Frequency responsive selective ringing circuit

Details Frequency responsive selective ringing circuit Frequency responsive selective ringing circuit

1989-02-02

1990-09-25

Ng, Jin F.

Telephonic communications

Polystation line system

Call alerting

379373, H04M 1300

Patent

active

049598538

ABSTRACT:
A frequency responsive selective ringing circuit detects a selected one of a plurality of frequency-distinctive ringing signals applied on either the tip or ring conductors of a telephone line, distinguishes between the respectively different frequencies on a rapid cycle-by-cycle basis, and either applies the ringing signal to telephone equipment to ring the telephone equipment if the ringing signal is one which is selected, or rectifies the ringing signal and applies the rectified DC signal to the ringing circuit of the telephone equipment. The rectified DC signal will not ring the telephone because the DC signal is not conducted through a capacitor in the ringing circuit of the telephone equipment.

REFERENCES:
patent: 4224476 (1980-09-01), Tuhy, Jr.
patent: 4653093 (1987-03-01), Zofan
patent: 4675899 (1987-06-01), Ahuja
patent: 4701949 (1987-10-01), Lynch et al.
patent: 4723271 (1988-02-01), Grundtisch
patent: 4761810 (1988-08-01), Perry
patent: 4782518 (1988-11-01), Mattley et al.
"Modern Electronic Devices: Circuit Design and Application", M. Rosenstein et al., Reston Publishing Co., Reston, Va. .COPYRGT. 1985, pp. 274-280.

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