The noise performance of the INA117 is dominated by the internal resistor network. The thermal or Johnson noise of these resistors produces approximately 550nV/√Hz noise. The internal op amp contributes virtually no excess noise at frequencies above 100Hz.

Many applications can be satisfied with less than the full 200kHz bandwidth of the INA117. In these cases, the noise can be reduced with a low-pass filter on the output. The two- pole filter shown in Figure 7-9 limits bandwidth to 1kHz and reduces noise by more than 15:1. Since the INA117 has a 1/f noise corner frequency of approximately 100Hz, a cutoff frequency below 100Hz does not further reduce noise.

Figure 7-8 Leakage Current Measurement Circuit

Figure 7-9 Output Filter for Noise Reduction

Figure 7-10 Summing V_X in Output

Figure 7-11 Common-mode Voltage Monitoring

Figure 7-12 Offsetting or Boosting Common-mode Voltage Range for Reduced Power-supply Voltage Operation

Figure 7-13 Battery Cell Voltage Monitor

Figure 7-14 Measuring Amplifier Load Current

Figure 7-15 AC-coupled INA117