Low voltage sensing and control of battery referenced transistors in subscriber loop applications

Abstract

A method includes the step of providing subscriber loop pull-down circuitry operating in a first voltage domain. The subscriber loop pull-down circuitry decreases at least one of a tip and a ring line current in response to a corresponding pull-down control signal. The method further includes the step of providing control circuitry operating in a second voltage domain, wherein the first and second voltage domains are substantially distinct. The control circuitry varies the pull-down control signal to decrease a selected one of the tip and ring line currents in response to a sensed current corresponding to an associated one of a tip pull-down current and a ring pull-down current. A subscriber line interface circuit apparatus includes pull-down circuitry operating in a first voltage domain. The pull-down circuitry varies line currents of the tip and ring lines in response to a pull-down control signal provided by control circuitry operating in a second voltage domain. The first and second voltage domains are substantially distinct. A control isolation stage is coupled to provide the pull-down control signals from the control circuitry to the pull-down circuitry. A feedback isolation stage provides feedback signals from the pull-down circuitry to the control circuitry. The feedback signals represent sensed pull-down currents associated with the tip and ring lines. The control circuitry provides the pull-down control signals for the tip and ring lines in response to the sensed pull-down currents.