Figure 2-3 shows the voltage reference circuit, output filtering, voltage divider, and buffer circuit. The REF5050 5-V, low-noise, low-drift voltage reference is used here. The voltage reference is connected to the ADC directly to the right of R34 on the VREF node. The filter R36 and C22 are selected for best noise performance and stability. As noted in the REF5050 data sheet, the series resistor R36 is included to keep the capacitor ESR in the desired range. The reference connects to a buffered input on the ADC so the reference does not need to respond to transient current demands. The voltage divider (R36, R31, and R37), and associated jumper (JP3) are used to set the common-mode input for the FDA. The jumper provides the option of changing the common-mode input from 2.5 V to 2.6 V. A common-mode of 2.5 V is midscale for a 0-V to 5-V FDA output swing. Because of output swing limitations, some distortion may occur when the signal swings towards 0 V. The 2.6-V common-mode shifts the signal away from ground to avoid this distortion. The theory behind this approach is documented in the Driving a SAR ADC with a Fully Differential Amplifier video.