EMI-shielded PCAP
An EMI-shielded PCAP refers to a Projected Capacitive Touch Panel that incorporates electromagnetic interference shielding. This design is commonly used in environments where electronic noise can affect touch accuracy or device performance.
How to Achieve a Stable EMI Design
- Keep ground connections (tracks or wires) as short as possible.
- Minimize impedance, especially in ground connections between display housings and touch controllers.
- The diameter of the ground connection also affects performance.
- Use self-drilling screws, serrated washers, and braided ground straps.
- Eliminate as many connectors as possible from the ground line.
- Avoid ground loops; use star topologies for ground distribution to prevent potential differences. An earth ground is ideal, if possible.
- Any floating conductive parts near the touch sensor can cause erratic touch behavior.
- Ensure all conductive parts share the same electrical ground potential as the touch controller.
- Do not rely solely on signal cables for grounding, as they are insufficient when high-frequency noise is present.
- Provide clearance for the FPC, with at least 1 mm between the FPC and the housing frame.
- Ensure the display housing and touch controller have the same ground potential; the frame can connect to the display/touch ground or a separate ground.
- Connect all conductive parts to ground, especially when using a plastic housing or for parts near the touch sensor, to avoid EMI from floating conductors.
- Use copper foil with conductive adhesive between the housing shell and the display housing.
- Shield against emission noise by using ferrite cores on feeding lines such as USB, power, and display cables.
- Include the touch controller in the system’s star-shaped ground layout.
- Place high-frequency-emitting components and other noise sources as far as possible from the sensor FPC and touch controller circuits.
- Burst voltage significantly affects the signal-to-noise ratio.
- Maintain adequate distance between LCDs and touch sensors.
- Carefully route emission sources: keep LVDS cables away from touch cables and position emitting components such as wireless transmitters and inverters away from touch sensors and controllers.
- Avoid parasitic capacitive couplings by maintaining sufficient distance between the touch FPC and any metal component and provide a mechanical barrier to prevent fluid bridging between touch components and a metal bezel.
Contact our specialists early in the design phase to prevent signal interference from internal and external sources, which can lead to false touches and EMI test failures.
