Touch Panel Multi-Phase TX Switching for Low-Emission Sensing
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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 emission and enhancing electromagnetic immunity due to conventional techniques like frequency spreading and sine-wave excitation, which 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 by aligning phase switches and reducing glitches during signal transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If frequency spreading technique is used to reduce electromagnetic emissions, then electromagnetic emissions are reduced, but sensing frequency range is limited
Solution Approach 1:
The patent segments the electrode driving into multiple phases with different switching patterns. Instead of using a single frequency-spreading approach that limits the sensing range, the system divides the driving signal into multiple temporal segments (phases), each with optimized switching characteristics. This segmentation allows the system to maintain low electromagnetic emissions while preserving a wide sensing frequency range by adapting the switching pattern across different phases.
Solution Approach 2:
The patent implements dynamic switching patterns that can be adjusted across different phases of electrode driving. The switching frequency and pattern are made dynamic rather than static, allowing the system to optimize electromagnetic emission reduction at each phase while maintaining adaptability across the full sensing frequency range. This dynamic approach resolves the contradiction by making the system flexible rather than constrained to a fixed frequency-spreading method.
2Object-generated harmful factors
If sine-wave excitation is used to reduce electromagnetic emissions, then electromagnetic emissions are reduced, but power consumption increases
Solution Approach 1:
The patent employs periodic switching patterns with multiple phases instead of continuous sine-wave excitation. By using periodic square-wave signals with optimized duty cycles and multi-phase switching, the system achieves electromagnetic emission reduction comparable to sine-wave excitation but with lower power consumption. The periodic action allows the system to turn off or reduce driving strength during certain phases, thereby reducing overall power usage while maintaining emission control.
Solution Approach 2:
The patent changes key parameters of the excitation signal from sine-wave to multi-phase square-wave with adjustable duty cycles and switching frequencies. By optimizing these parameters across different phases, the system achieves the same electromagnetic emission reduction effect as sine-wave excitation but with significantly lower power consumption. The parameter changes enable the system to operate more efficiently while meeting electromagnetic emission requirements.
3Device complexity
If conventional switching patterns are used in capacitance-sensing circuitry, then circuit operation is simple, but electromagnetic interference is high
Solution Approach 1:
The patent segments the electrode driving into multiple phases with distinct switching patterns. Instead of using a single conventional switching pattern that generates high electromagnetic interference, the system divides the driving cycle into multiple temporal segments, each with optimized switching characteristics. This segmentation reduces peak electromagnetic interference while maintaining relatively simple circuit operation through systematic phase-based control.
Solution Approach 2:
The patent implements dynamic switching patterns that adapt across different phases of electrode driving. The switching frequency, duty cycle, and pattern are made dynamic rather than static, allowing the system to optimize electromagnetic interference reduction at each phase. This dynamic approach maintains circuit simplicity through systematic control while achieving significant interference reduction compared to conventional fixed patterns.
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 lowers field and voltage amplitude by 7-9 times compared to conventional methods, while maintaining effective touch detection capabilities.
Implementation Method 1
capacitance-sensing circuitry that generates, over a first analog line, an in-phase drive signal and, over a second analog line, an opposite-phase drive signal
Implementation Method 2
When a finger touches a sensor element or is in close proximity to the sensor element, the capacitive coupling between the receiver and the transmitter of the sensor element is decreased as the finger shunts part of the electric field to ground
Data Source
AI summary
An apparatus includes circuitry to detect a crossing between an in-phase drive signal, received over a first analog line, and an opposite-phase drive signal, received over a second analog line of a touch panel. Multi-phase switching asserts an output in response to both detecting the crossing and receiving a signal indicative of a phase switch between the in-phase drive signal and the opposite-phase drive signal. The output controls timing of applying a multi-phase switching pattern to sets of switches coupled between the first and the second analog lines and respective ones of transmission (TX) electrodes of the touch panel.