[time-nuts] Re: Thunderbolts ...

[Bob kb8tq]

Hi

Most good DAC’s show you information on temperature / supply / and reference
stability (along with a bunch of other stuff like noise …). You are paying for those
parameters when you buy a “good” DAC. 

The TBolt has a “home brew” DAC and (maybe) feedback setup. For whatever reason
(one would guess cost) they did it all themselves in a FPGA rather than running
a “stock” chip. You can trace out portions of the setup. Once it goes back into 
the FPGA …. who knows. Some sort of Sigma Delta Something Somewhere is 
probably a good guess. 

Bottom line is, you can’t just go to the label on this or that chip and grab the 
data sheet for “the DAC”.  I don’t even recall anybody finding “the reference
IC” for “the DAC”. They may well have and I’ve simply forgotten over the last 10
or 15 years ...

What you *could* do is to rig up a Volt Nuts grade bench, set the DAC to various
voltages and run the beast over temperature. Somehow that sounds like a lot
of work. Unless you have a “group” it would only tell you part of the story ….

Bob

> On Jul 25, 2021, at 5:03 AM, Hal Murray <halmurray+timenuts at sonic.net> wrote:
> 
> 
> csteinmetz at yandex.com said:
>> If that were true, it would mean that the actual EFC voltage in those  units
>> was varying with respect to the DAC voltage as reported over the  Tbolt's
>> serial port.  While not impossible (after all, we know almost  nothing about
>> the internal architecture of the Tbolt), for a number of  reasons I think
>> that is unlikely. 
> 
> The only thing that the TBolt can report is the number that it feeds to the 
> DAC.
> 
> I expect the actual voltage out would vary with temperature, supply voltage, 
> age, and whatever.  Add in the reference voltage if that's not included in the 
> DAC.
> 
> I haven't looked at DAC data sheets recently.  How many of the modern ones 
> have a set of small graphs showing parameters like that?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
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