Immunity of communications systems using a balanced cable

In communications systems using balanced cables, there is a possibility of the common mode voltage induced on the cable causing damage to the LSI of a communication system. The authors measured the voltage induced by a strong electric field on a balanced cable, and confirmed the presence of a large induced common mode voltage. As effective approaches in the reduction of this common mode voltage, the use of a twisted pair with shielding and the use of a common mode choke coil are examined. As a result, it was shown clearly that these were able to decrease the common mode voltage by 20 dB, and that the protection of an LSI by using a common mode choke coil on the receiving end is possible