Capacitive Touch Sensing with Absolute and Transcapacitance Separation
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Solution Overview
Problem
Current capacitive sensing devices face limitations in accurately detecting touch inputs due to difficulties in controlling voltage on external objects and the inability to demodulate DC electret capacitive measurements, leading to ambiguity in positional information and noise interference.
Innovation Solution
The implementation of a capacitive sensor device with sensor electrodes that can perform both absolute and transcapacitive sensing using the same sensor electrodes, allowing for the differentiation of absolute capacitance and transcapacitive components through modulation techniques, enabling more accurate detection of positional information and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC electret capacitive measurements are used for touch detection, then the sensing capability is provided, but the measurements cannot be demodulated leading to ambiguity in positional information
Solution Approach 1:
The patent applies periodic modulation to the electret charge on the sensor electrode by switching between different charge states (e.g., +Q and -Q) at a specific frequency. This periodic action converts the static DC electret measurement into an AC signal that can be demodulated, thereby resolving the ambiguity in positional information while maintaining the sensing capability.
2Measurement precision
If voltage control on external objects is attempted, then touch detection capability is enhanced, but the voltage cannot be controlled on external objects leading to limitations
Solution Approach 1:
Instead of attempting to control voltage on external objects (which is difficult), the patent inverts the approach by controlling the voltage on the sensor electrode itself through electret charge switching. This allows precise touch detection without requiring voltage control of external objects, resolving the contradiction between detection accuracy and operational ease.
3Measurement precision
If absolute capacitance sensing is performed, then capacitive measurements are obtained, but noise interference and ambiguity remain
Solution Approach 1:
The patent employs demodulation of the periodically modulated electret signal to extract meaningful capacitive measurement information from the noisy DC electret measurements. This feedback-based demodulation process filters out noise interference and resolves ambiguity, thereby improving capacitive measurement accuracy while reducing the harmful effects of noise.
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 accuracy of touch input detection by allowing for simultaneous absolute and transcapacitive measurements, improving positional information determination and reducing ambiguity and noise, thereby enabling more reliable capacitive sensing.
Implementation Method 1
a sensor electrode that is electrically modulated relative to system ground and that detects changes in capacitance
Implementation Method 2
the sensor electrode detects changes in transcapacitance caused by external objects proximate to the sensor electrode
Data Source
AI summary
A capacitive sensor device comprises a first sensor electrode, a second sensor electrode, and a processing system coupled to the first sensor electrode and the second sensor electrode. The processing system is configured to acquire a first capacitive measurement by emitting and receiving a first electrical signal with the first sensor electrode. The processing system is configured to acquire a second capacitive measurement by emitting and receiving a second electrical signal, wherein one of the first and second sensor electrodes performs the emitting and the other of the first and second sensor electrodes performs the receiving, and wherein the first and second capacitive measurements are non-degenerate. The processing system is configured to determine positional information using the first and second capacitive measurements.