptation allows simultaneous capture of pixels with vastly different light levels within a single scene.
Solution Approach 2:
The patent segments the pixel array into multiple groups based on light level characteristics. Each group is assigned a different integration period, allowing independent optimization for each segment. This segmentation enables the system to handle both bright and dim pixels effectively without requiring a single fixed integration time for all pixels.
2Measurement precision
If multiple integration periods are used for different pixels, then dynamic range is improved, but the readout circuit complexity increases
Solution Approach 1:
The patent merges the functions of multiple readout circuits into a single integrated readout circuit that can handle multiple integration periods. The unified circuit includes memory structures that store pixel values from different integration periods and correlate them during readout, eliminating the need for separate readout circuits for each integration period while maintaining the ability to capture pixels with different light levels.
Solution Approach 2:
The readout circuit is designed with multi-functionality to handle both short and long integration periods within the same circuit architecture. The circuit can selectively apply different integration periods to different pixel groups and process all signals through a single correlated double sampling mechanism, reducing overall system complexity while maintaining high dynamic range capability.
3Measurement precision
If repeated sampling is performed during integration, then saturation is prevented and dynamic range is enhanced, but the sampling process consumes additional time
Solution Approach 1:
The patent implements periodic sampling during the integration period rather than continuous sampling. Multiple samples are taken at regular intervals throughout the integration time, allowing the system to detect saturation conditions and capture pixel values at optimal moments. This periodic approach prevents saturation while minimizing the total time consumed compared to continuous sampling.
Solution Approach 2:
The system performs preliminary sampling at the beginning of the integration period to establish baseline pixel values. These initial samples are used in correlated double sampling to subtract offset and reset signals, enabling the system to detect saturation conditions early and adjust subsequent sampling accordingly, thereby preventing saturation while optimizing sampling time.
Data Source
AI summary
A pixel readout circuit including at least first, second and third memory locations. During an integration period of a pixel, the pixel readout circuit repeatedly samples the pixel output level during the integration period, stores the first sample in the first memory location, and stores each subsequent sample in memory locations other than the first memory location. Each sample is stored with a time corresponding to when that sample was taken, such that at any one time subsequent to the first three samples having been stored, at least the first sample and the two most recent samples are stored. Also disclosed is a corresponding method of reading out of a pixel output over an undefined integration period.