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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
>