Arrangement in a subscriber line interface circuit

Abstract

In a subscriber line interface circuit connected to a telephone line having a high potential wire and a low potential wire, an arrangement for generating a signal for determining the line voltage comprises means (7, 10, 11) for alternately charging a capacitor (6), by means of a first DC current, to a first voltage, and discharging the capacitor (6), by means of a second DC current, to a second voltage. Hereby, a sawtooth wave having an amplitude corresponding to the difference between the first and second voltages is produced. This sawtooth wave is converted to a pulse train related to the line voltage, from which the line voltage can be determined.

Description

technical field [0001] The present invention relates generally to subscriber line interface circuits, and more particularly to means for determining line voltage within a subscriber line interface circuit. Background technique [0002] In order to be able to adjust the hybrid interface parameters and gains within the telephone circuit by means of the microprocessor on the line interface board to obtain good echo cancellation for different lengths of telephone lines and also for some testing purposes, knowing the length of each telephone line is necessary. [0003] One method of estimating the length of the line is to measure the line voltage, ie the voltage present between the line and the telephone when the connection is established. [0004] It is known to generate pulses with a length corresponding to the line voltage. The length of this pulse is then measured by a microprocessor on the line interface board in order to obtain information about the ...

AI Technical Summary

Problems solved by technology

[0005] When the length of the pulse is to be measured, it is difficult to achieve a good resolution because the pulse length determines the measurement time period

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