A directional coupler for a modem has a high common mode noise rejection
characteristic with low transmit signal leakage, and reduced distortion
of components mixed with a received signal. A primary filter network is
connected to a communications circuit. The primary filter network has an
output connected to an input of an amplifier. A feedback network is
connected between the input and output of the amplifier. The primary
filter network, the amplifier and the feedback network are arranged to
provide a virtual ground at the input of the amplifier, and a filter
characteristic which attenuates frequencies in the transmit signal band.
The advantage is reduced component count while providing excellent
transmit signal rejection and reducing received signal distortion.