Capacitive Sensor Interface Circuit Non-Linearity Compensation
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Solution Overview
Problem
Existing electronic interface circuits for capacitive sensors face challenges in reducing non-linearity, particularly in digital-analog converters, which affects the accuracy of measurements for physical parameters like acceleration, force, and pressure, and also increases the size and electrical consumption of integrated components.
Innovation Solution
A method and electronic interface circuit that involves measuring a physical parameter at a reference offset voltage different from zero, using a combination of positive and negative polarization phases, and averaging digital signals to reduce non-linearity, with digital processing after the charge transfer amplifier to eliminate voltage deviations and offset, thereby compensating for non-pairing capacitors in the digital-analog converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional electronic interface circuits are used for capacitive sensors, then the circuit can be integrated into a semiconductor substrate, but non-linearities are introduced due to parasitic capacitances that do not depend on electrode displacement
Solution Approach 1:
The patent replaces the traditional analog electronic interface circuit with a digital processing system. Instead of using analog components that introduce parasitic capacitances and non-linearities, the invention uses digital signal processing to acquire, process, and compensate for sensor signals, thereby eliminating the source of non-linearity while maintaining integration capability
Solution Approach 2:
The patent changes the operating parameters of the capacitive sensor by applying different polarization voltages (positive and negative) to the fixed electrodes. By measuring the mobile electrode position under different voltage conditions and processing these measurements digitally, the system compensates for non-linear effects caused by parasitic capacitances
2Device complexity
If the mobile electrode is positioned at an offset position in rest mode, then the sensor structure is simplified, but measurement errors occur without calibration
Solution Approach 1:
The patent performs preliminary calibration measurements by applying both positive and negative polarization voltages to the fixed electrodes before actual measurement. This preliminary action allows the system to determine the offset position of the mobile electrode and compensate for it through digital processing, enabling accurate measurements without requiring precise mechanical positioning
Solution Approach 2:
The patent implements a feedback mechanism where the digital processing system continuously monitors the sensor output and adjusts for offset errors. By measuring the electrode positions under different polarization conditions and using this information to correct subsequent measurements, the system maintains high accuracy despite structural simplifications
3Extent of automation
If digital-analog converters are used in the electronic circuit, then signal processing capability is improved, but non-linearity effects increase and component size increases
Solution Approach 1:
The patent eliminates digital-analog converters from the signal processing chain by implementing fully digital signal processing. Sensor signals are acquired and processed in digital form throughout, avoiding the non-linearities introduced by DAC components while maintaining advanced signal processing capabilities through software-based algorithms
Solution Approach 2:
The patent uses digital copying and processing of sensor signals instead of analog conversion. By representing sensor outputs as digital values and performing all processing operations in the digital domain, the system achieves high signal processing capability without the non-linearities associated with digital-analog conversion components
4Ease of manufacture
If the electronic circuit is fully integrated into the semiconductor substrate, then manufacturing is simplified, but parasitic capacitances from substrate connections increase non-linearity
Solution Approach 1:
The patent replaces the integrated analog electronic circuit with a digital processing system that can be implemented through software or digital logic. This substitution eliminates the parasitic capacitances inherent in analog substrate connections while maintaining the benefits of integration, as digital processing can be implemented with minimal analog interface 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 approach allows for quick stabilization of digital measurement signals, reduces the effect of non-linearity in digital-analog converters, and minimizes the size and electrical consumption of the electronic circuit, leading to more accurate measurements of physical parameters.
Implementation Method 1
The capacitive sensor is made up of at least two capacitors mounted in differential. A common electrode of the capacitors is capable of moving between two fixed electrodes under the action, for example, of a force to modify the capacitive value of each capacitor.
Implementation Method 2
The electronic interface circuit connected to the capacitive sensor thus makes it possible to provide an analog output signal. This analog output signal is defined in the form of a voltage depending on the variation of the capacitances of the two capacitors.
Implementation Method 3
the fixed electrodes of two capacitors or pairs of capacitors are polarized or cyclically excited by voltages of opposite polarity by relative to a resting reference voltage
Data Source
AI summary
The method involves implementing a dichotomy algorithm stored in a logic unit (5), based on an output value of a charge transfer amplifier (4), to supply a digital signal to a digital-analogue converter (7) to generate a measurement voltage. The electrodes of capacitors are polarized via a switching unit (3) based on the digital measuring signal of a preceding cycle supplied by the logic unit, to adapt a new digital measuring signal in the logic unit that removes any voltage offset linked to electronic components based on the obtained digital measuring signals. An independent claim is included for electronic interface circuit for capacitive sensor.