Capacitive Touch Sensor Activation Using Self and Mutual Capacitance
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Solution Overview
Problem
State-of-the-art capacitive touch sensors in vehicles cannot distinguish between a user's hand or finger and water, leading to undesired locking or unlocking of car doors under wet conditions.
Innovation Solution
An electronic device that measures both self-capacitance and mutual capacitance of a touch sensor, using an algorithm to generate a resultant signal, and compares it to a threshold to determine the activation status, distinguishing between intended touch by a human body part and unintended touch by water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If capacitive touch sensors are used for car door entry systems, then aesthetic integration is improved and mechanical components are eliminated, but the sensor cannot distinguish between water and user contact leading to false activation
Solution Approach 1:
The patent segments the capacitance measurement into two independent components: self-capacitance measurement (first measurement result) and mutual capacitance measurement (second measurement result). By measuring these two capacitance types separately and independently, the system can analyze their different response patterns to water versus human contact, thereby resolving the inability to distinguish between water and user contact while maintaining the aesthetic integrated design.
Solution Approach 2:
The patent changes the measurement parameters by introducing a second capacitance measurement dimension. Instead of relying on a single capacitance value, the system measures both self-capacitance and mutual capacitance, creating a two-dimensional parameter space for touch detection. This parameter expansion enables the algorithm to differentiate between water and human contact based on their distinct capacitance signatures.
2Device complexity
If simple capacitive touch sensors are used, then device complexity is reduced and manufacturing is easier, but measurement precision is insufficient to distinguish water from human contact
Solution Approach 1:
The patent transitions from one-dimensional capacitance measurement to two-dimensional capacitance measurement by incorporating both self-capacitance and mutual capacitance dimensions. This dimensional expansion allows the system to plot measurement results in a two-dimensional space where water contact and human contact occupy different regions, enabling accurate discrimination without significantly increasing device complexity.
Solution Approach 2:
The patent introduces an algorithm module as an intermediary that processes the two capacitance measurement results. This algorithm acts as a mediator between the raw capacitance data and the final touch detection decision, analyzing the relationship between self-capacitance and mutual capacitance to determine whether the contact is from water or a human user.
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
Accurately differentiates between intended and unintended touch events, preventing unwanted activation of touch sensors due to water exposure.
Implementation Method 1
the capacitance measurement circuit is configured to obtain a first measurement result based on a self-capacitance of the first electrode and a second measurement result based on a mutual capacitance between the first and the second electrodes
Data Source
AI summary
An electronic device for determining a status of a touch sensor includes a capacitance measurement circuit to be coupled to a touch sensor including first and second electrodes, the capacitance measurement circuit being configured to obtain a first measurement result based on a self-capacitance of the first electrode and a second measurement result based on a mutual capacitance between the first and the second electrodes. An algorithm may be applied to the first and second measurement results, thereby generating a signal. A threshold comparator is configured to compare the signal to a threshold, and to generate a comparison signal having a first value if the signal is greater than the threshold and a second value if the signal is less than the threshold. An output module is configured to provide an output signal indicative of the status of the touch sensor based on the comparison signal.