Subscriber line circuit for connection of a subscriber line for the transmission of analogue subscriber signals to a digital time division multiplex telephone exchange

摘要

The subscriber line is coupled capacitively (C, K). In the subscriber line interface circuit (SLIC) of the line circuit, a positive feedback path leading from the four-wire transmit output to the four-wire receive input and containing filter elements (F) is formed, by means of which a basic setting of the two-wire impedance is effected which is higher than the impedance of the feed bridge, this basic setting is complemented to form the required exact value with the aid of a programmable filter (Z, B) which connects the four-wire transmit branch to the four-wire receive branch in a chip (SICOFI) connected together with the interface circuit (SLIC1) and also ensures that the two-wire impedance is provided with a complex value. IMAGE