Multichannel Capacitive Sensing with Shared Reference Drift Compensation
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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, requiring improved stability and miniaturization with reduced terminal numbers to fit 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 sense and reference inputs to measure capacitance while minimizing interference and noise, and generating a corrected capacitance signal for proximity detection.
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 and components
Solution Approach 1:
The patent combines multiple reference capacitors into a single shared reference capacitor that serves all sense electrodes. The capacitive sensor device selectively connects this single reference capacitor to different sense inputs through switching circuitry, eliminating the need for separate reference capacitors for each sense electrode and reducing the terminal count while maintaining calibration precision.
Solution Approach 2:
The single reference capacitor is designed to serve multiple functions by being selectively connected to different sense electrodes through the switching mechanism. This universal reference capacitor can calibrate and compensate for thermal drift across all sense inputs, replacing what would traditionally require multiple dedicated reference capacitors, thus reducing device complexity while preserving measurement precision.
2Stability of the object's composition
If multiple reference capacitors are used for each sense input, then thermal drift compensation is improved, but the device size increases making it unsuitable for miniaturized circuits
Solution Approach 1:
The patent merges multiple individual reference capacitors into a single shared reference capacitor that provides thermal drift compensation for all sense electrodes. The switching circuitry enables this single capacitor to be sequentially connected to different sense inputs, achieving the thermal compensation function of multiple capacitors while occupying the space of only one, thus enabling device miniaturization.
Solution Approach 2:
The patent segments the operation of the reference capacitor into time-multiplexed intervals, where the single reference capacitor is sequentially connected to different sense electrodes through switching circuitry. This temporal segmentation allows one physical capacitor to serve multiple functional roles that would traditionally require multiple simultaneous capacitors, reducing the overall device volume while maintaining thermal drift compensation stability.
3Measurement precision
If the capacitance signal is measured with high precision, then proximity detection accuracy is improved, but noise and interference signals from the environment and device itself obscure the small capacitance variations
Solution Approach 1:
The patent implements a feedback mechanism where the capacitive sensor device measures the capacitance of the shared reference capacitor and uses this measurement to compensate for thermal drift and environmental effects in real-time. The system continuously monitors and adjusts based on the reference capacitor's behavior, which experiences similar environmental conditions but lacks the proximity signal, thereby filtering out common-mode noise and interference while preserving the small capacitance variations caused by proximity detection.
Solution Approach 2:
The shared reference capacitor acts as an intermediary that mediates between the sense electrodes and the measurement circuitry. By measuring the reference capacitor's capacitance under the same environmental conditions but without the proximity signal, the system can subtract or compensate for the environmental noise and interference, isolating the small capacitance variations that indicate proximity detection.
4Stability of the object's composition
If separate reference capacitors are used for each sense electrode, then thermal drift compensation is improved, but the number of terminals increases making integration in miniaturized circuits difficult
Solution Approach 1:
The patent merges multiple separate reference capacitors into a single shared reference capacitor that provides thermal drift compensation for all sense electrodes through selective connection via switching circuitry. This consolidation maintains the thermal compensation function while reducing the terminal count from multiple reference capacitor terminals to a single reference capacitor terminal, facilitating integration in miniaturized circuits.
Solution Approach 2:
The patent introduces dynamic switching capability that allows the single reference capacitor to be selectively connected to different sense electrodes based on which one is currently being measured. This dynamic reconfiguration enables one physical capacitor to fulfill the roles of multiple static reference capacitors, reducing device complexity while maintaining thermal drift compensation stability across all sense inputs.
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 enhances the stability and accuracy of proximity detection by effectively compensating for thermal drift and noise, enabling reliable operation in miniaturized portable devices with reduced pin count, improving the reliability of proximity awareness in smartphones and similar devices.
Implementation Method 1
using a separate reference capacitor for each sense input to compensate for thermal drift
Implementation Method 2
a capacitance-measuring circuit and multiple sense inputs, using a separate reference capacitor for each sense input
Data Source
AI summary
A capacitive sensor with a plurality of sense inputs connectable to capacitive sense electrodes and a common reference input, 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. 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.