Adaptive Stylus Detection Thresholds for Touch Panels
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Solution Overview
Problem
Existing touch screen systems with active styluses face inaccuracies in detecting stylus contact and lift-off due to fixed make and break thresholds, leading to issues like 'hooking' and missed detections, which affect user experience and input accuracy.
Innovation Solution
The implementation of adaptive make and break threshold detection using filtered signal averages and a state machine to dynamically adjust thresholds based on stylus signal variations, tilt angle, and stability scores, allowing for independent adaptation of make and break thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed make and break thresholds are used for stylus contact detection, then the detection system is simple and fast, but detection accuracy deteriorates due to hooking and missed detections
Solution Approach 1:
The patent implements dynamic threshold adaptation where make and break thresholds are no longer fixed values but are continuously adjusted based on filtered signal averages. The system maintains slow and fast exponential moving averages of the touch signal and adapts thresholds based on the relationship between current signal, slow average, and fast average, allowing the detection system to respond to varying touch conditions while maintaining accuracy
Solution Approach 2:
The system incorporates feedback mechanisms by continuously monitoring the touch signal and using filtered versions (slow and fast averages) to adjust detection thresholds. The make threshold is adapted when the signal is between slow threshold and slow average, while the break threshold is adapted when signal is between fast threshold and fast average, creating a self-regulating detection system that improves accuracy without requiring external calibration
2Measurement precision
If adaptive threshold detection is implemented, then detection accuracy improves, but computational complexity and processing time increase
Solution Approach 1:
The system performs preliminary filtering of the touch signal by maintaining slow and fast exponential moving averages in parallel with the detection process. These filtered values are pre-computed and ready for threshold comparison, eliminating the need for complex real-time filtering during the actual make/break detection moment, thus reducing processing latency
Solution Approach 2:
The patent changes the temporal parameters of signal processing by using exponentially weighted moving averages with different time constants (slow and fast). This allows the system to capture both short-term and long-term signal trends without requiring extensive historical data or complex computational algorithms, achieving adaptive detection with minimal processing overhead
3Reliability
If independent make and break threshold adaptation is used, then detection reliability improves, but system complexity increases
Solution Approach 1:
The patent segments the threshold adaptation process into distinct make and break components, each with its own threshold and adaptation logic. The make threshold is independently adapted when the signal rises above the slow threshold, while the break threshold is independently adapted when the signal falls below the fast threshold. This segmentation allows each threshold to be optimized for its specific detection purpose without interfering with the other
Solution Approach 2:
The system introduces slow and fast filtered signal averages as intermediary values that mediate between the raw touch signal and the threshold comparison. These intermediaries smooth out signal noise and provide stable reference points for threshold adaptation, reducing the complexity of direct signal-threshold comparison while improving detection reliability
Data Source
AI summary
In one aspect, the present disclosure relates to a method and system for performing an adaptive make/break detection technique including adapting make and break thresholds based on the sum of all signals measured on display electrodes when the sum is lower than a respective filtered sum value. The filtered sum values are produced by a fast and slow filter, which correspond to the break and make thresholds respectively. By performing this method, the accuracy of detecting stylus touch-down and lift-off from a display can be improved, even in the presence of confounding factors such as variation in stylus manufacture, user grip, stylus angle, and water on the display.