| 摘要 |
PROBLEM TO BE SOLVED: To provide a network interface circuit that determines whether a signal on a TIP/RING line represents an actual event or a transient noise signal. SOLUTION: A network interface circuit according to the present invention screens out (cancels) transient (noise) signals and provides an indication to the line side that an actual event has occurred, so that appropriate discrimination circuitry is powered up to determine the exact nature (type) of the actual event only when actually needed. More specifically, the present invention (network interface circuit) develops an AC signal that represents the events that are desired to be detected. This AC signal is timed so that it may have a sustained rate (e.g., a 1 millisecond burst) that is unlike any transient that would occur on the line. Thus, unless the incoming signal meets the timing requirements of the circuit, it is disregarded as being a transient signal and no action is taken to determine the exact nature (type) of the signal. This avoids the need to invoke (initiate) the discrimination circuits that have large power requirements until they are actually needed. COPYRIGHT: (C)2008,JPO&INPIT
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