5 volts single power supply ADSL analog front end design

摘要

A combination x digital subscriber line (xDSL) and analog modem including a computer bus interface, codecs, an analog front end (AFE) for xDSL communications coupled to a plain old telephone service (POTS) line and a direct access arrangement (DAA) for analog communications also coupled to the POTS line. The modem is designed on a peripheral component interconnect (PCI) card. Generally, ±12, 5 and 3.3 volts are available for PCI components. Traditionally, the AFEs for non-PCI modems were designed to operate on ±12 volts for differential POTS line driving. For differential POTS line driving, the AFE typically requires a regulated voltage. However, ±12 volts supplied to PCI cards are typically not as well regulated as the 5 and 3.3 volts, and therefore the ±12 volts is generally unsuitable for PCI modem AFE design. Furthermore, in computers that operate in different power management modes, ±12 volts may not be available to the PCI card while 5 and/or 3.3 volts may be available to the PCI card in certain power management modes. In one embodiment, the AFE operates on 5 volts. Power for the modem is made available from other parts of the computer supply in these power management modes.