Active Stylus Differential Synchronization Waveforms
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Solution Overview
Problem
Touch sensors face challenges in maintaining synchronization performance due to significant increases in capacitance when a user's body comes into contact with the electrode matrix, which can degrade current flow into the stylus tip, reducing synchronization accuracy.
Innovation Solution
Differential driving of sync-driven electrodes within stylus sync sub-frames using different synchronization waveforms to reduce current flow into the user's body, employing sets of electrodes with varying waveforms to create cancelling electrical conditions, thereby minimizing interference and maintaining strong synchronization signals for the stylus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple electrodes are driven simultaneously with a synchronization waveform, then synchronization signal strength is improved, but current flow into the user's body increases, degrading synchronization accuracy
Solution Approach 1:
The patent applies local quality by assigning different synchronization waveforms to different subsets of electrodes based on their spatial locations. Specifically, electrodes are divided into groups (e.g., first set and second set) with different waveform characteristics applied to each group. This localized differentiation allows the system to maintain strong synchronization signals at the stylus tip while reducing capacitive coupling effects that cause current flow into the user's body, thereby resolving the contradiction between signal strength and harmful current flow.
Solution Approach 2:
The patent segments the electrode matrix into multiple subsets that are driven with different synchronization waveforms. By dividing the electrodes into distinct groups (such as row-based or column-based subsets) and applying different waveforms to each subset, the system can optimize the synchronization signal delivery while minimizing the overall capacitive coupling to the user's body. This segmentation strategy enables the system to achieve both strong stylus synchronization and reduced harmful current flow.
2Reliability
If synchronization waveforms are applied to all electrodes, then synchronization signal coverage is improved, but capacitance interference from body contact increases, reducing current flow to stylus tip
Solution Approach 1:
The patent implements local quality by applying different synchronization waveforms to different electrode subsets based on their spatial distribution. This localized waveform differentiation creates regions of constructive and destructive interference that can be optimized to direct current flow preferentially toward the stylus tip while canceling out capacitive coupling paths to the user's body. The result is maintained synchronization performance with improved current delivery to the stylus.
Solution Approach 2:
The patent converts the harmful effect of body contact capacitance into a beneficial by using differential waveform driving to create cancelling electrical conditions. By strategically applying waveforms with different phases and amplitudes to different electrode subsets, the system creates destructive interference patterns that cancel current flow into the body while maintaining constructive interference that delivers strong signals to the stylus tip. This transforms the body contact from a harmful interference source into a manageable condition that can be compensated for through waveform design.
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 effectively reduces current flow into the user's body, ensuring robust synchronization performance even with body contact, enhancing the accuracy and reliability of stylus position determination.
Implementation Method 1
Some touch sensors are configured to detect touch input by sensing changes in capacitance at electrode locations in an electrode matrix
Implementation Method 2
Via capacitive coupling, this causes current to flow into a tip electrode of the stylus
Implementation Method 3
The synchronization waveform is communicated electrostatically to an active stylus to synchronize the active stylus and the touch sensor
Data Source
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AI summary
A touch-sensing system is disclosed. The system includes a display device including a touch sensor having a plurality of electrodes, and drive logic coupled to the plurality of electrodes and configured to drive the plurality of electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame during which the drive logic drives at least some of the plurality of electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms that are communicated electrostatically to cause synchronization of the display device with an active stylus. For each of the stylus sync sub-frames, the drive logic may be configured to differentially drive the sync-driven electrodes of such stylus sync sub-frame, such that a first synchronization waveform used to drive one of the sync-driven electrodes is different than a second synchronization waveform used to drive another of the sync-driven electrodes.