Touch Display Signal Discrimination via Frequency Multiplexing
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Solution Overview
Problem
Current touch-sensitive devices face challenges in detecting hover and pressure events with low latency and high accuracy, particularly in systems that require non-contact interactions and simultaneous multi-touch inputs, leading to inefficiencies in user interface responsiveness and interaction complexity.
Innovation Solution
The implementation of capacitive-based sensors employing frequency-division multiplexing (FDM) and code-division multiplexing (CDM) techniques, combined with orthogonal signaling, allows for the detection of touch events, including hover and pressure, through changes in signal coupling between row and column conductors, enabling low-latency and high-update-rate measurements on transparent surfaces, and distinguishing between different touch inputs, including those from fingers and styluses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensors use traditional single-frequency signaling, then the system is simpler to implement, but it cannot distinguish between different touch inputs (finger vs. stylus) and suffers from interference when multiple touches occur simultaneously
Solution Approach 1:
The patent segments the signaling frequency spectrum into multiple distinct frequency channels, with each conductor pair operating at a unique frequency. This allows the system to differentiate between multiple simultaneous touches by analyzing signals at different frequencies, thereby improving measurement precision without requiring complex spatial segmentation of the touch surface.
Solution Approach 2:
The patent changes the frequency parameter of the signaling system, transitioning from single-frequency to multi-frequency operation. By modulating signals at distinct frequencies on different conductor pairs and using orthogonal signaling, the system can distinguish between finger touches and stylus touches while maintaining manageable device complexity through systematic frequency assignment.
2Loss of time
If the system increases sampling rate to reduce latency, then responsiveness improves, but power consumption and processing load increase
Solution Approach 1:
The patent implements periodic scanning of conductor pairs at optimized intervals, using multiplexing techniques to systematically cycle through different frequency channels. This periodic action allows the system to maintain low latency by sampling at critical moments while reducing overall power consumption by keeping individual conductor pairs inactive between their scheduled sampling intervals, rather than continuously monitoring all channels simultaneously.
3Adaptability or versatility
If multiple conductor pairs are used to detect simultaneous touches, then multi-touch capability improves, but signal interference and crosstalk increase
Solution Approach 1:
The patent assigns distinct frequency characteristics to different conductor pairs, creating local quality differences in the signal domain. Each conductor pair operates with its own frequency signature, which prevents signal interference and crosstalk when multiple touches occur simultaneously on different parts of the touch surface, as each location's signal can be independently identified by its frequency characteristic.
Solution Approach 2:
The patent uses orthogonal signaling where each conductor pair transmits a unique frequency copy of the base signal. This copying approach with frequency multiplication allows multiple simultaneous measurements without interference, as the receiver can separately decode each frequency copy to identify touches at different locations, thereby improving multi-touch capability while eliminating signal conflict.
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 seamless and simultaneous interaction with touch screens, maintaining high frame rates and allowing for precise measurement of touch location, pressure, and distance, even without physical contact, thereby enhancing user interface responsiveness and interaction complexity.
Implementation Method 1
capacitive-based sensors employing frequency-division multiplexing (FDM) and code-division multiplexing (CDM) techniques, combined with orthogonal signaling, allows for the detection of touch events, including hover and pressure, through changes in signal coupling between row and column conductors
Data Source
AI summary
A touch display has conductors that are able to determine measurements of signals received due to touch events with a user's hand. The touch display is also able to determine measurements of signals received due to interaction with a stylus. Additionally the touch display is able to discriminate interactions between the hand holding the stylus and the free hand. Interactions with the touch display between all three may be measured and discriminated simultaneously.