10 MHz TCXO periodically jumping 20 mHz up and down
During long term testing of some 10 MHz TCXO the output frequency seems
to jump within one second 20 mHz ( millihertz) up in frequency every
110 seconds up and after a 25 seconds, again within one second, the same
amount down. The noise in the frequency measurement was well below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different counters
and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed a
different behavior for external temperature changes (fast jump away and
slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well within
spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long cycle?
Or what else?
Hello,
My guess is that it is a quirk of the temperature compensation network
inside the TCXO. I have seen similar behavior in commercial TCXOs as
temperature changes as a result of "break points" in the compensation
network. It is difficult to know exactly unless it is possible to
understand what kind of temperature compensation is used inside the
oscillator.
Cheers
Bill
On 18/02/22 11:11, Erik Kaashoek wrote:
During long term testing of some 10 MHz TCXO the output frequency
seems to jump within one second 20 mHz ( millihertz) up in frequency
every 110 seconds up and after a 25 seconds, again within one second,
the same amount down. The noise in the frequency measurement was well
below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different
counters and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed
a different behavior for external temperature changes (fast jump away
and slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well
within spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long cycle?
Or what else?
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Hi Erik.
What is your counter resolution/gate time? At 1second, the interval
difference from 10MHz + 5mHz is 500ps. --mike
On Fri, Feb 18, 2022 at 11:20 AM Erik Kaashoek erik@kaashoek.com wrote:
During long term testing of some 10 MHz TCXO the output frequency seems
to jump within one second 20 mHz ( millihertz) up in frequency every
110 seconds up and after a 25 seconds, again within one second, the same
amount down. The noise in the frequency measurement was well below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different counters
and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed a
different behavior for external temperature changes (fast jump away and
slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well within
spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long cycle?
Or what else?
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Mike, the counter resolution was 40ps with am RMS resolution of 120ps
Erik.
On 18-2-2022 11:36, Mike Ingle wrote:
Hi Erik.
What is your counter resolution/gate time? At 1second, the interval
difference from 10MHz + 5mHz is 500ps. --mike
On Fri, Feb 18, 2022 at 11:20 AM Erik Kaashoek erik@kaashoek.com wrote:
During long term testing of some 10 MHz TCXO the output frequency seems
to jump within one second 20 mHz ( millihertz) up in frequency every
110 seconds up and after a 25 seconds, again within one second, the same
amount down. The noise in the frequency measurement was well below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different counters
and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed a
different behavior for external temperature changes (fast jump away and
slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well within
spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long cycle?
Or what else?
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Hi Erik,
I think you have yourself a digital TCXO controller. Those use a
tempsensor, use the reading to calculate the compensation and the use a
normal varactor control to steer the frequency. Older TCXOs use a
resistor/thermistor network to do the same work. You can probably read
up on the vendors material to see that the keywords are there to support
the suspicion.
So, what you see is really the resolution limit of reading/control. As
long as it's within spec, and the transitions does not upset your system
downstreams, I guess it's just fine. If you have issues with the steps,
then another product is what you look for.
Cheers,
Magnus
On 2022-02-18 11:11, Erik Kaashoek wrote:
During long term testing of some 10 MHz TCXO the output frequency
seems to jump within one second 20 mHz ( millihertz) up in frequency
every 110 seconds up and after a 25 seconds, again within one second,
the same amount down. The noise in the frequency measurement was well
below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different
counters and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed
a different behavior for external temperature changes (fast jump away
and slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well
within spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long cycle?
Or what else?
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To unsubscribe, go to and follow the instructions there.
Bill,
To test I removed the thermal insulation to increase the heat loss
requiring more heat to be generated.
The jump pattern did not change!
Erik.
On 18-2-2022 11:26, bill wrote:
Hello,
My guess is that it is a quirk of the temperature compensation network
inside the TCXO. I have seen similar behavior in commercial TCXOs as
temperature changes as a result of "break points" in the compensation
network. It is difficult to know exactly unless it is possible to
understand what kind of temperature compensation is used inside the
oscillator.
Cheers
Bill
On 18/02/22 11:11, Erik Kaashoek wrote:
During long term testing of some 10 MHz TCXO the output frequency
seems to jump within one second 20 mHz ( millihertz) up in frequency
every 110 seconds up and after a 25 seconds, again within one second,
the same amount down. The noise in the frequency measurement was well
below 5 mHz
In an ASCII drawing of frequency versus time this looked like:
|~~~~||~~~~|_____
Sometimes the high frequency period was very short (some seconds) or
absent but the overall period was within 5 seconds constant
This was tested with 4 different power supplies, although all where
mains connected, not yet tested with battery only, 2 different
counters and two different reference frequency standards.
The TCXO was thermally shielded and testing with some cold air showed
a different behavior for external temperature changes (fast jump
away and slow return to stable frequency)
Also, with thermal shielding removed, touching the TCXO showed also a
fast jump away and slow returning to stable
Measuring the supply voltage did not show clear changes but the used
voltmeter only had 4 digits resolution.
The official spec of the TCXO is much worse so the device is well
within spec but I'm trying to understand why this could happen.
Does anyone know a possible cause for this behavior?
Could this be a small mains supply variation in a 110 seconds long
cycle?
Or what else?
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Hi Magnus,
Tom also replied to my question and suggested a 107.34 seconds interval
related to dithering with a 1e7/2^30 interval
Unfortunately the datasheet is rather short (sub $1 device) and does not
provide any hints to being a digital implementation.
Thanks to all for helping!
Erik.
Hi
If it’s a sub $1 device, it’s pretty much guaranteed that it has digital
“stuff” inside it. That circuitry will generate blips and pops totally
independent of any attempt it makes at compensation. If it “wakes
up” this or that digital sub section every 107.34 seconds, you get
an internal current spike. Spike hits grounding on the board ( or
the supply) and the output moves.
There are dozens of other possibilities. Just like the one above, all
of them require a knowledge of what’s inside the part. Taking a
hammer to it would be the first step ( = remove the lid :) ). Getting
a full schematic and the specs on the chips inside would be a somewhat
deeper dive. Dumping the programming information on top of all that
( = you have the layout of the PCB, the schematic, the parts list and
the specs on the parts) would top off the “need to know” details.
Bob
On Feb 18, 2022, at 6:52 AM, Erik Kaashoek erik@kaashoek.com wrote:
Hi Magnus,
Tom also replied to my question and suggested a 107.34 seconds interval related to dithering with a 1e7/2^30 interval
Unfortunately the datasheet is rather short (sub $1 device) and does not provide any hints to being a digital implementation.
Thanks to all for helping!
Erik.
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On Fri, 18 Feb 2022 11:56:02 +0100
Magnus Danielson via time-nuts time-nuts@lists.febo.com wrote:
I think you have yourself a digital TCXO controller. Those use a
tempsensor, use the reading to calculate the compensation and the use a
normal varactor control to steer the frequency.
Quick side note: On modern, cheap TCXO systems, expecially those
for RTCs, frequency control is being done by a bank of switched
capacitors. This is mostly because capacitors can be implemented
in a standard digital CMOS process (or analog CMOS process).
A varactor, on the other hand, would need a special doping
profile (high-doping concentration with an abrupt transition).
Or in other words an additional half a dozen processing steps
which cost a lot of time and money... especially for a single
diode on a chip.
Attila Kinali
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto
Hi Erik,
I only saw that thread later, and I will have to return to that as I
have a little more energy.
I'm trying to get you up to speed with the many variants there is, and
there is plenty experience here to feed from. What may be true for one
device will not make any sense for another. Please feel free to ask
questions on and off list. I've had to measure behaviours of many
devices over the years. Eventually the reduced the range of devices I
had to measure for qualification, since they learned what probably would
not work.
For the price-range, manufactures have been very inventive in their
approach to make compensations and also make a wide range of
frequencies. Today we have frequency synthesis so the distributor can
program the frequencies the customer wants. Now, combine that with TCXO
and you can let that synthesis also synthesize the output frequency for
compensation. Trouble is, it can cause jitter we do not want, but for
many applications that's just fine, as they even want more of it for
spread spectrum to make EMC compliance easier.
It might be that you are looking in the wrong range of oscillators for
your type of application.
Also, beware that different vendors have their different tweaks. They
may not even be the same over time. From bitter experience, check your
second sources before putting them onto the second source list.
Spending a bit more can get you out of certain troubles.
I do not recall what your application of choice was, sorry if I missed
that in the process.
Cheers,
Magnus
On 2022-02-18 12:52, Erik Kaashoek wrote:
Hi Magnus,
Tom also replied to my question and suggested a 107.34 seconds
interval related to dithering with a 1e7/2^30 interval
Unfortunately the datasheet is rather short (sub $1 device) and does
not provide any hints to being a digital implementation.
Thanks to all for helping!
Erik.
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