公开(公告)号：FR2296339A1

公开(公告)日：1976-07-23

申请号：FR7535236

申请日：1975-11-10

Applicant: IBM

Inventor： MULLER HANS-RUDOLF ,  SCHINDLER HANS DR ,  VETTIGER PETER

IPC: H04M1/00 ,  H04M19/00 ,  H04Q3/42 ,  H04Q3/72 ,  H04Q5/00 ,  H04M9/04

公开(公告)号：CH604453A5

公开(公告)日：1978-09-15

申请号：CH814476

申请日：1976-06-25

Applicant: IBM

Inventor： SCHINDLER HANS DR ,  VETTIGER PETER

IPC: H04M3/02 ,  H04M3/22 ,  H04M19/02 ,  H04Q1/22

Abstract: In an extension line circuit, an off-hook condition is detected during ringing by superimposing in each ringing cycle the values of the line current existing at two sampling instants exactly one-half cycle apart, and testing whether the sum (or mean value) exceeds a given threshold. When DC current starts flowing due to the set going off-hook, the mean value of the two values will pass a threshold.