Dynamic Correlated Double Sampling for Image Sensor Noise
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Solution Overview
Problem
Correlated Double Sampling (CDS) readout circuits in image sensors fail to effectively cancel noise that changes in frequency over time, known as aggressor noise, due to unsynchronized timing of reference and data value reads.
Innovation Solution
The CDS time of the CDS readout circuit is dynamically adjusted to sync with the current frequency of aggressor noise, using a programmable delay circuit and image sensor driver that receives indications of the current state of noise-generating components, ensuring optimal noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed CDS time is used in the CDS readout circuit, then the circuit structure remains simple, but noise cancellation becomes ineffective when aggressor noise frequency changes over time
Solution Approach 1:
The patent applies dynamics by making the CDS time adjustable rather than fixed. The CDS readout circuit incorporates a delay circuit that can dynamically change the CDS time parameter to match the frequency of aggressor noise, allowing the system to adapt to varying noise conditions and maintain effective noise cancellation.
Solution Approach 2:
The patent changes the CDS time parameter dynamically based on the detected frequency of aggressor noise. By adjusting this critical parameter in response to changing noise conditions, the system maintains optimal noise cancellation performance without requiring a completely redesign of the circuit architecture.
2Reliability
If the CDS time is dynamically adjusted to match aggressor noise frequency, then noise cancellation effectiveness is improved, but the system complexity increases due to additional control circuits
Solution Approach 1:
The patent implements feedback by detecting the frequency of aggressor noise and using this information to adjust the CDS time. The system continuously monitors the noise environment and adapts its CDS timing accordingly, creating a closed-loop control system that maintains optimal noise cancellation performance.
Solution Approach 2:
The patent introduces a delay circuit as an intermediary component between the noise detection mechanism and the readout process. This intermediary element enables dynamic adjustment of the CDS time without fundamentally altering the core CDS readout architecture, thereby managing system complexity while achieving improved noise cancellation.
3Ease of operation
If a fixed timing is used for reference and data value reads, then the readout process is simple, but noise that changes frequency cannot be effectively canceled
Solution Approach 1:
The patent applies dynamics by transforming the fixed timing approach into a dynamic timing system. The readout process maintains simplicity through automated control, while the CDS time adjusts dynamically to match aggressor noise frequency, resolving the contradiction between operational simplicity and noise rejection capability.
Data Source
AI summary
A method of reading a pixel value from an image sensor housed with a set of components includes determining a current state of the set of components; adjusting, at least partly responsive to the current state of the set of components, a correlated double sampling (CDS) time; and performing, in accordance with the adjusted CDS time, a CDS readout of at least one pixel in a pixel array of the image sensor.