Digital Interface Circuit for Capacitive Sensor Offset Compensation
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Solution Overview
Problem
Existing electronic interface circuits for capacitive sensors face challenges such as non-linearities and voltage offsets, leading to inaccurate force, acceleration, or pressure measurements, and require analogue output signals that increase component size and power consumption.
Innovation Solution
A method using a digital interface circuit with a charge transfer amplifier, switching unit, logic unit, and digital-analogue converter that adapts measurement cycles with self-adapting algorithms to provide precise digital output signals, reducing noise and eliminating voltage offsets by alternating biasing and adjusting step sizes based on charge transfer amplifier output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electronic interface circuit with charge transfer amplifier and digital processing is used, then measurement precision is improved by eliminating voltage offsets and non-linearities, but device complexity increases due to additional digital components
Solution Approach 1:
The patent replaces the conventional analogue electronic interface circuit with a digital interface circuit that uses a charge transfer amplifier and digital signal processing. The digital interface circuit includes a charge transfer amplifier connected to the capacitive sensor, a digital-to-analogue converter, and digital processing logic that eliminates voltage offsets and non-linearities through digital correction algorithms, thereby improving measurement precision while managing device complexity through integrated digital design
Solution Approach 2:
The patent changes the operating parameters of the interface circuit by implementing alternating biasing of the capacitive sensor electrodes with different voltage levels. The digital processing logic dynamically adjusts measurement parameters including step size adaptation based on charge transfer amplifier output, enabling precise measurement of physical parameters while compensating for substrate potential effects and electrostatic force variations
2Measurement precision
If analogue output signals are used from the electronic interface circuit, then measurement capability is maintained, but power consumption and component size increase
Solution Approach 1:
The patent substitutes the conventional analogue output stage with a digital output interface. The digital interface circuit processes sensor signals through the charge transfer amplifier and digital logic, generating digital output signals that directly represent measured physical parameters. This digital approach reduces power consumption and eliminates the need for power-hungry analogue output amplifiers and associated precision analogue components
Solution Approach 2:
The patent extracts and eliminates the analogue output signal generation stage from the interface circuit. By implementing digital signal processing and digital output, the circuit removes the need for analogue voltage amplification and buffering stages, thereby reducing component count, device area, and power consumption while maintaining full measurement capability through digital representation of sensor data
3Stability of the object's composition
If the common moving electrode is held equidistant from fixed electrodes at rest, then sensor symmetry is maintained, but non-linearities and voltage offsets occur due to substrate potential and stray capacitances
Solution Approach 1:
The patent implements a feedback mechanism through the charge transfer amplifier and digital processing logic that continuously monitors and corrects for voltage offsets and non-linearities. The digital interface circuit measures the actual sensor output and applies digital correction algorithms that compensate for substrate potential effects and stray capacitance variations, maintaining measurement accuracy despite the physical sensor structure remaining symmetric at rest
Solution Approach 2:
The patent changes the electrical parameters of the sensor operation by applying alternating bias voltages to the fixed electrodes rather than maintaining a static symmetric configuration. The digital processing logic dynamically adjusts measurement parameters including offset compensation values and gain correction factors based on calibrated reference measurements, thereby eliminating the adverse effects of substrate potential and stray capacitances while preserving the physical symmetry of the sensor structure
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 enables quick, error-free digital output signals for physical parameter measurements, reducing noise and power consumption while allowing for accurate measurements across multiple axes with reduced redundancy in the electronic circuit.
Implementation Method 1
the capacitive sensor may be capable of performing a measurement along one direction of movement of the moving electrode... the capacitive value of each capacitor varies inversely
Implementation Method 2
electronic interface circuit including a charge transfer amplifier, which is connected to the common electrode
Data Source
AI summary
The method is for measuring a physical parameter via an electronic circuit connected to a two differential capacitor sensor having two fixed electrodes and a common moving electrode. The circuit supplies first and second digital measuring signals. Each measuring cycle consists on biasing fixed electrodes by a first biasing and a second biasing reverse of the first biasing, alternated with biasing the electrodes by the measuring voltage based on first and second digital signals. Each conversion starts by a small step value added to or subtracted from each digital signal in each cycle. If the successive identical amplifier output states counted or counted down by a counter is higher than a threshold, a large step value is added to or subtracted from the digital signals in each cycle. Re-adaptation to the small step value occurs when a sign change is detected in the counter, until the conversion end.