US 5,402,482 AGranted

Ring trip deciding circuit

AssigneeFujitsu Limited

InventorsKazuyuki Minohara, Kenji Takato

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Abstract

A ring trip deciding method in a ring trip circuit detects voltage change in the on-hook state and the on-hook state of a terminal when the terminal such as telephone set connected to the telephone line is called. The ring trip deciding circuit has a ring trip detecting resistance connected in series with a ringer generator for detecting change of current value depending on the on-hook and off-hook states, a detector for detecting voltage change across the ring trip detecting resistance, a voltage comparator for outputting different values when the threshold value is larger or smaller by comparing a voltage outputted from the detector with the threshold value, a first state latch for latching and outputting different state values depending on different output values of the voltage comparator, a composite state latch for fetching, latching and outputting at least two state values outputted from the first state latch synchronously with a clock, and a state deciding circuit for comparing state values of the composite state latch to detect the on-hook and off-hook states of the terminal.

Claims12

Dependent claims

A ring trip deciding circuit which detects an off-hook state of a subscriber terminal unit, having an on-hook state and the off-hook state, when the subscriber terminal unit connected to the telephone line is called, said ring trip deciding circuit comprising:

a ring generator outputting a ring signal;
a ring trip detecting resistance, connected in series with said ring generator, detecting change of current value depending on the on-hook state and the off-hook state;
and
a ring trip circuit connected in parallel to said ring trip detecting resistance and comprising:
a detector detecting change of voltage across said ring trip detecting resistance;
a voltage comparator connected to said detector and successively comparing a voltage outputted from said detector with a threshold value and outputting different values when the voltage is larger than the threshold value,
first state latch means, coupled to said voltage comparator, for latching and outputting successive state values;
second state latch composite means, connected to the first state latch means, for successively fetching, latching and outputting at a common time two of the successive state values output by the first state latch means;
and
state deciding means for comparing the two successive state values with each other,
wherein said state deciding means determines voltage change at respective, different times detected by said ring trip detecting resistance by comparing the two state values with each other to detect the on-hook state and the off-hook state of the subscriber terminal unit.

8 more elements

A ring trip deciding circuit which detects an on-hook state and an off-hook state of a subscriber terminal unit when a subscriber terminal unit connected to a telephone line is called according to a predetermined timing, said ring trip deciding circuit comprising:

a ring generator outputting a ring signal;
a ring trip detecting resistance, which is connected in series with the ring generator, detecting change of current value depending on the on-hook state and the off-hook state;
a ring trip circuit connected in parallel to said ring trip detecting resistance and comprising:
a detector detecting change of voltage across said ring trip detecting resistance;
a voltage comparator connected to said detector and successive comparing a voltage outputted from said detector with a threshold value and outputting different values when the voltage is larger or smaller than the threshold value;
state latch composite means, coupled to said voltage comparator, for latching different state values depending on different output values of said voltage comparator and outputting the different state values synchronously with a clock;
threshold value storing means, coupled to the state latch composite means and to the voltage comparator, for fetching and latching a state value, based on the different values output by said voltage comparator, as the reference state value used in the predetermined timing, and outputting the reference state value synchronously with said clock;
and
state deciding means, coupled to the state latch composite means and to the threshold value storing means, for comparing the different state values of said state latch composite means and said reference state value, wherein,
said state deciding means determines voltage change at respective different times detected by the ring trip detecting resistance by comparing the different state values of the state latch composite means with the reference state value of said threshold value storing means to detect the on-hook state and the off-hook state of the subscriber terminal unit.

7 more elements

Dependencies are inferred from the claim text.