[time-nuts] Thunderbolt? (re simple gpsdo.)

Azelio Boriani azelio.boriani at screen.it
Fri Dec 30 18:22:38 EST 2011


No free lunch, of course, but I want to avoid dithering DACs. The 18bit DAC
(AD5680) is a 16bit+dithering, I think to use the AD5660 + AD5241 (already
available) the pot has a tempco of 30ppm/degree and a noise of
14nV/sqr(Hz). Maybe I have to find something better but to make the first
try is available.

On Fri, Dec 30, 2011 at 11:48 PM, <EWKehren at aol.com> wrote:

> Over the last two years along with two list members that may want to pipe
> in, I have spend a large amount of time on D/A's and we went as far as
> developing a test board using the LTC 2440 and testing numerous D/A's
> taking in
> to consideration performance, solderability, cost, availability and the
> winner  is LTC 1655 by a long shot, is even available in a DIP with 16 bits
> more than  you need for any Rb and if you want 20 bits, dithering is an
> option.
> My testing  consistently shows with OCXO's aging that will in most cases
> allow operation of  an OCXO for 3 years with out intervention. To top it
> off
> the LTC1655 cost less  than $ 10. Testing the old AD 1861 was an eye opener
> but considering what its  purpose was and its time the best choice.
> Bert
>
> In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time,
> timenuts at n4iqt.com writes:
>
> The DAC  and it's voltage reference looks to be the weak link in the
> digital
> control and the "simple" goal. The CPU I mentioned before on closer look
> doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure
> you
> can find it in the same package as the CPU. The cheap Rb standards  with
> digital control would not need a DAC and maybe this points to a  simpler
> GPSDO that doesn't control the XO with analog but corrects it with  a DDS
> but
> again finding them both in one chip is the problem. I have seen  OCXO and
> DAC
> in the same package and even the DDS and OCXO combined but  they didn't fit
> the simple goal. Not even sure how good they were. I know  they are hard to
> find.
>
> Stanley
>
>
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