CAN FD accelerates the bit rate beyond the conventional CAN standard.
As a result, the emission noise problem which occurs during CAN communication increases.
In CAN FD and other interfaces, a transmission system called "differential transmission" is used.
Because the signal is transmitted through the potential difference between the two signal lines in differential transmission, it has the characteristic of being resistant to radiated noise from the outside. Moreover, the radio waves occurring in both lines due to the signal cancel each other out, so it is unlikely to be externally emitted as noise.
However, on a circuit board a common mode current will be generated by various factors. When this current flows into the cable of the differential transmission line, common mode noise is emitted from the cable.