Anti-Eclipse Circuitry for Image Sensor Pixel Reset Accuracy
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Solution Overview
Problem
The eclipse phenomenon in imaging systems causes erroneous reset signals due to strong light exposure, leading to inaccurate pixel signals and over-illuminated pixels appearing dark instead of bright.
Innovation Solution
Incorporating anti-eclipse circuitry that clamps the pixel output voltage during reset sampling to a minimum value, ensuring accurate correlated double sampling by preventing voltage drops at the floating diffusion region, even under strong lighting conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pixels are exposed to strong light during reset operations, then the photodiode generates charge that should indicate bright areas, but the floating diffusion leaks causing erroneous reset signals that make over-illuminated pixels appear dark
Solution Approach 1:
The patent applies preliminary anti-action by introducing a clamp circuit that preemptively prevents the floating diffusion voltage from dropping below a threshold level during reset operations. The clamp circuit activates before the eclipse effect can fully corrupt the reset signal, applying a counteracting force (clamping voltage) to maintain the voltage at a valid level. This resolves the contradiction by ensuring that even under strong illumination, the reset signal remains accurate and over-illuminated pixels correctly appear bright rather than dark.
2Ease of operation
If the floating diffusion region is allowed to naturally discharge during reset, then the circuit operates normally under typical lighting, but under strong light the voltage drops below threshold causing signal errors
Solution Approach 1:
The patent introduces a clamp circuit as an intermediary element between the floating diffusion region and ground. This intermediary component (the clamp circuit with its transistor and threshold voltage reference) mediates the discharge process by allowing natural discharge when voltage is above threshold while preventing excessive discharge below threshold. The clamp circuit acts as a protective intermediary that maintains signal reliability under eclipse conditions without interfering with normal circuit operation, resolving the contradiction between ease of operation and reliability.
3Device complexity
If no additional circuitry is added to handle eclipse conditions, then the device complexity remains low, but the pixel signals become inaccurate when exposed to strong light
Solution Approach 1:
The patent applies local quality by implementing the clamp circuit selectively at only the critical point where the eclipse effect occurs (the floating diffusion region during reset operations). Rather than redesigning the entire pixel circuit or adding complex global correction mechanisms, the solution locally enhances the reset sampling circuitry with a simple clamp circuit. This localized approach maintains overall device complexity at a low level while effectively improving pixel signal accuracy under eclipse conditions, resolving the contradiction between device complexity and measurement precision.
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 by maintaining accurate pixel signal calculations, preventing column fixed pattern noise and ensuring that over-illuminated areas are correctly represented as bright in images.
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 image pixels arranged in rows and columns. Image pixels arranged along the same column may be coupled to a column line. The column line may be coupled to anti-eclipse control circuitry. In one suitable arrangement, the anti-eclipse control circuitry may include a comparator that compares the output signal on the column line to an anti-eclipse bias voltage. If, during a reset sampling period, the output signal on the column line is less than the anti-eclipse bias voltage, a transistor may be asserted that couples the floating diffusion region in the pixel to a power supply terminal. Using this arrangement, at least a minimum pixel level may be output when the eclipse condition is met and noise from the reset sample will correlated to noise in the incident light sample.