Capacitive Touch Noise Reduction via Axis Scanning
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Solution Overview
Problem
Touch-sensor devices face inaccuracies in position determination due to common-mode noise from charger and display components, leading to degraded accuracy and potential phantom touches.
Innovation Solution
Implementing a processing device with multiple receive channels to scan electrodes along axes in time slots, using equations like centroid or linear interpolation to remove noise and determine accurate touch coordinates, effectively mitigating the effects of charger and display noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance sensing methods are used to detect touch position, then the touch-sensor device can detect changes in capacitance, but common-mode noise from charger and display components degrades position determination accuracy
Solution Approach 1:
The patent segments the capacitance measurement into two independent components by scanning electrodes along different axes separately. By dividing the measurement process into X-axis scanning and Y-axis scanning with distinct signal paths, the common-mode noise affecting both measurements equally can be identified and removed, thereby improving position determination accuracy
Solution Approach 2:
The patent implements a feedback mechanism where the measured capacitance values from orthogonal electrode scans are processed to identify and eliminate common-mode noise components. The system uses the relationship between X and Y axis measurements to calculate and remove the noise feedback, resulting in corrected capacitance values that improve touch position accuracy
2Measurement precision
If multiple receive channels are used to scan electrodes along axes in time slots with equations like centroid or linear interpolation to remove noise, then accurate touch coordinates can be determined, but the device complexity increases
Solution Approach 1:
The patent employs periodic scanning of electrodes along different axes in alternating time slots. This periodic measurement approach allows the system to collect data from multiple receive channels at different times, process the data through noise removal equations, and reconstruct accurate touch coordinates while managing processing complexity through time-division multiplexing
Solution Approach 2:
The patent performs preliminary scanning and measurement of electrode capacitances along orthogonal axes before final touch coordinate calculation. By pre-collecting data from multiple receive channels and performing initial noise characterization, the system reduces the complexity of the final coordinate determination while maintaining high accuracy
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 approach allows for precise determination of touch location even in the presence of common-mode noise, enhancing the accuracy and reliability of touch-sensor devices.
Implementation Method 1
A touch-sensor device usually is in the form of a touch-sensor pad, a touch-sensor slider, or touch-sensor buttons, and includes an array of one or more capacitive sense elements. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the touch sensor.
Implementation Method 2
A change in capacitance of each sense element in the X and Y axes of the touch sense array can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance of the capacitive sense elements is measured and processed by a processing device
Data Source
AI summary
A processing device performs a first scan of a first plurality of electrodes along a first axis in a capacitive sense array to generate a first plurality of capacitance values corresponding to a mutual capacitance at electrode intersections of the capacitive sense array. The processing device performs a second scan of a second plurality of electrodes along a second axis in the capacitive sense array to generate a second plurality of capacitance values corresponding to the mutual capacitance at the electrode intersections of the capacitive sense array. The processing device determines a first coordinate of a conductive object proximate to the capacitive sense array based on the a first subset of first plurality of signals and a second coordinate of the conductive object based on a second subset of the second plurality of signals.