[time-nuts] DDS in GPSDO design?

[Bruce Griffiths]

A heroic effort that reduces DDS flicker and white PN by combining the 
outputs of several DDS generators:

http://www.ideals.illinois.edu/bitstream/handle/2142/16173/1_Comberiate_Thomas.pdf?sequence=3

Note this has no effect on spurs which are common to all the DDS generators.

Bruce

Bruce Griffiths wrote:
> These Xilinx datasheets indicate the performance of some techniques:
>
> http://www.xilinx.com/support/documentation/ip_documentation/ds794_dds_compiler.pdf 
>
>
> http://www.xilinx.com/support/documentation/ip_documentation/dds.pdf
>
> The Taylor series (amplitude and phase) correction technique is the 
> most effective.
>
> Bruce
>
> Mike Feher wrote:
>> With a finite number of bits for phase and amplitude, regardless of 
>> total
>> number of bits. How do you eliminate spurs by design? Thanks - Mike
>>
>> Mike B. Feher, EOZ Inc.
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960 office
>> 908-902-3831 cell
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Bruce Griffiths
>> Sent: Monday, May 28, 2012 12:10 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] DDS in GPSDO design?
>>
>> Michael Tharp wrote:
>>> On 05/27/2012 06:23 PM, Bruce Griffiths wrote:
>>>> The principal problem with conventional DDS implementations is phase
>>>> truncation spurs which can occur close to the desired carrier.
>>>> Virtually all commercial DDS chips produce such phase truncation 
>>>> spurs.
>>>>
>>>> It is possible to eliminate such spurs if one implements a custom DDS
>>>> using an FPGA and an external DAC.
>>>> In this case the performance is limited by the DAC.
>>> How specifically does the FPGA resolve the problem? I have a FPGA
>>> already for the phase comparator, it's just a "simple" matter of
>>> figuring out how big of a DAC to get and what data to feed it...
>>>
>> By implementing a design thats phase truncation spur free like:
>>
>> /Ultra low Phase noise DDS/ , Fred Harris, Chris Dick, Richard Jekel in
>> Proceedings of SDR06 Technical conference and Product exposition.
>> Both amplitude and phase errors arise due to phase truncation and its
>> essential to correct both.
>>
>> rather than the simplistic technique used in AD (and other) DDS chips 
>> where
>> the phase and amplitude errors due to truncation remain uncorrected.
>>>> Another approach is to use a cascaded mix and divide technique
>>>> <http://www.karlquist.com/FCS95.pdf>  to restrict the effective tuning
>>>> range of the DDS.
>>>> The amplitude of DDS generated spurs is thereby significantly reduced.
>>> Great paper, this looks like it could be interesting as a standalone
>>> filter. It's just a little over my head (self-taught digital guy) but
>>> since I don't need to hit a home run on the first try, I'll keep it in
>>> mind.
>>>
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