The INAx191 is different from many current-sense amplifiers because this device offers very low input bias current. The low input bias current of the INAx191 has three primary benefits.
The first benefit is the reduction of the current consumed by the device in both the enabled and disabled states. Classical current-sense amplifier topologies typically consume tens of microamps of current at the inputs. For these amplifiers, the input current is the result of the resistor network that sets the gain and additional current to bias the input amplifier. To reduce the bias current to near zero, the INAx191 uses a capacitively coupled amplifier on the input stage, followed by a difference amplifier on the output stage.
The second benefit of low bias current is the ability to use input filters to reject high-frequency noise before the signal is amplified. In a traditional current-sense amplifier, the addition of input filters comes at the cost of reduced accuracy. However, as a result of the low bias currents, input filters have little effect on the measurement accuracy of the INAx191.
The third benefit of low bias current is the ability to use a larger current-sense resistor. This ability allows the device to accurately monitor currents as low as 1 µA.