Capacitive Proximity Sensing With False Trigger Rejection
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Solution Overview
Problem
Existing proximity sensors in mobile devices are sensitive to environmental factors like temperature and humidity changes, leading to false trigger signals due to condensation of water or ice, particularly in severe conditions.
Innovation Solution
A capacitive proximity sensor system with two electrodes and a readout circuit that generates proximity signals based on capacitance variations, capable of rejecting spurious signals by analyzing time derivatives and data from other sensors to differentiate between user proximity and environmental changes, and includes directional sensitivity and decoupling circuits for RF transceivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor is used for proximity detection, then the sensor can detect body proximity effectively, but the sensor becomes sensitive to environmental factors like temperature and humidity changes causing false trigger signals
Solution Approach 1:
A reference electrode is introduced as an intermediary element that experiences the same environmental conditions (temperature, humidity, condensation) as the detection electrode but does not detect body proximity. The reference electrode's capacitance variations serve as a mediator to compensate for environmental effects on the detection electrode, allowing the system to distinguish between environmental noise and genuine proximity signals.
Solution Approach 2:
The system dynamically changes the parameter being measured by comparing capacitance values between the detection electrode and reference electrode. Instead of relying on absolute capacitance values which are sensitive to environmental changes, the system uses differential capacitance measurements and time-derivative analysis to detect changes in proximity conditions while filtering out environmental parameter variations.
2Productivity
If the sensor responds to all capacitance variations, then it can detect all proximity events, but it also triggers on spurious signals from environmental changes like condensation
Solution Approach 1:
The system performs preliminary analysis of capacitance variations by calculating time derivatives and comparing patterns before generating a proximity trigger. Environmental changes like condensation typically produce slow, monotonic capacitance changes, while genuine proximity events produce faster, more distinct variations. This preliminary differentiation action filters spurious signals before they can trigger false positives.
Solution Approach 2:
The system uses feedback from the reference electrode and environmental sensor data to continuously adjust the threshold for proximity detection. By monitoring environmental conditions and comparing detection electrode behavior against reference electrode behavior, the system dynamically adapts its response criteria to distinguish genuine proximity events from environmental noise, reducing false positives while maintaining responsiveness.
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
Effectively reduces false triggers from environmental factors, ensuring accurate proximity detection and adaptive RF power management, while maintaining device functionality and energy efficiency.
Implementation Method 1
a first electrode capacitively couplable with a body part of a user of the portable outside of the portable device; a second electrode capacitively couplable with a body part of a user of the portable outside of the portable device
Data Source
AI summary
A capacitive proximity sensor for use in mobile devices such as smartphones and connected tables, in which it is used to switch off a display (70) when the device is brought to the ear. The capacitive sensor is arranged for rejecting spurious detection induced, for example, by condensation, ingress of water, or thermal drift, based on the time variations of a capacity seen by the readout circuit (80), Additionally, the proximity sensor may integrate signals form motion sensors, temperature sensors or other sensors, to discriminate spurious proximity signals.