Figure 7-1 shows the basic connections required for operation of the INA106. Place power supply bypass capacitors close to the device pins as shown.

Figure 7-1 Basic Power Supply and Signal Connections

The differential input signal is connected to pins 2 and 3 as shown. The source impedance connected to the inputs must be equal for good common-mode rejection. A 5Ω mismatch in source impedance degrades the common-mode rejection of a typical device to approximately 86dB. If the source has a known source impedance mismatch, an additional resistor in series with one input can be used to preserve good common-mode rejection.

The output is referred to the output reference terminal (pin 1) which is normally grounded. A voltage applied to the Ref terminal is summed with the output signal. To maintain good common-mode rejection, keep the source impedance of a signal applied to the Ref terminal less than 10Ω.

Figure 7-2 shows a voltage applied to pin 1 to trim the offset voltage of the INA106. The known 100Ω source impedance of the trim circuit is compensated by the 10Ω resistor in series with pin 3 to maintain good CMR.

Figure 7-2 Offset Adjustment

Referring to Figure 7-1, the CMR depends upon the match of the internal R₄/R₃ ratio to the R₁/R₂ ratio. A CMR of 106dB requires resistor matching of 0.005%. To maintain high CMR over temperature, the resistor TCR tracking must be better than 2ppm/°C. These accuracies are difficult and expensive to reliably achieve with discrete components.