How to optimize the filtering of the I/O module's DI loop?

Optimizing the filtering of digital input circuits in I/O modules requires striking a balance between interference immunity and response speed. For low-speed switching signals such as pushbuttons, RC filtering can be used, with resistance values between 1kΩ and 10kΩ, capacitance values between 1nF and 100nF, and a time constant typically set to 1/10 to 1/5 of the minimum pulse width. To improve common-mode interference immunity, a common-mode choke, such as the CML4532A-510T, can be added before the RC filter. For high-speed pulse signals, RC filtering introduces excessive delay; LC filters with steep cutoff characteristics or dedicated digital filter chips should be used instead.

All filtering components should be placed as close as possible to the connector or optocoupler input side. At the software level, digital debouncing algorithms, such as multiple sampling voting, can be implemented in conjunction with hardware filtering. For long-haul applications, a TVS diode array, such as the ESDSRVLC05-4, can be added at the module entry point to suppress transient overvoltages introduced by the cable. After optimization, the signal must be verified through immunity tests such as EFT/Burst, and the actual impact of filtering on the rising and falling edges of the signal must be measured to ensure that it does not lead to misjudgment.