[time-nuts] yet another GPSDO design, or so

jimlux jimlux at earthlink.net
Wed Jun 30 01:01:28 UTC 2010

Hal Murray wrote:
>> or with a pair of current output DACs and a resistive divider/summer so  you
>> have a "high order" and "low order" voltage. 
> If it were that simple, the manufacturers would package it up into a single 
> chip. :)

And they do... hence delta sigma designs..

Back in the good old days before big monolithic converters were 
available you cold buy a fast wide DAC that basically was a hybrid with 
2 smaller DACs and a prom that was burned at the factory.

> I think there are two areas of interest.  One is the obvious one that steps 
> on the high-order DAC won't cleanly map into a constant number of steps in 
> the low-order DAC.

Yep.. but if  you're driving it from a CPU, memory is cheap...

> The other is things like temperature shifts.  You have to work out the specs 
> for both paths and take the worst one.

It certainly isn't easy..

But, if you need something that isn't readily available off the shelf 
(for one reason or another.. maybe you've got several thousand 8 bit 
DACs in your garage that you're dying to use... along with a well 
regulated power supply to run them all <grin>)

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