Method of providing d.c. feed to a telephone line
First Claim
1. A method of providing d.c. feed to a two-wire telephone line, comprising the steps of:
- generating a supply voltage for a drive circuit including two amplifiers each having an output coupled to a respective wire of the line;
supplying an a.c. transmission signal to the line via the amplifiers of the drive circuit;
determining potentials at the amplifier outputs in dependence upon the supply voltage and headroom voltages required for operation of the amplifiers to supply the transmission signal to the line, a difference between the potentials at the outputs of the two amplifiers producing a loop current on the line;
monitoring the loop current on the line; and
digitally controlling the generated supply voltage in dependence upon the monitored loop current by the steps of, iteratively at each of a plurality of successive time instants;
determining a target value corresponding to a target voltage inversely dependent upon an amount by which the monitored loop current exceeds a predetermined value; and
adjusting the generated supply voltage towards the target voltage in dependence upon the target value;
whereby the target voltage and the generated supply voltage converge over said plurality of successive time instants.
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Accused Products
Abstract
A two-wire telephone line is supplied with d.c. feed from a drive circuit including two amplifiers via which a transmission signal is supplied to the line. Output potentials of the two amplifiers determine a loop current on the line, which is monitored and used to control a supply voltage for the drive circuit, the amplifier output potentials being offset from the supply potentials by headroom voltages to accommodate the transmission signal. The resulting current limiting voltage control acts iteratively to converge the supply voltage and a target voltage which is inversely dependent on an amount by which the loop current exceeds a predetermined value, the rate of convergence being fast for high loop currents for rapid response and slow for small differences to provide stable operation. The headroom voltages can be increased to nearly the supply voltage to reverse the polarity of the d.c. feed while maintaining current limiting.
90 Citations
16 Claims
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1. A method of providing d.c. feed to a two-wire telephone line, comprising the steps of:
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generating a supply voltage for a drive circuit including two amplifiers each having an output coupled to a respective wire of the line; supplying an a.c. transmission signal to the line via the amplifiers of the drive circuit; determining potentials at the amplifier outputs in dependence upon the supply voltage and headroom voltages required for operation of the amplifiers to supply the transmission signal to the line, a difference between the potentials at the outputs of the two amplifiers producing a loop current on the line; monitoring the loop current on the line; and digitally controlling the generated supply voltage in dependence upon the monitored loop current by the steps of, iteratively at each of a plurality of successive time instants; determining a target value corresponding to a target voltage inversely dependent upon an amount by which the monitored loop current exceeds a predetermined value; and adjusting the generated supply voltage towards the target voltage in dependence upon the target value; whereby the target voltage and the generated supply voltage converge over said plurality of successive time instants. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification