How to filter the MC pulse port of a motion controller without losing accuracy?

When designing filter circuits for the pulse input/output ports of a motion controller (MC), noise must be suppressed without sacrificing timing accuracy. For pulse inputs, such as encoder signals, a Schmitt trigger is used for shaping; its hysteresis voltage can suppress small-amplitude noise without affecting edge timing. An RC low-pass filter can be added before the Schmitt trigger, with a time constant much smaller than the minimum pulse period; for example, for a 1MHz signal, the RC time constant should be set to 10ns.

For pulse outputs, such as PWM, a small inductor or ferrite bead is connected in series at the output of the driver chip, and a small capacitor is connected in parallel to ground to form a low-pass filter. The cutoff frequency should be much higher than 10 times the PWM frequency to retain the fundamental frequency while filtering out high-frequency harmonics. All filter components should be high-precision, low-temperature-drift models. During PCB layout, the filter circuit should be placed close to the port to avoid introducing additional delay. The impact of filtering on accuracy is verified by measuring the rise time, fall time, and jitter of the pulses before and after filtering, ensuring that the timing requirements of the control system are met.