Patent ID: 8648623

Claim:
A current sense amplifier comprising: a sense resistor configured to be connected to conduct a current to generate a sense voltage (Vsense) across the sense resistor; a filter coupled to the sense resistor to generate a filtered Vsense signal; a single-stage differential transconductance amplifier having high impedance input terminals couple to receive the filtered Vsense signal, the transconductance amplifier comprising: a differential pair of input transistors having control terminals coupled to receive the filtered Vsense signal; a gain control resistor directly coupled across first terminals of the pair of transistors, the gain control resistor conducting only a current equal to a difference in voltages at the first terminals of the pair of transistors, substantially equal to the filtered Vsense signal, divided by the value (Re) of the gain control resistor, such that the current (Ie) substantially equals the filtered Vsense signal divided by Re; a separate level shifting circuit coupled to each of the input transistors configured to lower a common mode voltage of the filtered Vsense signal at an output of the transconductance amplifier; and each level shifting circuit being part of a feedback loop for its associated input transistor to cause a current through each of the input transistors to be substantially constant and equal as the filtered Vsense signal varies to cause the filtered Vsense signal to substantially occur across the gain control resistor, wherein the transconductance amplifier generates a differential output, at differential output terminals, proportional to the current through the sense resistor.