[time-nuts] Thunderbolt? (re simple gpsdo.)
EWKehren at aol.com
EWKehren at aol.com
Fri Dec 30 22:48:24 UTC 2011
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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