Vref Advice needed (ADR3425 and the like)

[JPortici]

Hi folks,
for my new weekends project i want to design a small, portable, low-ish cost calibrator. At this moment i am trying to find out which voltage reference to use for the precision ADC/DAC (and multimeters vref of course)

one of the Vrefs i am considering is the ADR3425ARJZ-R7, not the best but the low frequency noise should be low enough to be less than a 16 bit LSB

Datasheet: http://www.mouser.com/ds/2/609/ADR3412_ADR3420_ADR3425_ADR3430_ADR3433_ADR3440_AD-878965.pdf


As you can see, the feedback path is not explicitely connected to the output pin and i wanted to use this at my advantage. The Load regulation is not that good BUT if i buffered the voltage reference output and took the feedback after the buffer opamp i should achieve a Vref independent on the current load and at the same time eliminate the offset introduces by the opamp so i could focus on a low noise, not necessarily low offset one.

The initial accuracy and the line regulation isn't that good either but, again i could use the two at my advantage: i could power the reference from a DAC and vary its supply voltage, hence adjusting the output to the required precision.

is all of that something that makes sense? (Let's forget about the temperature for one second, assume it to be fairly constant)

[TiN]

How portable is portable for you? Battery powered i'd expect? If few hours/day of battery life good enough for you, i'd go for good old heated LM399. Once you have it warmed up, aged and measured by calibrated 6.5d DVM, you will have good enough reference for any 5.5 digit needs.     

Check on Ian's box for good reference of such project: http://youtu.be/-bkINyHdLG4

[JPortici]

Portable is a self contained instrument (voltage sources, counter, awg, dc and waveform inputs, screen) about the size of the one in the video. i want to see how precise i can get