Capacitive Baseline Shift Reduction via Mixing Period Adjustments
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Solution Overview
Problem
Capacitive baseline shifts occur when switching between different sensing frequencies in capacitive sensing devices, leading to unpredictable average current values and requiring complex calibration and compensation, which increases memory requirements and costs.
Innovation Solution
Selecting predefined mixing periods for demodulation signals corresponding to specific sensing frequencies ensures a predictable relationship between average current values and sensing frequencies, simplifying compensation and reducing the need for individual calibration of sensor electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex calibration and compensation methods are used to handle capacitive baseline shifts, then measurement precision is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent changes the parameter of mixing period duration based on sensing frequency. By adjusting the mixing period to be inversely proportional to the sensing frequency, the system achieves frequency-invariant average current values, eliminating the need for complex calibration and compensation procedures while maintaining measurement precision across different frequencies
2Measurement precision
If individual calibration of sensor electrodes is performed, then measurement precision is improved, but manufacturing cost and time increase
Solution Approach 1:
The patent creates a universal mixing period adjustment mechanism that works for all sensor electrodes regardless of their individual characteristics. By applying the same inverse-frequency proportional mixing period adjustment across the entire sensor array, the system achieves uniform performance without requiring individual calibration of each sensor electrode, thereby reducing manufacturing complexity and cost
3Adaptability or versatility
If multiple sensing frequencies are used to avoid interference, then adaptability is improved, but capacitive baseline shift between frequencies increases
Solution Approach 1:
The patent introduces dynamic adjustment of the mixing period based on the selected sensing frequency. The mixing period is made inversely proportional to the sensing frequency, creating a dynamic relationship that compensates for frequency-induced baseline shifts. This allows the system to switch between multiple sensing frequencies while maintaining stable capacitive baselines, thereby achieving both adaptability and stability
Data Source
AI summary
A method and related processing system and input device are disclosed, the method comprising driving a first capacitive sensing signal with first sensing frequency onto a first group of a plurality of sensor electrodes, and acquiring first capacitive measurements of resulting signals received by a second group of the plurality of sensor electrodes. Acquiring first capacitive measurements comprises applying a first demodulation signal with a predefined first mixing period defined within a sensing period associated with the first sensing frequency. The method further comprises driving a second capacitive sensing signal having a second sensing frequency different than the first sensing frequency onto a third group of the plurality of sensor electrodes, and acquiring second capacitive measurements of resulting signals received by a fourth group of the plurality of sensor electrodes. Acquiring second capacitive measurements comprises applying a second demodulation signal having a different predefined second mixing period.