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Re: CDC and FDC characterization
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.
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
>