Imager Background Signal Removal via Dual-Capacitor Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional imaging sensors face challenges in distinguishing small signals from large parasitic background signals due to shrinking pixel geometries and increased downstream noise, requiring complex calibration and in-pixel counters, which limits their ability to accommodate large background signals.
Innovation Solution
The proposed imaging sensor integrates photocurrent on a background capacitor and switches it to a signal capacitor when a threshold is reached, allowing for background subtraction without in-pixel counters or memory, using global timing and identical background capacitors for all pixels to enhance signal integration while preventing excessive background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high full well is implemented to accommodate both background and signal without saturating, then the sensor can handle large background signals, but the capacitance shrinks as pixel geometries shrink, reducing the ability to accommodate large background signals and increasing downstream noise
Solution Approach 1:
The patent divides the integration capacitor into two separate capacitors: a background integration capacitor (C1) that accumulates background charge, and a signal integration capacitor (C2) that accumulates signal charge. This segmentation allows each capacitor to be optimized independently, with C1 handling the large background signal and C2 capturing the small signal, thereby resolving the contradiction between accommodating large background signals and maintaining small pixel geometries
Solution Approach 2:
The patent extracts the background signal integration function from the signal integration process by using a separate background capacitor (C1) that is reset periodically. This extraction allows the signal capacitor (C2) to focus solely on signal integration without being burdened by the large background signal, effectively separating the two functions to resolve the capacitance sizing contradiction
2Measurement precision
If digital pixels with in-pixel counters are used to track background subtraction, then background signal can be removed, but the counters occupy a large portion of each pixel and require complex calibration
Solution Approach 1:
The patent extracts the background subtraction function from the pixel level to the readout circuit level. Instead of using in-pixel counters, the background charge is integrated on a separate capacitor (C1) and subtracted during readout. This extraction eliminates the need for complex in-pixel counters and calibration, reducing pixel area and complexity while maintaining background removal capability
Solution Approach 2:
The patent introduces an intermediary mechanism using two separate capacitors (C1 for background, C2 for signal) and a dual-slope integration readout circuit. This intermediary approach allows background subtraction to be performed through analog charge comparison rather than digital counting, simplifying the pixel structure while achieving accurate background removal
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 enables a larger effective well capacity and improved noise reduction, allowing for clearer image detection by separating signal and background charges, thereby enhancing the sensor's ability to discern targets in high-background environments.
Implementation Method 1
integrates photocurrent on a background capacitor
Data Source
AI summary
Methods and apparatus for an imaging sensor having background subtraction including integrating photocurrent on a first capacitor, and, after a voltage on the first capacitor reaches a threshold, directing the photocurrent to a second capacitor. The first capacitor can be reset. This can be repeated a given number of times until a value on the second capacitor is read out.