Looking for datasheet for Oscilloquartz 8602
Hi
On Jun 1, 2013, at 4:24 PM, Jim Lux jimlux@earthlink.net wrote:
On 6/1/13 10:35 AM, Bob Camp wrote:
Both suffer from people talking about levels (-120 dbc or 1x10^-11) without mentioning the offset or tau. Since both are highly dependent on the offset or tau that's not a good thing. My observation is that ADEV is much more likely to be mentioned without an associated tau than phase noise without an offset . I've also observed that when the error is mentioned you are likely to get a "oops I'll fix that" on phase noise. On ADEV people often simply don't get the fact that tau matters even after it's pointed out.
For ADEV, a lot of oscillators have a sort of "floor" where the ADEV is relatively constant, say from tau in the range10-1000 seconds, and then it rises up (from thermal effects and such), so the shorthand is that the number quoted is that "floor value"
You see a lot of different ADEV plots. Some would suggest flat from 0.1 seconds out. The real world is rarely that simple ….
Looking at what the systems using OCXO's are actually doing, about half the time ADEV is probably the better / more important measure than phase noise. The system is more sensitive to the OCXO wandering around over 100 or 1000 seconds than it is on the level of a sideband offset how ever many Hz off carrier. Once you get past ADEV, you rarely see an OCXO specified for any of the other related specifications. That's a shame, since some of them are better measures of certain things than ADEV. Again, I blame the fact that people just don't understand / trust the measurements.
Certainly for "OC" applications this might be true. Although, a sort of trend is that the TCXO resonator has to have a lower Q, so the temperature compensating components can "pull" it to the right frequency over temperature, so the phase noise of a TCXO isn't as good as that of an OCXO, which can have a higher Q.
A lot of times, though, an OCXO is chosen because a TCXO doesn't have frequency stability needed over environmental changes. I don't think ADEV is really the right measure when you're looking at aging or temperature effects.
Well, I've certainly seen TCXO's spec'd and 100% tested for ADEV in the 50,000 pc / year quantities …
If you need 0.1 ppm accuracy over -50 to +60C, you probably aren't going to get it with a TCXO.
Again, a "that depends" sort of thing. There are several outfits that will sell you a 0.01 ppm TCXO over a 100 degree span. -50 is not normally paired up with +60C, so there isn't a lot out there for that exact range. Doing 0.05 is not unreasonable over that range.
For example, the Space Network using TDRSS on S-band (2.2 GHz) requires you know the actual frequency to within 700Hz. That's 0.3 ppm and tough to get in a TCXO over space qual temp range.
Temp range isn't the issue as much as the range plus the radiation hardness required.
Bob
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On 6/1/13 1:46 PM, Bob Camp wrote:
Hi
For ADEV, a lot of oscillators have a sort of "floor" where the
ADEV is relatively constant, say from tau in the range10-1000
seconds, and then it rises up (from thermal effects and such), so
the shorthand is that the number quoted is that "floor value"
You see a lot of different ADEV plots. Some would suggest flat from
0.1 seconds out. The real world is rarely that simple ….
Yes.. but still, a floor of sorts.. high at the low end, high at the
high end (for tau), and flattish in the middle.
Certainly for "OC" applications this might be true. Although, a
sort of trend is that the TCXO resonator has to have a lower Q, so
the temperature compensating components can "pull" it to the right
frequency over temperature, so the phase noise of a TCXO isn't as
good as that of an OCXO, which can have a higher Q.
A lot of times, though, an OCXO is chosen because a TCXO doesn't
have frequency stability needed over environmental changes. I don't
think ADEV is really the right measure when you're looking at aging
or temperature effects.
Well, I've certainly seen TCXO's spec'd and 100% tested for ADEV in
the 50,000 pc / year quantities …
Sure, but is ADEV of the oscillator at constant temp really relevant
when your application isn't at constant temp. I guess it is, because
your system ADEV can't be any better than the underlying oscillator, but
still, I'm not sure it's an entirely appropriate specification to be
calling out.
And, isn't "aging" (in the sense of slow long term drift) usually
excluded from the ADEV calculation (e.g. you fit a straight line to the
raw frequency data, and subtract that out)
If you need 0.1 ppm accuracy over -50 to +60C, you probably aren't
going to get it with a TCXO.
Again, a "that depends" sort of thing. There are several outfits that
will sell you a 0.01 ppm TCXO over a 100 degree span. -50 is not
normally paired up with +60C, so there isn't a lot out there for that
exact range. Doing 0.05 is not unreasonable over that range.
0.05 ppm in a TCXO over 100 degrees as a "assembly" or "component" level
device? That's quite impressive. I see that Vectron has the TX402 which
is 50 ppb -20 to +70 (for some frequencies, according to data sheet)
which is certainly in that ballpark.
For example, the Space Network using TDRSS on S-band (2.2 GHz)
requires you know the actual frequency to within 700Hz. That's 0.3
ppm and tough to get in a TCXO over space qual temp range.
Temp range isn't the issue as much as the range plus the radiation
hardness required.
LEO doesn't require much in the way of radiation hardness. After all,
people live in LEO, so it can't be that bad. Single event effects
maybe. Or frequency change with dose/single events.
Seeing the recent RAD data from MSL only racking up <100 rad on the way
to Mars makes me wonder why we ask for 20kRad kinds of performances.
Bob
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On 06/02/2013 12:58 AM, Jim Lux wrote:
On 6/1/13 1:46 PM, Bob Camp wrote:
Hi
For ADEV, a lot of oscillators have a sort of "floor" where the
ADEV is relatively constant, say from tau in the range10-1000
seconds, and then it rises up (from thermal effects and such), so
the shorthand is that the number quoted is that "floor value"
You see a lot of different ADEV plots. Some would suggest flat from
0.1 seconds out. The real world is rarely that simple ….
Yes.. but still, a floor of sorts.. high at the low end, high at the
high end (for tau), and flattish in the middle.
Certainly for "OC" applications this might be true. Although, a
sort of trend is that the TCXO resonator has to have a lower Q, so
the temperature compensating components can "pull" it to the right
frequency over temperature, so the phase noise of a TCXO isn't as
good as that of an OCXO, which can have a higher Q.
A lot of times, though, an OCXO is chosen because a TCXO doesn't
have frequency stability needed over environmental changes. I don't
think ADEV is really the right measure when you're looking at aging
or temperature effects.
Well, I've certainly seen TCXO's spec'd and 100% tested for ADEV in
the 50,000 pc / year quantities …
Sure, but is ADEV of the oscillator at constant temp really relevant
when your application isn't at constant temp. I guess it is, because
your system ADEV can't be any better than the underlying oscillator, but
still, I'm not sure it's an entirely appropriate specification to be
calling out.
It is, but only if you are asking the right question.
If your question is "How much RMS frequency noise does the oscillator
contribute at observation time tau?" then the ADEV is for you.
If your question is "How stable will my oscillator be over observation
time tau?" then the ADEV isn't going to give you remotely everything.
As tau increases, systematic effects will dominate. Notice how you
limited yourself to constant temperature. The constant temperature hints
that you have things changing with temperature, and that is a systematic
effect. ADEV was never meant to solve that for you.
Rather, you will have to characterize your oscillators systematic
behaviors to such degree that you can with needed certainty estimate the
systematic time or frequency errors you can expect. ADEV is very handy
to shine the light away from those issues, which is much hairier. We
have third-degree thermal curves, we have systematic drift (which needs
appropriate model for it, the linear drift is a simplification in
itself), you have memory effects and if your temperature shifts, how
quick does it shift and how will the temperature gradient over the
crystal be? ADEV never attempted to cover this.
When you see a bump in your ADEV which isn't motivated by a system
behavior (none of them usually are) then you need to figure out what
systematic caused it. ADEV might be one of several ways to illustrate
that you have an issue, but that bump does not represent a good answer
to the RMS frequency noise question, as the noise and the systematic
will need quite different treatment to get comparable answers.
When comparing systematic and noise effects on jitter (where white phase
noise dominates), the BER value of 10^-12 motivates a scale-up factor of
about 14 for a white noise RMS number to match up against the systematic
peak-to-peak number. Together the sum then needs to be below one cycle.
This scale-up number can be different depending on the confidence
interval you need. It however illustrates that you need to treat them
separate and then combine them back in such a way that they give you the
answer to the actual engineering question you ask.
And, isn't "aging" (in the sense of slow long term drift) usually
excluded from the ADEV calculation (e.g. you fit a straight line to the
raw frequency data, and subtract that out)
It is and it should be. You need to make a model and parameters that fit
your device. The confidence of those parameters will give you the
confidence interval for it's estimated behavor, just as the confidence
interval for the ADEV will be needed.
So, what was your engineering question, really?
Cheers,
Magnus
On 6/1/13 4:52 PM, Magnus Danielson wrote:
So, what was your engineering question, really?
responding to Bob's comment that people just say "ADEV <1E-15" without
specifying a tau.
On Sat, 01 Jun 2013 13:12:52 -0700
Jim Lux jimlux@earthlink.net wrote:
Or better, the 42ns PTTI conference paper by Greg Weaver at APL, who had
to build them.
That would be [2] then? A little question here: AFAIK satelites vibrate
a lot. How do they account/compensate for the vibrations in the oscillators?
yes..
Significant vibration is only during launch. And during pyro events for
deployments, of course. After you're in orbit, the vibration is very,
very small (bearing noise from the reaction wheels) . I doubt they're
making measurements while they use the thrusters. If they're changing
the orientation, it's probably using wheels. And wheel bearing noise is
probably fairly narrow band and harmonically related to the wheel speed.
I can ask some GRAIL-ers.
Did you get any word from them on this?
Is any of the design documents for those crystal oscillators available?
I would be very much interested to have a look at them.
Not a chance <grin>
Damn! It nearly worked ;-)
Attila Kinali
--
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who also happen to be insane and gross.
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