INCOMING CALL DETECTION SYSTEM BY SIMPLE RINGING FOR OFFICE TRUNK

摘要

PURPOSE:To facilitate LSI-implementation at low cost with small package area by realizing ringing detection by a logic circuit of timing logic by utilizing the output signal of a polarity detecting circuit. CONSTITUTION:When a ringing signal (a) is inputted, the polarity detecting circuit 30 of the office trunk 10 generates the polarity detection signal (b) and outputs it to a simple ringing incoming detecting circuit 40 and a state monitor circuit 50. When the polarity detection signal (b) is inputted, the trailing edge detecting circuit 41 of the simple ringing incoming detecting circuit 40 generates a trailing edge signal (d) and outputs it to a timing pulse generating circuit 42 and one input terminal sides of AND gates 44 and 45. The timing pulse generating circuit 42 generates a timing pulse (e) which becomes active for a time T2 elapsed a time T1 after the trailing edge signal (d) rises. The AND gate 44 ANDs the input trailing edge signal (d) and timing pulse (e).