Circuit for attenuation of echos caused by line variations and an interfacing system for capacitively coupling a plurality of sources to a two-wire communication line

摘要

A circuit attenuates echo caused by line variations and a transformerless, high DC impedance, two-wire line interface. To reduce echo, a test tone is introduced on the communication line with all station units connected to the line. The resultant receive signal is conditioned through a peak detector, digitized and read by a processor. The resistive and capacitive characteristics of a network are iterated by the processor and the results remeasured. The network is set to the best combination for least echo by the processor. An interfacing system capacitively couples a plurality of sources to a two-wire communication pair by means of a plurality of differential voltage-to-current amplifiers. Each source uses a differential receiving amplifier to receive signals from the line and is resistively coupled in parallel to all the sourcing entities coupled to the communication line at that particular interface. There is an echo balance network associated with each source.