How to design an HMI with capacitive touch for EMI suppression?

Designing EMI immunity for an HMI capacitive touchscreen requires a multi-dimensional approach, addressing sensor design, driver circuitry, signal processing, and overall shielding. Sensor pattern design should be optimized, such as using a diamond grid, and adding a shielded ground wire between the driver and sensing electrodes to resist external electric field interference. The driver circuit should use a low-noise LDO power supply, and use ferrite beads (e.g., PBZ1608E102Z0T) and MLCC capacitors for filtering at the power pins. The touch chip's clock frequency should avoid the frequency bands of other strong noise sources in the system, or spread spectrum technology should be used. On the touch chip's sensing input channel, a small resistor can be connected in series and a capacitor to ground in parallel to form a low-pass filter network to filter out high-frequency noise.

The ITO layer or FPC cable of the touchscreen is susceptible to interference; shielded cables should be used, and the shielding layer should be reliably grounded at the controller end. The entire touchscreen module's metal frame should be well-connected to the HMI housing to form a continuous shield. At the software level, digital filtering algorithms, such as median filtering and mean filtering, can be added to suppress periodic noise. By combining hardware filtering, shielding, and software processing, and by selecting filtering and ESD protection devices from Audiotech, a capacitive touch system that remains stable and reliable even in strong electromagnetic environments can be constructed.