Re: Charge range on tracking chambers

[Gerard Visser <gvisser@indiana.edu>]

Hall D Electronics:

Hi,
	I would like to point out as well, that interpreting the integrated 
charge (x*dE/dx) dynamic range (factor of 100 or whatever) directly as 
the dynamic range requirement of the preamp is not quite correct. The 
preamp dynamic range of signals will surely be something smaller than 
the integrated charge dynamic range, because a track of substantial 
length in the CDC probably must involve a large range of drift times. 
The ASIC has a shaping time of only ~11 ns, it will not see the whole 
pulse at once. Eventually on the ADC board where the pulse is 
numerically integrated, we can get a larger dynamic range than the 
preamp chip needs to provide on an instantaneous basis.
	Still, the factor 30 is no doubt too low as a basis for preamp design. 
But on the other hand, the GAS-1 performance surely indicates more than 
30, probably ~100, is available now...

	Gerard

p.s. It would probably be nice if some simulation addressed this issue, 
i.e., that would require actual simulation of CDC pulse shapes for 
various tracks and account for the electronics response. Do we have 
anything like that?

Elke-Caroline Aschenauer wrote:
> Hall D Electronics:
> 
> On Tue, 18 Mar 2008, Curtis A. Meyer wrote:
> 
> Curtis,
> 
> that is my point 30 is for sure not enough, just from dE in the mC I get
> 100. We need this number, because it influences the asic design and our
> dE/dx performance.
> 
> cheers elke
> 
> 
>> Date: Tue, 18 Mar 2008 12:31:23 -0400
>> From: Curtis A. Meyer <cmeyer@ernest.phys.cmu.edu>
>> To: Elke-Caroline Aschenauer <elke@jlab.org>
>> Cc: Fernando J. Barbosa <barbosa@jlab.org>,
>>      Daniel S. Carman <carman@jlab.org>, Simon Taylor <staylor@jlab.org>,
>>      Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>,
>>      "halld-electronics@jlab.org" <halld-electronics@jlab.org>,
>>      halld-tracking-hw@jlab.org, Eugene Chudakov <gen@jlab.org>
>> Subject: Re: Charge range on tracking chambers
>>
>> We are now trying come up with a number, but I would guess that 250 is a better
>> factor for the CDC if we consider the path-length variations over angles.
>>
>>    Curtis
>> On Tue March 18 2008, Elke-Caroline Aschenauer wrote:
>>> Hall D Electronics:
>>>
>>> On Mon, 17 Mar 2008, Fernando J. Barbosa wrote:
>>>
>>> Dear Fernando,
>>>
>>> the CDC I think needs more a dynamic range of 100. if you look to the dE
>>> under 20^o and under 90^o comparing pion DE and proton dE you get without
>>> modelling any fluctuation a factor of 30, If you take fluctuations into
>>> account you come closer to a factor 100.
>>>
>>> So I think that is what we should be able to cover a factor 100 in dynamic
>>> range.
>>>
>>> Eugene I have a question for you, how big of a problem is a non-linearity
>>> in the cdc detector response for the dE/dx performance.
>>>
>>> cheers elke
>>>
>>>
>>>> Date: Mon, 17 Mar 2008 22:02:12 -0400
>>>> From: Fernando J. Barbosa <barbosa@jlab.org>
>>>> To: Elke-Caroline Aschenauer <elke@jlab.org>
>>>> Cc: Daniel S. Carman <carman@jlab.org>, Simon Taylor <staylor@jlab.org>,
>>>>      Curtis Meyer <cmeyer@ernest.phys.cmu.edu>,
>>>>      Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>,
>>>>      "halld-electronics@jlab.org" <halld-electronics@jlab.org>,
>>>>      halld-tracking-hw@jlab.org
>>>> Subject: Charge range on tracking chambers
>>>>
>>>> Hi Elke,
>>>>
>>>> Document 747 on the portal shows the charge deposited on the CDC and FDC
>>>> detectors. These numbers were first estimated for the Electronics Review
>>>> in July 2003 and were based on geometrical constructs only. You can find
>>>> a brief summary on slide 22 (a back-up slide) of my presentation for the
>>>> Hall D Drift Chamber Review of 6-8 March 2007, document 751. Anyway,
>>>> these numbers have not changed in years....
>>>>
>>>> For the CDC, the dynamic range is shown to be 100 fC - 3 pC - a factor
>>>> of 30. Because the charge amplifier has a peaking time of about 11 ns,
>>>> the dynamic range of the preamp would be about 400 fC for point
>>>> ionization (~13% of total charge). The gain of the preamp would then be
>>>> ~ 1000 mV (a reasonable maximum amplitude to expect from a preamplifier)
>>>> divided by 400 fC times a factor to allow for some headroom before
>>>> saturation, say 80%. The result is 2 mV/fC.
>>>>
>>>> Similarly for the FDC, the dynamic range for the anodes was estimated to
>>>> be 300 fC - 3 pC, a factor of 10. For the preamp, 400 fC for point
>>>> ionization and 2 mV/fC for gain.
>>>>
>>>> For the FDC cathodes, the dynamic range was estimated to be 10 fC - 1
>>>> pC, a factor of 100. For the preamp, 133 fC for point ionization and 6
>>>> mV/fC for gain. Note that here, the estimate presumed a 1/3 of the
>>>> charge of the anode on the cathode (charge sharing on adjacent strips).
>>>> Later, it was decided that this number needed to be changed to 1/5 based
>>>> on published data. For the preamp, the point ionization was then
>>>> estimated to be 80 fC and 10 mV/fC for gain.
>>>>
>>>> According to these estimates, the CDC and the FDC anodes require the
>>>> same gain (2 mV/fC) and the FDC cathodes require x5 gain or 10 mV/fC.
>>>>
>>>> Obviously, this numbers must be updated to reflect the physics events in
>>>> the detectors. I hope this helps.
>>>>
>>>> Regards,
>>>> Fernando