Abstract: A method and apparatus for interference cancellation in a high-speed modem that includes a first coupler for receiving a differential signal including a received data signal, a second coupler for deriving a common mode signal for the transmitted signal, and a phase-shift circuit coupled to the second coupler for deriving orthogonal signals from the common mode signal. First and second multipliers mix the orthogonal signals with the received signal. First, second, and third integrators integrate the mixed orthogonal signals and the common mode signal to produce orthogonal signal level measurements ITONE and QTONE and a common mode signal level measurement CMTONE, respectively. A controller derives orthogonal correction signals from measurements by dividing ITONE and QTONE respectively by CMTONE and multiplying by an appropriate constant. This output is then used to increment or decrement the signals to the respective digital to analog converters, DACI and DACQ.