Touch Panel Multi-Phase Switching for EMI Reduction
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Solution Overview
Problem
Existing capacitance-sensing devices in touch panels, particularly those with large screen sizes, face challenges in minimizing electromagnetic emissions and increasing electromagnetic immunity, as conventional techniques like frequency spreading and sine-wave excitation either limit sensing frequency ranges or increase power consumption and do not effectively reduce emissions.
Innovation Solution
Implementing a multi-phase switching pattern in capacitance-sensing circuitry that differentially drives adjacent electrodes with sinusoidal wave signals, synchronized to minimize electromagnetic interference (EMI) by aligning phase switches and reducing glitches during signal transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional frequency spreading or sine-wave excitation is used, then electromagnetic emissions are reduced, but sensing frequency range is limited or power consumption increases
Solution Approach 1:
The patent segments the electrode driving into multiple phases, where different subsets of electrodes are driven in different phases. This allows the system to maintain reduced electromagnetic emissions through controlled phase switching while expanding the sensing frequency range by selectively activating different electrode groups at different frequencies.
Solution Approach 2:
The patent dynamically switches between different transmission patterns and phases during operation. The system can adaptively change which electrodes are active and in what phase configuration, allowing it to optimize between emission reduction and frequency range expansion based on operational requirements.
2Object-generated harmful factors
If conventional frequency spreading or sine-wave excitation is used, then electromagnetic emissions are reduced, but power consumption increases
Solution Approach 1:
The patent applies partial action by activating only specific subsets of electrodes in certain phases rather than all electrodes continuously. This reduces the overall power consumption while maintaining effective electromagnetic emission reduction, as not all sensor elements need to be actively driven at full power simultaneously.
Solution Approach 2:
The patent employs periodic switching between different transmission patterns and phases. By cycling through different electrode activation patterns periodically, the system reduces average power consumption while maintaining effective electromagnetic emission control through the periodic nature of the phase switching.
3Object-generated harmful factors
If multi-phase switching pattern is implemented, then electromagnetic interference is reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different phase characteristics to different electrode groups or regions. Each phase configuration is optimized for specific local requirements, allowing electromagnetic interference reduction through localized phase control rather than requiring complex global switching for the entire electrode array.
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 electromagnetic interference by up to 15 times and minimizes power consumption while maintaining signal-to-noise ratio, effectively addressing the limitations of conventional methods.
Implementation Method 1
When a conductive object, such as a finger, comes in contact or close proximity with the touch-sensing surface, the capacitance of one or more capacitive touch sensor elements changes. An electrical circuit can measure the capacitance changes of the capacitive touch sensor elements.
Implementation Method 2
Generating, by a sinusoidal wave generator, an in-phase drive signal and an opposite-phase drive signal to excite transmission (TX) electrodes of a touch panel... applying, responsive to receipt of the logical output, a multi-phase switching pattern to sets of switches coupled between the in-phase and opposite-phase drive signals and the TX electrodes
Data Source
AI summary
An apparatus includes a sinusoidal wave generator that generates, over a first analog line, an in-phase drive signal and, over a second analog line, an opposite-phase drive signal. A comparator has inputs respectively coupled to the first analog line and the second analog line and asserts a first output in response to detecting a crossing between the in-phase drive signal and the opposite-phase drive signal. Multi-phase switching logic is coupled to an output of the comparator. The multi-phase switching logic asserts a second output in response to both detecting the first output and receiving a signal indicative of a phase switch of the sinusoidal wave generator. The second output controls timing of applying a multi-phase switching pattern to sets of switches coupled between the first analog line and the second analog line and transmission (TX) electrodes of a touch panel.