Novel common mode noise cancellation techniques for xDSL applications

xDSL 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 to differential mode, disrupting the transmitted information signal. Two novel narrowband and wideband common mode noise cancellation techniques are presented. Simulation results show that both common mode noise cancellation techniques could provide 20 to 30 dB improvement in those radio frequency bands. Construction and testing of a hardware prototype is also presented. With finite-precision effects, initial tests suggest that common mode noise cancellation in the order of 15-20 dB can still be achievable.