Central office interface techniques for digital subscriber lines

摘要

A digital subscriber line and POTS voice interface between a telephone line and central office equipment is provided. For POTS band frequencies, a reactive impedance coupled across the two wire interface of the POTS line card, and serially coupled to the line side of the DSL coupling transformer, has an open state magnitude. The magnitude of the line side windings of the DSL coupling transformer is low at POTS band frequencies. POTS band signal power is therefore delivered to the POTS line card. For DSL band frequencies, the reactive impedance across the POTS line card has a closed state magnitude. The POTS line card is therefore essentially short-circuited at DSL band frequencies, and DSL band signal power is delivered to the DSL modem. The frequency band in which the reactive impedance transitions from an open state magnitude to a closed state magnitude corresponds to the frequency band between the POTS frequency band and the DSL frequency band. Negative impedance synthesis techniques provide compensation for the reactive impedance across the POTS line card.