Abstract: An apparatus for separating dc current and ac current signal portions of a composite signal. The apparatus has a main current path for carrying the composite signal. This path splits into a dc current path and into two dc blocked ac current paths. At the node a virtual ground potential for the ac current signal portions is generated with the aid of an inverting amplifier with negative feedback located in one of the ac current paths. Thus, only the dc current portions flow over the dc current path. In a preferred embodiment, the dc blocking is implemented by a capacitor in each ac current path, and the inverting amplifier is an operational amplifier, whose non-inverting input is at ground potential, whose inverting input is connected with the respective capacitor and whose output is connected both with the inverting input via an ohmic negative feedback resistor and with an impedance in the other ac current path.

Abstract: An arrangement for full-duplex data transmission over a two-wire circuit (1) comprises a transmit channel (2) connected to a baseband data transmitter (6) and including a smearing filter (18), a receive channel (3) connected to a baseband data receiver (9) and including a complementary smearing filter (19), a hybrid junction (4), an echo canceller (14) with an adaptive filter (15) and an adjusting circuit (16), and a combining circuit (17) inserted in the receive channel (3).