Telephone ringing detector.

摘要

To accurately detect the short bursts of distinctive ringing signals within 100 milliseconds, a magnitude comparator (12) produces a binary signal indicative of whether the instantaneous tip-ring voltage exceeds a predetermined magnitude. The binary signal is integrated (18) over a predetermined period of time controlled by a timer (36). If the time integral is below a first predetermined value, the absence of ringing is detected; if above a second predetermined value, ringing is detected; if in between, the integrating interval is extended until the integral falls outside the two values.