| 摘要 |
A second output transmission signal ("TX<SUB>2</SUB>") added to a line driver is a scaled version of the main output transmission signal ("TX<SUB>1</SUB>"). TX<SUB>2 </SUB>is scaled from TX<SUB>1 </SUB>by a variable scale factor K. An adaptive hybrid circuit subtracts TX<SUB>1 </SUB>and TX<SUB>2 </SUB>from a line signal carrying both a line transmission signal and a line received signal ("RX"). A programmable impedance Z<SUB>tune </SUB>is coupled between the TX<SUB>2 </SUB>output of the line driver and the RX output of the adaptive hybrid circuit. A transmission echo in the output RX signal is measured. K and Z<SUB>tune </SUB>are then adaptively tuned to minimize the transmission echo. The hybrid in this case becomes a 4-port network, one port specifically added to adaptively cancel the transmission echo in the RX output of the adaptive hybrid circuit. Alternatively, the hybrid may be a 3-port hybrid including variable impedances to cancel the line transmission signal.
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