Very quick question: I am looking at using the AD9629-20 in an application, and I am trying to determine if a voltage follower is required for fast current response on the VREF input of the AD9629-20.
My external reference circuit consists of a LDO with 1.8Vout tied through a resistor to a 1V zener diode, which is tied directly to Vref of the AD9629-20, and nowhere else. The Vref output is decoupled as shown in Fig. 42 of the datasheet, with both (1) 1uF and (1) 0.1uF capacitors.
However, on your evaluation board for the AD9629, you have a voltage follower (AD822) on your external reference. Is that necessary and why?