sPHENIX HCal discussion

["Boose, Stephen" <boose AT bnl.gov>]

Eric,
I'm re-posting a blurb I sent out about the transformers a while back FYI 
(see below). Aside from that I don't know what would change the relative 
gains from channel to channel except small differences in SiPM gain. The 
preamps on Martin's test setup should all be the same to within 1-2%. The 
differential receiver is being finalized today so we probably won't have any 
built until another week or two but I think it should help somewhat in these 
tests.

***************
All,
This is for anyone who is concerned about reading the specific voltage levels 
out of the HCal Preamps. I neglected to tell you about the voltage gain of 
the matching transformer “lollipop” (ADT2-1) circuit that we’ve been using. 
This is a 2:1 impedance transformer for matching the 100 ohm balanced line 
from the preamp to the 50 ohm input of our scopes. This means the turns 
(voltage) ratio is actually 1.414:1. The transformer loss in our frequency 
band is about 0.3db. Put this all together and you get a forward voltage gain 
of about 0.68. On the bench I measured this value at about 0.64 by connecting 
a differential probe across the preamp outputs and comparing levels. So if 
you want to know the actual differential output voltage you have to multiply 
the scope trace by about 1/0.64=1.56.
 
Eventually we should probably build some boards that mimic the Nevis ADC 
receiver so we can view most accurately what that ADC will be seeing on a 
scope, but the “lollipops” are a simple way around it for now.
***************

Steve Boose
PHENIX Experiment
Brookhaven National Laboratory
BLDG 510C
Upton, NY 11973
Ph: (631) 344-2897
Fx: (631) 344-3253


> -----Original Message-----
> From: eric mannel [mailto:mannel AT bnl.gov]
> Sent: Tuesday, September 22, 2015 10:50 PM
> To: Boose, Stephen
> Cc: sphenix-hcal-l AT lists.bnl.gov
> Subject: HCal tile teststand electronics gains
> 
> Steve-
> 
> During today's HCal meeting, Martin reported preliminary results of the
> studies that he and Abhisek have done over the last week.  While most of
> the results are consistent with what we expect, there is a large variation 
> in
> the signal between tiles that is not fully understood.  It would be helpful 
> if
> we could get a relative gain measurement between the different preamp
> channels including the transformer.
> 
> Ultimately we are going to redo this test with the new tiles that Edouard 
> has
> received from UNIPLAST.  Hopefully we will also use the new differential
> receiver that you and Sal are working on.  But for now it would be good to 
> try
> and understand what we are observing in the current setup so a relative gain
> measurement between the channels would be useful.
> 
> I think Megan will be around to help and knows how to run the DAQ, and I
> will also be  available to assist as needed.
> 
> Thanks
> 
> Eric
> 
> --
> Eric J. Mannel, Ph.D.
> PHENIX Group
> Physics Dept.
> Brookhaven National Laboratory
> 631/344-7626 (Office)
> 914/659-3235 (Cell)