| 摘要 |
A method and apparatus for implementing DC mode selection in a data access arrangement (DAA). The present invention overcomes the geographic constraints of the prior art by providing a plurality of selectable DC modes. Each of the selectable DC modes may be designed to meet the DC mask specifications of a desired country or region. The apparatus of the present invention may then be utilized in any of the desired countries or regions by selecting the appropriate DC mode. To accommodate several possible DC mask parameters, embodiments of the present invention include selection between a plurality of DC mode voltage levels, selection between current limiting and non-current limiting DC modes, and selection between a plurality of current limit values. Control elements, such as opto-couplers controlled by a microcontroller, are used to perform the selection by enabling and disabling circuit elements or connections. One embodiment provides for temperature compensation of DC current limiting. A thermistor with a negative temperature coefficient compensates for temperature variance in a feedback transistor to maintain stable current limiting performance over a range of temperatures.
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