DDS wisdom

Am 06.12.2014 um 22:37 schrieb John Larkin:
> On Sat, 06 Dec 2014 16:17:49 -0500, Phil Hobbs
> <hobbs@electrooptical.net> wrote:

>>> It's pronounced "Keysight"
>>
>> Five years from now it'll be "FuzzyNuts".  You heard it here first.
>>
>
>
> Maybe they'll buy Rigol and put them out of business. Ditto!

No, Rigol will buy them.

They will follow the HP wafer tester operation.

HP-> Agilent -> Verigy -> outsource your hardware production
to China until you are unable to deliver -> move it somewhere else
(India IIRC) -> sell the farm to Advantest.

But you are right, too. While the Chinese could not produce
the high end hardware, they were able to do a low-end tester
that was compatible to Verigy's as a private stealth activity.
Verigy had to buy it back, I heard saying.

Gerhard

On Sun, 07 Dec 2014 14:07:26 +0100, Gerhard Hoffmann
<ghf@hoffmann-hochfrequenz.de> wrote:

>Am 06.12.2014 um 22:37 schrieb John Larkin:
>> On Sat, 06 Dec 2014 16:17:49 -0500, Phil Hobbs
>> <hobbs@electrooptical.net> wrote:
>
>>>> It's pronounced "Keysight"
>>>
>>> Five years from now it'll be "FuzzyNuts".  You heard it here first.
>>>
>>
>>
>> Maybe they'll buy Rigol and put them out of business. Ditto!
>
>No, Rigol will buy them.
>
>They will follow the HP wafer tester operation.
>
>HP-> Agilent -> Verigy -> outsource your hardware production
>to China until you are unable to deliver -> move it somewhere else
>(India IIRC) -> sell the farm to Advantest.
>
>But you are right, too. While the Chinese could not produce
>the high end hardware, they were able to do a low-end tester
>that was compatible to Verigy's as a private stealth activity.
>Verigy had to buy it back, I heard saying.
>
>Gerhard

Agilent acquired Varian Inc a few years ago. That included the NMR
operation. They promptly fired most of the US workers and moved the
operation to Maylasia. That turned out to not work very well, so they
recently shut it down.

Is this what is called "creative destruction"?



-- 

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

In article <m60oe9$28a$1@dont-email.me>, rickman <gnuarm@gmail.com>
wrote:

> On 12/6/2014 7:02 PM, Joe Gwinn wrote:
> > [[ This message was both posted and mailed: see
> >     the "To," "Cc," and "Newsgroups" headers for details. ]]
> >
> > In article <XnsA3FBA89E133D1idtokenpost@69.16.179.23>, Tom Swift
> > <spam@me.com> wrote:
> >
> >> Joe Gwinn <joegwinn@comcast.net> wrote:
> >>
> >>> In article <54826A1A.9080101@electrooptical.net>, Phil Hobbs
> >>> <hobbs@electrooptical.net> wrote:
> >>>
> >>>> On 12/5/2014 7:44 PM, Joe Gwinn wrote:
> >>
> >>>>> ADI has a very good tutorial on DDS theory, "MT-085: Fundamentals
> >>>>> of Direct Digital Synthesis (DDS)".  I'd read it.
> >>>>
> >>>> Thanks.  I did read it, but it didn't say what you said.
> >>>
> >>> Hmm.  I must be misremembering where I saw that.  I think they mention
> >>> the wheel, but they may not go into what happens at rollover.
> >>
> >> Don't give up so soon. I think you may be referring to Section 4, "The
> >> Effect of Truncating the Phase Accumulator on Spurious Performance,"
> >> starting on Page 19 of
> >>
> >>
> >> <http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tutoria
> >> l_rev12-2-99.pdf>
> >
> > Ahh.  Perhaps so.
> >
> >
> >> Fred Harris may have ways to help reduce it, discussed in "Ultra Low
> >> Phase Noise DSP Oscillator", at
> >>
> >>
> >> <https://www.researchgate.net/profile/Fred_Harris2/publication/3321879_Ultr
> >> a_Low_Phase_Noise_DSP_Oscillator_DSP_Tips__Tricks/links/542425050cf238c6ea6
> >> e953a>
> >
> > I may remember this.  I'll look into my trove at work.
> >
> >
> >>> I discovered the effect when analyzing why a prototype DMTD (Dual Mixer
> >>> Time Difference) instrument was suffering periodic phase bumps.  When
> >>> one is measuring the performance of Rubidium clocks (10^-11 fractional
> >>> frequency error), it doesn't take much.
> >>
> >> What did you use to solve the problem?
> >
> > I didn't.  The prototype belonged to one of our vendors (who shall
> > remain nameless), and they had developed it first for use in their own
> > lab, with distant theories about maybe selling it as well.  But no such
> > product has appeared in their catalog.  I bet they bought a Symmetricom
> > 5115a, which would cost a lot less than the effort to develop a good
> > enough unit.  The vendor was trying to use their prototype DMTD unit
> > for testing of a product being developed for my employer, and were
> > getting unexpected results.  My contribution was to figure out why.
> >
> > The way Symmetricom (actually Timing Solutions, acquired by
> > Symmetricom) solved the whole DDS spur and bump problem is by computing
> > the sine wave amplitudes directly (no DDS chip) and loading it into a
> > clock-indexed RAM unit.  These numbers are fed directly to a digital
> > multiplier (replacing an analog mixer). The actual frequency is tweaked
> > such that there is no glitch when the memory rolls over.  I got this
> > from a Timing Solutions patent.  That too is in the trove.
> 
> I can't say I follow exactly what you are describing that is different 
> from a DDS.  But your description is not perfectly clear so I can't be 
> sure.

Timing Solutions was not trying to implement a DDS.  They were
implementing a test set incorporating a DMTD architecture, and needed
to eliminate the forest of spurs, an application that isn't really
compatible with plain DDS sinewave generation.  

Joe Gwinn

[[ This message was both posted and mailed: see
   the "To," "Cc," and "Newsgroups" headers for details. ]]

In article <XnsA3FBE4901679Fidtokenpost@69.16.179.23>, Tom Swift
<spam@me.com> wrote:

> Joe Gwinn <joegwinn@comcast.net> wrote:
>  
> > In article <XnsA3FBA89E133D1idtokenpost@69.16.179.23>, Tom Swift
> > <spam@me.com> wrote:
> 
> >> Don't give up so soon. I think you may be referring to Section 4,
> >> "The Effect of Truncating the Phase Accumulator on Spurious
> >> Performance," starting on Page 19 of
>  
> >> <http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tu
> >> torial_rev12-2-99.pdf> 
>  
> > Ahh.  Perhaps so.
>  
> >> Fred Harris may have ways to help reduce it, discussed in "Ultra Low 
> >> Phase Noise DSP Oscillator", at
>  
> >> <https://www.researchgate.net/profile/Fred_Harris2/publication/3321879
> >> _Ultra_Low_Phase_Noise_DSP_Oscillator_DSP_Tips__Tricks/links/542425050
> >> cf238c6ea6e953a> 
> > 
> > I may remember this.  I'll look into my trove at work.
>  
> >> > I discovered the effect when analyzing why a prototype DMTD (Dual
> >> > Mixer Time Difference) instrument was suffering periodic phase
> >> > bumps.  When one is measuring the performance of Rubidium clocks
> >> > (10^-11 fractional frequency error), it doesn't take much. 
> >>  
> >> What did you use to solve the problem?
>  
> > I didn't.  The prototype belonged to one of our vendors (who shall
> > remain nameless), and they had developed it first for use in their own
> > lab, with distant theories about maybe selling it as well.  But no
> > such product has appeared in their catalog.  I bet they bought a
> > Symmetricom 5115a, which would cost a lot less than the effort to
> > develop a good enough unit.  The vendor was trying to use their
> > prototype DMTD unit for testing of a product being developed for my
> > employer, and were getting unexpected results.  My contribution was to
> > figure out why. 
> 
> Thanks for the info. The 5115a was from Timing Solutions. Johm Miles 
> developed a less expensive version called the TimePod 5330A and sold for 
> US $4995.00:
> 
> <https://www.febo.com/pipermail/time-nuts/2012-June/068069.html>
> 
> This was later acquired by Symmetricom, which now Microsemi. 
> Theoretically, you can build one from information in the user manual:
> 
> <http://www.miles.io/TimePod_5330A_user_manual.pdf>

The manual has no real principles of operation discussion, but it does
appear to be the RF front end of the Timing Solutions 5110 (40 MHz top
end) not the 5115 (400 MHz?).


> It runs on John's Timelab software available at
> 
> <http://www.ke5fx.com/timelab/readme.htm>
> 
> Ulrich used the SR620 to find the phase bump in his post at
> 
> <https://www.febo.com/pipermail/time-nuts/2011-January/053863.html>
> 
> Here's the user manual:
> 
> <http://www.thinksrs.com/downloads/PDFs/Manuals/SR620m.pdf>
> 
> With all these heavyweights and specialized equipment in the frequency 
> and time field, I am extremely impressed that you managed to find the 
> problem with no outside support. Congratulations!

Well, thanks, but I didn't come to the issue without any related
background in Time.  I'm a Time-Nut lurker as well.

For the record, I was getting plots like those published by Ulrich, and
the regular sawtooth error was a dead giveaway, and a
back-of-the-enevelop calculation showed that the sawtooth period was at
the rollover rate.


> > The way Symmetricom (actually Timing Solutions, acquired by
> > Symmetricom) solved the whole DDS spur and bump problem is by
> > computing the sine wave amplitudes directly (no DDS chip) and loading
> > it into a clock-indexed RAM unit.  These numbers are fed directly to a
> > digital multiplier (replacing an analog mixer). The actual frequency
> > is tweaked such that there is no glitch when the memory rolls over.  I
> > got this from a Timing Solutions patent.  That too is in the trove.
> 
> Interesting. I'd like to find that patent. It may help solve a problem 
> I'm having with generating small frequency offsets.
> 
> I have been searching for Timing Solutions patents with not very good 
> luck so far. I hope you have some time soon to open your treasure chest 
> and sprinkle some of the delights around.

I recall having that problem when I was looking, circa 2007 when 
Symmetricom had just purchased TS, and I borrowed and tested their
early versions of the 5110.  Many of the TS patents were in the name of
their founder, Samuel Stein.

Anyway, Ill dig the patent numbers out.  I bet there are more patents
now.


> Also, if you happen to come across anything from Holzworth 
> Instrumentation in Boulder, please let me know. They have a propretary 
> synthesizer technique that doesn't use plls and apparently no DDS. They 
> can switch frequencies anywhere from anywhere to in 50us, and nearby 
> frequencies in 5us. It is driving me mad to figure out how they do it. 
> There is apparently nothing in the literature or anything on the web that 
> talks about anything that can do that.

Yeah, I know.  Their sales engineers were giving me the
I've-got-a-secret routine as well.  But the founder (Jason Breitbarth)
is the main brain, and as is often the case with small technology
companies, the core technology was developed for his PhD thesis, and
it's all there:   
<http://ecee.colorado.edu/microwave/docs/theses/jasonb_phd_thesis.pdf>

Joe Gwinn

On 12/7/2014 2:26 PM, Joe Gwinn wrote:
> In article <m60oe9$28a$1@dont-email.me>, rickman <gnuarm@gmail.com>
> wrote:
>
>> On 12/6/2014 7:02 PM, Joe Gwinn wrote:
>>> [[ This message was both posted and mailed: see
>>>      the "To," "Cc," and "Newsgroups" headers for details. ]]
>>>
>>> In article <XnsA3FBA89E133D1idtokenpost@69.16.179.23>, Tom Swift
>>> <spam@me.com> wrote:
>>>
>>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>>
>>>>> In article <54826A1A.9080101@electrooptical.net>, Phil Hobbs
>>>>> <hobbs@electrooptical.net> wrote:
>>>>>
>>>>>> On 12/5/2014 7:44 PM, Joe Gwinn wrote:
>>>>
>>>>>>> ADI has a very good tutorial on DDS theory, "MT-085: Fundamentals
>>>>>>> of Direct Digital Synthesis (DDS)".  I'd read it.
>>>>>>
>>>>>> Thanks.  I did read it, but it didn't say what you said.
>>>>>
>>>>> Hmm.  I must be misremembering where I saw that.  I think they mention
>>>>> the wheel, but they may not go into what happens at rollover.
>>>>
>>>> Don't give up so soon. I think you may be referring to Section 4, "The
>>>> Effect of Truncating the Phase Accumulator on Spurious Performance,"
>>>> starting on Page 19 of
>>>>
>>>>
>>>> <http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tutoria
>>>> l_rev12-2-99.pdf>
>>>
>>> Ahh.  Perhaps so.
>>>
>>>
>>>> Fred Harris may have ways to help reduce it, discussed in "Ultra Low
>>>> Phase Noise DSP Oscillator", at
>>>>
>>>>
>>>> <https://www.researchgate.net/profile/Fred_Harris2/publication/3321879_Ultr
>>>> a_Low_Phase_Noise_DSP_Oscillator_DSP_Tips__Tricks/links/542425050cf238c6ea6
>>>> e953a>
>>>
>>> I may remember this.  I'll look into my trove at work.
>>>
>>>
>>>>> I discovered the effect when analyzing why a prototype DMTD (Dual Mixer
>>>>> Time Difference) instrument was suffering periodic phase bumps.  When
>>>>> one is measuring the performance of Rubidium clocks (10^-11 fractional
>>>>> frequency error), it doesn't take much.
>>>>
>>>> What did you use to solve the problem?
>>>
>>> I didn't.  The prototype belonged to one of our vendors (who shall
>>> remain nameless), and they had developed it first for use in their own
>>> lab, with distant theories about maybe selling it as well.  But no such
>>> product has appeared in their catalog.  I bet they bought a Symmetricom
>>> 5115a, which would cost a lot less than the effort to develop a good
>>> enough unit.  The vendor was trying to use their prototype DMTD unit
>>> for testing of a product being developed for my employer, and were
>>> getting unexpected results.  My contribution was to figure out why.
>>>
>>> The way Symmetricom (actually Timing Solutions, acquired by
>>> Symmetricom) solved the whole DDS spur and bump problem is by computing
>>> the sine wave amplitudes directly (no DDS chip) and loading it into a
>>> clock-indexed RAM unit.  These numbers are fed directly to a digital
>>> multiplier (replacing an analog mixer). The actual frequency is tweaked
>>> such that there is no glitch when the memory rolls over.  I got this
>>> from a Timing Solutions patent.  That too is in the trove.
>>
>> I can't say I follow exactly what you are describing that is different
>> from a DDS.  But your description is not perfectly clear so I can't be
>> sure.
>
> Timing Solutions was not trying to implement a DDS.  They were
> implementing a test set incorporating a DMTD architecture, and needed
> to eliminate the forest of spurs, an application that isn't really
> compatible with plain DDS sinewave generation.

You seem to be very confused.  The circuit you described *is* a DDS. 
How is it different?  From what you describe it is more limited in ways 
that remove the possibility of setting the step size.  That is the only 
way to preclude spurs which arise because the output frequency is not a 
divisor of the input frequency.

You snipped my explanation of this.  Do you not agree with me or do you 
not understand it?

-- 

Rick

In article <m62j8h$o39$1@dont-email.me>, rickman <gnuarm@gmail.com>
wrote:

> On 12/7/2014 2:26 PM, Joe Gwinn wrote:
> > In article <m60oe9$28a$1@dont-email.me>, rickman <gnuarm@gmail.com>
> > wrote:
> >
> >> On 12/6/2014 7:02 PM, Joe Gwinn wrote:
> >>> [[ This message was both posted and mailed: see
> >>>      the "To," "Cc," and "Newsgroups" headers for details. ]]
> >>>
> >>> In article <XnsA3FBA89E133D1idtokenpost@69.16.179.23>, Tom Swift
> >>> <spam@me.com> wrote:
> >>>
> >>>> Joe Gwinn <joegwinn@comcast.net> wrote:
> >>>>
> >>>>> In article <54826A1A.9080101@electrooptical.net>, Phil Hobbs
> >>>>> <hobbs@electrooptical.net> wrote:
> >>>>>
> >>>>>> On 12/5/2014 7:44 PM, Joe Gwinn wrote:
> >>>>
> >>>>>>> ADI has a very good tutorial on DDS theory, "MT-085: Fundamentals
> >>>>>>> of Direct Digital Synthesis (DDS)".  I'd read it.
> >>>>>>
> >>>>>> Thanks.  I did read it, but it didn't say what you said.
> >>>>>
> >>>>> Hmm.  I must be misremembering where I saw that.  I think they mention
> >>>>> the wheel, but they may not go into what happens at rollover.
> >>>>
> >>>> Don't give up so soon. I think you may be referring to Section 4, "The
> >>>> Effect of Truncating the Phase Accumulator on Spurious Performance,"
> >>>> starting on Page 19 of
> >>>>
> >>>>
> >>>>
> >>>> <http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tutor
> >>>> ia
> >>>> l_rev12-2-99.pdf>
> >>>
> >>> Ahh.  Perhaps so.
> >>>
> >>>
> >>>> Fred Harris may have ways to help reduce it, discussed in "Ultra Low
> >>>> Phase Noise DSP Oscillator", at
> >>>>
> >>>>
> >>>>
> >>>> <https://www.researchgate.net/profile/Fred_Harris2/publication/3321879_Ul
> >>>> tr
> >>>>
> >>>> a_Low_Phase_Noise_DSP_Oscillator_DSP_Tips__Tricks/links/542425050cf238c6e
> >>>> a6
> >>>> e953a>
> >>>
> >>> I may remember this.  I'll look into my trove at work.
> >>>
> >>>
> >>>>> I discovered the effect when analyzing why a prototype DMTD (Dual Mixer
> >>>>> Time Difference) instrument was suffering periodic phase bumps.  When
> >>>>> one is measuring the performance of Rubidium clocks (10^-11 fractional
> >>>>> frequency error), it doesn't take much.
> >>>>
> >>>> What did you use to solve the problem?
> >>>
> >>> I didn't.  The prototype belonged to one of our vendors (who shall
> >>> remain nameless), and they had developed it first for use in their own
> >>> lab, with distant theories about maybe selling it as well.  But no such
> >>> product has appeared in their catalog.  I bet they bought a Symmetricom
> >>> 5115a, which would cost a lot less than the effort to develop a good
> >>> enough unit.  The vendor was trying to use their prototype DMTD unit
> >>> for testing of a product being developed for my employer, and were
> >>> getting unexpected results.  My contribution was to figure out why.
> >>>
> >>> The way Symmetricom (actually Timing Solutions, acquired by
> >>> Symmetricom) solved the whole DDS spur and bump problem is by computing
> >>> the sine wave amplitudes directly (no DDS chip) and loading it into a
> >>> clock-indexed RAM unit.  These numbers are fed directly to a digital
> >>> multiplier (replacing an analog mixer). The actual frequency is tweaked
> >>> such that there is no glitch when the memory rolls over.  I got this
> >>> from a Timing Solutions patent.  That too is in the trove.
> >>
> >> I can't say I follow exactly what you are describing that is different
> >> from a DDS.  But your description is not perfectly clear so I can't be
> >> sure.
> >
> > Timing Solutions was not trying to implement a DDS.  They were
> > implementing a test set incorporating a DMTD architecture, and needed
> > to eliminate the forest of spurs, an application that isn't really
> > compatible with plain DDS sinewave generation.
> 
> You seem to be very confused.  The circuit you described *is* a DDS. 
> How is it different?  From what you describe it is more limited in ways 
> that remove the possibility of setting the step size.  That is the only 
> way to preclude spurs which arise because the output frequency is not a 
> divisor of the input frequency.
> 
> You snipped my explanation of this.  Do you not agree with me or do you 
> not understand it?

You were complaining that it wasn't a correct DDS.  You are right -- it
isn't a DDS.  No further comment required.

Joe Gwinn

On Saturday, December 6, 2014 12:52:34 PM UTC-5, Phil Hobbs wrote:
> On 12/6/2014 11:27 AM, George Herold wrote:
> > On Friday, December 5, 2014 9:37:20 PM UTC-5, Phil Hobbs wrote:
> >> On 12/5/2014 7:12 PM, George Herold wrote:
> >>> On Thursday, December 4, 2014 3:04:06 PM UTC-5, Phil Hobbs wrote:
> >>>> Hi, all,
> >>>>
> >>>> I have a gig coming in that will have me revisiting my thesis research
> >>>> from nearly 30 years ago, on interferometric laser microscopes.  (Fun.)
> >>>>
> >>>> Back in the day, I made a nulling-type phase digitizer at 60 MHz by
> >>>> driving a phase shifter with a 12-bit DAC (AD-DAC80), and wrapping a
> >>>> 13-bit successive approximation loop round it (AM2904 with an extra
> >>>> flipflop).  With quite a lot of calibration, that got me a 13-bit, 2-pi,
> >>>> 50 ks/s phase measurement that I was pretty happy with.  (The extra bit
> >>>> came from deciding which null to head for, which is why I needed the
> >>>> extra FF.)  It was all interfaced to an HP 9816 computer via a GPIO
> >>>> card, and (eventually) worked great.  I published one of my only two
> >>>> instruments papers on it (this was before I realized the total futility
> >>>> of almost all instruments papers).
> >>>
> >>> Hi Phil, I've been sorta half following this thread,
> >>> and I wonder if you could tell me what a nulling type phase digitizer is?
> >>> (I "turn" the phase knob of a lockin type mixer/detector till the signal goes to zero?)
> >>> Maybe just a reference to your instrument paper...?
> >>>
> >>> George H.
> >>
> >>
> >> Hi, George,
> >>
> >> The idea is to use a phase detector wrapped in a successive
> >> approximation loop.  Like other SAR ADCs, you run the register to null
> >> out the error signal to N bits' accuracy, and read off the value from
> >> the DAC control word corresponding to the null.  In this case, the 'DAC'
> >> is a phase shifter.
> >>
> >> I looked around for a copy of the instruments paper, but couldn't find
> >> it--it predates my earliest digital archives, having been published in
> >> 1987.  It's at http://dx.doi.org/10.1063/1.1139391 .
> >>
> >> Cheers
> >>
> >> Phil Hobbs
> > Got it, and by 2-D you mean fixing the phase
> > and measuring the amplitude and phase in both I/Q channels.
> >
> > I'll check out your paper on Monday.
> > We have the whole series of RSI that a library
> > was pitching.
> > Makes great fodder for the "reading room."
> 
> Youch, that smarts. ;)  (But not too inaccurate for the most part.)
Ohh.. my fault, Re: "reading room" fodder is RSI not your article.  

Though I do some of my best thinking in the bathroom,  
the shower mostly. 

George H.  
> 
> Cheers
> 
> Phil Hobbs
> 
> 
> -- 
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
> 
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 
> hobbs at electrooptical dot net
> http://electrooptical.net

On 12/7/2014 6:51 PM, Joe Gwinn wrote:
> In article <m62j8h$o39$1@dont-email.me>, rickman <gnuarm@gmail.com>
> wrote:
>
>> On 12/7/2014 2:26 PM, Joe Gwinn wrote:
>>> In article <m60oe9$28a$1@dont-email.me>, rickman <gnuarm@gmail.com>
>>> wrote:
>>>
>>>> On 12/6/2014 7:02 PM, Joe Gwinn wrote:
>>>>> [[ This message was both posted and mailed: see
>>>>>       the "To," "Cc," and "Newsgroups" headers for details. ]]
>>>>>
>>>>> In article <XnsA3FBA89E133D1idtokenpost@69.16.179.23>, Tom Swift
>>>>> <spam@me.com> wrote:
>>>>>
>>>>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>>>>
>>>>>>> In article <54826A1A.9080101@electrooptical.net>, Phil Hobbs
>>>>>>> <hobbs@electrooptical.net> wrote:
>>>>>>>
>>>>>>>> On 12/5/2014 7:44 PM, Joe Gwinn wrote:
>>>>>>
>>>>>>>>> ADI has a very good tutorial on DDS theory, "MT-085: Fundamentals
>>>>>>>>> of Direct Digital Synthesis (DDS)".  I'd read it.
>>>>>>>>
>>>>>>>> Thanks.  I did read it, but it didn't say what you said.
>>>>>>>
>>>>>>> Hmm.  I must be misremembering where I saw that.  I think they mention
>>>>>>> the wheel, but they may not go into what happens at rollover.
>>>>>>
>>>>>> Don't give up so soon. I think you may be referring to Section 4, "The
>>>>>> Effect of Truncating the Phase Accumulator on Spurious Performance,"
>>>>>> starting on Page 19 of
>>>>>>
>>>>>>
>>>>>>
>>>>>> <http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tutor
>>>>>> ia
>>>>>> l_rev12-2-99.pdf>
>>>>>
>>>>> Ahh.  Perhaps so.
>>>>>
>>>>>
>>>>>> Fred Harris may have ways to help reduce it, discussed in "Ultra Low
>>>>>> Phase Noise DSP Oscillator", at
>>>>>>
>>>>>>
>>>>>>
>>>>>> <https://www.researchgate.net/profile/Fred_Harris2/publication/3321879_Ul
>>>>>> tr
>>>>>>
>>>>>> a_Low_Phase_Noise_DSP_Oscillator_DSP_Tips__Tricks/links/542425050cf238c6e
>>>>>> a6
>>>>>> e953a>
>>>>>
>>>>> I may remember this.  I'll look into my trove at work.
>>>>>
>>>>>
>>>>>>> I discovered the effect when analyzing why a prototype DMTD (Dual Mixer
>>>>>>> Time Difference) instrument was suffering periodic phase bumps.  When
>>>>>>> one is measuring the performance of Rubidium clocks (10^-11 fractional
>>>>>>> frequency error), it doesn't take much.
>>>>>>
>>>>>> What did you use to solve the problem?
>>>>>
>>>>> I didn't.  The prototype belonged to one of our vendors (who shall
>>>>> remain nameless), and they had developed it first for use in their own
>>>>> lab, with distant theories about maybe selling it as well.  But no such
>>>>> product has appeared in their catalog.  I bet they bought a Symmetricom
>>>>> 5115a, which would cost a lot less than the effort to develop a good
>>>>> enough unit.  The vendor was trying to use their prototype DMTD unit
>>>>> for testing of a product being developed for my employer, and were
>>>>> getting unexpected results.  My contribution was to figure out why.
>>>>>
>>>>> The way Symmetricom (actually Timing Solutions, acquired by
>>>>> Symmetricom) solved the whole DDS spur and bump problem is by computing
>>>>> the sine wave amplitudes directly (no DDS chip) and loading it into a
>>>>> clock-indexed RAM unit.  These numbers are fed directly to a digital
>>>>> multiplier (replacing an analog mixer). The actual frequency is tweaked
>>>>> such that there is no glitch when the memory rolls over.  I got this
>>>>> from a Timing Solutions patent.  That too is in the trove.
>>>>
>>>> I can't say I follow exactly what you are describing that is different
>>>> from a DDS.  But your description is not perfectly clear so I can't be
>>>> sure.
>>>
>>> Timing Solutions was not trying to implement a DDS.  They were
>>> implementing a test set incorporating a DMTD architecture, and needed
>>> to eliminate the forest of spurs, an application that isn't really
>>> compatible with plain DDS sinewave generation.
>>
>> You seem to be very confused.  The circuit you described *is* a DDS.
>> How is it different?  From what you describe it is more limited in ways
>> that remove the possibility of setting the step size.  That is the only
>> way to preclude spurs which arise because the output frequency is not a
>> divisor of the input frequency.
>>
>> You snipped my explanation of this.  Do you not agree with me or do you
>> not understand it?
>
> You were complaining that it wasn't a correct DDS.  You are right -- it
> isn't a DDS.  No further comment required.

Ok, if you want to play games then you win.   If you don't understand, 
that's one thing.  If you don't *want* to understand no one can make you.

-- 

Rick

Joe Gwinn <joegwinn@comcast.net> wrote:

> In article <XnsA3FBE4901679Fidtokenpost@69.16.179.23>, Tom Swift
> <spam@me.com> wrote:

>> Theoretically, you can build one from information in the user
>> manual:

>> <http://www.miles.io/TimePod_5330A_user_manual.pdf>

> The manual has no real principles of operation discussion, but it
> does appear to be the RF front end of the Timing Solutions 5110
> (40 MHz top end) not the 5115 (400 MHz?).

Yes. That makes it useless for 100MHz or 1GHz and above. For this
reason, I have decided to go the E5052A route with quadrature mixers
and cross-correlation. This requires local oscillators as good as
what you are trying to measure, so I am very interested in very low
phase noise synthesizers.

>> With all these heavyweights and specialized equipment in the
>> frequency and time field, I am extremely impressed that you
>> managed to find the problem with no outside support.
>> Congratulations!

> Well, thanks, but I didn't come to the issue without any related
> background in Time. I'm a Time-Nut lurker as well.

> For the record, I was getting plots like those published by
> Ulrich, and the regular sawtooth error was a dead giveaway, and a
> back-of-the-enevelop calculation showed that the sawtooth period
> was at the rollover rate.

Your employer is very fortunate to have you. Anyone else would have
been totally baffled.

> I recall having that problem when I was looking, circa 2007 when
> Symmetricom had just purchased TS, and I borrowed and tested their
> early versions of the 5110. Many of the TS patents were in the
> name of their founder, Samuel Stein.

> Anyway, I'll dig the patent numbers out. I bet there are more
> patents now.

Actually, I'm more interested in Holzworth, but I'll be very
interested in anything you come up with. In the meantime, I'll start
searching and see if I can find anything useful.

>> Also, if you happen to come across anything from Holzworth
>> Instrumentation in Boulder, please let me know. They have a
>> propretary synthesizer technique that doesn't use plls and
>> apparently no DDS. They can switch frequencies anywhere from
>> anywhere to in 50us, and nearby frequencies in 5us. It is driving
>> me mad to figure out how they do it.

>> There is apparently nothing in the literature or anything on the
>> web that talks about anything that can do that.

> Yeah, I know. Their sales engineers were giving me the
> I've-got-a-secret routine as well. But the founder (Jason
> Breitbarth) is the main brain, and as is often the case with small
> technology companies, the core technology was developed for his
> PhD thesis, and it's all there:

> <http://ecee.colorado.edu/microwave/docs/theses/jasonb_phd_thesis.pdf>

That's a neat trick! I had the privilege of living in Boulder for a
number of years, and I can see that someoe who lives there would be
reluctant to move. After they get their degree, they'd rather start
a company if they have any brains. So all you need to do is search
Boulder University for their thesis. Brilliant!

I read through the entire thesis but it's basically a 4.6GHZ coaxial
resonator oscillator and nonlinear transmission lines using a YIG
filter. There's nothing on wideband synthesizers. Multiplying up
from 100MHz would create sidebands that would be very hard to
remove, especially for a variable frequency system.

> Joe Gwinn

On 12/7/2014 12:00 AM, rickman wrote:
> On 12/6/2014 4:01 PM, Phil Hobbs wrote:
>> On 12/5/2014 11:24 PM, rickman wrote:
>>> On 12/5/2014 10:19 PM, John Larkin wrote:
>>>> On Fri, 05 Dec 2014 21:29:46 -0500, Phil Hobbs
>>>> <hobbs@electrooptical.net> wrote:
>>>>
>>>>> On 12/5/2014 7:44 PM, Joe Gwinn wrote:
>>>>>> In article <5481273A.6010107@electrooptical.net>, Phil Hobbs
>>>>>> <hobbs@electrooptical.net> wrote:
>>>>>>
>>>>>>> On 12/4/2014 7:44 PM, Joe Gwinn wrote:
>>>>>>>> In article <cYydnTNwFPGvIx3JnZ2dnUU7-W-dnZ2d@supernews.com>, Phil
>>>>>>>> Hobbs
>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>>
>>>>>>>>> Hi, all,
>>>>>>>>>
>>>>>>>>> I have a gig coming in that will have me revisiting my thesis
>>>>>>>>> research
>>>>>>>>> from nearly 30 years ago, on interferometric laser microscopes.
>>>>>>>>> (Fun.)
>>>>>>>>>
>>>>>>>>> Back in the day, I made a nulling-type phase digitizer at 60
>>>>>>>>> MHz by
>>>>>>>>> driving a phase shifter with a 12-bit DAC (AD-DAC80), and
>>>>>>>>> wrapping a
>>>>>>>>> 13-bit successive approximation loop round it (AM2904 with an
>>>>>>>>> extra
>>>>>>>>> flipflop).  With quite a lot of calibration, that got me a
>>>>>>>>> 13-bit, 2-pi,
>>>>>>>>> 50 ks/s phase measurement that I was pretty happy with.  (The
>>>>>>>>> extra bit
>>>>>>>>> came from deciding which null to head for, which is why I needed
>>>>>>>>> the
>>>>>>>>> extra FF.)  It was all interfaced to an HP 9816 computer via a
>>>>>>>>> GPIO
>>>>>>>>> card, and (eventually) worked great.  I published one of my only
>>>>>>>>> two
>>>>>>>>> instruments papers on it (this was before I realized the total
>>>>>>>>> futility
>>>>>>>>> of almost all instruments papers).
>>>>>>>>>
>>>>>>>>> The advantage of nulling detection is that you only need 1-D
>>>>>>>>> calibration
>>>>>>>>> tables for phase shift and amplitude, whereas getting that sort of
>>>>>>>>> accuracy with I/Q techniques requires a 2-D calibration table,
>>>>>>>>> which is
>>>>>>>>> a gigantic pain.
>>>>>>>>>
>>>>>>>>> I need to do this again, 2015 style.  The speed requirements are
>>>>>>>>> set by
>>>>>>>>> the acoustic delay in the AO scanner, so 50-100 ks/s is about all
>>>>>>>>> I can
>>>>>>>>> use.  Rather than all that squishy analogue stuff, I'm planning
>>>>>>>>> to do
>>>>>>>>> the SAR in software and use a pair of AD9951 DDS chips, one to
>>>>>>>>> generate
>>>>>>>>> the desired signal and one to be the phase shifted comparison
>>>>>>>>> signal.
>>>>>>>>>
>>>>>>>>> So far so straightforward.
>>>>>>>>>
>>>>>>>>> What I'm less sure about is being able to keep the two channels
>>>>>>>>> sufficiently isolated to be able to maintain 12 or ideally 14
>>>>>>>>> bits of
>>>>>>>>> phase accuracy.  Even with a full-scale input, I'll need 85 dB of
>>>>>>>>> isolation to get 14 bits, and it gets harder with weaker signals.
>>>>>>>>> (There'll be a DLVA/limiter ahead of the phase detector, which
>>>>>>>>> will help.)
>>>>>>>>>
>>>>>>>>> I've never used DDSes before, and I'd appreciate some wisdom from
>>>>>>>>> folks
>>>>>>>>> who have.  How hard is that likely to be, and what should I
>>>>>>>>> particularly
>>>>>>>>> watch out for?
>>>>>>>>
>>>>>>>> DDSs have a forest of rational-multiple (but not necessarily
>>>>>>>> harmonic)
>>>>>>>> spurs, and it can be difficult to get them below -60 dBc unless
>>>>>>>> you can
>>>>>>>> place some restrictions on the frequency resolution.
>>>>>>>
>>>>>>> I can pick my IF to be anything I like, which I expect will help.
>>>>>>>>
>>>>>>>> Also beware phase jumps when the DDS phase wheel rolls over.
>>>>>>>
>>>>>>> Could you elaborate a bit?  I thought the whole idea was to keep
>>>>>>> phase
>>>>>>> continuity.
>>>>>>
>>>>>> Lots of people have elaborated on the point, so I won't recite it.
>>>>>>
>>>>>> It's true that choosing tuning words with the lower k (one chooses a
>>>>>> suitable value such that nothing is truncated in lookup tables) bits
>>>>>> zero will greatly reduce the number of spurs, and get rid of the
>>>>>> phase
>>>>>> bump when the phase wheel rolls over, but there will still be lots of
>>>>>> spurs from the limited width of the lookup tables and DACs.
>>>>>
>>>>> If the 'hidden' bits in the phase register are always zero, then the
>>>>> output of the DAC should be strictly periodic at f_out.  That means
>>>>> that
>>>>> all, and I mean *all*, of the artifacts will be harmonics of f_out.
>>>>> Isn't that so?
>>>>
>>>> Sure. Absolutely everything repeats at Fout.
>>>
>>> No, that's not correct.  All of the phase words will repeat every cycle
>>> of Fout only if the modulus is a multiple of the phase step which in the
>>> case of a 2^N modulus means the step size is power of 2 as well.  Or in
>>> other words, the clock rate is a power of 2 harmonic of Fout or octaves.
>>
>> How is that different from saying that the hidden bits of the phase
>> accumulator remain constant?  It seems like we're in violent agreement,
>> except that you haven't noticed yet. ;)
>>
>> If the hidden bits are always zero, then in each cycle, all the DAC
>> codes repeat,  so the waveform is ideally perfectly periodic.  No?
>
> I am trying to explain to you that zeros in the lower bits of the phase
> step is not the same as a zero value in the truncated bits of the step
> size.  Lets say there are no truncated bits in the phase step or
> accumulator just to make it easier to talk about.  You are saying that
> anything you then program into the phase step word will give you a
> waveform that is exactly the same on each cycle of that waveform.  This
> is not correct.  Easy example, 4 bit accumulator with a phase step of 3.
>   Modulus of 16 gives cycles of 0,3,6,9,12,15 - 2,5,8,11,14 -
> 1,4,7,10,13.  Notice not only  are the cycles not the same, they aren't
> even the same number of samples.
>
> To have each cycle of the output be identical the modulus has to be an
> integer multiple of the step size.  If you have a remainder when
> dividing the modulus by the step size, this remainder will be an offset
> at the start of the next cycle which means it won't be the same as the
> first cycle.  With a modulus of 2^n that requires the step size to be
> 2^m.  That is not the same requirement than having zero value in the
> truncated bits of the step size.
>
> In fact, having zero in the truncated portion of the step size is not
> even a requirement as long as the ratio of the modulus to the step size
> is an integer.  Again, with a modulus of 2^N, if the msb of the
> truncated portion of the step size is 1 and the rest of the word is
> zeros the Fout cycle will repeat exactly each cycle of Fout.  As I said
> before, you will get larger spurs, but they will all be clock related
> spurs exactly the same as having no truncated bits with a clock rate
> half the actual rate.  Easy example - Modulus of 16, 3 bits output, 1
> truncated bit, step value of 1 - 0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7 and
> repeat.
>
> So we are *not* in violent agreement... and it is you who hasn't
> noticed... yet.  I hope this covers it.
>

Quite right, thanks.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net