Method and apparatus for implementing automatic number identification system for DAA

摘要

The present invention provides apparatus and method for automatic number identification (ANI) for a data access arrangement (DAA) of a modem. Modems or telephones equipped with an ANI system use the caller ID (ANI) signals to identify the calling telephone or modem. For automatic number identification, the invention uses a new switch element on the secondary winding side of a transformer and a standard DAA circuit on the primary winding side of the transformer. The invention does not require an additional AC coupling path for the caller ID (ANI) signals. During an ANI operation, the new ANI switch on the secondary winding side is opened so that the impedance looking into the modem from the telephone line side becomes relatively high and the prior art voltage divide effect is eliminated or reduced. Consequently, the caller ID (ANI) signals that appear at the secondary winding of the transformer have virtually the same amplitudes as the caller ID (ANI) signals that appear at the telephone line with little or zero attenuation. During normal modem operations, the new ANI switch remains closed to allow signal transmissions and support impedance matching.