Mode conversion and transfer characteristics of conducted disturbance to Ethernet device from power supply cable

Conducted disturbances from communication or power supply cables affect Ethernet devices. A conducted disturbance, which is generated when several switching power devices reach a communication device, degrades the quality of signal communications. In addition, a disturbance passing through an Ethernet device influences neighboring devices connected by the communication cables. Herein we propose a system to measure the propagation modes of conducted disturbances in power supply cables and Ethernet cables. The results indicate that mode conversion occurs in not only an Ethernet hub but also an AC adapter supplying DC voltage to Ethernet devices. The conducted disturbance to the AC and DC power supply cable is strongly transmitted to the Ethernet cable as the primary common mode and the differential mode. Conversion from the common mode in the power supply cable to the primary common mode in the Ethernet cable is dominant in the measured frequency range.