Capacitive Touch Signal Compensation for Mechanical Deflection
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Solution Overview
Problem
Single-layer capacitive touch input devices are susceptible to background interference due to stray capacitance and mechanical deflection, which increases manufacturing costs and reduces accuracy in determining touch location.
Innovation Solution
Compensating for undesired signals by measuring output signals from electrodes separated from the point of contact and estimating the amount of background capacitance due to mechanical deflection, allowing for more accurate determination of touch location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single electrode layer is used to reduce manufacturing cost, then manufacturing cost decreases, but susceptibility to background interference increases
Solution Approach 1:
The patent measures the background interference signal itself (stray capacitance and mechanical deflection effects) and uses this measurement to compensate for the interference. By converting the harmful background signal into useful information about the interference level, the system can subtract this from the total measurement to obtain accurate touch location data while maintaining single-layer simplicity
Solution Approach 2:
The system implements a feedback mechanism where output signals from electrodes separated from the contact point are measured to determine the background interference level. This feedback information is then used to compensate the touch location calculation, creating a closed-loop system that continuously corrects for interference effects
2Object-affected harmful factors
If the dielectric layer thickness is increased to reduce stray capacitance, then stray capacitance decreases, but manufacturing complexity increases
Solution Approach 1:
Rather than changing the physical parameter of dielectric layer thickness, the patent changes the signal processing parameter by measuring and compensating for stray capacitance effects mathematically. This approach achieves the same goal of reducing stray capacitance impact without modifying the physical structure or increasing manufacturing complexity
3Ease of manufacture
If cost-saving measures are taken to leave an air gap and eliminate ground planes, then manufacturing cost decreases, but mechanical deflection susceptibility increases
Solution Approach 1:
The patent measures the mechanical deflection signal directly from the electrode outputs and converts this harmful effect into useful information. By measuring the background signal that includes mechanical deflection effects at electrodes separated from the contact point, the system can compensate for these effects and achieve accurate touch detection without requiring expensive ground planes or rigid structures
Solution Approach 2:
The patent uses electrodes separated from the contact point as intermediary elements to measure the background interference signal. These intermediary electrodes provide information about the mechanical deflection and stray capacitance effects, which then serves as a mediator to compensate the main touch measurement and achieve accurate location detection
4Measurement precision
If electrodes are placed close together to improve resolution, then measurement precision increases, but susceptibility to mechanical deflection increases
Solution Approach 1:
The system uses a feedback mechanism where measurements from electrodes separated from the contact point provide information about mechanical deflection levels. This feedback is used to compensate the measurements from closely-spaced electrodes, allowing high resolution while correcting for the increased susceptibility to mechanical deflection
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
Improves the accuracy of touch location detection in single-layer capacitive touch devices by effectively mitigating the effects of background interference and mechanical deflection, reducing manufacturing costs while maintaining touch performance.
Implementation Method 1
capacitive touch input devices may include a touch sensitive electrode layer that enables determination of a point of contact... A group of sensing electrodes enable determining the X and Y location of the point of contact... capacitance sensing circuitry including analog-to-digital converters that measure values associated with the electrodes, such as the capacitance
Implementation Method 2
The ratio of undesired palm background signal to the desired finger touch signal increases as the thickness of the dielectric layer between electrodes and the touch surface increases
Data Source
AI summary
A location of contact with a touch sensitive device is determined. Output signals associated with a plurality of electrodes such as formed on a single layer of the touch sensitive device are measured to identify a first electrode positioned at an approximate location of contact with the touch sensor. An output signal associated with a different electrode that is separated from the first electrode is measured to determine an undesired signal amount, such as due to deflection. An undesired single amount associated with the first electrode may be estimated based on the undesired signal amount measured at the other electrode. The signal amount measured at the first electrode is then compensated by the estimated undesired signal amount. The location of contact with the touch sensor is then determined based on the compensated signal amount.