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Re: [Star-fst-l] noise vs bias for worst channel and typical channel?

From: Gerard Visser <gvisser AT indiana.edu>
To: Xu Sun <sunxuhit AT gmail.com>
Cc: "star-fst-l AT lists.bnl.gov" <star-fst-l AT lists.bnl.gov>
Subject: Re: [Star-fst-l] noise vs bias for worst channel and typical channel?
Date: Wed, 12 Aug 2020 23:55:08 -0400

hi Xu, Zhenyu,
So it is the two smallest radius (farthest from readout) rings of the sensors which are extra noisy in both the inner and outer sensor case. That is curious indeed.
Capacitances through the bulk of the sensor should be smaller there. I thought that sort of capacitance would be the worst for CMN.
Routing line capacitance and resistance is of course largest there. What is the routing line resistance, is there any estimae from Hamamatsu? That resistance adds noise voltage, I think with basically the same effect as noise voltage of the frontend amplifier. I guess one would want 1-2 nV/sqrt(Hz) at most (though the number is really a guess; for sure we want "not more than about the voltage noise of the APV frontend" whatever that is). 2 nV/sqrt(Hz) would be 240 Ohms -- how does it compare w/ the sensor design?
I don't understand though how any noise from the routing line resistance would appear as CMN.
A different theory is that these rings are farther from the bypass capacitors on the nybrid (inevitably). The bias voltage there might be picking up some external noise more than it is closer to these capacitors. (If so, it could maybe be improved in our design.)
Sincerely,

Gerard

On 8/12/2020 11:35 PM, Xu Sun wrote:

Hi Gerard,

0-3 is for the inner sector from smallest radius to largest radius. And 4-7 is for the outer sector from smallest radius to largest radius.
Hope this helps.

Best,

Xu

On Wed, Aug 12, 2020 at 10:29 PM Gerard Visser <gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>> wrote:

hi Xu,
Thanks, that is very good to see these plots including also the
case from
unbonded APV on the IST hybrids (+IST cable and T-board). I am glad to
see that
the case of FST and IST unbonded chips is about the same. We do have to
decipher
still if the difference between FST and IST with detector indicates a
problem or
merely the normal effect of different detector capacitances. I don't think
it is
clear; but of course it _could_ be a problem.
I don't know the definition for R strip number 0-7, but your
plots
show that
for R-strips 2, 3, 6, and 7 the CMN is about the same as the unbonded
case. So,
which strips are those?
Sincerely,

Gerard

On 8/12/2020 10:44 PM, Xu Sun wrote:
> Hi Gerard,
>
> We just had a quick look at 2013 IST data before and after sensor
mounting and
> compared it with current FST data. You could find a summary slides in
the
> attached file.
> The total noise and random noise of IST increased significantly after
sensor
> mounting, but the CMN from IST data didn't. This suggests that CMN is
only
> weakly dependent on detector capacitance in the case of IST.
>
> For FST, total noise, CMN and random noise increased after sensor
mounting.
>
> Best,
>
> Xu
>
> On Tue, Aug 11, 2020 at 6:27 PM Visser, Gerard <gvisser AT indiana.edu
<mailto:gvisser AT indiana.edu>
> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>> wrote:
>
> hi Zhenyu,
> All I am saying is that these plots do not indicate to me
evidence of a
> problem. If the IST capacitance is "negligible enough" for instance
it would
> look similar to FST unbonded. I wish we had such plots for an
unbonded IST
> chip...
> The pattern of higher noise every four timebins for sure
looks like
> something we don't want to see, but I think explanation for _that_
ties into
> some internal details of the APV chip that we have no choice but to
live with.
> Anyway, I think we need to keep investigating, we agree. At the
moment I
> would say I believe the FST noise looks a bit worse than IST simply
because
> the capacitances are worse, but if we think the S/N ratio is still
adequate
> I don't see a clear worry. Of course we should check everything
that
we can
> though.
>
> Gerard
>
>
> p.s. At least the capacitance of IST to the backside contact / bias
supply
> is << than that of FST. This could be the capacitance that matters
most for
> CMN. (I'd naively expect that capacitance to at least adjacent
channels of
> same chip, does not generate CMN, or not significantly.)
>
> ________________________________________
> From: Zhenyu Ye <yezhenyu2003 AT gmail.com
<mailto:yezhenyu2003 AT gmail.com> <mailto:yezhenyu2003 AT gmail.com
<mailto:yezhenyu2003 AT gmail.com>>>
> Sent: Tuesday, August 11, 2020 7:14 PM
> To: Visser, Gerard
> Cc: Xu Sun; star-fst-l AT lists.bnl.gov
<mailto:star-fst-l AT lists.bnl.gov> <mailto:star-fst-l AT lists.bnl.gov
<mailto:star-fst-l AT lists.bnl.gov>>
> Subject: Re: [Star-fst-l] noise vs bias for worst channel and
typical channel?
>
> 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
<mailto:gvisser AT indiana.edu>
> <mailto:gvisser AT indiana.edu <mailto: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>
> <mailto:yezhenyu2003 AT gmail.com <mailto:yezhenyu2003 AT gmail.com>>
<mailto:yezhenyu2003 AT gmail.com <mailto:yezhenyu2003 AT gmail.com>
> <mailto: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>
> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>
> >> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>
<mailto: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>>
> >> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>
<mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>>
> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>
<mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>
> >> <mailto: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>>
> >> <mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>
<mailto:gvisser AT indiana.edu <mailto:gvisser AT indiana.edu>>>
> >> >> <mailto:gvisser AT indiana.edu
<mailto:gvisser AT indiana.edu> <mailto:gvisser AT indiana.edu
<mailto:gvisser AT indiana.edu>>
> <mailto: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
> >> >> _______________________________________________
> >> >> Star-fst-l mailing list
> >> >> Star-fst-l AT lists.bnl.gov
<mailto:Star-fst-l AT lists.bnl.gov>
<mailto:Star-fst-l AT lists.bnl.gov <mailto:Star-fst-l AT lists.bnl.gov>>
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<mailto:Star-fst-l AT lists.bnl.gov <mailto:Star-fst-l AT lists.bnl.gov>>>
> >> <mailto:Star-fst-l AT lists.bnl.gov
<mailto:Star-fst-l AT lists.bnl.gov> <mailto:Star-fst-l AT lists.bnl.gov
<mailto:Star-fst-l AT lists.bnl.gov>>
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<mailto:Star-fst-l AT lists.bnl.gov <mailto:Star-fst-l AT lists.bnl.gov>>>>
> >> >> https://lists.bnl.gov/mailman/listinfo/star-fst-l
> >> > _______________________________________________
> >> > Star-fst-l mailing list
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<cmn_noise_comparison.pdf>_______________________________________________
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Re: [Star-fst-l] noise vs bias for worst channel and typical channel? , (continued)