[sdiy] My latest 'DIY' project

[Paul Schreiber]

> Looks very nice... but I never believe anyone (even someone of your
> reputation, sorry) when they claim something to be accurate at that many
> digits of precision. But I'm just being picky and annoying.
>

It's a matter of simply willing to *pay* for this level of accuracy.

a) the DAC I use costs $27 in 100pc quantities. It's 16-bit, accurate to +-1LSB 
*maximum* error untrimmed. Then, it's trimmed in both hardware AND software 
(each of the 4 outputs has a unique calibration table in FLASH).
b) the DAC is fed by a 7PPM, 0.05% accurate voltage reference. About $6 at 
100pcs.
c) the op amps are Analog Devices AD822AR that are very low DC offset/drift but 
high speed. There are 4 (1 per channel) at $4.50ea
d) every resistor in the CV chain is an IRC Tantalum Nitride mil spec part, 
10ppm at 0.1% tolerance. There are like 33 of them at about $0.75ea ($25 just 
for the resistors!)

So, this sort of accuracy is possible if you specify the proper parts. Not that 
big a deal, really.

Paul S.