Application of the imbalance difference method to the EMC design of automotive ECUs

Controlling the common-mode currents induced on wiring harnesses plays an important role in meeting automotive electromagnetic compatibility requirements. For high-frequency signals, the key to controlling these common-mode currents is maintaining the same electrical balance in the harness that was present on the circuit board. When routing differential signals such as LVDS or CAN signals, designers are generally careful to maintain the balance in the differential signal pair. However, driver skew and other sources of common-mode current in these routing pairs makes it equally important to maintain the balance of the wire pair and system ground relative to distant objects. This paper employs the imbalance difference method to demonstrate the importance of maintaining the electrical balance of the common-mode currents that return on system ground. These examples should help engineers to make better decisions regarding the optimum harness configuration for a given automotive system.