Ring trip detection circuit

Details Ring trip detection circuit Ring trip detection circuit

1992-09-03

1994-08-02

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379377, 379252, 379251, H04M 302

Patent

active

053352718

ABSTRACT:
A ring trip detection circuit detects an OFF-hooked state of a telephone receiver during ringing of a telephone set by detecting a change in a voltage across two terminals of a transmission resistor through which a ringing signal is supplied to the telephone set from a ringing signal source. The ring trip detection circuit includes a voltage dividing circuit coupled to the two terminals of the transmission resistor for dividing voltages at the two terminals and for outputting divided voltages, a pair of transistors having bases for respectively receiving the divided voltages from the voltage dividing circuit, a constant current source, a pair of resistors having first terminals respectively coupled to emitters of the pair of transistors and second terminals coupled in common to the constant current source, where the pair of resistors have the same resistance, and a current mirror circuit coupled to collectors of the pair of transistors for outputting an output current which indicates whether or not the telephone receiver is OFF-hooked.

REFERENCES:
patent: 4356355 (1982-10-01), Ferrieu et al.
patent: 4827505 (1989-05-01), Takato et al.
patent: 4995111 (1991-02-01), Tojo et al.

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