Capacitive Sensor Dynamic Filter Adjustment for S/N Ratio
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Solution Overview
Problem
Existing capacitive sensors face challenges in maintaining a high signal-to-noise ratio (S/N ratio) while balancing responsiveness, leading to false operation ratios when detecting distant objects and delayed responses when objects are close, due to the trade-offs inherent in digital lowpass filtering and time-directional filtering processes.
Innovation Solution
A capacitive sensor system that dynamically adjusts its filter characteristics based on the difference value between detected capacitance and a reference value, using a filter parameter calculation unit to adjust the cutoff frequency of the digital lowpass filter, thereby optimizing S/N ratio and responsiveness by changing the filter parameter α in response to changing proximity of the detection target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed cutoff frequency is used in digital lowpass filtering, then the S/N ratio can be improved by increasing filter strength, but the responsiveness deteriorates
Solution Approach 1:
The patent applies dynamics by making the filter characteristics adjustable rather than fixed. The control unit dynamically changes the filter parameters (cutoff frequency or filter coefficient) based on the detected capacitance value, allowing the system to adapt between strong filtering for distant objects and weak filtering for close objects, thus resolving the trade-off between S/N ratio and responsiveness
Solution Approach 2:
The patent implements parameter changes by modifying the filter characteristics (cutoff frequency or coefficient) according to the detection distance. When the object is distant, the filter strength is increased to improve S/N ratio; when the object is close, the filter strength is decreased to maintain responsiveness, thereby eliminating the need to sacrifice one parameter for the other
2Ease of operation
If a fixed threshold value is used for touch detection, then light touch operation is enabled with low noise, but false operation occurs with high noise
Solution Approach 1:
The patent applies dynamics by making the threshold value variable rather than fixed. The control unit dynamically adjusts the threshold based on the detected capacitance value, which reflects the detection distance. This allows the system to use lower thresholds for light touch operations when objects are close and higher thresholds to prevent false operations when objects are distant and noise is higher
Solution Approach 2:
The patent implements parameter changes by modifying the threshold value according to the detection conditions. When the capacitance value indicates a distant object, the threshold is increased to reduce false operations; when the capacitance value indicates a close object, the threshold is decreased to enable light touch operation, thus resolving the contradiction between ease of operation and reliability
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 system reduces false operation ratios when detecting distant objects and maintains responsiveness when objects are close by dynamically adjusting the filter strength, improving the accuracy of touch, hover, and non-proximity mode determinations.
Implementation Method 1
the detection principle for a capacitive sensor is mainly used in touch input devices... the capacitive sensor is essentially a sensor that detects a value in accordance with the capacitance between the sensor and the GND (the human body)
Data Source
AI summary
A capacitive sensor includes a sensor unit including a detection electrode, a capacitance detection unit configured to detect a capacitance value of the detection electrode of the sensor unit, a difference value calculation unit configured to calculate a difference value between the capacitance value and a reference value, a filter calculation unit configured to perform a time-directional filtering process using a filter parameter on the difference value and calculate a filter calculation value, a determination unit configured to determine a condition around the sensor unit on the basis of the filter calculation value calculated by the filter calculation unit, and a filter parameter calculation unit configured to calculate the filter parameter on the basis of the difference value calculated by the difference value calculation unit.