Feasibility study of optical isolator in reducing CM conducted emission from PLC modem

One of the major concerns in designing a modem for power line communication (PLC) is the existence of common mode (CM) RF current, which generates radiated emissions that could interfere with some other communications users. Magnetic transformers have long been used in the analog front end (AFE) circuit of PLC modems to transmit high frequency (1 to 30 MHz) broadband signals onto power network and isolate users from high voltage hazards. However, a magnetic transformer has an adverse effect of coupling CM currents from the modem onto the power lines over this frequency range. This paper studies the feasibility of implementing an optical isolator within the AFE circuit to reduce CM coupling onto the power lines. The measurement results collected show encouraging signs of reduction of CM coupling onto the power lines by including an optical isolator into the AFE circuit.