We need reference voltage of 4,096V with the lowest noise.
We try ADR444 + output filter+pA low noise buffer amplifier.
Before we start counting and beating a dead path, you do not have a appnote or reference design with similar problem?
For specify. We need voltage reference with 0.1-10Hz output noise ~250nVp-p
Capacity how much can hang on output ADR4xx?
The ADR444 is a good choice in that, at 1.8uV, it has the lowest integrated noise from 0.1-10Hz of any of our references. It's rated load capacitance is 0.1uF.
You may also want to consider the new ADR4540. It has slightly higher 0.1-10Hz noise of 2.8uV but it has a max load capacitance of 100uF. So you should be able to hang much higher filter capacitance from it and still maintain stabillity of the reference's output.
A 100u, but make sure it is the lowest resistance polymer capacitor (not standard tantalum) you can find