| 摘要 |
A line card integrates subscriber line interface circuitry, A/D and D/A converters, and digital signal processing technology. The digital signal processing technology performs many line card tasks such as switch hook detection, ground key detection, DC feed control, polarity reversal, ringing tests, fault detection, power cross detection, and ring trip detection. Actual subscriber loop parametric conditions may be determined by a digital signal processor using sensed small signals on both the A and B conductors of subscriber loop. By sensing small signals, saturation of sensing circuitry may be avoided. Furthermore, relatively high speed digital signal processing facilitates accurate and expeditious switch hook status determination.
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