US Patent 7994766 Differential current sensor device and method

A current sensor having a pair of sense transistors is disclosed. The sense transistors sense a current conducted by a power transistor of a voltage regulator. The ratio in size between the power transistor and the sense transistors corresponds to a scaling factor M. Each sense transistor has an associated series connected sense resistor. The two sense resistors are unbalanced and provide a differential voltage based on the sensed current at the sense transistor to a transconductor. The transconductor has heavy emitter degeneration to provide an output current substantially proportional to the current conducted by the primary power transistor, the proportion determined by the scaling factor M and a ratio of the emitter degeneration and sense resistors.