The INA146 is laser-trimmed for low offset voltage and drift. Most applications require no external offset adjustment. Figure 6-2 shows an optional circuit for trimming the offset voltage. A voltage applied to the Ref terminal is summed with the output signal. This feature can be used to null offset voltage. To maintain good common-mode rejection, the source impedance of a signal applied to the Ref terminal must be less than 10 Ω and a resistor added to the positive input terminal must be 10 times that, or 100 Ω. Alternatively, the trim voltage can be buffered with an operational amplifier such as the OPA277.