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Are there any high-stability oscilators, which are not crystal based, given that temperature is stable down to 0.01 C and voltage down to 0.001V?

Will LC-based oscillator be able to show performance comparable to crystals in such conditions (probably in wierd variants like LC-opamp-LC-opamp-LC-opamp... so that any energy loss on each stage is recovered and we are getting narrower bandwidth)?

Price is not limited here, to a some degree (so brand new atomic clocks are above the budget, but 100$ for peltier/oven & parts is ok).

From my (naive) point it seems that it should be possible to achieve better short & long-term stability than with crystals...

BarsMonster
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    What do you mean by "high-stability"? – The Photon Mar 04 '12 at 05:43
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    http://www.leapsecond.com/ten/clock-powers-of-ten-tvb.pdf – tyblu Mar 04 '12 at 06:31
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    @BarsMonster, the reason people use crystals is almost nothing compares for the price. You need to be more clear with your definitions. Engineers take so much training so that they can attach numerical values to what others use general language for(ie high precision being 1 part per trillion or 1 part per million, depending on your implementation). – Kortuk Mar 04 '12 at 06:51
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    Look at some of the amateur radio circuits (ARRL, RSGB, ...) , especially from a few decades back, where people valued wide range tunability plus stabiity and did some very clever things to achieve the best results they could get. Sme thing approaching a badly performed crystal, but with tunability, should be able to be achieved. – Russell McMahon Mar 04 '12 at 07:10
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    Do the math. Look up Q of some crystals and then find what the series resistance of a inductor would have to be to match that in a L-C resonant circuit. – Olin Lathrop Mar 04 '12 at 14:43
  • @Kortuk - well, I need 'comparable to crystal' stability, so somewhere at +-10-100 ppm at the worst case. – BarsMonster Mar 04 '12 at 16:03
  • @Olin Lathrop Hmm, wouldn't having multiple LC circuits do a better job? – BarsMonster Mar 04 '12 at 16:06
  • I don't see how multiple L-C circuits is going to increase the Q to the level of what crystals do routinely. – Olin Lathrop Mar 04 '12 at 17:41
  • @Olin Lathrop i see, but if we do LC-opamp-LC-opamp-LC-opamp... so that any energy loss on each stage is recovered and we are getting narrower bandwidth? – BarsMonster Mar 04 '12 at 18:48
  • @BarsMonster, Put that in the question. – Kortuk Mar 05 '12 at 04:07
  • Check this article; that's all I can offer, but maybe it can help – clabacchio Mar 06 '12 at 09:58
  • @clabacchio Hehe, awesome photo, but MEMS also feels similar to crystal in terms of limitations. – BarsMonster Mar 06 '12 at 11:37
  • @BarsMonster I've taken literally the non-crystal and high stability requirements: don't ask me more :) – clabacchio Mar 06 '12 at 12:23
  • @clabacchio Well, I forgive you, you are right :-) – BarsMonster Mar 06 '12 at 14:26
  • @BarsMonster, You have opened two +500 bounties, but you only have 852 rep to give. How are you going to pay out on both bounties? – The Photon Mar 06 '12 at 16:35
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    @ThePhoton You know, credit from Stackexchange for 10% per year.... ;-) Actually I had 1852 before I placed these bounties, they are subtracted immediately. – BarsMonster Mar 06 '12 at 17:23
  • One thing to Google: coaxial resonator. Mostly used for frequencies above what crystals can easily do (500 - 2000 MHz). Another one is the SAW resonator (surface acoustic wave)...dunno if you consider that "crystal based" or not...also mostly used for higher frequencies. – The Photon Mar 06 '12 at 17:57

3 Answers3

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Superb mechanical construction of the inductor is a major factor. See Czech Tesla report cited below for specific advice.

If you can track down this 1941 [!!!] original and/or the many derivatives based on it using both "valves" and 'solid state" circuits you will probably find circuits with performance about as good as you can get.

"E. O. Seiler, "A Low-C Electron-Coupled Oscillator," QST, Nov 1941."

A circuit based on Seiler's work was published in QST with , I think, a title like "A synthetic rock" or "The synthetic rock. (Rock == crystal).

One reference noted that the oscillator output was designed to be plugged into a crystal socket and when used at eg 12 MHz to provide the reference fquency for a 2 m,etre band (144-148 Mhz) transmitter, produced a signal which was zero beat stable for hours ata time when compared with a crystal controlled test unit. Zero beat stable means drift is within a few Hz at most as otherwise you hear "rumbling" as the two signals heterodyne.

I don't speak or read Croatian and gargoyle was having a bad day but I believe the circuits below are based on Seiler's ideas. See pages 147-148 here. Translation to English (unless you read Croatian) looks worthwhile. Many other related circuits there too. These may come from US "hams' W8PK & W3EB.

Note that these two circuits do NOT look overly special. I think a significant part of the "trick" is in the relative (lack of) loading of the tuned circuit.

enter image description here

This mentions the Synthetic Rock in passing, with approval.

Valuable albeit old !!!

Resources for Understanding Oscillators {2003} - with references to MUCH older material.

Look for Seiler references.

The following are from the above reference -

E. O. Seiler, "A Low-C Electron-Coupled Oscillator," QST, Nov 1941.

  • Describes the circuit that D. Stockton, ARRL Handbook, 1995+, p. 14.14, mistakenly calls "the original Colpitts circuit ... now often referred to as the parallel-tuned Colpitts..."

W. B. Bernard, "Let's Increase V.F.O. Stability," QST, Oct 1957.

  • Suggests using grounded-cathode triode with separate buffer instead of the electron-coupled pentode circuit. Also suggests using the Seiler or Colpitts circuit with the largest available value of tuning variable capacitor instead of the Clapp circuit with a low value of tuning capacitor.

J. Vackar, "LC Oscillators and their frequency stability," Tesla Tech. Reports, Czechoslovakia, Dec 1949.

  • He discusses mechanical design of tuning circuits, presents general analysis of oscillator circuits and their sensitivity to changes of internal capacities of valves (vacuum tubes). He reviews existing circuits, including Gouriet-Clapp, Seiler, and Lampkin, comparing their amplitude dependence on frequency and hence useful tuning range. He describes in detail the design process for circuit we commonly refer to as the Vackar oscillator, which has greater tuning range. He then goes on to describe a slight variation with still greater tuning range. This last circuit, which I have never seen elsewhere, he describes as a compromise between the first-mentioned Vackar circuit and that due to Seiler.

1949 original of the above report in Czech. Superb][(http://www.scribd.com/doc/62276627/Vackar-wholepaper)
Starts with a description of mechanical requirements for high stability.

J. K. Clapp, "Frequency Stable LC Oscillators," Proc. IRE, Aug 1954.

  • Shows that Gouriet-Clapp, Seiler, and Vackar oscillators have equivalent frequency stability given equal resonator Q. They differ only in how much the amplitude of oscillation changes when they are tuned. The three circuits are useful over frequency ranges of 1.2, 1.8, and 2.5 to one, respectively.

The above suggests that the Vackar oscillator is potentially more useful.

See refs here Discrete Oscillator design- Rhea on page 261.

Russell McMahon
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For a budget of $100 you could easily put together a GPS based standard. For example A Simplified GPS-Derived Frequency Standard.

This particular project has a measured accuracy and the author states: "I have made observations over several months, and concluded that the 10-10 decade (from 10-10 to 10-9) is a reasonable expectation from this system."

This is a project put together in 2006 and not optimized for stability.

Another option is a cheap oscillator using a phased locked loop (PLL) tied to a received radio signal from WWV or other national authority. Their short term stability isn't that great but their long term stability is probably as good as it gets. This is how the cheap "atomic clocks" that you see in the store for $20-30 (the kind that hang on the wall and display the time) work.

As an aside, you state "so brand new atomic clocks are above the budget". That is true, but you could pickup a used one for about $50-60.

JonnyBoats
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    Another option: pickup a used Rubidium atomic frequency standard off eBay (they're generally pulled from decommissioned cell phone tower equipment): http://www.ebay.com/sch/i.html?_from=R40&_trksid=p5197.m570.l1313&_nkw=rubidium+frequency+standard&_sacat=See-All-Categories – Craig Mar 10 '12 at 17:33
  • There is a slight problem with the VE2ZAZ GPSDO. He uses an FLL instead of a PLL. Which means the output frequency error will be dominated by the measurement error of his system, which is limited by the GPS receiver output noise, which is in the order of ~1e-7, at a tau of 1s. He uses the 10MHz signal to measure the PPS arrival time directly, which means he gets a resolution of 100ns with measurements done every 16s. Ie his theoretical peak performance is 6.25e-9 at tau=16s. The noise in the system helps a bit to keep it lower, but not by much. Using a PLL instead would be better. – Attila Kinali Sep 26 '17 at 13:55
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There are MEMs oscillators, resistant to shock in the order of tens of thousands of G's. For example, see http://www.abracon.com/Oscillators/ASEM.pdf

user3812
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