CMOS Image Sensor Differential Double Sampling Bandwidth Reduction
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Solution Overview
Problem
4T CMOS image sensor pixel designs using digital double sampling double the output signals on the column circuit, leading to increased bandwidth usage and issues with kTC noise and analog disturbances.
Innovation Solution
A method and CMOS image sensor design that performs differential double sampling by resetting and reading out dark values, then transferring and adding charges to storage nodes in a pixel array, allowing for parallel sampling of two bright values from adjacent pixels to reduce bandwidth and suppress noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital double sampling is performed using conventional 4T pixel design, then noise suppression is improved, but output bandwidth usage is doubled
Solution Approach 1:
The patent combines the readout operations of two adjacent pixels into a single shared readout circuit. The first pixel provides a bright value and the second pixel provides a dark value, which are processed together to achieve noise suppression without requiring separate output paths. This merging approach reduces the total output bandwidth requirement while maintaining the noise suppression benefits of digital double sampling.
Solution Approach 2:
The shared readout circuit is designed to handle multiple functions: it reads out both bright and dark values from different pixels, performs differential processing, and outputs the result. This multi-functional design allows a single circuit to replace what would traditionally require multiple dedicated circuits, thereby reducing overall bandwidth usage while maintaining noise suppression capabilities.
2Object-affected harmful factors
If digital double sampling is performed using conventional 4T pixel design, then noise suppression is improved, but circuit complexity increases
Solution Approach 1:
The patent merges the readout circuits of two adjacent pixels into a single shared circuit. Instead of having separate readout paths for each pixel, the invention combines them so that one readout circuit handles both pixels' data, performing the necessary differential processing. This reduces the total number of circuits required and simplifies the overall device architecture while maintaining noise suppression performance.
Solution Approach 2:
The invention extracts the essential noise suppression functionality from the complex conventional DDS circuitry and implements it through a simplified shared readout approach. By taking out only the necessary differential processing operations and applying them to paired pixel readings, the circuit complexity is reduced while retaining the core noise suppression capability.
3Stability of the object's composition
If conventional digital double sampling is used, then reset level reference is maintained, but analog disturbances and kTC noise are not suppressed
Solution Approach 1:
The patent converts the previously harmful kTC noise and analog disturbances into beneficial information by reading both bright and dark values that contain these artifacts. By performing differential processing on these paired readings, the common-mode noise and disturbances are rejected, transforming what was previously harmful into a means for achieving superior noise suppression while maintaining reset level reference stability.
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 required output bandwidth, suppresses noise, and avoids artifacts like Black sun and fluctuating analog disturbances, enabling efficient digital double sampling across the entire analog chain.
Implementation Method 1
The photodiode generates electric charges using absorbed light
Data Source
AI summary
A method for performing differential double sampling and a CMOS image sensing device for performing the same. In one example, the CMOS image sensing device includes a pixel array include a multitude of pixels with each pixel formed by a plurality of photodiodes, a floating diffusion point and a plurality of transistors electrically coupled the plurality of photodiodes. Moreover, a column readout circuit with four storage capacitors is selectively coupled to the pixel array by switches so that the storage capacitors can store sampled pixel values. A control circuit connected to the pixel array and the column readout circuit selectively activates the transistors to output to the column readout circuit sampled dark value and bright values of one photodiode and a sampled double bright value of the one photodiode and one additional photodiode.