US Patent 7804904 Active replica transformer hybrid

A communication circuit includes a near end transmitter, a hybrid having an input in communication with an output of the near end transmitter, and a near end adjustable load replication transmitter having an adjustable load. The communication circuit further includes a subtractor configured to subtract an output from the near end adjustable load replication transmitter from the output from the near end transmitter and the hybrid. The communication circuit further includes a near end receiver responsive to an output of the subtractor and a calibration circuit configured to adjust the adjustable load against a reference load.