Constant current line circuit with class features
AssigneeMitel Networks Corporation
InventorChuk Seto
Life of this patent
Estimating the term…
Abstract
A line circuit utilizing a differential amplifier whose output is regulated to zero volts D.C. (when the subscriber's set is off-hook) by a negative feedback circuit, for controlling a voltage controlled power supply which provides a constant current feed to the subscriber's loop. The differential amplifier also transmits audio signals received from the subscriber's loop directly to a PABX via an unbalanced terminal. When the loop range exceeds a predetermined threshold, the circuit reverts to a voltage feed operation thereby allowing operation over long loop lengths and the ability to provide on-hook CLASS services.
Claims5
A line circuit for providing loopfeed current to a subscriber's line, comprising:
- driver circuitry for driving said subscriber's line with said loopfeed current;
- an input amplifier circuit connected to said subscriber's line for sensing and comparing current flowing in said line with a predetermined constant current and generating an error signal proportional to any difference therebetween;
- and
- an integrator for receiving said error signal and in the event said error signal is less than a predetermined amount then controlling said driver circuitry with a variable voltage so as to maintain constant loopfeed current to said subscriber's line and in the event said error signal exceeds said predetermined amount generating a constant saturation voltage for controlling said driver circuit to provide a constant voltage feed to said subscriber's line.
Dependencies are inferred from the claim text.