公开(公告)号：CA1100651A

公开(公告)日：1981-05-05

申请号：CA295077

申请日：1978-01-17

Applicant: IBM

Inventor： GRANGE JEAN-CLAUDE ,  HERNANDEZ PHILIPPE ,  REYNES DANIEL ,  SUZZONI JEAN-PIERRE ,  TU NGHIEM

IPC: H04M19/02

Abstract: TELEPHONE LINE SWITCHING The subject invention relates to a telephone line circuit and to the logic associated therewith, in order to detect the various possible line status, more especially to detect an off hook status during ringing. The circuit is essentially comprised of a first detector (DA) sensitive to the line current phase, a second detector (DB) sensitive to the ringing voltage phase, and two pulse generators (RTG1 and RTG2), 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 the first generator are simultaneously present (once per period). When the called subscriber lifts his handset, the signals from both detectors and the second generator are also simultaneously present once per period. These pulse coincidences are detected and processed by an appropriate logic. FR9-76-016 - 1