Thanks - I'll look those over. Just seems the initial accumulator setting always needs to be known, or preset to a pre-defined number for anything to help. On top of that to apply a series, even with a limited length, just would add to settling time or introduce other issues. Regards - 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-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths Sent: Monday, May 28, 2012 12:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] DDS in GPSDO design? These Xilinx datasheets indicate the performance of some techniques: http://www.xilinx.com/support/documentation/ip_documentation/ds794_dds_compi ler.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-boun...@febo.com [mailto:time-nuts-boun...@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. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.