| 摘要 |
A telephone ring signal detector distinguishes a telephone ring signal voltage from a telephone pre-ring signal voltage on a telecommunication line at a premise, and is unresponsive to the pre-ring voltage and responsive only to the ring signal voltage for providing a telephone ring signal detect output signal during a first quarter cycle time period of a first telephone ring signal. A line switch couples an off-hook terminal impedance to the line in response to the ring detect signal for the purpose to exchanging telecommunication signals to and from the line. The detector provides a signal translating device for translating the ring and pre-ring signal voltages into a translated telephone signal having a translated peak ring signal voltage and a translated peak pre-ring signal voltage. During an adaptive voltage mode, an adaptive reference device responds to the translated telephone signal to provide an adaptive reference voltage which is adapted to be less than the translated peak ring signal voltage and greater than the translated peak pre-ring signal voltage when the off-hook impedance is uncoupled from the line. During a ring signal detect mode, a comparator provides the ring signal detect output signal when the translated telephone signal exceeds the adaptive reference voltage. The ring detect signal is independent of variations in a peak ring signal voltage, variations in a peak pre-ring signal voltage, variations in a pre-ring signal voltage transition time interval, variations in a telecommunication line resistance due to variations in a telecommunication line length, and independent of variations in a total ring signal impedance coupled to the line at the premise.
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