Patent ID: 7457258

Claim:
A system comprising: a tunable filter driven by an output signal of a transmitter to provide a filtered output signal, the filtered output signal being combined with a signal from an associated communications network to provide a receiver signal that is substantially free from echo caused by the output signal of the transmitter, the tunable filter comprising a biquad filter that comprises a first amplifier and a second amplifier connected in series, the first amplifier having at least one feedback path that comprises at least one first variable passive component and at least one feedforward path coupled between the first amplifier and the second amplifier that comprises at least one second variable passive component; and a control system configured to selectively adjust the at least one first variable passive component and the at least one second variable passive component of the tunable filter to set at least one pole and at least one zero of a transfer function of the tunable filter so that the transfer function of the tunable filter approximates loop characteristics of the associated communications network.