Capacitive Touch Sensing Calibration for Water-Finger Differentiation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive touch sensing systems face challenges with contamination, particularly water, leading to signal shifts and false triggers due to the inability to distinguish between water and finger inputs effectively, resulting in reduced robustness and accuracy.
Innovation Solution
A calibration method and system that combines self-capacitance and mutual capacitance measurements, using a scale factor to differentiate between water and finger inputs by capacitively coupling a pulse into the electrodes, thereby eliminating analog signal shifts caused by high permittivity objects like water, without requiring software pattern recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water resistance is implemented using mutual capacitance only, then water contamination can be detected, but a negative shift on the signal occurs when water is introduced and a positive shift when a finger is introduced, causing false triggers
Solution Approach 1:
The patent combines both mutual capacitance and self-capacitance measurements to detect water contamination. By merging the detection capabilities of both measurement types, the system can distinguish between water and finger touches more accurately, eliminating false triggers while maintaining water resistance.
Solution Approach 2:
The patent changes the measurement parameters by using both mutual capacitance (Cmutual) and self-capacitance (Cself) measurements simultaneously. This parameter change allows the system to detect different electrical characteristics of water versus finger contacts, resolving the signal shift problem.
2Reliability
If a software pattern-matching algorithm is used to detect the difference in behavior between water and a finger, then differentiation can be achieved, but large overhead and the possibility that not all patterns of behavior have been considered occur
Solution Approach 1:
The patent replaces the software pattern-matching algorithm with an analog circuit-based detection method. By using hardware circuits to perform the differentiation, the system eliminates software overhead and processing delays while achieving real-time water-finger distinction.
Solution Approach 2:
The patent introduces an intermediate analog processing stage that combines mutual and self-capacitance measurements before digital processing. This intermediary analog circuit performs preliminary differentiation, reducing the burden on software and enabling faster response.
3Adaptability or versatility
If the touch surface is exposed to liquids or other materials in certain environments, then capacitive touch sensing can be used in diverse applications, but contamination of the surface occurs which has a negative effect on the sensing characteristics
Solution Approach 1:
The patent performs preliminary detection of water contamination using both mutual and self-capacitance measurements before a touch input is registered. This preliminary action allows the system to identify and filter out water-related signals, preventing false triggers in contaminated environments.
Solution Approach 2:
The patent uses feedback from both mutual capacitance and self-capacitance measurements to continuously monitor the touch surface condition. This dual-feedback mechanism enables the system to adapt to environmental changes and maintain sensing accuracy even when contamination occurs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the robustness of capacitive touch sensing by accurately differentiating between water and finger inputs, reducing false triggers and maintaining system accuracy even under contaminated conditions, without the need for additional software processing or filtering.
Implementation Method 1
generating a pulse by the output and capacitively coupling the pulse into the first electrode via the second electrode thereby performing the overlapping mutual capacitance measurement
Implementation Method 2
performing an individual self-capacitance measurement of the first electrode and performing an individual mutual capacitance measurement between the first and second electrode
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
In a method for performing a touch determination with a capacitive sensor, a self capacitance measurement of a capacitive sensor is initiated, wherein at the same time a mutual capacitance measurement including the capacitive sensor is performed. Such a method can be performed such that the self capacitance measurement and the mutual capacitance measurement differentially cancel with ungrounded conductive objects approaching or touching the capacitive sensor and additively combine for grounded objects approaching or touching the capacitive sensor.