Method and circuit for feeding, when needed, call signals to telecommunication lines, especially in telephone exchanges

摘要

1. Method of providing ringing signals the composition and duration of which are determined by ringing circuits (74-78) and by ringing supervision circuits (122-124) for a plurality of telecommunication lines (42 to 48) interconnectable via a switching network, the connection status of said lines being supervised line by line and said lines being connectable group by group, via a common ringing signal bus (82), to a common ringing circuit (74-78) and connected group by group each with a ringing answering detector (122), especially for digital telephone switching systems in which the analogic number lines are connected to the switching network via line termination circuits (12) in which conversion takes place between the analog signals on the subscriber line and the digital signals in the switching network, characterized in, that in the ringing circuit (74-78) a.c. voltages of different frequencies (f1 to f4), generated from several ringing signal reference voltage sources (100 to 106), are transmitted to the common ringing signal bus (82) as an amplified a.c. ringing voltage depending on control signals provided by ringing interval detectors (124), that the ringing a.c. voltages are supplied to the connecting circuits (50 to 56) of the corresponding group (0) of telecommunication lines (42 to 48) via the ringing signal bus (82), that the control signals supplied by the ringing interval detectors (124) are also supplied to the connecting circuits (50 to 56) of the corresponding group (0) of telecommunication lines (42 to 48), that in the connecting circuits (50 to 56) each individual telecommunication line is connected to the ringing signal bus (82) at the correct time on the basis of the control signals formed by the ringing interval detector (124) depending on the ringing status on the ringing signal bus (82), and that in the corresponding connecting circuit (50-56) the connecting of a telecommunication line to be run to the ringing signal bus is controlled in such a way that the telecommunication line receives immediate ringing by this path.