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
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
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?).
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.
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.
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:
Joe Gwinn
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
You were complaining that it wasn't a correct DDS. You are right -- it isn't a DDS. No further comment required.
Joe Gwinn
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.
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
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.
Your employer is very fortunate to have you. Anyone else would have been totally baffled.
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.
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.
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
That's something you don't see in s.e.d every day, a polite response... lol
BTW, I see my opening sentence was double talk. I think I meant to say "zeros in the lower bits of the phase step is not the same as the modulus being a multiple of the phase step."
Anyway, I'm glad we found common ground.
Now if I could get some of the other posters here to tell me what they mean by the mythical "phase jump" when the phase accumulator rolls over.
-- Rick
If I thought I was always right about everything, I wouldn't need to talk to anybody. ;)
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
Lol, yeah. That's a large part of why I'm here, to learn something in the areas I know less about, like most things analog. Joerg helped me a lot a couple of weeks ago to learn about the Miller effect and cascode circuits.
Have you figured out what people are referring to when they talk about the "phase jump" as the accumulator wraps around? I'm thinking they are talking about the remainder that results from the non-integral ratio of the step size and modulus. It's not really a "jump", but I can see someone referring to it that way in a conversation.
I find it funny that some don't seem to really understand how a DDS works. Joe Gwinn seems to think there is something different about the way Timing Solutions implemented a non-DDS so it didn't have spurs. "The actual frequency is tweaked such that there is no glitch when the memory rolls over." I believe all they did was use the equivalent of a DDS circuit with limitations so there was no remainder. I expect they incremented the phase by 1 and could only generate outputs that were integer ratios to the reference clock.
-- Rick
It seems like the issue is that for many choices of the phase increment, there's a spur very close to the carrier, associated with the actual periodicity of the waveform. With an N-bit accumulator, it's quite possible for this to be many times longer than 2**N clock cycles, i.e. far too long to be visible on frequency-domain instruments such as spectrum analyzers, and long enough to be surprising to even fairly sophisticated users.
The paper referenced upthread that used (instead of a sine LUT) a two-turn CORDIC algorithm with AGC to generate the output is a pretty good read.
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
Yes, but a spur would not be described as a "phase jump" on "rollover". Do you think this is what they are talking about? That would be so far removed from what *is* happening that it's hard to imagine.
I didn't dig into all the papers people referenced. I looked at some and didn't find much to explain what they were talking about. What Joe described was a simple lookup table with sine values in it which is how a DDS works. There are two forms of spurs from digital implementations. One is from phase quantization and the other is from amplitude quantization. Then the DAC has its own type of distortion which can also produce spurs but are not directly related to the fact that the data is digital. The other two types are an inherent limitation of digital data representation of a sine wave. The phase quantization can be completely eliminated by using only integer ratios between the reference clock frequency and the synthesized frequency. Amplitude quantization can not be eliminated and ultimately is imposed by the resolution of the DAC.
I designed a DDS a couple of years ago and used a reasonable size LUT with linear interpolation. I think the ultimate sine values were accurate to about 20 or maybe 22 bits. But that was all overkill. Even though I had 24 bit DACs the SNR and SINAD were in the 90s and 100s of dB. At least I was confident it wasn't the digital stuff that limited the result.
-- Rick
Well, the vendor's engineers were baffled to be sure. They knew about time, but not so much DDS theory.
On reflection, I think it was more like 2008 or 2009 that I was doing this, because Timing Solutions was already a part of Symmetricom.
I did find the Timing Solutions patent numbers from back in the day. There may be more patents. Search on the inventor names, and the "referenced by" section in Google Patents and the US Patent Office. Stein pat5315566, Stein pat5155695, Stein pat5128909, Solbrig (Phase Det) pat7227346, Solbrig (DDS) pat7436166, pat7511469, pat6194918, and pat6172533.
Rickman - see Solbrig (DDS) pat7436166.
So, you still live in Boulder?
Hmm. The mapping from the various boasts about Holtzworth's products and sales pitches to the thesis seemed pretty clear to me. If I recall, he was using a vernier set of frequency combs, arranged such that it was easy to lock a PLL onto a specified multiple. After that, one used mixers.
Joe Gwinn
The Solbrig patent includes a way of designing a DDS (they even call it a DDS) that uses a table of variable size. But they are still limited to the frequencies they can generate. They can only produce frequencies that are rationally related to the reference clock frequency.
The point is that the spurs that were eliminated are not *inherent* in DDS designs. They arise from trying to generated output frequencies that are not related to the reference clock.
You never did explain what you meant by the "phase bumps".
-- Rick
Well, I think I have egg on my face. All of the above discussion was based on two assumptions. One was that the modulus of the phase accumulator was 2^N and the other was that a necessary condition for not having phase error generated spurs was that the exact same pattern of values be produced on each output cycle. The first is just the assumption we made to ease the math and so is fine as long as we remember that was our assumption and then consider the more general case as well. But the second assumption was wrong!
The requirement for producing an sine wave without spurs is to produce each sample with no errors. That does *not* imply that each output cycle have the exact same data. For each output cycle to have the same data the modulus has to be an integer multiple of the phase step size. But any pattern that does not produce a phase error will produce perfectly good sine wave values other than the limitations of the finite word width (amplitude errors).
Eliminating spurs caused by phase errors actually requires two things, to have integer ratios between the modulus and the step size (not hard since they are always integers in digital systems) and that the phase never be truncated. Ah! That is the one that requires the lower order bits of the phase step size to be zeros!!! So we are back to *your* original statement of needing zeros in the truncated portion of the phase step size.
I guess we are back to *violent* agreement.
-- Rick
Thanks, there are several new ones I haven't seen before.
I wish. I moved back to Canada some time ago and often regret it. But my green card expired after a year and it would be very difficult to move back.
The thesis talks about NLTL comb generators followed by a YIG filter and pll to drive the 4.6GHz oscillator. It reads like an undergrad lab paper reviewing old technology. There is nothing new or phd-worthy anywhere in the thesis.
The technology I am interested in has no pll and offers reasonable phase noise and very fast switching. Here's some numbers from the HS6002A RF Synthesizer (8MHz to 6GHz)
Frequency Resolution : 0.001 Hz
Switching Speed
50 us : Any frequency over full instrument BW 5us : Any frequency within 5% BWThey stress the non-pll design constantly. Here's a blurb from the web site:
Holzworth non-PLL Design Overview
Holzworth synthesizers are designed with a digital front end and a proprietary, direct analog back end. The proprietary architecture maintains low spurious response while also providing industry leading phase noise performance, exhibiting signal jitter performance of far less than 100fs.
The PLL was excluded from the Holzworth designs for optimal signal stability and fast switching speeds. Unlike PLL designs, there is no post switch settling time to reach the new frequency. Holzworth synthesizers exhibit little or no settling time under most switching scenarios.
After reading the thesis, it doesn't seem like Breitbarth could come up with something this clever. However, it appears the company was based on the new synthesizer design, so it seems like he joined forces with the actual inventor who may now be an upper-level executive in the company.
So the next step may be to research the executives, find out where they graduated, and get their thesis papers. Thanks for your interest and replies. I really appreciate your comments.
Just a final remark to close the discussion about this approach: undersampling?
Best regards, Piotr
Nope, won't work. The required waveform accuracy to reach 14 bits of amplitude and phase is very difficult to attain, and requires a gigantic
2-D calibration to fix. That's the whole basis for using nulling.What I'm planning to do is to put both the MPD-1 and ECLips Lite D-flops on the board, and try both. I'm too chicken that the strobed comparator is going to oscillate fiercely.
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
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