[time-nuts] GPS Locked and Unlocked Performance Comparison

[Didier Juges]

Hi Said,

It seems we are at the same point. I have been using a TI/Burr-Brown
microprocessor with a 24 bit ADC and 8 input multiplexer (the MSC1210, which
is actually advertised as a precision ADC which happens to have a full blown
8051, 32k of Flash and all the usual goodies including a long timer on the
same die) , and it seems the most practical way to make a 24 bit DAC for one
of those is to use two 16 bit DACs and use one ADC channel to verify and
tweak the DAC as necessary. Not very elegant, but practical, as long as the
other specs can be met. 

I have to settle on a voltage reference. Based on a posting on this or
another mailing list, we have been evaluating a Thaler reference for a
military project I am working on (day job) and I have been quite impressed,
even though they are more intended for harsh environment than for low noise,
which will not really help for this project. I have not quantified the
close-in noise, but I will be using some of Bruce's recommendations to build
something using my PC's sound card to measure it.

All this is a relatively far-out project, but I am getting the pieces
together.

Didier KO4BB

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of SAIDJACK at aol.com
> Sent: Thursday, February 14, 2008 2:36 PM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] GPS Locked and Unlocked Performance 
> Comparison
> 
> Hello Didier,
>  
> maybe you are right, and that's not easy to find. I remember 
> an app not  from LT (Jim WIlliams?) that discussed how to 
> build a high-accuracy DC output  DAC using a Sigma Delta ADC 
> and some logic etc.
>  
> Finding a 24 bit ADC is pretty easy, ADI, TI, Linear, Maxim 
> etc seem to offer these.
>  
> One could also build a composite DAC out of two 16 bit DAC's 
> or two 20 bit DAC's etc. The voltage reference is key to good 
> performance here, and should have <<3ppm tempco to get 
> anywhere near the 24 bits of accuracy.
>  
> bye,
> Said
>  
>  
> In a message dated 2/14/2008 02:02:36 Pacific Standard Time, 
> didier at cox.net
> writes:
> 
> What 24  bit DAC do you have in mind?
> 
> I have been looking for a standalone 24  bit DAC in a small 
> package and have not found anything I liked  :-(
> 
> 
> 
> 
> 
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