Capacitive Touch Sensing with Redundant Electrode Integrity Checks
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Solution Overview
Problem
Traditional capacitive touch sensing methods fail to meet the safety integrity requirements for safety-critical applications, such as automotive systems, due to their inability to detect malfunctions effectively, leading to potential hazards.
Innovation Solution
A capacitive touch sensing system with redundant touch sensing methods and self-capacitance and mutual-capacitance measurements is implemented, using three electrodes to verify the integrity of each electrode and related wiring, ensuring continued operation in a degraded mode even if a sensing electrode or wiring is compromised.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitive touch sensing methods are used, then cost is reduced and implementation is simplified, but safety integrity level is insufficient for safety-critical functions
Solution Approach 1:
The touch sensing function is segmented into multiple independent sensing electrodes (first, second, and third electrodes) that can be individually monitored. Each electrode's integrity is verified separately through mutual-capacitance measurements, allowing the system to detect and isolate faults in specific electrodes while maintaining overall system safety integrity.
Solution Approach 2:
The system implements continuous feedback by measuring mutual-capacitance between electrode pairs to verify electrode integrity. The processor monitors these measurements in real-time, compares them against expected values, and can detect malfunctions or hazards, providing feedback that enables safety-critical decisions about system operation.
2Reliability
If traditional capacitive touch sensing methods are used, then device simplicity is maintained, but malfunction detection capability is insufficient
Solution Approach 1:
The system uses mutual-capacitance measurements as an intermediary verification mechanism. By measuring the capacitive coupling between pairs of electrodes (first and second, second and third, first and third), the system creates indirect probes that reveal the integrity state of each electrode without directly testing the electrodes themselves, enabling sophisticated fault detection through relatively simple measurements.
Solution Approach 2:
The sensing electrodes serve multiple functions: they detect touch events for normal operation and simultaneously serve as test objects for integrity verification. The same electrode structures used for touch sensing are also used in mutual-capacitance measurements to verify their own integrity, eliminating the need for separate test electrodes or wiring.
3Reliability
If redundant mechanical switches are used to achieve safety integrity, then safety level is improved, but device bulk and cost increase
Solution Approach 1:
The system replaces mechanical switches with capacitive touch sensing electrodes that provide equivalent safety functionality. Instead of using multiple mechanical switches with physical contacts and wiring, the invention uses electrical capacitive fields that can be monitored through mutual-capacitance measurements, achieving the same safety integrity goals without mechanical components.
Solution Approach 2:
The system merges the safety verification function with the normal touch sensing function into a single integrated system. The same electrodes used for touch detection are also used for integrity verification through mutual-capacitance measurements, combining what would traditionally require separate safety circuits and mechanical switches into one unified capacitive sensing system.
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 provides a low-cost, robust solution that meets higher Automotive Safety Integrity Levels (ASIL) requirements, reducing the need for bulky and expensive mechanical switches while maintaining reliable finger touch detection and fault detection capabilities.
Implementation Method 1
a first mutual-capacitance of an electrode pair comprising two of a first electrode, a second electrode and a third electrode, and a self-capacitance between the third electrode and a body biased to a fixed voltage
Data Source
AI summary
A method for capacitive touch sensing with high safety integrity includes measuring at least one of a first mutual-capacitance of an electrode pair comprising two of a first electrode, a second electrode and a third electrode, and a self-capacitance between the third electrode and a body biased to a fixed voltage. A contact of the body to a dielectric overlaying each of the first electrode, the second electrode and the third electrode is detected by comparing at least one of the first mutual-capacitance of the electrode pair to a first reference range, and the self-capacitance to a second reference range.