[time-nuts] DDS module

Didier Juges shalimr9 at gmail.com
Sun Jul 21 22:42:06 EDT 2013

I am familiar with the Epson Seiko SG8002 series and nowhere does it say they are programmable. They are not user programmable for sure, only the distributor has the tools to do it. The data sheet does not have any information that would be a hint that they are PLL's.



Hal Murray <hmurray at megapathdsl.net> wrote:
>lists at rtty.us said:
>> A number of them are sigma delta PLL's and have some really nasty
>jitter and
>> spur issues. Anything that shows up listed as "user programmable" -
>> out. 
>But "user programmable" won't find all the nasty ones.
>I haven't been looking recently.  There used to be some that were field
>programable.  The idea was that the distributor would do it so you
>have to wait for the factory to grind the crystal to order if you
>wanted an 
>oddball frequency.  They didn't mention the PLL in the data sheet.  You
>to read between the lines.
>I assume the distributor stocked a handful of basic frequencies and
>there was 
>a PC that told them which one to use and did the programming if you
>told it 
>what frequency you wanted.
>It looks like a fun math problem.  How many frequencies do you need to
>in order to cover a given frequency range with a given PLL chip?  The
>doesn't have to be a direct hit.  You can include some fudge as part of
>overall accuracy spec.  (If you claim 100 PPM, but cut the crystal
>within 50 
>PPM, then you have 50 PPM left for the PLL.)
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