Patent ID: RE42237

Claim:
For use with a subscriber line interface circuit (SLIC) having tip and ring amplifiers, each of said tip and ring amplifiers having a first polarity input and a second polarity input, said first polarity input being coupled to a voltage-dividing node of a voltage divider, said voltage divider having an input terminal to which a DC input voltage is applied, and a grounded reference terminal, said second polarity input of said tip amplifier being coupled to receive a first current that is produced by a first current source in accordance with current flowing through said voltage divider as a result of application of said DC input voltage to said input terminal thereof, and independent of the output of said tip amplifier, and said second polarity input of said ring amplifier being coupled to receive a second current that is produced by a second current source in accordance with current flowing through said voltage divider as a result of application of said DC input voltage to said input terminal thereof, and independent of the output of said ring amplifier, the improvement comprising: a voltage regulator, referenced to ground and coupled to said voltage divider, and being operative, for a first value of DC voltage relative to ground, that is generated at said voltage, dividing node of said voltage divider as a result of said current flowing through said voltage divider in response to application of said DC input voltage to said input terminal thereof, said first value of DC voltage being less than a prescribed value of regulated DC voltage Vreg relative to ground, to cause said first value of DC voltage to be provided by said voltage-dividing node of said voltage divider, and applied thereby to said first polarity inputs of said tip and ring amplifiers and, for a second value of DC voltage relative to ground, that is generated at said voltage-dividing node of said voltage divider as a result of said current flowing through said voltage divider in response to application of said DC input voltage to said input terminal thereof, said second value of DC voltage being at or above said prescribed value of regulated DC voltage Vreg, to limit the value of DC voltage provided by said voltage-dividing node of said voltage divider, and applied thereby to said first polarity inputs of said tip and ring amplifiers, to said prescribed value of regulated DC voltage Vreg relative to ground, so that each of said first and second currents is limited in accordance with said regulated DC voltage Vreg relative to ground, irrespective of said DC input voltage exceeding said prescribed value of regulated DC voltage Vreg relative to ground.