Ring trip deciding circuit

Details Ring trip deciding circuit Ring trip deciding circuit

1993-03-05

1995-03-28

Chin, Stephen

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379382, 379 7, 379161, 379168, 379184, 379194, H04M 124, H04M 300, H04M 160, H04M 1300

Patent

active

054024820

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a ring trip deciding circuit for detecting transfer condition from the on-hook state to the off-hook state of a terminal such as a telephone set connected to the telephone line while it is called.


BACKGROUND OF THE INVENTION

The transfer condition from the on-hook state to the off-hook state of a terminal connected to the telephone line while the terminal is called is detected by the ring trip detecting circuit by connecting in series a ring trip circuit detecting resistor to a ringer generator. The voltage change generated by a change of current flowing into the ring trip detecting resistor during transfer between the on-hook state and the off-hook state depending on the response from a terminal is then detected.
However, a current value of the ring trip resistor and a rate of change of such current between the on-hook state and off-hook state are different depending on the condition in a side of load, such as the line length of telephone line and the number of terminals connected. Therefore, the accurate detection of the on-hook and off-hook conditions has been very difficult.
FIG. 1 is an explanatory diagram of a ring trip deciding method.
In FIG. 1, element 10 is a subscriber circuit; element 11 is an equivalent circuit of a telephone set forming a series resonant circuit; element 12 is a ring trip detecting resistance (RS) for detecting a change of current generated depending on the transfer condition between the on-hook state and off-hook state of the telephone set; element 13 is a ring trip detector; element 14 is a ringer generator for generating a low frequency AC voltage for ring trip decision. The letter B indicates a switch that opens for the on-hook condition and closes for the off-hook condition.
Operations of the ring trip deciding method shown in FIG. 1 will be explained hereunder.
The ringer generator 14 outputs an AC voltage superposed on a low frequency (about 20 Hz) DC voltage of -48 V. A current flowing into the ring trip detecting resistance (RS) 12 is detected by a detector 13 as an interterminal voltage, and the detected voltage is outputted to the output point A.
In the on-hook state, a low level AC voltage is outputted from the output point A since a DC element is zero.
In the off-hook state, the switch B in the subsrcriber circuit 10 closes, applying a DC element to the circuit and increasing a current flowing into the ring trip detecting resistance (RS) 12 and an outputting an AC voltage in which an AC element is superposed on the DC element from the output point A.
The on-hook state and off-hook state can be decided by detecting the voltage at the point A, which is different depending on these conditions.
FIGS. 2A and 2B show an example of a conventional ring trip deciding circuit. FIG. 2A shows a ring trip deciding circuit and FIG. 2B shows an output voltage waveform at the point A of the detector 14. In FIG. 2A, element 11 is a ringer generator; element 12 is a ring trip detecting resistance (RS); element 13 is a ring trip circuit for deciding the on-hook and off-hook states; element 14 is a detector for detecting and outputting a voltage change across the ring trip detecting resistance (RS) 12 generated depending on the on-hook state and off-hook state; element 15 is a detecting circuit for detecting a voltage across the ring trip detecting resistance (RE) 12; element 16 is a filter/integrating circuit consisting of R, C circuit for eliminating an AC element of the voltage detected by the detecting circuit 15 and integrating the signal; element 17 is a decision circuit for deciding the on-hook state and off-hook state depending on an output voltage of the detector 14.
Operations of the structure of FIG. 2A are then explained hereunder.
The detecting circuit 15 detects a low frequency AC voltage generated across the ring trip detecting resistance (RS) 12. The filter/integrating circuit 16 removes an AC element and integrates the signal to output the integrated signal.
In the structure of the conventional converter 14

REFERENCES:
patent: 4429185 (1984-01-01), Adrian et al.
patent: 4455456 (1984-06-01), Cochran
patent: 4899372 (1990-02-01), Wahi et al.

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