Hybrid dc-feed controller for a subscriber line interface circuit

Abstract

A method and apparatus in a DC-feed controller for controlling a subscriber line interface circuit controlling voltage (alternately, current) on a telephone line comprising a pair of wires. A digital feedback signal is subtracted from a predetermined voltage (alternately, current) limit digital value to provide a digital error signal that represents the difference between the voltage (alternately, current) limit digital value and the digital feedback signal. The digital error signal is multiplied by a predetermined digital gain value to provide a scaled digital error value. The scaled digital error value is integrated over time to generate an integrated digital error signal having a first predetermined number n of significant bits. A modified digital error signal is received, comprising a second predetermined number m of bits, where m<n, of the integrated digital error signal as an input and an output an analog error signal is provided that is representative of the modified digital error signal and that comprises the control voltage. A sense signal is received, the sense signal representing a sensed voltage (alternately, current) on the telephone line, and is converted to a digital sense signal that is a representation of the sense signal. Finally, the digital sense signal is digitally low pass filtered to provide the digital feedback signal.