Multi-channel Capacitance Sensing Circuit with Diagnostic Switching
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Solution Overview
Problem
Capacitive sensing systems in automotive applications face challenges in diagnosing the integrity of sense-guard sensors, particularly in multi-channel devices, where hardware faults like electrical interruptions can compromise measurement reliability with limited additional hardware resources.
Innovation Solution
A capacitance measurement circuit that includes a first and second sensing circuit, a measurement signal voltage source, a diagnostic signal voltage source, and a current measurement circuit, allowing for selective connection of sense electrodes to a common node and their corresponding guard electrodes, with a remotely controllable switching unit and transimpedance amplifier for diagnostic purposes, enabling reliable detection of hardware faults with minimal additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-channel capacitive sensing device is used for automotive applications, then the sensing coverage and functionality are improved, but the difficulty of diagnosing hardware faults increases due to limited additional hardware resources
Solution Approach 1:
The measurement circuit is designed to perform both normal capacitive sensing measurements and diagnostic measurements using the same hardware resources. The circuit can selectively connect different sense electrodes and guard electrodes to measurement nodes, enabling the same circuit to serve multiple functions: routine operation and fault diagnosis without requiring separate dedicated diagnostic hardware for each channel
Solution Approach 2:
A remotely controllable switching unit is introduced as an intermediary component that enables selective connection between sense electrodes, guard electrodes, and measurement nodes. This switching mechanism allows the system to reconfigure the measurement circuit for different purposes (normal sensing vs. diagnostic testing) without adding permanent dedicated diagnostic hardware to each channel, thus resolving the contradiction between multi-channel functionality and fault diagnosis capability
2Reliability
If additional hardware resources are added for diagnostic purposes, then the detection capability is improved, but the device complexity increases
Solution Approach 1:
The measurement circuit performs dual functions: normal capacitive sensing and diagnostic testing. The same voltage sources, current measurement circuits, and signal processing paths are used for both operational measurements and fault diagnosis, eliminating the need for separate dedicated diagnostic hardware and thereby maintaining reliability without increasing overall device complexity
Solution Approach 2:
The diagnostic functionality is merged with the existing measurement circuit rather than being implemented as a separate system. The voltage sources and measurement paths are combined to serve both operational and diagnostic purposes, reducing hardware complexity while maintaining comprehensive fault detection capability across all channels
3Measurement precision
If selective connection of sense electrodes is implemented, then the diagnostic precision is improved, but the device complexity increases
Solution Approach 1:
A remotely controllable switching unit acts as an intermediary that enables selective connection of individual sense electrodes and guard electrodes to measurement nodes. This switching mechanism provides precise control over which electrodes are measured during diagnostic operations, achieving high diagnostic precision through software-controlled switching rather than through complex hardwired connection schemes
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
Facilitates the diagnosis of capacitive sensor integrity in multi-channel devices with reduced hardware effort, allowing for the detection of hardware faults like electrical connections interruptions without compromising the functional availability of the sensing system.
Implementation Method 1
the at least one measurement current-to-voltage converter is connected with its signal input port to the common sense node and with its reference input port to the output port of the signal voltage source
Data Source
AI summary
A capacitance measurement circuit for determining complex electric currents in a multi-channel capacitive sensing device includes a first sensing circuit for selectively connecting one of a plurality of sense electrodes to a common sense node and for connecting a corresponding guard electrode of the sense electrode to a common guard node, and at least a second sensing circuit. A measurement signal voltage source provides an alternating measurement voltage to the common guard node in a remotely controllable manner. A diagnostic signal voltage source provides an alternating diagnostic voltage to the common guard node in a remotely controllable manner. A current measurement circuit is connected with a signal input port to the common sense node and with a reference input port to the output port of the measurement signal voltage source.