Imaging Pixels With Storage Capacitors For Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors suffer from artifacts such as the eclipse phenomenon, fixed pattern noise, and dark current, particularly when exposed to strong light or in dark lighting conditions, due to floating diffusion leakage and high temporal noise.
Innovation Solution
The implementation of an imaging pixel with a storage capacitor that receives a modulated control signal, allowing for dual conversion gain modes and noise compensation through the use of a dual conversion gain capacitor and modulated control signals to reduce leakage and enhance dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a storage capacitor is included in the image sensor, then dynamic range is improved, but temporal noise and dark signal non-uniformity increase
Solution Approach 1:
The patent applies dynamics by making the control signal to the storage capacitor modulated rather than static. The control signal varies over time with different voltage levels during different operational phases (reset, integration, readout), allowing the capacitor to adapt its behavior dynamically. This temporal modulation enables the system to achieve both high dynamic range and low noise by optimizing the capacitor's charging and discharging characteristics at different times.
Solution Approach 2:
The patent changes the voltage parameter of the control signal to the storage capacitor. By varying the control signal between different voltage levels (e.g., first voltage during reset, second voltage during integration), the patent optimizes the capacitor's performance characteristics. This parameter modulation allows the system to reduce dark signal non-uniformity and temporal noise while maintaining enhanced dynamic range.
2Ease of manufacture
If conventional image sensors are used, then manufacturing is simpler, but eclipse phenomenon and fixed pattern noise occur under strong light exposure
Solution Approach 1:
The patent applies preliminary action by performing a reset operation before the actual image capture. The reset transistor resets the floating diffusion region to a known voltage level prior to light exposure, ensuring that subsequent measurements start from a consistent baseline. This preliminary reset action prevents the accumulation of charge that would otherwise cause the eclipse phenomenon and fixed pattern noise under strong light conditions.
Solution Approach 2:
The patent implements feedback through correlated double sampling. The system samples the floating diffusion voltage at two different times (before and after charge transfer) and computes the difference. This feedback mechanism cancels out fixed pattern noise and eclipse effects, as these artifacts appear in both samples and are eliminated through subtraction, while preserving the actual image signal.
3Device complexity
If floating diffusion is used for charge storage, then device complexity is reduced, but leakage occurs under strong light exposure
Solution Approach 1:
The patent introduces a storage capacitor as an intermediary element between the photodiode and the floating diffusion region. During the integration phase, charge is transferred from the photodiode to this storage capacitor rather than directly to the floating diffusion. This intermediary capacitor holds the charge without the leakage problems of the floating diffusion, and only later transfers the charge to the floating diffusion for readout, thus preventing leakage under strong light exposure.
Solution Approach 2:
The patent segments the charge storage function into two separate components: a storage capacitor for temporary charge holding during integration, and the floating diffusion region for final charge transfer and readout. This segmentation allows each component to perform its specialized function optimally - the capacitor provides stable charge storage without leakage, while the floating diffusion enables voltage-based readout, together solving the leakage problem while maintaining circuit functionality.
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 solution effectively mitigates the eclipse phenomenon, reduces fixed pattern noise and dark current, and improves signal-to-noise ratios under bright conditions while maintaining performance in low light conditions.
Implementation Method 1
Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate
Data Source
AI summary
An image sensor may include an array of imaging pixels and row control circuitry. Each imaging pixel may include a photodiode, a floating diffusion region, a transfer transistor configured to transfer charge from the photodiode to the floating diffusion region, a dual conversion gain transistor coupled to the floating diffusion region, and a storage capacitor coupled to the dual conversion gain transistor. The capacitor may have a plate that receives a modulated control signal and the row control circuitry may be configured to modulate the control signal. To reduce image artifacts, the modulated control signal may be modulated low during the integration time of the pixel and may be modulated high during the high conversion gain readout time of the pixel.