Arrangement in a subscriber line interface circuit

Details Arrangement in a subscriber line interface circuit Arrangement in a subscriber line interface circuit

1997-10-30

2001-07-17

Woo, Stella (Department: 2643)

Telephonic communications

Subscriber line or transmission line interface

C379S400000

Reexamination Certificate

active

06263076

ABSTRACT:

TECHNICAL FIELD
The invention relates generally to an arrangement for measuring the voltage across a telephone line connected to a line interface circuit.
BACKGROUND
Line interface circuits are provided on line interface boards and are controlled by a control processor on the line interface board, the control processor being common to a plurality of line interface circuits.
In order to be able to compensate for line resistance dependent attenuation on the line, the control processor needs information about the resistance of the line connected to the respective line interface circuit. A method of obtaining information about the line resistance when the current characteristic and supply voltage of the line interface circuit are known, comprises measuring the line voltage and calculating the line resistance from the measured line voltage.
To transfer the line voltage information to the control processor, either an external analog-to-digital converter or an internal analog-to-digital converter in the line interface circuit, is used today.
In the case of an external analog-to-digital converter, a separate output terminal is necessary on the line interface circuit to output an output voltage proportional to the line voltage.
With an internal analog-to-digital converter in the line interface circuit, at least one separate output terminal is needed on the line interface circuit for communication with the control processor.
SUMMARY
The object of the invention is to bring about an arrangement for line voltage measurement and, thereby, line resistance calculation which does not require any extra components or any extra output terminal.
This is attained according to the invention in that the control processor controls the detector output terminal of the line interface circuit to a first signal state at a first point of time at the same time as the line interface circuit is controlled to initiate the measurement of the line voltage. After a time interval whose length is proportional to the measured line voltage, the detector output terminal of the line interface circuit is controlled to a second signal state. The control processor is adapted to convert the time interval during which the detector output terminal of the line interface circuit is in the first signal state to a voltage value corresponding to the measured line voltage. Since the current characteristic and supply voltage of the line interface circuit are known, the control processor can calculate the line current on the basis of this voltage value and, thereby, also the line resistance.
Thus, the measurement can be carried out without any extra components or any extra output terminal, i.e. no extra wiring is needed on the line interface board.


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