Touch Screen Controller Hover Rejection via Dynamic Thresholding
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Solution Overview
Problem
Current touch screen devices face challenges in accurately distinguishing between hover and touch inputs, particularly with passive styluses having small tips, due to the small size of the tip which complicates capacitance measurement.
Innovation Solution
A touch screen controller calculates the variance and sharpness of touch data islands by applying different weights to nodes, determining an island strength threshold as a product of variance and normalized sharpness to differentiate between touch and hover inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance measurement is used to detect touch inputs, then the touch screen can detect finger touches, but it cannot accurately distinguish between hover and touch inputs when using passive styluses with small tips
Solution Approach 1:
The patent segments the touch data matrix into multiple candidate islands, where each island represents a potential touch or hover region. By dividing the detection space into discrete islands and analyzing their individual characteristics (variance, sharpness, strength), the system can precisely differentiate between hover and touch states without requiring complex overall analysis of the entire touch screen surface.
Solution Approach 2:
The patent implements dynamic thresholding where the hover detection threshold is not fixed but adapts based on the calculated variance and sharpness of each candidate island. The threshold is dynamically adjusted according to the specific characteristics of each detected island, allowing the system to accurately distinguish hover from touch across varying conditions and stylus types, thereby improving measurement precision.
2Measurement precision
If the tip size of the passive stylus is reduced to improve precision, then positioning accuracy improves, but the capacitance signal becomes too weak to reliably distinguish between hover and touch
Solution Approach 1:
The patent changes the parameters used for detection from relying solely on absolute capacitance magnitude to using derived parameters such as variance and sharpness. By transforming the detection basis from raw capacitance values to these calculated parameters, the system can reliably detect even the weak signals produced by fine-tipped styluses, maintaining both positioning accuracy and signal detection reliability.
Solution Approach 2:
The patent moves the detection problem from a one-dimensional threshold comparison to a multi-dimensional analysis by incorporating variance and sharpness calculations. This dimensional expansion allows the system to extract more information from the same capacitance data, enabling reliable differentiation between hover and touch even when the absolute signal strength is very weak, thus improving reliability without sacrificing precision.
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 enhances the precision and accuracy of touch detection by effectively distinguishing between touch and hover inputs, improving the performance of touch screen devices.
Implementation Method 1
The capacitance between the sensing lines and the driven drive line is sensed at the point where they intersect. Presence of a human finger or a conductive object such as a passive stylus alters the expected capacitance at the intersection point, and by measuring the change in capacitance, a touch between the finger or conductive object and the touch sensitive display can be detected.
Data Source
AI summary
Disclosed herein is a touch screen controller that calculates a variance of an island in acquired touch data values. Where the variance exceeds a variance threshold, the island is validated as a representing touch. Where the variance does not exceed the variance threshold, whether the island represents a touch or a hover is determined by calculating a sharpness by applying weights to nodes of the island, where neighboring nodes adjacent to a peak node are weighted less than non-neighboring nodes not adjacent to the peak node. An island strength threshold is determined as a function of a product of the variance and the sharpness. It is determined that the island represents a touch where a highest touch data value of the island is greater than the island strength threshold, and a hover where the highest touch data value of the island is less than the island strength threshold.