A study of estimation of balance degree using CMRR mesurement for power distribution interconnection on printed circuit board

Common-mode currents through the DC power supply cable attached to small electronic device causes EMI (Electro-Magnetic Interference). When the primary factor of common-mode is corresponding to mismatch balance on the wiring, balance degree may be obtained from CMRR (Common Mode Rejection Ratio) of the printed circuit board in the equipment. We made some experiment boards, measured the CMRR and considered the relations with mismatching balance. As a result, it is confirmed that the CMRR shows the similar tendency to the balance degree, although we could not find the complete correlation between them. Further, the wiring structure with parallel narrow conductor plates was proved to suppress the common mode.