[time-nuts] Re: Counter internal resolution error

[Magnus Danielson]

Hi,

Typically it occurs through ground-bounce. It is addressed through 
isolation, so rather using a common comparator chip, one separate the 
channels to separate comparators, and with relevant decoupling to 
further achieve isolation. I know at least two vendors that have worked 
on this, and it becomes relevant as you reach below 100 ps in overall 
performance. Digital electronics signal integrity wise it is relatively 
bread and butter design issues these days.

A good introductionary book is "High speed digital design - a handbook 
of black magic". It is very pragmatic in teaching rule of thumbs and 
illustrating things. There is a follow up which has much more practical 
details.

A curious fact is that Wavecrest and their high resolution (2 ps total 
performance, 800 fs to 200 fs single shot resolution) counters is 
relatively unknown in the professional time and frequency field, because 
they focused on signal integrity issues. Eventually their market share 
was eaten as oscilloscope vendors such as Agilent and Tektronix started 
to include similar features, which reduced the need for another instrument.

Having done my fair share of signal integrity work it has not been too 
hard to follow.

Cheers,
Magnus

On 2023-03-18 00:03, Demetrios Matsakis wrote:
> On fact one of our best engineers concluded that there was leakage 
> across the inputs, as Magnus mentioned. Â I thought at the time he had 
> measured it, but I am not 100% sure of that.
>
>> On Mar 17, 2023, at 13:47, Magnus Danielson <magnus at rubidium.se> wrote:
>>
>> 
>>
>> I also recall one paper relating to laser ranging measurement of the 
>> moon which also looked at temperature dependence of counters, and 
>> SR620 showed more sensitivity than some other counters. For some 
>> measurement purposes, the impact is less than for others.
>>
>> A fun experiment would be to use a delay-stepper to plot this. I 
>> accumulated equipment for that over the years, with increasing 
>> resolution and performance but never got around to it. Good little 
>> practical experiment now that I was able to steer the Colby DL10 
>> programmable trombone delay.
>>
>> There is two common reasons for non-linearity, one is from the 
>> interpolator itself where error-pulse shaper as well as 
>> pulse-to-voltage converter has non-linearities. Another one is du to 
>> leakage of either clock or other input shifts the trigger point due 
>> to lacking isolation. Such non-linearities can be handled through 
>> measurement setup and at times with averaging.
>>
>> Some properties can be managed through wise use of the autocalibration.
>>
>> Then again, most of the times I do not bother to go the extra 
>> stretch, but it is good to know the effects are there so one can 
>> consider them and if needed cope with them.
>>
>> So, time to close down computer, check out and leave Vancouver after 
>> a WSTS conference.
>>
>> Cheers,
>> Magnus
>>
>> On 2023-03-17 16:57, Demetrios Matsakis wrote:
>>> I don’t know how SR counters are today, but when we were upgrading 
>>> our infrastructure over a decade ago we found other counters had 
>>> better linearity.  Rover et al’s open source article has a good 
>>> discussion of these issues, although of course you need to have one 
>>> if you are going to experiment. Â See G. D. Rovera, M. Siccardi, S. 
>>> Romisch, and M. Abgrali, “Time delay measurements: estimation of the 
>>> error budget”, Metrologia 56, 2019 035004
>>>
>>>> On Mar 17, 2023, at 9:46 AM, Magnus Danielson via time-nuts 
>>>> <time-nuts at lists.febo.com> wrote:
>>>>
>>>> Dear Michael,
>>>>
>>>> On 2023-03-16 08:17, Michael Wouters via time-nuts wrote:
>>>>> Dear time-nuts
>>>>>
>>>>> Counter specs often include an “internal resolution” error. For 
>>>>> example,
>>>>> the SR620 specs say that it is 25 ps in single-shot, but this can be
>>>>> reduced to 4 ps with sufficient, repeated measurements. Can anyone 
>>>>> Â Â Â offer
>>>>> any enlightenment as to the origin of this error, and the statistical
>>>>> distribution it has? I mentioned the SR620 but information about 
>>>>> the 53230A
>>>>> would be interesting too.
>>>>
>>>> First of all, the single-shot resolution is somewhat of a hallmark 
>>>> measure when it comes to counters.
>>>>
>>>> The interpolator resolution is part of this, but consider that 
>>>> there exists non-linearities in the interpolator which makes the 
>>>> error larger. I recall there being a plot of the non-linearity in 
>>>> the SR620 manual.
>>>>
>>>> It is not uncommon to have interpolator resolution better than 
>>>> non-linearities, but the later may be more subtle to most.
>>>>
>>>> Averaging can help, but depending to specifics, it's hard to give a 
>>>> number.
>>>>
>>>> Cheers,
>>>> Magnus
>>>>
>>>>>
>>>>> Cheers
>>>>> Michael
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