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

Azelio Boriani azelio.boriani at screen.it
Fri Dec 30 17:02:12 EST 2011


Yes, the DAC+reference is challenging and one way to go may be the
coarse+fine approach to avoid large (18bit and beyond) DAC. My last GPSDO
has an 18bit DAC but now I'm thinking to try the 8bit digital pot + 16bit
DAC op-amp combined. The reference can't be overlooked anyway.

On Fri, Dec 30, 2011 at 10:24 PM, Stanley <timenuts at n4iqt.com> wrote:

> 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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