sPHENIX discussion of electronics

[eric mannel <mannel AT bnl.gov>]

I have been slow in following up last weeks discussion about SiPM 
testing at UofM, but here is what I think the goals of this effort 
should be.

We have to do due diligence and verify that the devices that we are 
shipped are correct and meet the terms of the contract.  That is, the 
right devices are shipped, the quantities are as stated and that devices 
in a given tray have a gain of 2.4x10^5 at 25C when the Vop is within 
the stated range of the tray.  Since we do not know the exact Vop of the 
individual devices in a tray, we need to use the mid-point of the range 
and measure the gain, correcting to 25C if required.  If the precision 
of the measurement is fine enough, we should see a distribution of gains 
centered around the nominal with a spread that corresponds to the 
variation of the gain as a function of bias within the range of the 
tray. What that distribution looks like is an open question and may vary 
from tray to tray.  Some trays may have a  majority of devices with the 
same Vop (as defined above) to within a micro-volt and others may be 
spread uniformly over the entire range of the tray. While that might be 
interesting, it is not critical.

The second part is to group trays together with the same Vop range from 
multiple deliveries and possibly combine trays to make the assembly 
process more straight forward.

Keep in mind on the scale of this effort we will not be able to track 
every individual SiPM and associate them with specific EMCal/HCal 
Towers.  Further more, we will not always be running them at the same 
temperature ( and the temps may vary as a function of time and location) 
and we don't know on an large scale if all the devices will track the 
same way with radiation damage.

While there are a number of interesting questions about the uniformity 
of devices over a large scale one might want to answer, we are no longer 
in the R&D stage, but rather production, which means we have to do the 
minimal testing required to insure that the devices meet our 
requirements on a time scale that is consistent with the project objectives.

The first 2K HCal devices will be mounted in the next few weeks and we 
will need to start the EMCal assembly by early August. For the EMCal 
assembly, while the numbers are yet to be finalized, the next batch of 
boards will be for of order 2 1/2-Sectors.  For this I would like to 
minimize the number of Vop bins, so as new deliveries come in, the 
selection of trays should be adjusted to maximize the number of trays 
(full + combined) for a specified Vop range. For that order, 3500 
devices will be required.  A followup order for the next 10 1/2-Sectors 
(3-12) will need another 19K devices.  That order I expect to place 
around the first of September.

We can discuss this more Wednesday.

Eric


--
Eric Mannel, Ph.D.
PHENIX Group
Dept of Physics
Brookhaven National Lab.
631/344-7626 (Office)
914/659-3235 (Mobile)