Image Sensor Analog Differential Charge Storage
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Solution Overview
Problem
Conventional image sensors using global shutters require digital buffers to perform differential operations, which consume power and introduce noise, and existing methods to eliminate ambient light interference are inefficient.
Innovation Solution
An image sensor that performs analog differencing outside the pixel circuit, eliminating the need for a digital buffer and improving signal-to-noise ratio by storing and comparing charges within specific exposure and readout intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital buffers are used to perform differential operations on digital image frames, then ambient light interference can be eliminated, but power consumption increases and image quality deteriorates due to noise
Solution Approach 1:
The patent replaces the digital differential operation system with an analog differential system. Specifically, it uses analog storage circuits to hold charge signals and analog subtraction circuits to perform differential operations directly on the analog signals before digital conversion. This substitution eliminates the need for digital buffers, reduces power consumption, and avoids the noise introduced by digital processing of entire image frames.
Solution Approach 2:
The patent changes the parameter of differential operation from digital domain to analog domain. By performing the subtraction operation on analog charge signals rather than digital image frames, the system achieves the same ambient light elimination function while consuming less power and introducing less noise. The key parameter change is the domain of operation (digital vs. analog) and the timing (after ADC vs. before ADC).
2Object-affected harmful factors
If digital buffers are used to store digital image frames for differential operation, then ambient light can be removed, but device complexity increases
Solution Approach 1:
The patent substitutes the complex digital buffer storage system with a simpler analog charge storage system. Instead of buffering entire digital image frames in memory, the system uses analog storage circuits to hold charge signals temporarily. This substitution dramatically reduces device complexity while maintaining the ambient light elimination capability through analog differential operations.
3Device complexity
If rolling shutter is used to successively activate rows of sensing pixels, then device complexity is reduced, but image distortion occurs for fast moving objects
Solution Approach 1:
The patent segments the image capture process into multiple short exposure intervals for different rows of pixels, with each row exposed at a slightly different time. By using analog differential operations on these segmented exposures and a light source that remains constant throughout the sequential exposure, the system achieves motion-freeze capability similar to global shutter while maintaining the simpler rolling shutter architecture.
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
This approach reduces power consumption and enhances image quality by directly comparing voltage signals from different exposure times, effectively eliminating ambient light interference without the need for digital buffers.
Implementation Method 1
Each of the pixel circuits includes an optoelectronic conversion circuit OE. The optoelectronic conversion circuit is configured to generate a photocurrent.
Implementation Method 2
The pixel buffer circuit is configured to receive the photocurrent within a first exposure time to store a first charge and store the first charge for a selectable storage interval, and receive the photocurrent within a second exposure time to store a second charge
Data Source
AI summary
There is provided an operating method of an image sensor including: storing a first charge from an optoelectronic circuit to a pixel buffer circuit within a first exposure period; storing a second charge from the optoelectronic circuit to the pixel buffer circuit within a second exposure period; transferring the first charge from the pixel buffer circuit to a first storage circuit outside of pixel circuits; transferring the second charge from the pixel buffer circuit to a second storage circuit outside of pixel circuits; and comparing the first charge with the second charge to output an analog image signal.