International Business Machines Corporation

Philippe Hernandez

Jean-Pierre L Suzzoni

Daniel F Reynes

Jean-Claude C Grange

Nghiem H Tu

A circuit associated with a telephone line to detect line status includes a first detector sensitive to the line current phase, a second detector sensitive to the ringing voltage phase, and two pulse generators of the same frequency as the ringing voltage, appearing at the positive and negative zero-crossings of the ringing voltage, respectively. When only the ringing current is applied to the line, only the signals from both detectors and one generator are simultaneously present (once per period). When the called subscriber lifts his handset, the signals from both detectors and the other generator are also simultaneously present once per period. These pulse coincidences are detected and processed by an appropriate logic.

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Nice, France

Philippe Hernandez