Dual voltage, self-monitoring line circuit

Abstract

A line circuit provides BORSCHT functions and supplies the customer loop through a feed resistor network and current limiter either from a high voltage battery to provide for maximum signaling range or from a lower voltage battery to conserve power. The current limiter operates under the control of a microprocessor/DSP which selectively applies or denies power to isolate or include components for testing and controls the switching in and out of transistors to control the scaling factor between the channel width-to-length ratios of the current mirror's input and output FET transistors according to the type of test or operating condition dictated by the microprocessor while the input reference current to the current mirror is maintained constant.

Dependencies are inferred from the claim text.