Capacitive Sensor Image Filtering for Ghost Finger Reduction
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Solution Overview
Problem
Capacitive sensor devices face issues with persistent 'ghost fingers' and dead spots due to baseline side effects, necessitating the validation or elimination of baselining in input devices.
Innovation Solution
A processing system comprising a sensor module, filter module, and determination module that drives transmitter electrodes, receives signals, produces a first sensor image, applies a spatial filter in reduced accuracy mode to the image, and determines positional information and baseline validity, thereby reducing reliance on baselining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If baselining is used in capacitive sensor devices, then position information can be determined, but ghost fingers and dead spots occur
Solution Approach 1:
The system performs preliminary filtering of the sensor image before baseline comparison by applying a spatial filter to reduce high-frequency noise and artifacts. This preprocessing step eliminates spurious signals that would otherwise be interpreted as ghost fingers, allowing reliable baselining to proceed without the harmful side effects
Solution Approach 2:
The patent segments the signal processing into distinct stages: raw signal acquisition, spatial filtering to separate signal components, baseline comparison, and ghost finger detection. By segmenting the processing pipeline and applying appropriate filtering at each stage, the system can distinguish true input objects from baseline artifacts
2Reliability
If spatial filtering is applied to sensor images, then ghost fingers are reduced, but processing complexity increases
Solution Approach 1:
The spatial filter is applied locally to specific regions of the sensor image where ghost fingers are most likely to occur, rather than processing the entire image uniformly. This localized approach reduces computational complexity while maintaining effectiveness in eliminating artifacts
Solution Approach 2:
The system adjusts filtering parameters dynamically based on sensor conditions and input patterns. By changing filter strength, kernel size, and application regions adaptively, the system maintains ghost finger reduction effectiveness while optimizing processing complexity for different operating conditions
Data Source
AI summary
A processing system for an input device includes a sensor module, a filter module, and a determination module. The sensor module is configured to drive a plurality of transmitter electrodes with transmitter signals; receive, with a plurality of receiver electrodes, resulting signals comprising effects corresponding to the transmitter signals; and produce a first sensor image based on the resulting signals. The filter module is configured to produce a transformed sensor image by applying a spatial filter to the first sensor image. The determination module is configured to positional information and/or the validity of a baseline for the input device based on the transformed sensor image.