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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 23:29:01 -0400

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>> 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>>
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>
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>> 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>>> 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>>> 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>>>> 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>>>> 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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Re: [Star-fst-l] noise vs bias for worst channel and typical channel? , (continued)