Figure 9-4 shows the use of the OPAx863 devices as a SAR ADC input driver and reference buffer driving the ADS7945. Sensors, which are used for interface with the physical environment, exhibit high output impedance and cannot drive SAR ADC inputs directly. A wide-GBW amplifier like the OPAx863 devices are needed to charge the switching capacitors at the SAR ADC input and to settle fast to the required accuracy within the given acquisition time. The ADC core draws transient current from the reference input during the conversion (digitization) phase, which needs to be driven with a wide-GBW amplifier to offer fast settling and maintain a stable reference voltage for superior digitization performance. The OPAx863 devices reference buffer is used in a composite loop with the OPA378 precision amplifier due to limitations in precision performance of wide-GBW amplifiers. The precision amplifier maintains low-offset output, whereas the OPAx863 devices provide the output drive and fast-settling performance.