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

[Attila Kinali]

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
-- 
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
        -- Richard W. Hamming, The Art of Doing Science and Engineering