Abstract: A channel unit interface circuit for interconnecting a two-wire, bidirectional signal transmitting path and a four-wire signal transmitting path in a communication system includes a tip terminal transconductance amplifier driver, a ring terminal transconductance amplifier driver, a voice sense amplifier, a balance network, A/D signal processing circuit, D/A signal processing circuit, filter network, a voice codec/PCM filter, a channel logic circuit, and a DC-to-DC converter. The tip terminal transconductance driver is formed of a first switching operational amplifier, and the ring terminal transconductance driver is formed of a second switching operational amplifier. Each of the first and second switching operational amplifiers is formed of a low voltage transconductance amplifier, high voltage comparator, a filter network, and a feed forward compensation amplifier.

Abstract: An echo cancelling device for use between a line receiving an incoming signal and a line transmitting an outgoing signal, for cancelling out echo, comprising a plurality of processing channels connected in parallel relation and assigned to successive mutually adjacent sub-bands of the spectral band of the outgoing signal, each channel having: a first analysis band-pass filter receiving the echo-affected signal to be transmitted, whose output is connected to the additive input of a subtractor; a second analysis band-pass filter, identical to the first filter, receiving the incoming signal and feeding an adaptive filter delivering an estimated echo value in the sub-band to the subtractive input of the subtractor; and a synthesis filter, symmetrical with the analysis filters and whose output feeds the transmission line.