Offset voltage is an important consideration when choosing an output amplifier circuit for use with a high-precision current-output DAC such as the LTC2757. The sensitivity of the DAC linearity to output amplifier offset is dependent upon the DAC implementation. The output amplifier used with a current-output R-2R DAC requires not only high open loop gain (>110 dB at 18-bits), but also low-offset voltage. The offset voltage becomes important because any voltage difference between the amplifier inputs will generate a code dependent error current, which will appear as an INL error at the DAC output. The input bias current of the output buffer is less critical, and will appear primarily as an offset at the DAC output. For the LTC2757, an offset voltage of ±80µV will result in about ±1LSB of INL error at the DAC output.