Sample and Hold Circuit Noise Cancellation Using Dark Reference Pixels
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Solution Overview
Problem
Unwanted noise generated in image sensors degrades the quality of captured images, and existing methods are inadequate for effectively eliminating this noise.
Innovation Solution
An image sensor system comprising pixels, dark reference pixels, and a sample and hold circuit that cancels noise by correlating and subtracting noise from both the image and reset levels using dark reference pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If noise cancellation is implemented using dark reference pixels, then image quality is improved, but device complexity increases
Solution Approach 1:
The sensor array is segmented into functional regions: image pixels for capturing the scene and dark reference pixels for noise characterization. This segmentation allows independent optimization of each region's function while maintaining overall system performance.
Solution Approach 2:
Dark reference pixels create a copy of the noise characteristics present in the image pixels during reset operations. By measuring noise in these reference pixels, the system can model and subtract noise from the image signal without requiring complex real-time noise estimation algorithms.
2Measurement precision
If noise cancellation processing is applied to image signals, then unwanted noise is eliminated, but processing time increases
Solution Approach 1:
Noise characteristics are captured in advance during the reset operation of dark reference pixels before the actual image measurement. This preliminary noise characterization allows the noise subtraction to be performed efficiently during image processing without requiring time-consuming real-time analysis.
Solution Approach 2:
The noise measurements from dark reference pixels provide feedback about the noise characteristics affecting the image signal. This feedback information is stored and used to correct the image signal through subtraction, enabling efficient post-processing noise removal.
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
Effectively cancels unwanted noise from image sensors, improving image quality by isolating and eliminating noise from both the image and reset levels.
Implementation Method 1
Each pixel includes a photodiode that receives incident light that is converted to charge packets
Data Source
AI summary
An image sensor includes a plurality of pixels for capturing incident light that is converted to a signal representing an image; wherein noise is combined with a signal representing both the image and a reset level; a plurality of dark reference pixels that generate noise that substantially correspond or equally correspond to the noise in the image and reset level; and a sample and hold circuit that reads out the image signal and cancels or substantially cancels out the noise from the image signal and reset level by canceling the noise from image and reset level with the noise generated from the dark reference pixels.