Touch Panel Capacitance Switching for Skin Moisture Measurement
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Solution Overview
Problem
Display devices with touch sensors experience reduced accuracy in measuring skin moisture levels due to a low ground mass (LGM) state, which affects the mutual capacitance value in the touch area.
Innovation Solution
A display device measures skin moisture levels by employing a touch panel that operates in both mutual sensing and self-sensing modes, comparing capacitances to determine and compensate for variations in capacitance values, thereby maintaining accuracy regardless of the LGM state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If mutual capacitance sensing mode is used for skin moisture measurement, then the measurement area is larger, but the measurement accuracy is reduced in LGM state
Solution Approach 1:
The system dynamically switches between mutual capacitance sensing mode and self-capacitance sensing mode based on the detected LGM state. When LGM is detected (indicated by reduced mutual capacitance values), the system transitions to self-capacitance mode for accurate skin moisture measurement, thereby adapting the measurement method to current conditions to maintain both large measurement area and high accuracy.
Solution Approach 2:
The system changes the sensing parameter from mutual capacitance to self-capacitance when LGM state is detected. By monitoring mutual capacitance values and comparing them against threshold values, the system identifies LGM state and switches to using self-capacitance values for skin moisture measurement, which remain accurate even when mutual capacitance is reduced.
2Area of stationary object
If touch sensor measurement area is increased, then more skin area can be measured, but mutual capacitance value decreases in LGM state
Solution Approach 1:
The system uses self-capacitance values as an intermediary measurement parameter when mutual capacitance values become unreliable in LGM state. By measuring both mutual capacitance (for large area coverage) and self-capacitance (for accurate quantification), the system can accurately determine skin moisture levels even when mutual capacitance is reduced, effectively using self-capacitance as a mediator to overcome the LGM problem.
3Device complexity
If only mutual capacitance sensing is used, then the system is simpler, but skin moisture measurement fails in LGM state
Solution Approach 1:
The touch sensor system is designed to perform multiple functions: it can operate in mutual capacitance sensing mode for normal conditions and switch to self-capacitance sensing mode for LGM conditions. This multi-functionality allows the same hardware to reliably measure skin moisture across different environmental conditions without requiring separate dedicated sensors for each mode.
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
The method and device ensure accurate skin moisture level measurement by compensating for capacitance changes, ensuring reliable results even when the user is not grounded.
Implementation Method 1
measuring, in response to a touch on a touch panel, a first capacitance for a touch area in association with driving a first electrode and a second electrode of the touch panel in a mutual sensing mode
Data Source
AI summary
A method of measuring skin moisture includes: measuring, in response to a touch on a touch panel, a first capacitance for a touch area in association with driving first and second electrodes of the touch panel in a mutual sensing mode; measuring, in response to the touch, a second capacitance for the touch area in association with driving one electrode of the first and second electrodes in a self-sensing mode; comparing the first capacitance with a first reference capacitance; determining, in response to the first capacitance being greater than the first reference capacitance, a skin moisture level using the first capacitance and the second capacitance; comparing, in response to the first capacitance being less than the first reference capacitance, the second capacitance with a second reference capacitance; and compensating, in response to the second capacitance being greater than the second reference capacitance, the first capacitance using the second capacitance.