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Re: CDC and FDC characterization



Hi Yves,


Yves Van Haarlem wrote:
> Hi All,
>
>> Gerard Visser wrote:
>>> Hi Fernando,
>>>     Thanks, this is a very interesting document! In particular I 
>>> hope that people are encouraged more to do the gain studies in terms 
>>> of pulse integrals rather than peak height... :)
>> Indeed.  I am not sure if Simon and Yves have done this 
>> systematically but they could re-check their analysis.
> For the CDC the gas gain is determined by tuning GARFIELD to Fe-55 
> data with the gas gain as only free parameter. For the shaper gain 
> both CDC/FDC use the signal amplitude to measure the shaper gain. This 
> gain is signal shape dependent.
Ok, but when you analyze the data from the fADCs (amplitude 
distributions), you need to sum all the samples within a time window 
(drift time?) for each trigger, instead of just peak values.

Regards,
Fernando


>
> Cheers,
>     Yves
>
>
>
>>>     FYI the capacitance (in free space, far from any ground plane) 
>>> of one strip to it's neighbors, I think you are saying it is about 
>>> 38.8 pF/m, is indeed in excellent agreement with the analytical 
>>> formula I mentioned a long time ago for the capacitance of one strip 
>>> to all other strips. (The neighbors being expected to dominate of 
>>> course).
>>>     The capacitance of so-called "coplanar waveguide" which consists 
>>> of a strip (of width w), with gaps (of width s) on each side, with a 
>>> half-infinite ground plane after that, should be a very good 
>>> approximation to the total capacitance from one of the cathode 
>>> strips to all others.
>>>     Anyway, (infinitely thin) coplanar waveguide capacitance is 41.4 
>>> pF/m for w=4mm, s=1mm.
>>>     The formula for coplanar waveguide capacitance is
>>>
>>> C/length =
>>> 4 pi epsilon0 / ( -ln( q( w/(w+2s) ) ) ),
>>>
>>> where q(k) is the theta-function nome function of the elliptic 
>>> modulus k (conveniently this is a built-in function in Mathematica, 
>>> "EllipticNomeQ").
>> The 38.8 pF/m capacitance is to the ground foil for the present 
>> configuration of the FDC; 12 pf/m to the adjacent strips. In free 
>> space, the inter-strip capacitance will increase, as you suggest. 
>> This is in very good agreement with your earlier estimates and 
>> regarding the input load to the preamp.
>>>     Sincerely,
>>>
>>>     Gerard
>>>
>>> p.s. ASIC design simulations (for the FDC case) should probably be 
>>> done with 12-15pF between adjacent channels and 39-50pF to ground, 
>>> according to your results. I believe this is not something to ignore 
>>> - lab tests with GAS-1 confirmed that capacitance between channels 
>>> has a different impact on the noise frequency spectrum than 
>>> capacitance to ground. I don't think that was a surprise or a 
>>> problem, it is just a fact. Now we have real numbers (actually you 
>>> may be able to inflate not by wild guesses as I did but by 
>>> measurement of bare preamp boards and signal routing boards) for the 
>>> capacitance they should be used for ASIC design.
>> I have additional simulations and tests left to perform and noise is 
>> one of the most important.
>>
>> Thanks,
>> Fernando
>>
>>
>>>
>>>
>>> Fernando J. Barbosa wrote:
>>>> Hello everyone,
>>>>
>>>> I have performed electrical simulations on the CDC and FDC 
>>>> detectors, both anodes and cathode strips. I have placed 
>>>> GlueX-doc-1031 on the portal. Please review and provide feedback.
>>>>
>>>> Thanks,
>>>> Fernando
>>
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