| 摘要 |
An apparatus (10) for detecting an off-hook condition on a telephone, the apparatus being connected to the tip line (14) and the ring line (16) of a telephone line (12), a first potential difference existing between the tip line and the ring line, the telephone line connected to the telephone having a handset. A circuit (20) generates a difference signal (30) representative of the absolute value of the first potential difference. A first comparator (48), responsive to the difference signal, generates a first indicator signal (54) when the difference signal is above a first value (42) corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook. A second comparator (44), responsive to the difference signal, generates a second indicator signal (52) when the difference signal is below a second value (46) corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook. A circuit (60), responsive to the first indicator signal (54) and the second indicator signal (52), indicates when the handset is off-hook.
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