Fingerprint Sensing Array Zero-Sum Filtering for Noise Reduction
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Solution Overview
Problem
Fingerprint sensing systems face challenges in reducing common-mode noise while preserving fingerprint information, as existing differential sampling methods attenuate valuable frequency components.
Innovation Solution
The method involves filtering analog sensing signals from a set of sensing elements using linear combinations with coefficients summing to zero, avoiding common-mode noise by discarding the sum output from Hadamard transformations, and converting these filtered signals to digital form, allowing for improved noise suppression with minimal loss of fingerprint information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If differential sampling is used to reduce common-mode noise, then common-mode noise is suppressed, but fingerprint information in the lower frequency spectrum is attenuated
Solution Approach 1:
The sensing elements are divided into multiple groups (first set, second set, third set, fourth set) with different orientations. Each group processes signals independently through linear combinations, allowing selective extraction of differential components while preserving different spatial frequency information. This segmentation enables parallel processing of multiple signal components that would otherwise be mixed.
Solution Approach 2:
The patent extends the traditional single differential measurement to a multi-dimensional signal space by using four differently oriented sensing element sets. Each set provides a different projection of the fingerprint pattern, creating a richer signal representation that captures both common-mode noise characteristics and fingerprint details across multiple dimensions, allowing subsequent separation of these components.
2Measurement precision
If spatial differential sampling is applied to reduce analog dynamic range, then analog dynamic range is reduced and effective gain is increased, but lower frequency fingerprint components are attenuated
Solution Approach 1:
The sensing element array is segmented into four distinct groups with different spatial orientations. Each group performs differential sampling independently, producing four separate signal streams. This segmentation allows the system to maintain high effective gain in each stream while collectively preserving a broader frequency spectrum through the combination of multiple oriented measurements.
Solution Approach 2:
The multiple sets of sensing elements serve multiple functions simultaneously: each set performs common-mode noise rejection through differential sampling, while the collection of all sets together preserves low-frequency fingerprint information that would be lost in single-differential approaches. The system achieves both noise suppression and information preservation through this multi-functional architecture.
Data Source
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AI summary
The present invention relates to providing a filtered fingerprint pattern signal indicative of a fingerprint pattern with a fingerprint sensing device comprising an array of sensing elements for sensing the fingerprint pattern.Each sensing element is configured to provide a sensing signal indicative of a local fingerprint pattern feature. The method comprises: receiving analog sensing signals from each of a set of sensing elements comprising at least four sensing elements, filtering the set of sensing signals to provide a set of filtered output signals each comprising a linear combination of the set of sensing signals in which each sensing signal has a respective coefficient. The coefficients in each linear combination sum up to zero, and wherein the linear combinations are different from each other. The set of filtered output signals are converted to a filtered digital sensing signal indicative of the user's fingerprint pattern.