Dark Reference Pixel Oversampling for Row Noise Reduction
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Solution Overview
Problem
Conventional image sensors require a large number of dark reference pixel columns to mitigate row noise, which occupies significant semiconductor area and increases costs.
Innovation Solution
Implementing oversampling analog-to-digital converters for dark reference pixels to perform signal averaging in the time domain, reducing the need for redundant dark reference columns by using higher sampling and resolution rates, thereby reducing the required number of dark reference pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of dark reference pixel columns are used to mitigate row noise, then row noise ratio is improved, but semiconductor area occupied increases significantly
Solution Approach 1:
The patent changes the sampling rate parameter from conventional single-rate sampling to multi-rate oversampling. By sampling dark reference pixel signals at multiple different rates and combining these samples, the system achieves better noise characterization with fewer pixels, thereby reducing the semiconductor area required while improving row noise ratio measurement precision
Solution Approach 2:
The patent creates multiple temporal copies of the dark reference pixel signals through oversampling at different rates. Instead of using spatial redundancy (many dark pixels side by side), the system uses temporal redundancy (multiple samples over time) to achieve the same noise mitigation effect, reducing the need for physical dark reference pixel columns
2Reliability
If hundreds of dark reference pixel columns are used per row to achieve acceptable row noise ratio, then row noise is mitigated, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent modifies the sampling rate parameter to implement multi-rate oversampling of dark reference pixels. This parameter change allows the system to achieve reliable row noise mitigation through temporal averaging of multiple samples taken at different rates, replacing the need for hundreds of dark reference columns and thereby reducing device complexity
Solution Approach 2:
The patent transitions from spatial dimension (using many dark reference columns across the pixel array) to temporal dimension (using multiple oversampled readings over time). This dimensional shift allows noise mitigation to be achieved through time-based sampling strategies rather than space-based pixel multiplication, reducing the number of required dark reference columns
Data Source
AI summary
An image sensor may include an array of image pixels arranged in rows and columns. A first portion of the array may include active pixels that are read out using first analog-to-digital converter (ADC) circuits. A second portion of the array may include dark reference pixels that are read out using second analog-to-digital converter (ADC) circuits. The first ADC circuits may have a first sampling rate, a first resolution, and a first size. The second ADC circuits may have an oversampling rate that is greater than the first sampling rate, a second resolution that is greater than the first resolution, and a second size that is bigger than the first size. Configured in this way, the second ADC circuits may perform averaging of a row noise via direct time-domain oversampling, which can help dramatically reduce the number of dark reference pixel columns in the array.