A novel common-mode noise cancellation technique for VDSL applications

Very-high-speed digital subscriber loop modems operate in frequency bands which coincide with many significant radio-frequency interference sources, particularly commercial AM radio. In these bands, the balance of most twisted-pair cables is low enough to allow substantial interference to transfer via the differential mode, disrupting the transmitted information signal. A novel wideband common-mode noise cancellation technique is presented. Simulation results show that the common-mode noise cancellation technique could provide 20- to 30 dB improvement in those radio frequency bands. Construction and testing of a hardware prototype are also presented. With finite-precision effects, measured test results show that common-mode noise cancellation in the order of 15-20 dB is achievable.