[email protected] tracker week, january 20021 lab measurements and simulations of hips...
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[email protected] CMS Tracker Week, January 2002 1
Lab measurements and simulations of hips
• previously presented APV measurements* assumed signal divided equally between 7 channels -> significant deadtime predictions for CMS
• but relative absence of –ve saturated baseline events (no signal) in test beam dataeither beam test analysis biased (true for results presented previously)or 7 channel model pessimistic (probably also true)
=> worth investigating effects of different hip signal distributions
OUTLINE Introduction Simulations (SPICE) New deadtime measurements for hip signals on one/two channels Hit loss rate predictions for new deadtime measurements Summary
*http://cmsdoc.cern.ch/Tracker/managment/Agenda_GTM/GM_01_12/Mark_CMShipstalk.ppt
[email protected] CMS Tracker Week, January 2002 2
~ 8 miprange
• X5 hip event shows up as saturated signals in several channels
• APV output range only ~ 8 mip (0.7 MeV) so no information on actual signal size in saturated channels
• First measurements on APV modelled hip charge shared equally between 7 channels (choice simply governed by number of chans available on test setup)
• Recoil nucleus should have short range (e.g. < 43m for E < 100 MeV) but true situation more complicated • V. large signals on one/two channels still give > 0.7 MeV signals on neighbours due to inter-channel
capacitance
saturated signalsin 4 strips inthis example
X5 hip event
Introduction
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vCM
vi vo = -vi + vCMhip
signal
SPICE simulations
R (on hybrid 1/chip)
preamp
s.f.inverter
1.0
0.8
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0.0
Vol
ts
2.5x10-6
1.51.00.50.0time
1.0
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Vol
ts
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source follower O/P inverter O/P
sensor APV
• motivation: can’t see what’s going on inside chip otherwise
• model: 128 channels with nearest neighbour interstrip capacitance (10pF) and AC coupling to APV I/P
• preamp o/p (after s.f.) linear to ~ 50 mips (4.5 MeV)
• inverter O/P linear to ~35 mips (3.2 MeV)
• signals > ~ 50 mips on a single channel cause that channels inverter to draw max current
-> significant voltage disturbance on vCM
10
80 mip
10 mipsteps
[email protected] CMS Tracker Week, January 2002 4
vCM
vivo = -vi + vCM
Simulations (2)
R (on hybrid 1/chip)
results here for 200 mip (18 MeV) signal on one channel only
• saturated signal in hip channel• big signal in nearest neighbours (~25 mip), shorter duration• combination -> transient disturbance vCM on R• vCM disturbance couples to inverter O/Ps of all channels• reduced value of R reduces effect• “spikey” behaviour of vCM interesting, could be decoupled
preamp
s.f.inverter
source follower O/P
inverter O/P
vCM
hip channel
nearest neighbours
non-hip channel
1.0
0.8
0.6
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0.0
Vol
ts
2.5x10-6
1.51.00.50.0time
1.0
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Vol
ts
2.5x10-6
1.51.00.50.0time
R=50 R=100
1.30
1.25
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Vol
ts
2.5x10-6
1.51.00.50.0time
R=100 R=50
[email protected] CMS Tracker Week, January 2002 5
Lab measurements - “improved” setup for charge injection
7 APV I/Pssee hip chargeshared equally
hip charge injected onone or two channelsother channels see
signal due to interstripcapacitance
10pF
10pF
10pF
10pF
10pF
10pF
previous
200
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0
AD
C u
nits
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050
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111 mips 500 mips 1111 mips• These results for hip charge injection on one channel only
• Inter-channel capacitance -> signal sharing and saturated signals in several channels
• i.e. localised hip signal still shows results consistent with beam data
this study
10 MeV 45 MeV 100 MeV
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Deadtime measurement technique300
250
200
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50
0
AD
C u
nits
10008006004002000100
50
0
10008006004002000
time [nsec]
Inject and measure amplitude (in APV O/P frame)of normal size signal
sweep injection time of hip signal
normal signal disappears during period whenhip signal causing baseline saturation for all channels
unplug normal signal and repeat to get baseline
subtract baseline measurement from measurementwith signal -> result gives deadtime = periodduring which the chip is insensitive to signals
all measurements here in deconvolution mode
t
inject normal signaltrigger on
normal signallatency
vary injection time of hip signal
[email protected] CMS Tracker Week, January 2002 7
Deadtime measurements • hip signal confined to 1 channel only
AD
C u
nits
5002500time [nsec]
111
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442
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794
1111
hip signal size[300 m Si Mips]
R = 100W
5002500time [nsec]
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1111
hip signal size[300 m Si Mips]
R = 50W
• Deadtime dependence on hip signal size characterised by a threshold and then rising to a saturated level
• Main difference when R -> 50 is increase in energy threshold required to produce deadtime
•Deadtime saturation level~125 ns R=100W (5 bunch crossings)~100 ns R=50W (4 bunch crossings)
10 MeV
100 MeV
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Deadtime measurements• hip signal shared between 2 channels
• Threshold energy for onset of deadtime significantly worse than for signal on one channel case
• Significant improvement in threshold energy and deadtime duration when R -> 50W
• Deadtime saturation level~300 ns R=100W (12 bunch crossings)~100 ns R=50W (4 bunch crossings)
AD
C u
nits
5002500time [nsec]
111
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1111
R = 100W
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5002500time [nsec]
111
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794
1111
R = 50W
10 MeV
100 MeV
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vCM measurements vs. simulation
• Voltage measured (with scope probe) on inverter supply resistor -> some similarity between measurement and simulation
• Decoupling inverter supply effective at removing spike
• Effect on deadtime worth investigating
simulationmeasurement
1.25
1.20
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1.10
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Vol
ts
time [sec/div.]
1.3
1.2
1.1
1.0
0.9
Vo
lts
3x10-6
0time
R=100W, C=0.1F R=100W
[email protected] CMS Tracker Week, January 2002 10
Deadtime measurements – effect of decoupling inverter supplyA
DC
uni
ts
5002500time [nsec]
111
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1111
R = 100W
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5002500time [nsec]
111
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1111
R = 100W + 0.1F
5002500time [nsec]
111
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1111
R = 50W
5002500time [nsec]
111
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R = 50W + 0.1F
• Results here for signal shared between 2 chans
• Effect of decoupling “spike” on inverter supply quite dramatic for R=100W case,
• Less so in 50W case, but still some improvement
10 MeV
100 MeV
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Deadtime measurements – comparison with previous result
• Results here for 100W inverter supply resistor (existing situation)
• 7 channel case shows smooth rise (up to ~ 60 bunch crossings at high energies)
• one/two channel + inter-channel capacitance model show big reduction in saturation level over 7-channel equal sharing model (5 – 12 bunches)
• but deadtime starts to appear sooner in 2 chan case and hit loss calculation sensitive to this threshold
111 MeV 1111 MeV
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0
Dea
dtim
e [n
sec]
12008004000
Hip energy [ Mips in 300m Si]
signal shared equally between 7 channels signal on 2 chans with interchannel capacitance signal on 1 chan with interchanel capacitance
R = 100W
[email protected] CMS Tracker Week, January 2002 12
400
300
200
100
0
Dea
dtim
e [n
sec]
12008004000
Energy [ Mips in 300m Si]
signal on 2 chans signal on 1 chan
R = 100W
12008004000
Energy [ Mips in 300m Si]
signal on 2 chans signal on 1 chan
R = 100W + 0.1F
12008004000
Energy [ Mips in 300m Si]
signal on 2 chans signal on 1 chan
R = 50W
12008004000
Energy [ Mips in 300m Si]
signal on 2 chans signal on 1 chan
R = 50W + 0.1F
Deadtime measurements – effect of decoupling and/or reducing R
• Deadtime dependence on whether hip signal on 1 or 2 channels significant only in R=100W case• Decoupling and/or reducing R -> substantial improvement in deadtime• Can parameterise deadtime and use to predict deadtime in CMS but already obvious that R-> 50W and/or adding decoupling will give significant improvement
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X5
CMS
3.0x10-3
2.5
2.0
1.5
1.0
0.5
0.05 6 7 8 9
1002 3 4 5 6 7 8 9
1000Ionisation energy (MIPs in 300µm Si)
X5 CMS
for 1% occupancy
Prob. of missing hit (E) = Prob.(E)*[deadtime(E)/25ns]*128*occupancy
Hit loss rate predictions - method
Total probability of hit loss per layer = Prob.(E)
(note: above plots taken from previous talk (7 – channel case))
E
Prob.(E) deadtime(E)Prob. of missing hit (E)
10 MeV 100 MeV1 MeV
1.2
0.8
0.4
0.010008006004002000
Ionisation energy (MIPs in 300µm Si)
Parameterised deadtime Measured values
10 MeV 100 MeV
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Total probability of hit loss (per 300(500)m layer, per % occupancy)
Hit loss rate predictions – for CMS (G.H.)
signal shared equally between 7 chans (previous result adjusted for latest simulations (M.H.)
signal shared equally between 2 chans(+ inter-channel capacitance)
R=100W R=50W
0.33 (0.76) % 0.20 (0.49) %
0.34 (0.65) % 0.023 (0.053) %
• 7 chan vs. 2 chan: No significant difference in hit loss prob. for R = 100 - reduction in deadtime at high hip energy compensated for by lower threshold for deadtime onset
• 7 channel results: R: 100 -> 50 gives ~ 40% reduction in hit loss probability but in 2 channel case get better than order of magnitude reduction - presumably reduction in vCM transient much more effective for charge distribution produced
by 2 chan. + inter-chan capacitance model
• not calculated exhaustively but other variants (1 chan only and/or decoupling) will give results similar to 2 chan/50W case
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Threshold hip energy required for saturated baseline
• APV lab measurements7 – channel equal sharing 9 – 18 Mev1 chan + inter-channel capacitance 13 – 16 MeV2 chan + inter-channel capacitance 6 – 8 Mev
• simple linear CM assumptiondepends on analogue O/P baseline position if ¼ to ½ output range 25 – 50 MeV
• discrepancy => saturated baseline threshold = non-linear function of hip energy
• actual hip energy required to saturate baseline depends on details of charge distribution
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Summary
• Modelling hip signal as large charge deposited in one or two channels-> saturated signals in more channels if inter-channel capacitance included
• Resulting hit loss rate prediction (2 chan.) similar to previous 7 chan equal sharing measurementsbut order of magnitude improvement if R -> 50Wrelative hit loss rate could go from 0.3% -> 0.02% per 300 m layer per % occ.)
• One/two channel results here suggest deadtime resulting from hip events could be in range 5 – 12 bunch crossings for existing inverter power scheme
-> some evidence for this in existing X5 beam data.
• Accurate determination of hit loss rate in CMS depends on:how well hip spectrum known (magnitude and rate)hip energy distribution between channels (will vary from event to event)