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[Zhenyu Ye <yezhenyu2003 AT gmail.com>]

Hi Gerard,

In the other email, you argued that the CMN increases with input capacitance 
(I agree). But the argument you are making here, which is based on "CMN: IST 
with sensor ~ FST w/o sensor" and concluding there is no issue with FST, 
seems to neglect the fact that the input capacitance is different between IST 
with sensor and FST w/o sensor.

CMN:
FST with sensor >> FST w/o sensor ~ IST with sensor 

CMN/Total 
FST with sensor ~ FST w/o sensor >> IST with sensor

Zhenyu


> On Aug 11, 2020, at 5:59 PM, Gerard Visser <gvisser AT indiana.edu> wrote:
> 
> hi Xu, Zhenyu,
>       I put the plot from IST that Xu sent the other day on a slide 
> (attached) together with the plot from FST03 with no detector that he sent 
> today, at the same scale. I think it looks fairly comparable, there is no 
> obvious reason I can see that these results indicate a problem.
>       I wish we had some understanding why the noise would be larger every 
> 4th timebin. I have no clue about that. It is especially odd since things 
> (readout, in particular) happen in the APV chip in groups of three 
> timebins, but I don't know of anything except some "black-box" internal 
> feature that happens in groups of four.
>       It is very likely related to some internal feature of the APV. That 
> doesn't mean we can conclude that it is not affected by some factor under 
> our control though, of course.
>       Sincerely,
> 
>               Gerard
> 
> 
> On 8/11/2020 5:56 PM, Xu Sun wrote:
>> Hi Gerard,
>> As Zhenyu mentioned, please find the plot of noise before sensor mounting 
>> (APV chips only) of FST03 attached. Please ignore the APV 7 which shows an 
>> abnormal behavior, it is from the cable we used to take the noise run.
>> We see the large CMN with strong time-bin dependence with the noise from 
>> APV chips only. This time bin dependence is the same as noise with sensor 
>> mounted, therefore it is very likely from APV chips on FST.
>> Best,
>> Xu
>> On Tue, Aug 11, 2020 at 4:28 PM Zhenyu Ye <yezhenyu2003 AT gmail.com 
>> <mailto:yezhenyu2003 AT gmail.com>> wrote:
>>    Hi Gerard,
>>    The total capacitance of a readout strip for silicon strip detectors is
>>    given by the sum of the strip-backplane capacitance, and the inter-strip
>>    capacitance. The latter usually dominates.
>>    As we know, the APV noise is linearly dependent on input capacitance, 
>> i.e.,
>>    the total capacitance of the readout strip. For FST, we have seen that 
>> outer
>>    (larger R, Rstrip3 for the inner sensor or Rstrip7 for the outer sensor 
>> in
>>    Xu’s plots) strips have much smaller noises than the inner strips 
>> (Rstrip0
>>    for the inner sensor or Rstrip4 for the outer sensor), despite the fact 
>> that
>>    outer strips have larger area and thus large strip-backplane 
>> capacitance.
>>    This is consistent with the above statement that the interstrip 
>> capacitance
>>    dominates.
>>    The CMN, by definition, affects a group of channels in a coherent way. 
>> It is
>>    usually caused by a common electromagnetic pick-up, or noise on the 
>> supply
>>    voltage, etc. The fact that we see large CMN in FST, suggests to me 
>> that we
>>    should check FST inner cable/T-board/hybrid, such as grounding.
>>    P.S. Xu will send some plots on FST prototype modules before sensors 
>> were
>>    mounted. We see large CMN with strong time-bin dependence. I think this 
>> is
>>    consistent with my above assessment.
>>    Best,
>>    Zhenyu
>>     > On Aug 10, 2020, at 3:45 PM, Gerard Visser <gvisser AT indiana.edu
>>    <mailto:gvisser AT indiana.edu>> wrote:
>>     >
>>     > hi Xu, Zhenyu,
>>     >       Thanks; I didn't realize about this timebin dependence in the 
>> IST.
>>    By the way do we see any dependence of noise on the "cap id" (i.e. the
>>    "address" reported in the APV header)? I am assuming we are triggering 
>> at a
>>    low rate and asynchronous to the clock (ARC-II local clock) so we 
>> should be
>>    getting data in all values of capid. This could show some features (and
>>    perhaps can allow for some capid-dependent correction applied offline).
>>     >
>>     >       I make some estimate of the capacitances as follows: 
>> Neglecting the
>>    capacitance to neighbor pads, and all the capacitance of the routing 
>> line on
>>    the detector, let's consider only the infinite-parallel-plate 
>> capacitance in
>>    bulk of the detector:
>>     >
>>     > IST: Pad size is 594 x 6275 um, thickness 300 um, k=11.7  ==> C=1.3 
>> pF (I
>>    think this must certainly then be dominated by the other, neglected
>>    capacitances mentioned above).
>>     >
>>     > FST: worst case outer pad size is (about) 1087 x 28750 um. (Right? 
>> If you
>>    have more precise info please say.) Also 300 um thick. ==> C=10.8 pF. (+
>>    other again)
>>     >
>>     >       If you have some info about the gap in contact/metal between
>>    adjacent pads in the case of IST and FST I could try to roughly 
>> estimate the
>>    perimeter capacitance to neighbor pads.
>>     >       If you have some measured capacitance info or real calculated
>>    capacitances from detector design, of course we could better think 
>> about those.
>>     >       Anyway, my guess is that the capacitances in FST (outer at 
>> least)
>>    are probably 2-3x the capacitances in IST. This is probably responsible 
>> for
>>    the larger common mode noise and larger noise. If so unfortunately it
>>    probably means there is nothing that we can do about it.
>>     >       If we have an IST stave with a defective detector and wanted 
>> to do
>>    further tests, we could bond some APV input pads to test capacitors of 
>> value
>>    similar to the FST detector and see how that looks. I think this could 
>> be a
>>    significant effort though.
>>     >       Really the only question that we must answer is whether the 
>> PPB,
>>    purple cable, T-board, and hybrids are working well together to deliver
>>    clean supply voltages and clock/trigger signals to the APV chips (and 
>> clean
>>    bias to the sensors). This is probably so, I think all your noise plots 
>> look
>>    reasonable, but we could try to check more directly with low noise 
>> probing
>>    of the supply voltages on one of the prototype hybrids. We probably 
>> would
>>    have done this already if it weren't for the virus situation.
>>     >       Sincerely,
>>     >
>>     >               Gerard
>>     >
>>     >
>>     > p.s. I suppose that, at least for lower trigger rates <3 kHz or so, 
>> we
>>    should consider to setup to read 4 timebins and ignore 0 in offline, use
>>    only 1-3. If 3 timebins is all that we really need, that is. What do 
>> you think?
>>     >
>>     >
>>     > On 8/10/2020 2:29 PM, Xu Sun wrote:
>>     >> Hi Gerard,
>>     >> Sorry for the late reply. Please find the FST & IST noise study in 
>> the
>>    attached file.
>>     >> I see a similar behaviour for IST with a much smaller magnitude.
>>     >> Best,
>>     >> Xu
>>     >> On Tue, Aug 4, 2020 at 1:12 PM Gerard Visser <gvisser AT indiana.edu
>>    <mailto:gvisser AT indiana.edu> <mailto:gvisser AT indiana.edu
>>    <mailto:gvisser AT indiana.edu>>> wrote:
>>     >>    Hi Xu, Zhenyu,
>>     >>             Do we see the timebin-dependece of noise as you show 
>> here
>>     >>
>>    
>> https://drupal.star.bnl.gov/STAR/event/2020/05/04/star-forward-silicon-tracker-meeting/prototype-module-assembly-and-test
>>     >>    in the IST data too?
>>     >>             Thanks,
>>     >>                     Gerard
>>     >>    p.s. And, if possible to answer, there is also the question 
>> whether
>>    this was
>>     >>    seen in the IST installed in STAR/HFT? I don't remember hearing 
>> about
>>    it before.
>>     >>    On 8/4/2020 12:39 PM, Zhenyu Ye wrote:
>>     >>     > Hi Gerard,
>>     >>     >
>>     >>     >> On Aug 4, 2020, at 11:19 AM, Gerard Visser 
>> <gvisser AT indiana.edu
>>    <mailto:gvisser AT indiana.edu>
>>     >>    <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>> wrote:
>>     >>     >>
>>     >>     >> hi Zhenyu,
>>     >>     >>      That timebon dependence sounds definitely odd. Are you 
>> sure?
>>    Do we
>>     >>    see that in IST too, only more mildly? I wasn't aware of this.
>>     >>     > ‘
>>     >>     > Please take a look at Xu’s presentation in FST meeting on May 
>> 4
>>    (FST) and
>>     >>    11 (FST and IST):
>>     >>     >
>>     >>     >
>>     >>
>>    
>> https://drupal.star.bnl.gov/STAR/event/2020/05/04/star-forward-silicon-tracker-meeting/prototype-module-assembly-and-test
>>     >>     >
>>     >>
>>    
>> https://drupal.star.bnl.gov/STAR/event/2020/05/11/star-forward-silicon-tracker-meeting/prototype-module-assembly-and-test
>>     >>     >
>>     >>     >>      The capacitance of FST is much larger than IST, I think.
>>    This may
>>     >>    certainly be relevant. For sure it is relevant to CMN.
>>     >>     >>      Anyway, I agree we should investigate these noise 
>> issues, I
>>    do not
>>     >>    like to ignore them. However on the other hand it _may_ be an 
>> inherent
>>     >>    property of APV chips.
>>     >>     >
>>     >>     >>      - Gerard
>>     >>     >>
>>     >>     >>
>>     >>     >>
>>     >>     >> On 8/4/2020 12:12 PM, Zhenyu Ye wrote:
>>     >>     >>> Hi Gerard,
>>     >>     >>>  From the plots that Xu sent, there is a clear pattern 
>> where the
>>     >>    channels showing enhanced noise level after mounting the sensors,
>>    also show
>>     >>    enhanced noise level before mounting the sensors.
>>     >>     >>> An independent topic, we see that the CMN in FST is much 
>> higher than
>>     >>    IST, and show a strong time-bin dependence, i.e., when we read 
>> in 9 time
>>     >>    bins, the 1st, 5th and 9th time bins have much higher CMN than 
>> the other
>>     >>    time bins. I don’t feel comfortable to ignore it w/o knowing the
>>    cause, as
>>     >>    it may get worse in the real experiment.
>>     >>     >>> Best,
>>     >>     >>> Zhenyu
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