Multichannel Capacitive Sensor Layout for Drift-Stable Proximity Sensing
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Solution Overview
Problem
Capacitive proximity sensors in portable devices face challenges with small signal detection due to noise and thermal drift, and require miniaturization, necessitating improved stability and reduced terminal count for integration in small packages.
Innovation Solution
A capacitive sensor device with a capacitance-measuring circuit and multiple sense inputs, using a separate reference capacitor for each sense input to compensate for thermal drift, allowing for selective configuration of input states to enhance signal accuracy and reduce noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference capacitor is used to calibrate the response of sense electrodes, then measurement precision is improved, but device complexity increases due to additional terminals required for integration
Solution Approach 1:
The patent combines multiple sense electrodes and reference capacitor connections into a single shared reference input terminal. The capacitive sensor device uses one reference input that can be selectively connected to different reference capacitors associated with different sense electrodes, eliminating the need for separate reference terminals for each sense electrode. This merging approach maintains measurement precision while reducing terminal count and device complexity.
Solution Approach 2:
The reference input terminal is designed to serve multiple functions: it can be connected to different reference capacitors depending on which sense electrode is being measured, and it participates in both measurement modes (measuring sense electrode capacitance and measuring reference capacitor capacitance). This multi-functional design allows a single terminal to replace what would traditionally require multiple dedicated terminals.
2Volume of moving object
If miniaturized circuits are used to reduce package size, then volume is reduced, but measurement precision deteriorates due to increased noise and interference signals
Solution Approach 1:
The patent introduces reference capacitors as intermediary elements that mediate between the sense electrodes and the measurement circuit. These reference capacitors are specifically designed to track thermal drift without being affected by external conducting bodies. By using the reference capacitors as intermediaries for calibration and compensation, the system can maintain high measurement precision in miniaturized packages where noise and interference are significant.
Solution Approach 2:
The system implements a feedback mechanism where the measured capacitance of reference capacitors is used to compensate for thermal drift in the sense electrode measurements. The device selectively measures reference capacitor capacitance and uses this information to correct the sense electrode capacitance readings, thereby maintaining measurement precision despite the noisy environment of miniaturized circuits.
3Stability of the object's composition
If thermal drift compensation is implemented using separate reference capacitors for each sense input, then stability is improved, but device complexity increases
Solution Approach 1:
The patent implements a dynamic configuration system where the connections between sense inputs, reference inputs, and reference capacitors can be selectively changed based on the measurement mode. The device can switch between measuring sense electrode capacitance and measuring reference capacitor capacitance, and can dynamically connect different reference capacitors to the shared reference input. This dynamic reconfiguration allows thermal drift compensation with separate reference capacitors while managing circuit complexity through intelligent switching rather than permanent complex wiring.
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 provides improved stability and accuracy in detecting body proximity by correcting capacitance measurements, reducing noise interference, and allowing for flexible placement of components without increasing pin count, thus enhancing the performance of capacitive proximity sensing in portable devices.
Implementation Method 1
Thermal drifts are significative and can easily obliterate the capacitance variation that is sought
Implementation Method 2
The approach of a hand, or of a part of the body is detected through a variation in the self-capacitance of a sense electrode
Data Source
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AI summary
A capacitive sensor with a plurality of sense inputs (M1, M2, M3) connectable to capacitive sense electrodes (21, 22, 23) and a common reference input (REF), each sense input and the reference input can be put in a measure state, in a ground state, or in a shield state. The sensor can be equipped with external reference capacitors between each of the sense input and the common reference terminal. One measurement mode is for determining the self-capacitance of the respective sensing electrode. In this mode the capacitance of a selected sense input (M1, M2, M3) is measured and the common reference input (REF) is operated as an active shield having the same potential as the selected sense input. In order to determine the compensation value, in a further mode, the capacitance of the reference input (REF) is measured and the selected sense input is grounded. During this mode, the other sense inputs, which are not selected, are operated as active shields having the same potential as the reference node. The latter value is used to compensate the value determined in the self-capacitance mode. When operating the sensor in this way, the reference capacitor can be read individually by selectively pulling one of the input terminals to ground and driving the other to be equipotential with the reference input.