Patent ID: 7123897

Claim:
A modem comprising: a) a communications circuit for coupling a signal source of the modem to a telecommunications network, the communications circuit comprising a signal line adapted to simultaneously carry a transmit (Tx) signal and a receive (Rx) signal and a compensation network connected to the signal line for balancing an impedance of the signal line; and b) a directional coupler for coupling a signal receiver of the modem to the communications circuit, the directional coupler circuit comprising: i) a primary network connected to the communications circuit, the primary network being tuned to attenuate frequencies in a frequency band of the Tx signal, and having a respective primary network output; ii) an amplifier having a respective amplifier input connected to the primary network output, and a respective amplifier output connected to the receiver; and iii) a feedback network tuned to attenuate frequencies in a frequency band of the Tx signal, and connected between the amplifier input and the amplifier output; wherein the primary network, the amplifier, and feedback network are arranged to provide a virtual ground at the amplifier input.