Imager Black Level Correction Using Tied and Optically Black Pixels
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Solution Overview
Problem
Existing semiconductor imagers face challenges in accurately setting a stable black level due to noise sources like blooming and IR reflections when using optically black pixels, and tied pixels fail to account for dark current variations, leading to incomplete noise compensation.
Innovation Solution
A pixel array with both optically black and tied pixels is used, where the difference in outputs between optically black and tied pixels is calculated to generate a stable black level, effectively compensating for row-specific noise and maintaining a constant black level across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optically black pixels are used to set black level, then black level correction can be performed, but noise sources like blooming and IR reflections contaminate the black level measurement
Solution Approach 1:
The dark rows are segmented into two distinct types: optically black pixels (with metal plates) and tied pixels (with fixed voltage). This segmentation allows the system to separate and process different noise characteristics - optically black pixels capture dark current and IR reflection effects, while tied pixels provide stable reference points that do not respond to light variations. By processing these segmented pixel types differently, the system achieves more accurate black level correction that is not contaminated by blooming or IR reflections.
Solution Approach 2:
Tied pixels serve as intermediary reference elements between the optically black pixels and the active pixels. The tied pixels are fixed at a known voltage level and do not respond to light, creating a stable intermediary that can be used to calibrate and correct the measurements from optically black pixels. This intermediary allows the system to distinguish between true dark current signals and artifacts caused by blooming or IR reflections.
2Stability of the object's composition
If tied pixels are used to set black level, then stability is improved, but dark current variations are not accounted for
Solution Approach 1:
The system merges the advantages of both tied pixels and optically black pixels by combining them in the same dark row structure. Tied pixels provide stable reference points that maintain consistent voltage levels, while optically black pixels capture dark current variations and IR reflection effects. By merging these two pixel types and processing their outputs together through the feedback loop, the system achieves both stability and accuracy in black level correction, overcoming the limitations of using either pixel type alone.
3Reliability
If dark rows are added to correct row-specific noise, then noise compensation is improved, but device complexity increases
Solution Approach 1:
The dark rows with combined tied and optically black pixels serve multiple functions simultaneously: (1) providing stable black level references, (2) capturing dark current variations, (3) enabling row-specific noise correction, and (4) maintaining image data integrity. This multi-functionality allows the system to achieve reliable noise compensation without proportionally increasing device complexity, as the same structural addition (dark rows) provides multiple corrective capabilities.
Data Source
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AI summary
An imaging pixel array includes an active area of pixels, organized into rows and columns of pixels. The array also includes a plurality of dark pixel columns adjacent to the active area of pixels such that rows of pixels in the active area of pixels extend across the plurality of dark pixel columns. The plurality of dark pixel columns are composed of tied pixels. The array also includes a plurality of dark pixel rows adjacent to the active area of pixels and the plurality of dark pixel columns such that columns of pixels in the active area of pixels extend across the plurality of dark pixel rows. The plurality of dark pixel rows are composed of both optically black pixels and tied pixels on the same row.