Multi-Frequency Projection Scan for Passive Stylus Detection
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Solution Overview
Problem
Current touch-sensitive surfaces face challenges in accurately detecting non-linear passive input devices, such as styluses, due to their inability to differentiate between the device and other conductive objects without internal power supplies, leading to interference and inaccurate location determination.
Innovation Solution
The implementation of a touch-sensitive surface that uses a non-linear passive input device with a diode component, which produces frequency content at higher harmonics of the drive signal, allowing for precise location determination by sensing the frequency content and reversing the drive and sense electrodes to determine absolute and relative positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-frequency projection scan is used to detect conductive objects, then the detection process is simple, but non-linear passive input devices cannot be differentiated from other conductive objects leading to inaccurate location determination
Solution Approach 1:
The system dynamically switches between multiple drive frequencies (first and second frequencies) during the detection process. By varying the frequency dynamically rather than using a fixed single frequency, the system can differentiate non-linear passive input devices from other conductive objects, thereby improving location determination accuracy without requiring permanent structural complexity
Solution Approach 2:
The system changes the electrical parameter (frequency) of the drive signal to improve detection accuracy. By using multiple frequencies and analyzing the response at different frequency points, the system can identify non-linear passive input devices based on their frequency-dependent capacitive coupling characteristics, resolving the contradiction between measurement precision and device complexity
2Measurement precision
If multi-frequency projection scan is implemented to differentiate non-linear passive input devices, then location precision is improved, but the detection process becomes more complex
Solution Approach 1:
The detection process is segmented into distinct phases: first frequency drive and detection, second frequency drive and detection, and comparative analysis. By dividing the complex multi-frequency detection into sequential simpler steps, the system achieves high location precision while managing detection complexity through structured process segmentation
Solution Approach 2:
The system uses feedback by comparing the response at the first frequency with the response at the second frequency. This feedback mechanism allows the system to automatically differentiate non-linear passive input devices from other conductive objects based on their differential frequency response, improving location precision while using an automated rather than manually complex process
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 enables accurate detection and differentiation of non-linear passive styluses from other conductive objects, improving location precision and reducing noise interference, thereby enhancing the accuracy of touch input recognition.
Implementation Method 1
the non-linear passive input device can produce a non-linear output that includes frequency content at the second and other higher harmonics of the fundamental frequency of the drive signal
Implementation Method 2
The passive stylus can include one or more conductive components that can capacitively couple to an electrode of the touch screen to produce or modify a signal sensed by the electronic device
Data Source
AI summary
In some examples, an input device includes a non-linear component, such as a diode. In response to a drive signal, such as a sinusoidal wave, the non-linear passive input device can produce a non-linear output that includes frequency content at the second and other higher harmonics of the fundamental frequency of the drive signal, for example. In some examples, drive electrodes can be driven with a drive signal having one of two fundamental frequencies such that the frequency of the drive signals are applied in an alternating pattern. The electronic device can sense the signal of the stylus to determine the coarse location of the stylus along the sense electrodes and, based on the frequency content of the received signal, a fine location along the axis of the drive electrodes.