Capacitive Fingerprint Sensor Defective Pixel Correction
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Solution Overview
Problem
Capacitive fingerprint sensors degrade over time due to mechanical and chemical impacts, leading to defective pixels that compromise authentication reliability and product lifetime, resulting in security risks and costly sensor discarding.
Innovation Solution
A computer-implemented method that uses a two-step filtering strategy to detect and correct corrupted charge values from defective capacitive sensor elements, preserving fingerprint information for authentication purposes by computing replacement values from reliable charge values within optimized filter windows, thereby extending the usability of fingerprint sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive fingerprint sensors are used for authentication, then authentication capability is provided, but sensor elements degrade over time due to mechanical and chemical impacts, leading to defective pixels and reduced reliability
Solution Approach 1:
The system performs preliminary detection of defective sensor elements by capturing a test fingerprint image and identifying pixels with abnormal charge values before actual authentication. This preliminary action allows the system to pre-map defective pixel locations and compensate for them during subsequent authentication operations, maintaining reliability throughout the sensor's lifetime.
Solution Approach 2:
The system changes the operational parameters by adjusting the charge threshold values and filter window sizes based on detected defective pixels. By dynamically modifying these parameters, the system adapts to sensor degradation over time, maintaining authentication reliability even as the sensor ages and develops defective elements.
2Reliability
If defective pixels are present in the fingerprint sensor, then information is missing from the fingerprint image, but discarding the sensor is costly at production line and customer levels
Solution Approach 1:
The system extracts and identifies defective pixel locations by comparing charge values against threshold criteria and isolating them from the rest of the sensor array. Once identified, these defective pixels are excluded from authentication calculations, allowing the remaining functional pixels to provide sufficient information for reliable authentication without discarding the entire sensor.
Solution Approach 2:
The system applies local compensation by using spatial filtering around defective pixels, where charge values from neighboring functional pixels are weighted and combined to compensate for missing information at defective locations. This localized approach preserves authentication accuracy by addressing only the specific defective areas rather than compromising the entire sensor.
3Reliability
If a two-step filtering strategy is applied to correct corrupted values, then authentication reliability is maintained, but processing complexity increases
Solution Approach 1:
The correction process is segmented into two distinct steps: first detecting defective pixels using threshold-based filtering, then compensating for them using spatial filtering with configurable window sizes. This segmentation allows each step to be optimized independently and enables efficient implementation through lookup tables and pre-computed filter kernels, reducing overall processing complexity.
Solution Approach 2:
The system creates a compensation map that copies and stores the locations and characteristics of defective pixels. This copied information is then used during authentication to automatically adjust processing, avoiding repeated complex calculations and enabling fast compensation through simple table lookups and predefined filter applications.
Data Source
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AI summary
A method of correcting charge values acquired from a capacitive fingerprint sensor, comprising acquiring a list (304) of one or more defective capacitive sensor elements and for defective capacitive sensor element in the list (304), selecting its position as a first position and: - performing a first operation (313) by placing a first filter window about the first position and computing a replacement value for the first position from charge values within the first filter window, but forgoing computing a replacement value for the first position in case a first threshold number of defective capacitive sensor elements located within the first filter window is exceeded; - in case the first operation (313) forgo computing a replacement value for the first position, performing a second operation (314) by placing a second filter window about the first position and computing a replacement value for the first position from charge values within the second filter window, but forgoing computing a replacement value for the first position in case a second threshold number of defective capacitive sensor elements located within the second filter window is exceeded; wherein the second filter window has a wider expanse than the first filter window.