How to protect the EMC of analog interfaces in HMI (Human Machine Interface) systems?

Protecting the EMC of HMI analog interfaces hinges on protecting their high-precision, low-amplitude signals from interference. Analog interfaces are typically used to connect sensors such as temperature and pressure sensors, whose signals are susceptible to noise contamination. Protective measures include: installing π-type or T-type RC low-pass filters at signal line entry points; the filter's cutoff frequency should be higher than the signal frequency but much lower than the interference frequency. Adding TVS diodes or Zener diodes between the signal line and power/ground to limit overvoltage, such as using SMBJ5.0CA. For long-distance transmission, shielded twisted-pair cable must be used, and the shielding layer must be grounded at a single point at the HMI end (usually at the interface) to avoid ground loops.

On the PCB, analog input circuitry should be centrally located and completely enclosed by an analog ground plane, isolated from the digital area via grounding trenches or ferrite beads. The power supplies for operational amplifiers and other analog chips require precise filtering; LC filters or low-noise LDOs can be used. High-impedance input nodes should not be exposed; drive buffers or guard ring technology can be added. If ambient noise is severe, consider using isolation amplifiers or V/F converters to convert analog signals to digital or frequency signals for transmission. By employing filtering, protection, and isolation devices from Audiotech and combining them with rigorous analog circuit design rules, highly reliable analog interfaces can be constructed.