Browse Prior Art Database

Trip Detecting Circuit

IP.com Disclosure Number: IPCOM000088871D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Ferry, M: AUTHOR

Abstract

The drawing shows a trip detection circuit for detecting the off-hook action at a subscriber's extension during the ringing period of an incoming call.

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Trip Detecting Circuit

The drawing shows a trip detection circuit for detecting the off-hook action at a subscriber's extension during the ringing period of an incoming call.

The subscriber extension is connected by wires a and b to the trip detector located in the telephone exchange serving the extension.

Wire a is linked to the ground through feeder A and to negative voltage -V1 (- 48 volts) through two resistors R1 and R2. Wire b is linked to negative voltage - V1 through feeder B and to ground through resistors R'1 and R'2. Resistors R1 and R2 are equal to resistors R'1 and R'2, respectively, and are of high value with respect to the resistors of feeders A and B.

Resistors R1, R2 and R'1, R'2 form a differential bridge sensitive to opposite polarity signals on wires a and b generated by the off-hook action at the subscriber extension. Parasitic signals having the same polarities are rejected.

The detected signal on nodes a' and b' is applied to a comparator (COMP), the output of which indicates the status of the subscriber loop.

A resistive network, comprising resistors R3 and R'3 connected to a positive voltage +V2 (+6 volts) and resistors R4 and R'4 connected to the ground, attenuates common-mode signals and makes the levels on nodes a' and b' compatible with the integrated circuit low voltages used in the comparator.

Ringing signals are eliminated by a filtering circuit composed of resistors R5, R'5 and capacitor C.

The voltage across nodes a' and b' is in...