Capacitive Touch Panel EMI Suppression via Edge Capacitors
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Solution Overview
Problem
Existing methods for suppressing electromagnetic interference (EMI) from display devices, particularly those with capacitive touch panels, interfere with capacitive sensing functionality and fail to meet stringent aircraft emission regulations, especially in the VHF and GPS frequency ranges.
Innovation Solution
The method involves determining the capacitive impedance required to suppress EMI at specific frequencies and using capacitors to connect the capacitive touch panel's electrically conductive surface to the chassis, with capacitors formed into U-shaped strips along the panel's edges to provide the necessary capacitance, allowing higher frequencies to pass through while attenuating lower frequencies that cause regulatory failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conductive transparent sheet or coating is used to suppress electromagnetic interference through the display, then electromagnetic interference radiation is attenuated, but capacitive sensing performance is adversely impacted
Solution Approach 1:
The patent applies different electrical properties to different parts of the display system: the display area maintains transparency and capacitive sensing capability, while the peripheral border region provides EMI suppression through conductive materials connected to ground, creating localized functional zones that resolve the contradiction between EMI attenuation and touch sensing performance
Solution Approach 2:
The EMI suppression function is segmented from the display area and implemented separately through conductive borders and ground connections around the display perimeter, rather than applying a uniform conductive layer across the entire display surface, thereby preserving capacitive sensing in the display region while providing EMI suppression in the border regions
2Object-affected harmful factors
If a conductive transparent coating is applied to suppress EMI radiation, then electromagnetic interference attenuation is achieved, but touch sensitivity is degraded
Solution Approach 1:
The conductive EMI suppression materials are applied locally to the border regions surrounding the display rather than uniformly across the entire display surface, allowing the display area to maintain its capacitive touch sensitivity while the borders provide the necessary electromagnetic interference attenuation
Solution Approach 2:
Conductive border elements act as intermediary structures that provide EMI suppression through ground connections without directly interfering with the capacitive sensing field in the display area, serving as a mediator between the display and the chassis ground
3Object-affected harmful factors
If a substantial conductive layer is used for EMI suppression, then electromagnetic interference radiation is reduced, but transparency of the display is compromised
Solution Approach 1:
Conductive EMI suppression materials are applied only to the border regions surrounding the display rather than the entire display surface, maintaining the transparency and visual quality of the display area while providing effective EMI suppression in the non-display border regions
Solution Approach 2:
The display surface is segmented into a transparent display area and a conductive border area, where EMI suppression functionality is confined to the border region, preserving the optical properties of the display while achieving electromagnetic interference attenuation
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 effectively suppresses EMI radiation without degrading the capacitive touch panel's performance, ensuring compliance with EMI regulations while maintaining touch sensitivity and transparency.
Implementation Method 1
A capacitor is provided having a capacitance corresponding to the determined capacitive impedance
Implementation Method 2
The capacitor is formed of a length or strip of capacitive material disposed along the peripheral edge of the capacitive touch panel on the nonconductive side
Data Source
AI summary
A display device for displaying information to a user in correspondence with a display signal. The display device includes an LCD receiving the display signal and displaying information in accordance with the display signal. The display device additionally includes a capacitive touch panel having an electrically conductive surface. The capacitive touch panel provides a signal corresponding to the location of an object touching or placed in close proximity to the surface of the capacitive touch panel for providing user input. A chassis supports the LCD and capacitive touch panel in the device. A capacitor capacitively connects the electrically conductive surface of the capacitive touch panel to the chassis.