Ringing signal detection circuit

Details Ringing signal detection circuit Ringing signal detection circuit

1983-12-27

1985-08-20

Rubinson, Gene Z.

H04M 100

Patent

active

045366195

ABSTRACT:
A ringing signal detection circuit for a subscriber's apparatus which is connected to a telephone office line together with an attached telephone set. An incoming signal on the telephone line is converted to a pulse signal with a repetition frequency twice the incoming signal by a full-wave rectifier and a differentiating circuit. The pulse signal is applied to a retriggerable mono-stable multivibrator through a photo-coupler and an inverter. The time period of a metastable state of the multivibrator by one trigger pulse is selected to be longer than the break period in the dial pulse signal but longer than a half cycle of the ringing signal. Therefore, the multivibrator is maintained at the high level for a longer time period at a time when the incoming signal is the ringing signal than the time when the incoming signal is the dial pulse signal. Therefore, the ringing signal can be detected from the time period when the high level signal is continuously maintained and distinctly distinguished from the dial pulse signal. The time period of the high level signal can be detected by the use of a clock pulse generator, an AND gate to which the high level signal and the clock pulse are applied, and a pulse counter connected to the output of the AND gate. The time period is, thus, represented by the number counted in the counter.

REFERENCES:
patent: 3753130 (1973-08-01), Pezzutti
patent: 4049916 (1977-09-01), Danner
patent: 4390843 (1983-06-01), Betts et al.

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