Bi-directional buffer line amplifier

摘要

An improved bi-directional buffer line amplifier is disclosed that provides a high performance analog interface between a Digital Network Interface Circuit (DNIC) and a transmission line. The buffer line amplifier includes a transmit amplifier network including an input connected to a DNIC transmit signal output. The input is arranged to receive transmit signals from the DNIC. A transmit output is connected to a matching network via a selectable gain amplifying circuit. The selectable gain amplifying circuit applies the transmit signals to the matching network in a first or a second gain level. In the first gain level the gain amplifying circuit is removed from the transmit amplifier network and the transmit amplifier network operates as a unity gain amplifier. This allows the buffer line amplifier to work efficiently with transmission line loop lengths from zero to a nominal distance. In the second gain level the gain amplifying circuit is connected in series between the transmit amplifier network and the matching network, thereby, significantly amplifying the transmit signals. This allows the buffer line amplifier to work efficiently with transmission line loop lengths of a substantially greater distance than the nominal distance. A receive amplifier network is also included that cancels the transmit signals from receive signals. This provides the necessary phase error cancellation required by the DNIC for the error free reception of the receive signals.