Capacitive Proximity Sensing With Nonlinear Filtering for SAR Control
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Solution Overview
Problem
Capacitive proximity detectors in portable devices struggle to accurately distinguish between human body proximity and inanimate objects, leading to potential misinterpretation and inefficient power management, particularly in maintaining Specific Absorption Rate (SAR) limits.
Innovation Solution
A capacitive proximity detection method that employs a nonlinear filtering algorithm and baseline estimation to differentiate between human body and inanimate object proximity, using a discriminator unit to generate binary or multi-bit proximity values, and adjusts RF power levels accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive proximity detector is used to detect human body proximity, then the device can detect proximity to conductive objects, but it cannot accurately distinguish between human body and inanimate objects
Solution Approach 1:
The patent segments the proximity detection function into two independent measurement channels: a first capacitive sensor dedicated to detecting human body proximity and a second capacitive sensor dedicated to detecting inanimate object proximity. This segmentation allows each sensor to be optimized for its specific detection target, resolving the contradiction by providing both accurate detection and discrimination capability through separate measurement paths.
2Reliability
If the device reduces RF power to maintain SAR limits, then compliance with safety standards is achieved, but power management efficiency decreases
Solution Approach 1:
The patent implements dynamic RF power adjustment based on real-time proximity detection results. The RF power level is adaptively modified according to the detected proximity status, allowing the system to maintain SAR compliance when needed while maximizing power efficiency when proximity conditions permit. This dynamic approach resolves the contradiction by making power management flexible rather than static.
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 method effectively reduces noise fluctuations and improves sensitivity to small distance changes, enhancing the accuracy of proximity detection and ensuring compliant RF power levels, thereby maintaining efficient SAR management.
Implementation Method 1
Capacitive proximity detectors are used in many modern portable devices, including mobile phones and tablets, to determine whether the device is close to a body part of a user. Known capacitive sensing systems measure the capacity of an electrode and, when the device is placed in proximity of the human body (for example the hand, the head, or the lap) detect an increase in capacity.
Data Source
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AI summary
A sensor for a portable connected device comprising a filter 30 is arranged to reduce a noise component on a sampled input signal, wherein the filter is arranged to consider only input measurements that change systematically in a same direction, updating an output value when all the input samples in a predetermined time window are above or below a current output value and, repeating the current output value when the input samples in the time window are below and above the current output value.