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some high rate measurements at IC
Mark [email protected]
attempt to re-produce CERN high-rate behaviour in the lab at IC
a few new (I think) observations
CMS readout chain (transmission/FED system) can be ruled out
module (hybrid) without sensor does not show problem
2
setup
UTRI cardLV regs,interface buffers
CK/T1
I2C
CK/T1 and I2C provided bycustom VME modules (no CCU)
SeqSi digitalpattern
generator
triggerveto
outputdata stream
ADC, 128kdeep memory
digitalheaderdetect
count up
count down
trigger veto using simple counterincrements on scintillator triggerdecrements as APV frames outputveto if count reaches 9 (safety margin)
source
PM/scint.
front end
experimental techniquefree run system with random triggerstrigger and readout all 128k ADC samples(accommodates ~ 300 data frames at ~ 100 kHz)repeat to build up larger data setsanalyse data
source generatesrandom triggers
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reproduction of effect on TEC module70
60
50
40
30
20
10
0
rms
AD
C u
nits
250200150100500channel number
TEC module, ~20 kHz random triggers
70
60
50
40
30
20
10
0
rms
AD
C u
nits
250200150100500
channel number
TEC module, ~100 kHz random triggers
noise dependence on channel number
(couple of bad channels)
noise increases with trigger rate
readout interface completely differentto CMS system => problem confined to front end module
chip 1 chip 2
4
effect on TIB hybrid only25
20
15
10
5
0
rms
AD
C u
nits
250200150100500
channel number
TIB hybrid only, ~20 kHz random triggers
25
20
15
10
5
0
rms
AD
C u
nits
250200150100500
channel number
TIB hybrid only, ~100 kHz random triggers
no sensor
noise unaffected by trigger rate
=> sensor necessary to reproduce effect?
maybe but TIB hybrid layout slightly different to TEC
=> look at TIB module
chip 1 chip 2
5
reproduction of effect on TIB module
70
60
50
40
30
20
10
0
rms
AD
C u
nits
250200150100500
channel number
TIB module, ~ 20 kHz random triggers
70
60
50
40
30
20
10
0
rms
AD
C u
nits
250200150100500
channel number
TIB module, ~ 100 kHz random triggers
effect also reproducible in TIB module
=> confirms sensor required
(some bad channels on this module too)
chip 1 chip 2
6
problem data frames
-300
-200
-100
0
100
200
300
AD
C u
nits
250200150100500
channel number
-300
-200
-100
0
100
200
300
AD
C u
nits
250200150100500
channel number
some “bad” examples
note anti-correlation between
chip 1/ch127 and chip 2/ch 0
chip 1 chip 2
7
coupling speculation
GND
V250
GND seems to be only terminal in the right place?
disturbance on GND would couple more strongly to
chip 1, chan 127, 127, 125, ….. than to chip 2, chan 0, 1, …
weak coupling here
stronger coupling here?
but …
anti-phase ch127chip1/ch0chip2 doesn’t makesense to me
maybe this is misleading …
chip 2
chip 1
127
0
PA
8
coupling speculation …
…. maybe this is misleading
chip 2/ch0 noise might still be there even if chip 1 not there
could confirm by removing power to chip 1
would have to pull bonds to stop all chip 1 digital functionality bit drastic but maybe worth doing?
-300
-200
-100
0
100
200
300
AD
C u
nits
250200150100500
channel number
put it another way
would chip 2 effect still look like this without chip 1
chip 1 chip 2
9
observations
a worthwhile exercise I think
effect reproduced without conventional CMS readout chain=> front end problem – data transmission/FED system not implicated
effect not seen on hybrid alone=> sensor presence is required
shape of effect (data frames) is strange – per APV rather than per hybrid=> APV is somehow implicated?
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extra
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APV picture
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APV pads
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APV front end
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APV back end
