Capacitance Sensing Noise Filtering via Adaptive Local Scanning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitance sensing systems face challenges in filtering out external noise, which is localized to specific electrodes and not addressed by common mode filtering, leading to erroneous touch events and non-sense events.
Innovation Solution
Implementing a noise listening circuit that monitors noise levels and switches between standard and extended scanning with local filtering, including median filtering, to address both common and external noise, and triggers an alarm if noise levels exceed a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common mode filtering is used to filter internal noise, then internal noise is reduced, but external noise remains and causes erroneous touch events
Solution Approach 1:
The patent segments the filtering process into two distinct stages: common mode filtering for internal noise and local filtering for external noise. By dividing the filtering function, the system can address different noise types with appropriate methods, resolving the contradiction between filtering internal noise and maintaining accuracy against external noise.
Solution Approach 2:
The patent introduces local filtering that operates specifically on electrodes affected by external noise, rather than treating all electrodes uniformly. This localized approach allows the system to filter external noise at its source location while preserving the effectiveness of common mode filtering for internal noise, thereby resolving the contradiction.
2Reliability
If extended scanning with local filtering is implemented, then external noise is filtered, but processing time increases
Solution Approach 1:
The patent implements dynamic scanning adjustment where the system switches between standard and extended scanning modes based on detected noise levels. When external noise is detected, the system activates local filtering with extended scanning; when noise is absent, standard scanning is used. This dynamic adaptation resolves the contradiction by applying time-consuming filtering only when necessary.
Solution Approach 2:
The patent employs noise level detection as feedback to control the scanning mode. The system continuously monitors noise levels and uses this feedback to determine whether to implement extended scanning with local filtering or standard scanning. This feedback mechanism ensures that processing time is increased only when external noise is present, resolving the contradiction between filtering effectiveness and time loss.
3Measurement precision
If noise listening and adaptive filtering is implemented, then filtering accuracy improves, but device complexity increases
Solution Approach 1:
The patent implements a noise listening circuit that performs multiple functions: detecting noise levels, determining noise types (internal vs. external), and controlling filtering mode selection. By making the noise detection system multi-functional, the patent reduces the need for separate dedicated circuits for each function, thereby resolving the contradiction between improved measurement precision and device complexity.
Data Source
AI summary
A capacitance sensing system can filter noise that presents in a subset of electrodes in the proximity of a sense object (i.e., finger). A capacitance sensing system can include a sense network comprising a plurality of electrodes for generating sense values; a noise listening circuit configured to detect noise on a plurality of the electrodes; and a filtering circuit that enables a filtering for localized noise events when detected noise values are above one level, and disables the filtering for localized noise events when detected noise values are below the one level.