To get unipolar output from DACx1001, connect the negative reference input to ground as shown in Figure 59. The OPA189 is a zero-drift amplifier with ±0.02 ppm/°C. The DACx1001 has a temperature drift of offset error of ±0.04 ppm/°C. The temperature drifts of the DAC and amplifier might be neglected when compared to the temperature drift of the reference source. The best reference sources offer temperature drifts of the order of
±2.5 ppm/°C to ±3 ppm/°C. A temperature calibration is needed for the voltage reference to achieve the goal of ±2 ppm/°C.