[time-nuts] DDS module
shalimr9 at gmail.com
Mon Jul 22 00:15:44 EDT 2013
There is no "cleanup" PLL in the SG8002, the output spectrum looks like that of a cheap PLL-on-a-chip. I did not see any evidence of wide band spurs but the phase noise is terrible, as you would get when the VCO and it's tank components are on-chip, which is the only way they could achieve the price point.
My experience also shows that high level of radiated noise around the device (as when used inside a high power switching supply) causes it to malfunction, as if it was losing lock. In our applications, they have to be shielded.
Tim Shoppa <tshoppa at gmail.com> wrote:
>SG8002 is definitely a distributor programmable unit.
>It is a digital synthesizer in a can with no effort towards clean
>PLL? They would not bother to put a cleanup PLL in the can for the
>intended microprocessor application.
>On 7/21/13, Didier Juges <shalimr9 at gmail.com> wrote:
>> I am familiar with the Epson Seiko SG8002 series and nowhere does it
>> they are programmable. They are not user programmable for sure, only
>> 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
>>>> spur issues. Anything that shows up listed as "user programmable" -
>>>But "user programmable" won't find all the nasty ones.
>>>I haven't been looking recently. There used to be some that were
>>>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
>>>oddball frequency. They didn't mention the PLL in the data sheet.
>>>to read between the lines.
>>>I assume the distributor stocked a handful of basic frequencies and
>>>a PC that told them which one to use and did the programming if you
>>>what frequency you wanted.
>>>It looks like a fun math problem. How many frequencies do you need
>>>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
>>>overall accuracy spec. (If you claim 100 PPM, but cut the crystal
>>>PPM, then you have 50 PPM left for the PLL.)
>>>These are my opinions. I hate spam.
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