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<div class="moz-cite-prefix">HI Fernando, Mark and Werner,<br>
<br>
The order for the SiPMs is out and if a change is going to be
made, it should be done before Hamamatsu gets started. From
Fernando's tests, it seems wise to revert to the well-tested 50 um
sensors for all applications, including the ST. Sasha is planning
to contact the Hamamatsu rep to find out if and when the switch
can be made. The decision should be made a soon as possible.<br>
<br>
Cheers, Elton.<br>
<pre class="moz-signature" cols="72">Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax </pre>
On 7/16/12 10:34 PM, Fernando J Barbosa wrote:<br>
</div>
<blockquote cite="mid:5004CF1C.9080208@jlab.org" type="cite">Hi
Mark, Werner,
<br>
<br>
I have been optimizing and testing the ST readout for the 50 um
and 100 um SiPMs. There are 4 SiPMs connected together (current
sum) to one readout channel on each of two SiPM PCBs (50 um and
100 um). The sensor capacitance is the same in both cases so one
optimization is all that is required for fast risetimes for the
group of 4 SiPMs.
<br>
<br>
The prototype is fully functional but I determined that the
micro-coax ribbon cable assembly (connects the readout to the
breakout PCB) is not good enough due to cross-talk (primarily due
to the connectors on these cable assemblies - a single micro-coax
cable assembly provides the power to the electronics, 3 bias
supplies, 6 outputs [3 channels w/ 3 for ADCs and 3 for TDCs] and
has a thermocouple two-wire output for readout). The readout is
temperature compensated via thermistors. The workaround has two
coax cables (ADC and TDC), in addition to the micro-coax, which
bypass the micro-coax signal connections. So, the final design
will change but the current prototype will be useful for tests
with ST detector prototype.
<br>
<br>
I have attached two pics: ST50 is for the 50 um and ST100 is for
the 100 um. These were taken with a laser and a diffuser
stimulating all 4 SiPMs in the group. Some comments:
<br>
<br>
1. 50 um - Fast pulses with width of 37 ns (~10%-10%)
<br>
2. 100 um - Fast pulses with width of 125 ns (~10%-10%), step/kink
~ 5 ns after peak.
<br>
<br>
The leading edge slew rate is about the same for both but the 100
um has a slower recovery w/a kink (the quench resistor on each
pixel would need to be ~3x smaller for similar recovery but there
are other factors at play, i.e. Geiger current) . I will
investigate this a little further but these are definitely
characteristics of these SiPMs and I will write a GlueX note soon.
<br>
<br>
In the meantime, let me know if there is interest in pursuing the
100 um further. Even though the rates are expected to be in the
KHz range, the long recovery time will likely lead to pileup.
<br>
<br>
Best regards,
<br>
Fernando
<br>
<br>
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