[time-nuts] Re: DMTD and TICC with YimeLab question

[John Ackermann N8UR]

FWIW, here are year-to-date plots of a BME280 temp/pressure/humidity as 
well as an RTD thermometer in my clockroom.  I don't know how accurate 
the pressure is, but it seems to be stable over time.

I find the difference in temp reported by the BME280 and the RTD 
interesting.  They are located within a few inches of each other (at the 
top in the middle of my racks of equipment, a definite warm spot).

John


On 11/29/22 04:45, Attila Kinali via time-nuts wrote:
> On Fri, 25 Nov 2022 12:39:21 +0100
> Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>> What would the SNR of the input to the TICC have to be to have a no
>> noise in the zero crossing when the time has been stretched by a factor 1e6?
>> 1e6 calculates to 120 dB, 1e17 to 320 dB
>> Is that a problem when cascading a DMTD and a TICC?
> 
> There is not a problem when using a TICC as counter for a DMTD. If anything,
> it's even a rather good approach. If one wants to build an analog DMTD.
> 
> But your calculation is not quite right. 1e6 does not calculate to 120dB.
> You have to consider how much noise is in your instrument's bandwidth and
> integrate over this noise bandwidth.
> See Walt Kester's app note on converting phase noise to jitter for details [1]
> 
> 
> On Fri, 25 Nov 2022 09:34:34 -0500
> Bob kb8tq via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 
>> If you head back into the archives and search for “Collins Limiter” ( hopefully spelled
>> correctly ) you will find a whole bunch of info on attempting to convert low frequency
>> sine waves to fast edge square waves. It suggests that the “SNR” needs to be managed
>> against the slew rate through a number of stages to do things well.
>>
>> There are a lot of designs out there that don’t use the Collins approach. There also are
>> papers from various well known folks calling into question some of the basic assumptions
>> made in the paper. Possibly somebody will chime in with links to a range of papers.
> 
> The main source is Collins' paper [2]. But be aware that his approximation
> leads to large errors when first few stages have low amplifications. For an
> accurate calculation see [3].
> 
> 
>> Bottom line is that you are doing well to get a net of 1x10^-13 out of a system like this.
>> Getting to 1x10^-14 at one second seems to be out of range for whatever reason.
> 
> The limit is mostly the SNR of the input signal. Having a 10dBm signal
> only leaves you with an SNR of at most 184dB. Assuming only white noise
> and a conservative signal bandwidth of 1Hz-1kHz, this leads to a jitter
> of 28ns RMS. I.e. proper filtering and amplification is key to achieve
> the 1e-13 that is currently state of the art. But narrow band filters
> have the problem that they have temperature dependent delay, thus cause
> additional instability.
> 
> 				Attila Kinali
> 
> [1] "Converting Oscillator Phase Noise to Time Jitter", by Walt Kester, 2008
> http://www.analog.com/static/imported-files/tutorials/MT-008.pdf
> 
> [2] "The Design of Low Jitter Hard Limiters", by Oliver Collins, 1996
> https://doi.org/10.1109/26.494304
> 
> [3] "A Fresh Look at the Design of Low Jitter Hard Limiters", by yours truly, 2019
> https://people.mpi-inf.mpg.de/~adogan/pubs/IFCS2019_collins_isf.pdf
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