Active Stylus Signal Detection via Cross-Correlation
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Solution Overview
Problem
Current touch sensors and active styluses face challenges in accurately detecting and processing touch or proximity inputs due to noise and interference in signal transmission, which affects the precision and reliability of interactions with touch-sensitive devices.
Innovation Solution
The implementation of a capacitive touch sensing system with an active stylus that uses a predefined code sequence and cross-correlation signal processing to enhance signal transmission and detection, allowing for precise identification of touch inputs and improved interaction with touch-sensitive devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitive touch sensing is used, then the system is simple and energy-efficient, but noise and interference reduce detection accuracy
Solution Approach 1:
The system transmits a known predefined code sequence (training sequence) before the actual data transmission. This preliminary action allows the receiver to establish a reference signal pattern and perform cross-correlation processing, which enhances the signal-to-noise ratio and enables accurate detection of subsequent touch inputs even in noisy environments.
Solution Approach 2:
Cross-correlation signal processing acts as an intermediary mechanism between the transmitted signal and the detected touch input. By comparing the received signal with the known predefined code sequence, the system filters out noise and interference, extracting the genuine touch signal with high precision.
2Measurement precision
If signal processing complexity is increased to reduce noise, then detection accuracy improves, but processing time and computational resources increase
Solution Approach 1:
The predefined code sequence is designed with specific properties (such as auto-correlation characteristics) that enable rapid cross-correlation processing. This preliminary structuring of the signal allows the system to perform noise filtering and signal detection efficiently, achieving high accuracy without excessive processing time.
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 significantly reduces noise interference and enhances the accuracy of touch input detection, enabling reliable and precise interactions with touch-sensitive devices by using cross-correlation signal processing to filter out noise and accurately decode touch signals.
Implementation Method 1
When an object touches or comes within proximity of the surface of the capacitive touch screen, a change in capacitance may occur within the touch screen at the location of the touch or proximity.
Implementation Method 2
In one embodiment, the electrodes are electrically coupled to a capacitor. In another embodiment, the electrodes are capacitively coupled to a transmit electrode of the touch sensor.
Data Source
AI summary
In certain embodiments, a method includes wirelessly receiving, by an electrode of a stylus, a signal sent from a touch sensor of a computing device. The received signal includes a data bit and is based on a predefined code sequence. The method also includes producing, by the electrode of the stylus, a derivative signal from the received signal, the derivative signal corresponding to a derivative with respect to time of the received signal. The method further includes performing, by the stylus, a cross-correlation of the derivative signal and an expected-signal pattern, the expected-signal pattern based on a derivative with respect to time of the predefined code sequence, where the cross-correlation produces a cross-correlation signal including one or more cross-correlation pulses. The method also includes determining, by the stylus, based on the cross-correlation signal, that the received signal is associated with the predefined code sequence.