| 摘要 |
A line powered data access arrangement (DAA) is disclosed which adaptively allows proper operation with power supplied from a telephone line as conditions warrant, while at the same time satisfying the relevant requirements of many countries. In the line powered codec, a startup procedure for the international line powered codec uses register settings, e.g., country-specific register settings, which are powered and maintained from the low voltage side (e.g., from the PC or modem side) of the line powered codec. In this way, even during low line power conditions the programmed state of the line powered codec can be maintained, thus a default condition will not necessarily returned to by the line powered codec upon reset due to a power loss in the telephone line. In another aspect, a charge storage device such as a charge capacitor is charged from a charge pump formed from a differential clock signal from the low voltage side. A current and voltage detection module in the line powered codec is always powered from the telephone line. Upon detection of an off-hook signal or a power down condition, the current detection module determines if/when the current and voltage on the telephone line is sufficient to power certain circuits on the line powered codec. If sufficient power is not present, the line powered codec does not power up. However, the line powered codec will power up if sufficient current is detected. In another aspect, a plurality of power rails may be provided. A first power rail may be associated with the line power, a second power rail may be associated with a low voltage side power source, e.g., a charge storage device. A third (and other) power rails may be switchably connected to either the first power rail or second power rail as line power conditions and on-hook/off-hook conditions warrant. <IMAGE> |
