Capacitive Proximity Detection With Environmental Drift Cancellation
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Solution Overview
Problem
Current proximity and touch detection in mobile devices is inaccurate due to environmental capacitance changes and the challenge of calibrating capacitive touch sensors to ignore environmental factors while detecting human presence, leading to potential health risks from excessive RF radiation due to inadequate power control.
Innovation Solution
A capacitive touch controller with a sensing element and shielding areas that cancel environmental capacitance, allowing for precise detection of human proximity by measuring self-capacitance changes, and adjusting RF power output to comply with safety regulations by using a configurable capacitor bank and temperature compensation to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive touch sensors are used for proximity detection, then touch functionality is enabled, but environmental capacitance changes cause detection inaccuracy
Solution Approach 1:
A dedicated sensing element is introduced as an intermediary component specifically for proximity detection, separate from the touch sensor electrodes. This sensing element works with a capacitive touch controller to measure self-capacitance changes caused by proximity, while the touch electrodes continue to handle touch input. The shielding areas act as additional intermediaries to block environmental capacitance interference from affecting the measurement.
Solution Approach 2:
The proximity detection function is extracted from the general touch sensor system by using a dedicated sensing element and capacitive touch controller. This separation allows the touch electrodes to focus on touch detection while the sensing element handles proximity measurement, with environmental capacitance being excluded through shielding areas and selective measurement of self-capacitance changes.
2Power
If RF power is increased to maintain connectivity, then signal strength improves, but excessive RF radiation may be absorbed by the human body causing health risks
Solution Approach 1:
A feedback mechanism is implemented where the capacitive touch controller continuously monitors self-capacitance changes of the sensing element. When a change indicating human proximity is detected, the system automatically reduces RF power output to prevent excessive radiation absorption. When no proximity is detected, normal RF power levels are maintained for optimal connectivity.
3Measurement precision
If calibration is performed to ignore environmental capacitance, then detection accuracy improves, but calibration may be performed with body parts in proximity leading to incorrect baseline
Solution Approach 1:
The system performs preliminary actions by continuously monitoring self-capacitance changes and maintaining an accurate baseline of environmental capacitance. Before performing calibration or making detection decisions, the system ensures the baseline is established without body part interference, and can recalculate the baseline at any time to maintain accuracy.
4Measurement precision
If shielding areas are added to cancel environmental capacitance, then proximity detection accuracy improves, but device complexity increases
Solution Approach 1:
The shielding areas are merged with the existing sensor structure, and the proximity sensing function is merged with the capacitive touch controller that already exists in the device. This integration approach minimizes additional complexity while achieving accurate environmental capacitance cancellation and proximity detection.
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
Enhances the accuracy of proximity detection, reducing RF power when near the body to prevent excessive absorption and maintaining connectivity by accurately distinguishing human presence from environmental factors, thus ensuring compliance with safety standards.
Implementation Method 1
measuring self-capacitance changes
Implementation Method 2
cancel environmental capacitance
Data Source
Figure 1a~1b
Figure 1c~2c
Figure 3a~3b
AI summary
A mobile device has a proximity sensor. A compensation value of the proximity sensor is determined. The compensation value is compared to a reference compensation value to determine validity of the compensation value. A capacitance of the proximity sensor is measured. A value of the capacitance of the proximity sensor is adjusted based on the compensation value. A coefficient defining a relationship between a capacitance of the proximity sensor and a temperature of the mobile device is calculated. A temperature sensor is coupled to the proximity sensor. The temperature of the mobile device is measured. A value of the capacitance of the proximity sensor is adjusted based on the coefficient and the temperature of the mobile device. The adjusted capacitance value is compared to a threshold capacitance value to determine proximity of an object to the mobile device. A radio frequency signal is adjusted by detecting proximity.