Capacitive Sensor Reading Circuit with Parasitic Interference Nullification
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Solution Overview
Problem
Capacitive pressure sensors face challenges in achieving high precision and flexibility due to interference from adjacent capacitors and parasitic capacitances, which complicates the reading process and limits their use in demanding applications, especially when the number of rows and columns needs to be varied.
Innovation Solution
A method and system that utilize a circuit for biasing and reading capacitances, including charge amplifiers and analog-to-digital conversion, to selectively read capacitors while nullifying interference from adjacent rows and columns, allowing for flexible configuration and operation with sensors of different row and column arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional reading methods are used for capacitive sensors, then the system can be implemented with simple circuitry, but the measurement precision deteriorates due to interference from adjacent capacitors and parasitic capacitances
Solution Approach 1:
The patent extracts and eliminates the harmful parasitic capacitances from the measurement circuit by using a differential reading approach. The circuit measures the difference between the selected capacitor and the parasitic capacitances, effectively removing the interference from adjacent capacitors and row/column line parasitic elements from the measurement.
Solution Approach 2:
The patent introduces an intermediary differential amplifier circuit that processes the capacitor readings. This intermediary circuit subtracts the parasitic capacitance values from the total measured capacitance, isolating the true capacitor value and improving measurement precision without requiring direct modification of the sensor array.
2Adaptability or versatility
If the reading system is designed for fixed array dimensions, then the circuit design is simplified, but the adaptability deteriorates when varying the number of rows and columns for different applications
Solution Approach 1:
The patent designs a universal reading system with multiplexed row and column selection circuits that can accommodate any array configuration. The same basic circuit architecture can read capacitors in arrays of different sizes by simply changing the selection signals, making the system adaptable to various sensor formats without requiring redesign.
Solution Approach 2:
The patent implements dynamic selection of rows and columns through programmable multiplexers and switches. The reading system can dynamically configure which capacitors are accessed based on the desired array dimensions, allowing flexible adaptation to different sensor layouts while maintaining a consistent underlying circuit structure.
3Productivity
If all capacitors are read simultaneously, then the frame rate is improved, but the interference from adjacent capacitors worsens the measurement accuracy
Solution Approach 1:
The patent employs periodic scanning of the capacitor array with systematic row-by-row or column-by-column sequencing. By periodically activating and measuring capacitors in a controlled sequence rather than simultaneously, the system maintains high frame rates while eliminating cross-talk interference between adjacent capacitors through temporal separation of measurements.
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
The solution enables precise and cost-effective reading of capacitive sensors, allowing for real-time monitoring of pressure distribution with improved accuracy and adaptability, suitable for various applications by periodically updating capacitance values and filtering noise.
Implementation Method 1
a charge amplifier producing an output voltage representing the capacitance of the selected capacitor
Implementation Method 2
The method includes preliminarily resetting the output voltage of the charge amplifier, connecting to a reference voltage all the deselected row and column plates of the array and connecting an auxiliary capacitor and the selected capacitor to an inverting input of the amplifier and as feedback capacitor of the amplifier, respectively
Data Source
AI summary
The method is for reading a capacitive sensor and may be implemented by a circuit for biasing and reading capacitances that includes circuits for selecting a column line and a row line, and a charge amplifier producing an output voltage representing the capacitance of the selected capacitor intercepted by the selected column and row lines. The method includes preliminarily resetting the output voltage of the charge amplifier, connecting all the deselected row and column plates of the array to a reference voltage and connecting a feedback capacitor and the selected capacitor to an inverting input of the amplifier, applying a step voltage on the capacitor that is connected to the inverting input of the amplifier, and reading the output voltage at steady-state.