Capacitive Sensor Interface Circuit Digital Signal Processing
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Solution Overview
Problem
Existing electronic interface circuits for capacitive sensors suffer from non-linearities and voltage offsets due to stray capacitances and substrate potentials, leading to inaccurate force, acceleration, or pressure measurements, and require analogue output signals that are not efficient in terms of component size and power consumption.
Innovation Solution
A method and electronic interface circuit that uses a charge transfer amplifier connected to a common electrode via a switching unit, with a logic unit for digital processing and a digital-analogue converter to supply measurement voltages based on binary word conversions, employing successive measuring cycles with adaptive step values to minimize errors and noise, allowing for quick and precise digital output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analogue output signals are used in conventional electronic interface circuits, then measurement capability is maintained, but component size and power consumption increase
Solution Approach 1:
The patent replaces the conventional analogue signal processing system with a digital signal processing system. The charge transfer amplifier converts capacitor charges to digital signals directly, eliminating the need for analogue output stages, resistors, and capacitors associated with analogue processing. This substitution of digital for analogue electronics reduces component count, chip area, and power consumption while maintaining measurement functionality.
2Ease of operation
If conventional electronic interface circuits are used with capacitive sensors, then basic measurement function is provided, but non-linearities and voltage offsets occur due to stray capacitances and substrate potentials
Solution Approach 1:
The patent extracts and separately measures the error components (stray capacitances and substrate potential effects) from the main measurement signal. By applying opposite polarity voltages to the fixed electrodes in successive measuring cycles and processing the differential charges, the circuit isolates the signal related to common electrode displacement from signals related to substrate effects and stray capacitances, thereby eliminating measurement errors.
Solution Approach 2:
The patent employs a feedback mechanism where the digital signal processing unit continuously adjusts the measurement based on previous cycle results. The charge transfer amplifier and associated logic circuits use feedback to compensate for offset voltages and non-linearities by comparing successive measurements and correcting for systematic errors, thereby improving measurement accuracy.
3Use of energy by moving object
If digital signal processing is implemented with charge transfer amplifier, then component size and power consumption are reduced, but measurement speed and precision may be affected
Solution Approach 1:
The patent uses periodic action by implementing successive measuring cycles with opposite polarity voltages applied to the fixed electrodes. Each cycle consists of a defined sequence of charge transfer operations followed by digital processing. This periodic structure allows the circuit to maintain high measurement speed through efficient time-multiplexed operation while using digital processing to reduce power consumption compared to continuous analogue processing.
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 the rapid supply of accurate digital output signals without errors, reducing noise and voltage offsets, and allows for efficient power consumption and component size reduction, while supporting multi-axis measurements with a single amplifier and logic unit.
Implementation Method 1
The capacitive sensor is formed of at least two differential connected capacitors... capable of moving between two fixed electrodes under the action, for example, of a force in order to alter the capacitive value of each capacitor
Implementation Method 2
said electronic circuit including a charge transfer amplifier, which is connected to the common electrode via a switching unit
Implementation Method 3
the measured electrostatic force is not zero in the sensor and electronic circuit in a rest mode. Because of the influence of the substrate potential on the electrostatic force
Data Source
AI summary
The method is for measuring a physical parameter by an electronic circuit connected to a two differential capacitor sensor having two fixed electrodes and a common moving electrode. The electronic circuit supplies first and second digital measuring signals. Each measuring cycle consists on biasing the electrodes by the measuring voltage based on the first digital signal, connecting the fixed electrodes to a supply voltage source for a first biasing, biasing the electrodes by the measuring voltage based on the second digital measuring signal, and inversely connecting the fixed electrodes to a supply voltage source for a second biasing. In first successive measuring cycles, the first and second digital signals are adapted to each cycle by a large step value. In second successive measuring cycles, the first and second digital signals are adapted to each cycle by a small step value until the end of the conversion.