Current limited subscriber line feed circuit
First Claim
1. An automatic signal equalization circuit for remotely providing an optimized d.c. current to one or more telephone subscriber sets independently of the subscriber loop length and the presence or absence of an equalizer at said subscriber sets comprising:
- signal generation means for supplying a regulated d.c. voltage to the telephone tip and ring lines in accordance with a controllable reference voltage signal;
means for sensing the subscriber line current when a subscriber set is in the OFF HOOK condition and for generating a digital logic signal related to the amount by which said sensed line current exceeds a predetermined threshold signal;
means responsive to said logic signal for incrementally varying said reference voltage signal to regulate the d.c. voltage across the tip and ring lines such that said line current is limited to said threshold; and
means responsive to said logic signal for incrementally varying the attenuation in the subscriber loop to optimize the transmission characteristics of the subscriber loop and telephone subset.
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Accused Products
Abstract
The present invention discloses a reduced power dissipation telephone subscriber line feed circuit in which the battery feed current from the central office is determined by the subscriber loop resistance for medium to long loops, and for shorter loops, for which the battery feed current would exceed a given predetermined threshold, the feed current is limited to the threshold value. The invention also relates to compensation for loop and subset attenuation characteristics.
During operation in the current limited mode, attenuation is automatically inserted into the signal transmission and receiving paths in order that normal equalizer operation will not be impaired by current limiting of the battery feed current. A multiple telephone subscriber system is disclosed wherein the circuitry used in deriving current limiting control signals is shared in a multiplexed arrangement by a plurality of subscriber lines. Line feed current is limited in discrete steps to a predetermined threshold value in each subscriber loop upon the detection of an OFF HOOK condition when the feed current drawn by the subset exceeds the threshold value. A plurality of discrete signals are derived by sensing the amount by which the line voltages exceeds a predetermined selected reference voltage value. These discrete signals are used to determine both the effective battery voltage which will produce a d.c. feed current corresponding to the limiting value and the amount of attenuation to be added at the central office by the line circuit to compensate for the equalizer effect in the subscriber set which occurs as a result of the current limiting.
57 Citations
11 Claims
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1. An automatic signal equalization circuit for remotely providing an optimized d.c. current to one or more telephone subscriber sets independently of the subscriber loop length and the presence or absence of an equalizer at said subscriber sets comprising:
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signal generation means for supplying a regulated d.c. voltage to the telephone tip and ring lines in accordance with a controllable reference voltage signal; means for sensing the subscriber line current when a subscriber set is in the OFF HOOK condition and for generating a digital logic signal related to the amount by which said sensed line current exceeds a predetermined threshold signal; means responsive to said logic signal for incrementally varying said reference voltage signal to regulate the d.c. voltage across the tip and ring lines such that said line current is limited to said threshold; and means responsive to said logic signal for incrementally varying the attenuation in the subscriber loop to optimize the transmission characteristics of the subscriber loop and telephone subset. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A current limited subscriber line feed circuit comprising:
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signal generation means for supplying a regulated d.c. voltage to the telephone tip and ring lines in accordance with a controllable reference voltage signal; means for sensing the subscriber line current when a subscriber set is in the OFF HOOK condition and for generating a digital logic signal related to the amount by which said sensed line current exceeds a predetermined threshold signal; means responsive to said logic signal for incrementally varying said reference voltage signal to regulate the d.c. voltage across the tip and ring lines such that said line current is limited to said threshold; and means responsive to said logic signal for incrementally inserting either attenuation or gain in the subscriber line to compensate for signal loss due to differences in subscriber loop length. - View Dependent Claims (10, 11)
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Specification