Capacitive Sensor Circuit with Switched Reference Potential
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Solution Overview
Problem
Capacitive door handle sensors face limitations in evaluating electrode capacitances against ground potential due to the transmitter-receiver measurement principle, which restricts their functionality and packing density, especially in environments with space constraints and high energy demands.
Innovation Solution
A capacitive sensor circuit with a switch at the reception electrode allows for capacitance measurement against ground potential, enabling two electronically switchable operating modes to adapt to different requirements, and uses a charge amplifier with a microcontroller to facilitate efficient charge transport and measurement processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the transmitter-receiver measurement principle is used to measure capacitance between transmission and reception electrodes, then the measurement can be performed with existing circuit designs, but the capacitance against ground potential cannot be evaluated
Solution Approach 1:
The charge amplifier circuit is designed to perform multiple measurement functions: it can measure capacitance between transmission and reception electrodes using the transmitter-receiver principle, and simultaneously measure capacitance against ground potential by switching the reference potential of the reception electrode to ground. This multi-functionality resolves the contradiction by making the same circuit adaptable to different measurement requirements.
Solution Approach 2:
The circuit dynamically switches between different measurement modes by changing the reference potential connection of the reception electrode through electronic switching. This allows the system to adapt between measuring capacitance between electrodes (with virtual reference potential) and capacitance against ground (with ground reference), resolving the versatility limitation.
2Volume of moving object
If space-optimized electrode arrangements are implemented, then packing density improves, but parasitic capacities and long feed lines restrict sensor function
Solution Approach 1:
The invention extracts and eliminates the problematic virtual reference potential from the measurement circuit by switching it to ground potential. This removes the parasitic capacity issues and feed line restrictions that plague compact sensor designs, allowing space-optimized electrode arrangements to function reliably.
Solution Approach 2:
The reference potential parameter of the reception electrode is changed from virtual reference potential to ground potential. This parameter change eliminates the restrictions imposed by parasitic capacities and long feed lines, enabling reliable operation in compact sensor designs with optimized electrode arrangements.
3Measurement precision
If a virtual reference potential is used at the receiver input, then capacitance between transmission and reception electrodes can be measured, but voltage swings from charge transport cannot be avoided
Solution Approach 1:
Instead of maintaining a virtual reference potential to enable charge transport measurement, the invention inverts the approach by using ground potential as the reference. This allows the charge transport to be measured as a change in voltage against ground, eliminating the voltage swing problem while preserving measurement capability through the ground-related capacitance measurement mode.
4Adaptability or versatility
If only ground-related capacitance measurement is implemented, then single electrode sensors can be used, but capacitances between transmission and reception electrodes cannot be evaluated
Solution Approach 1:
The charge amplifier circuit is designed to perform multiple measurement functions: it can measure capacitance between transmission and reception electrodes using the transmitter-receiver principle, and simultaneously measure capacitance against ground potential by switching the reference potential of the reception electrode to ground. This multi-functionality resolves the contradiction by making the same circuit adaptable to different measurement requirements.
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 solution allows for the detection of capacitive coupling between reception and transmission electrodes, as well as the capacitive load of the reception electrode against ground, with reduced energy demand and insensitivity to environmental influences, enabling optimal adaptation and rapid measurement processing.
Implementation Method 1
The feedback is usually realized via a capacitance, wherein for each charge transfer at the input a voltage swing at the output is produced, which represents a measure of the charge quantity at the input for a known feedback capacitance.
Implementation Method 2
A capacitive sensor circuit with a switch at the reception electrode allows for capacitance measurement against ground potential
Data Source
AI summary
Capacitive door handle sensor comprising at least one transmission electrode and a reception electrode, an operational amplifier configured as a charge amplifier and connected to the reception electrode, a switch for charge transfer, a first and a second switch for discharging the two operational amplifier inputs and, a capacitor arranged between the output and the inverting input of the operational amplifier, and a control unit for controlling and evaluating the measurement, wherein the control unit comprises a reference potential switching output which is connected to a terminal of the switch and is configured to selectively control a capacitance measurement between the transmission electrodes and the reception electrode or between the reception electrode and ground. Furthermore, methods for setting different operating modes are claimed.