If the DAC is 10 bits and the ADC ENOB is, say, 22 bits then it would seem that we could get to 7.5 digit precision. There are a lot of details, of course, that need to be correct.
I worked with LTC2400 for couple of months but never get ENOB above 19.5 bits.
What has happened to this post?
Nothing! Hey you are reviving it. Although I'm not the OP here I *am* still working on this idea. I feel like a different person posted the stuff above--is there some other Randall McRee? No, I think it more likely that is just a feeling.
So, what I *think* I have learned so far, in no particular order:
Yes, a linear PWM is do-able and I built one that I think will do the job (another thread for that, also moribund)
This is called a differential voltmeter, e.g. Fluke 895, but modernized,
An adc with high linearity and ENOB of 19 bits ought to get you in the 7.5 digit ballpark (overall bits ~ 10+19 = 29)
The devil is in the details; all of those ppm error sources add up so...the devil.
What I am working on now is a 10volt source based on several PX ref LTZ1000 boards.
I acquired a calibrated Keithley 2001 to test all this out. So, yeah, still coming along for me....
Anyone else make any progress? How did you achieve the 19.5 ENOB? How did you verify that?
Irony note: not lost on me that I bought a 7.5 digit meter on the way to making a 7.5 digit meter. Make of that what you will. I try not to judge.
Randall