EMI Suppression Filters (EMC and Noise Suppression)CAN FD Noise Suppression-1 (1/2)

CAN FD is a type of interior LAN that connects and communicates between the ECU and computer in an automobile. CAN FD can communicate at a faster speed than the conventional CAN standard.

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.

A common mode choke coil is suited as a measure to address common mode noise.
A common mode choke coil is a coil that magnetically couples both lines and can remove the common mode noise without affecting the differential signal or other differential mode signals.

In principle, the common mode choke coil has the effect of removing the common mode noise, but when the balance between the coils of both lines is lost, a mode conversion occurs and part of the differential mode signal may be converted to common mode and become noise. Therefore, it is important to use a balanced common mode choke coil with little mode conversion.