Capacitive Sensor Circuit Self-Test for Switching Matrix Integrity
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Solution Overview
Problem
Existing capacitive sensor systems in the automotive sector lack an effective method to reliably and easily check the functionality of safety-relevant components, such as switches and resistors in the switching matrix, without requiring additional components.
Innovation Solution
A sensor circuit with a DC reference driver and a sensor driver that generates both AC and DC signals, utilizing a switching matrix with RT switches and load resistors to measure the impedance changes and verify the functionality of components during a self-test, without additional components like comparators or switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional components like comparators or switches are added to test safety-relevant components, then the reliability of component testing improves, but the device complexity increases
Solution Approach 1:
The sensor driver performs self-testing by generating test signals and measuring its own output characteristics through existing circuit paths. The sensor driver outputs test signals at its output port and measures the corresponding measurement current at the current output port, enabling autonomous verification of its functionality without external testing equipment.
Solution Approach 2:
The existing sensor driver circuit is designed to perform both its primary function of driving capacitive sensors and a secondary function of self-testing. The same output port and current measurement capability are utilized for both normal operation and safety verification, eliminating the need for dedicated testing components.
2Adaptability or versatility
If the sensor driver outputs both AC and DC signals, then the versatility of the sensor driver improves, but the stability of signal generation worsens
Solution Approach 1:
The sensor driver dynamically switches between different operating modes (AC signal generation for sensor operation and DC signal generation for self-testing) based on the testing requirements. This dynamic capability allows the driver to adapt its output characteristics without compromising the stability of each individual signal type when generated in its designated 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
Enables a reliable and cost-effective self-test of safety-relevant components within the capacitive sensor system, using existing circuits for impedance measurement, thereby ensuring the integrity of measuring paths without additional hardware, and detecting errors like short circuits or line interruptions.
Implementation Method 1
a sensor driver for generating a sine signal for powering the capacitive sensors... a current output port for outputting a measurement current corresponding to the sinusoidal signal output at the output port
Implementation Method 2
a DC reference driver for generating a DC reference signal... The other sensor ports are supplied with a DC reference signal from the DC reference driver to raise the ports to a defined potential
Data Source
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AI summary
A sensor circuit (20) for capacitive sensors (50) comprises a DC reference driver (22) for generating a DC reference signal, a sensor driver (24) for generating an AC signal, with an output port (28) for outputting the AC signal to power the capacitive sensors (50) and with a current output port (29) for outputting a sensing current corresponding to the AC signal, and multiple sensor ports (40) for connecting to individual capacitive sensors (50). The sensor circuit (20) includes a switching matrix (30) between the sensor ports (40) and the drivers, wherein the switching matrix (30) has a switching path for each sensor port (40) with an RT switch (34), a sensor switch (36), and a load resistor (32). A DC decoupling (62) between switching matrix (30) and capacitive sensor (50) serves to DC decouple the switching matrix (30) from the capacitive sensors (50).The sensor circuit (20) can perform a self-test in which the sensor driver (24) outputs a DC signal, creating a voltage difference between the DC reference driver (22) and the sensor driver (24), which is applied across the switching matrix (30). The current flowing across the switching matrix (30) during the self-test is measured. The invention also relates to a measuring system with a sensor circuit (20) and capacitive sensors (50).