Shielded Pixel Photosensitive Portion Dark Current Noise Cancellation
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Solution Overview
Problem
Current image sensor technologies face challenges in effectively canceling dark current noise, which is temperature-dependent and varies spatially and temporally, especially in applications requiring low light detection, leading to errors and self-heating issues with existing methods.
Innovation Solution
A pixel design with a first photosensitive portion and a second shielded photosensitive portion, connected to an operational amplifier with a negative feedback loop and adjustable capacitance, allows for differential dark current cancellation by matching dark current ratios and capacitances, reducing noise and temperature-related errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shielded border portion is used to generate dark current reading, then dark current can be subtracted from pixel outputs, but spatial variation of dark current across the die is not accounted for leading to cancellation errors
Solution Approach 1:
Each pixel is divided into multiple photosensitive portions (first, second, third, fourth portions) with different shielding configurations. The first and second portions are shielded while the third and fourth are unshielded, allowing separate dark current measurements from each portion to account for spatial variations across the pixel area.
Solution Approach 2:
Different regions within each pixel are assigned different shielding characteristics. The shielded photosensitive portions measure local dark current at their specific locations, while unshielded portions capture both signal and dark current. This local differentiation enables accurate spatially-resolved dark current cancellation.
2Measurement precision
If signals are taken from outputs of different pixels for dark current comparison, then dark current can be cancelled, but switching and transfer errors are introduced
Solution Approach 1:
Multiple photosensitive portions (both shielded and unshielded) within the same pixel are merged into a single readout circuit. This allows dark current cancellation to be performed using signals from different portions of the same pixel, eliminating the need for inter-pixel signal transfer and avoiding associated switching and transfer errors.
3Measurement precision
If mechanical shutter is used to enable/disable light for dark current cancellation, then dark current can be measured and subtracted, but self-heating effects alter dark current between readings
Solution Approach 1:
The shielded and unshielded photosensitive portions continuously measure their respective signals simultaneously without interruption. This continuous simultaneous measurement eliminates temporal gaps between dark current and signal measurements, preventing self-heating effects from altering dark current characteristics between readings.
Solution Approach 2:
The shielded photosensitive portions act as intermediaries that continuously measure dark current in the same pixel as the unshielded portions. This eliminates the need for mechanical shutters and external light blocking mechanisms, providing continuous dark current monitoring that tracks temperature variations in real-time.
4Object-generated harmful factors
If dark current compensation is implemented, then noise is reduced, but temperature-dependent variations and non-uniformity cause cancellation errors
Solution Approach 1:
The invention changes the shielding parameter (light blocking) applied to different photosensitive portions within each pixel. By having some portions shielded and others unshielded, the system creates differential measurements that capture both dark current and optical signal, enabling accurate cancellation that accounts for temperature-dependent variations and spatial non-uniformity.
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 effectively cancels dark current noise, improving the accuracy of low-light detection in image sensors by minimizing temperature-dependent variations and reducing self-heating effects, suitable for applications like bioluminescence sensors.
Implementation Method 1
an operational amplifier arranged to receive a signal from the first photosensitive portion at a first input, and to receive a signal from the second photosensitive portion at a second input
Implementation Method 2
an operational amplifier with a negative feedback loop and adjustable capacitance
Implementation Method 3
adjustable capacitance
Implementation Method 4
a second photosensitive portion shielded from incident light
Implementation Method 5
The energy of incident photons removes electrons from the outer orbits of atoms within the photosensitive portion thus generating a charge
Data Source
AI summary
A pixel structure includes two different photosensitive portions. One portion is shielded from incident light and the signals from both are fed into an op amp so that the differential signal is output as the pixel output, thereby cancelling dark current.