How to control the minimum signal loop in a Human-Machine Interface (HMI)?

Minimizing the signal loop area on an HMI PCB is the golden rule for reducing radiated emissions and enhancing immunity. Loop area refers to the area enclosed by the outflow and return paths of signal current. A larger area results in higher antenna efficiency and stronger resistance to radiated and received interference. The primary method for controlling loop area is to provide an adjacent, low-impedance return path for each signal line. This is typically achieved through a complete ground plane, with the signal line running above it. The return current flows mirrored directly below the signal line on the ground plane, thus minimizing the loop area. Therefore, ensuring ground plane continuity is crucial, avoiding signal lines crossing ground plane dividers. For power loops, such as the input/output circuits of switching power supplies, short, wide traces should be used, and decoupling capacitors should be placed close to the chip to minimize power loops. Differential signals, with currents flowing in opposite directions through two lines, have magnetic fields that cancel each other out, naturally resulting in a small equivalent loop area, and should be preferred. During layout, related components (such as drivers and receivers) should be placed close together to shorten trace lengths. For critical signals such as clock signals, isolation can be achieved using ground plane surrounds or ground via arrays. By adhering to these design rules and leveraging the optimized layout of Echotronics components, the loop area of various signals and power supplies on the HMI board can be systematically reduced, thereby significantly improving its EMC performance.