Capacitance Proximity Sensor Dynamic Electrode Shielding
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Solution Overview
Problem
Capacitance-type proximity sensors used in portable devices face challenges in reducing external noise and maintaining detection sensitivity, especially when the user's hand is used to hold the device, leading to interference with the sensor's output signals.
Innovation Solution
The sensor employs a configuration of internal and external electrodes that can function as both shielding and detecting elements, with a multiplexer and driving circuit to dynamically change electrode connections, allowing for improved noise reduction and accurate detection of object position in three-axis directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shielding electrodes are arranged around detecting electrodes to shield from capacitance variation in directions other than detection target direction, then detection sensitivity is improved, but external noise from user's hand when holding portable apparatus is not sufficiently reduced
Solution Approach 1:
The electrode structure is segmented into multiple types: first detecting electrodes, second detecting electrodes, first shielding electrodes, and second shielding electrodes. This segmentation allows each electrode type to be optimized for specific functions - detecting electrodes for sensitivity and shielding electrodes for noise reduction - resolving the contradiction between detection sensitivity and external noise rejection.
Solution Approach 2:
Different regions of the sensor are assigned different electrode configurations tailored to local requirements. Areas closer to the detection target have detecting electrodes optimized for sensitivity, while areas more exposed to external noise have shielding electrodes optimized for noise rejection. This local differentiation allows simultaneous optimization of both detection sensitivity and noise immunity.
2Object-affected harmful factors
If shielding voltage is applied to shielding electrodes to equalize potential with detecting electrodes, then capacitance variation from external noise is reduced, but calibration is required when usage environment changes
Solution Approach 1:
The sensor system performs self-calibration by automatically detecting the holding state of the portable apparatus and adjusting the reference value accordingly. The system monitors capacitance variations and identifies when calibration is needed, then performs calibration without user intervention, making the system self-adapting to different usage environments.
Solution Approach 2:
The system continuously monitors output signals from detecting electrodes and uses this feedback to detect changes in usage environment. When calibration is detected to be necessary, the system automatically adjusts the reference value based on the monitored capacitance variations, creating a closed-loop calibration system that adapts to environmental changes.
3Object-affected harmful factors
If multiple electrode types are used to reduce external noise, then noise reduction performance is improved, but device complexity increases
Solution Approach 1:
Multiple electrode types (detecting electrodes and shielding electrodes) are merged into a single integrated sensor structure. The first and second detecting electrodes along with first and second shielding electrodes are arranged in a unified configuration where shielding electrodes surround detecting electrodes, combining multiple functions into one compact structure that reduces external noise without proportionally increasing complexity.
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 configuration effectively reduces external noise interference and enhances detection sensitivity, enabling precise detection of object position and movement, even when used in portable devices.
Implementation Method 1
capacitance is formed between adjacent electrodes
Implementation Method 2
capacitances Ca and Cb formed between the detecting electrodes and a ground potential
Data Source
AI summary
A capacitance-type proximity sensor device includes internal electrodes that are arranged such that capacitance is formed therebetween, external electrodes that are arranged in the outer circumference of the internal electrodes, a driving circuit that outputs a driving voltage, a detecting circuit that detects an output signal, a multiplexer that connects an electrode serving as a driving electrode to the driving circuit, connects an electrode serving as a detecting electrode to the detecting circuit, and connects an electrode serving as a shielding electrode to the ground, and a CPU that calculates the position of an object to be detected. When the object to be detected is detected, the multiplexer changes the internal electrodes and the external electrodes to the detecting electrodes, the driving electrodes, and the shielding electrodes.