[Halld-pid] f1TDC timing resolution

[Beni Zihlmann]

Hi Sasha,
just for clarification. You have the same type of F1TDC
as I do. There is no new version yet available. The new
versions will be only available by October 2012.

cheers,
Beni
> Beni,
>
> As a follow up, I tried to repeat your F1 TDC resolution study in our
> setup. I also plugged 2 outputs of the TI board into F1TDC. The
> resolution I measured is 0.866*56.6ps=49.0ps (see the attached plot).
> While it is not that far off from your value of 41.7ps (based
> on your plot with 56ps bin width), it is still 15% worse. At this point,
> I don't know if  the newer F1TDC works 15% better than the older
> one which we have, or if I should blame our VME crate with its
> problematic -12V for that.
>
> The good news is that directly measured 49ps is pretty close to
> 55ps resolution which I got with a pulser-simulated 3-bar method.
> This means that, apart from F1TDC, there is very little contribution
> to the resolution (i.e., about sqrt[55ps^2-49ps^2]=25ps only) either
> from a discriminator jitter (for a fixed-amplitude signal), or from the
> assumptions of the method itself (in which the 6-signal and 4-signal
> distributions are used to extract the resolution of the remaining
> 2-signal distribution).
>
> Sasha
>
>
> On Monday, February 21, 2011, Beni Zihlmann wrote:
>> Hi Sasha,
>> attached are two fits to the same data with different bin sizes.
>> one very fine with 25ps/channel and one with 56ps/channel
>> the actual bin size of the F1TDC. As you can see the fit results
>> do change a little but not drastically. The chi2/ndf is bad in
>> both cases because it is not really a Gaussian distribution
>> but closer to a square.
>>
>> cheers,
>> Beni
>>
>>> Hi Beni,
>>>
>>> Thanks for making these measurements! I have a quick question
>>> about your timing resolution plot. Why did you choose a bin size of
>>> 50ps for this histogram? After all, TDC measurements (and their
>>> differences) are integers, and it would be natural to histogram them
>>> in these units, with a bin size of 1 TDC count or, at least, with the
>>> proportional 56.6ps bin size. With your bin size choice, a bin with
>>> about 3000 counts is followed by a bin with 0 counts, followed by
>>> a bin with 5000 counts. This is "statistically unnatural" and is a
>>> pure artifact of a non-aligned binning. Fitting a very narrow
>>> (literally, a couple of bins) histogram to a gaus might be very
>>> sensitive to how the binning is done. Seeing chi2 / ndf = 4892 / 9
>>> makes me wonder how stable the obtained 36.7ps resolution value
>>> is. Would it be possible to plot your data with the "natural" bin size
>>> of one TDC count? Thanks.
>>>
>>> Sasha
>>>
>>> On Monday, February 21, 2011, Beni Zihlmann wrote:
>>>> Hi All,
>>>> to follow up on the discussion about the timing resolution of our
>>>> F1TDC I looked at the data I took to test the Hamamatsu H10534 PMT.
>>>> Attached is a plot that shows the timing difference between the
>>>> trigger signal going to the TI board and the trigger signal output
>>>> from the TI board. The Gaussian fit gives a width of 36.7ps while
>>>> the position is 31.85 ns. This means that the TI response time to
>>>> the triggers was 31.85ns with a timing resolution of 36.7ps. This
>>>> resolution includes the timing jitter
>>>> of the TI board as well as the intrinsic timing resolution of the
>>>> F1TDC. In other words the intrinsic timing resolution of the F1TDC
>>>> is expected to be better than 36.7ps.
>>>>
>>>> On a side note: looking at the open PMT and its base the active base
>>>> circuitry
>>>>
>>>>                             is based on 3 transistors.
>>>>
>>>> cheers,
>>>> Beni
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>
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