How should the filtering of the HMI bus interface be designed?

The design of the filtering circuit for the HMI bus interface aims to suppress external interference and internal noise transmission without affecting signal integrity. Different bus types require different filtering designs. For digital parallel buses, such as memory buses, direct filtering on the data lines is usually not possible; the focus is on power supply decoupling and good PCB layout. For low-speed serial buses, such as I2C, SPI, and UART, small resistors (e.g., 22Ω-100Ω) can be connected in series on the clock and data lines, with a small capacitor connected in parallel to ground at the pull-up resistor to form a low-pass filter. However, the RC time constant must be calculated to ensure it does not affect the communication rate. For differential buses such as CAN and RS485, a common-mode choke (e.g., CMZ3225A-510T) can be connected in series on the signal lines, with a TVS diode and capacitor connected in parallel between the A/B lines and ground. Filtering components must be placed as close as possible to the bus interface chip or connector. Power supply filtering is equally important, providing a clean power supply to the bus transceiver using ferrite beads and decoupling capacitors. In terms of PCB layout, bus signal lines should be as short as possible and reference a complete ground plane. During the design process, signal integrity simulation is necessary to evaluate the impact of the filtering circuit on the eye diagram or timing. Etymotic offers common-mode chokes, ferrite beads, and TVS products suitable for various buses. Combined with proper circuit design, effective bus interface filtering can be achieved.