How can differential mode filtering in a power DTU not affect data transmission?

Designing a differential-mode filter for a DTU that does not affect data transmission requires controlling the filter's cutoff frequency and phase response. For data lines, an RC low-pass filter is used, with the cutoff frequency set to at least 5 times the data rate; for example, for RS485 at 1Mbps, the cutoff frequency is set to 5MHz. High-quality capacitors (C0G dielectric) and precision resistors (1% tolerance) are used to ensure phase linearity. For differential signals, filter elements are symmetrically arranged on both lines to maintain balance. The signal quality after filtering is verified through eye diagram testing; the eye opening should be greater than 80%. After differential-mode filtering optimization, signal integrity is maintained, and the bit error rate is below 10^-9.