[email protected] tracker week, january 20021 lab measurements and simulations of hips...

[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


~ 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


vCM

vi vo = -vi + vCMhip

signal

SPICE simulations

R (on hybrid 1/chip)

preamp

s.f.inverter

1.0

0.8

0.6

0.4

0.2

0.0

Vol

ts

2.5x10-6

1.51.00.50.0time

1.0

0.8

0.6

0.4

0.2

0.0

Vol

ts

2.5x10-6

1.51.00.50.0time

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


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

0.4

0.2

0.0

Vol

ts

2.5x10-6

1.51.00.50.0time

1.0

0.8

0.6

0.4

0.2

Vol

ts

2.5x10-6

1.51.00.50.0time

R=50 R=100

1.30

1.25

1.20

1.15

1.10

Vol

ts

2.5x10-6

1.51.00.50.0time

R=100 R=50


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

160

120

80

40

0

AD

C u

nits

200

160

120

80

40

050

200

160

120

80

40

0

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


Deadtime measurement technique300

250

200

150

100

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


Deadtime measurements • hip signal confined to 1 channel only

AD

C u

nits

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

hip signal size[300 m Si Mips]

R = 100W

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

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


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

140

175

222

279

350

442

500

630

794

1111

R = 100W

88

70

56

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

R = 50W

10 MeV

100 MeV


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

1.15

1.10

1.05

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


Deadtime measurements – effect of decoupling inverter supplyA

DC

uni

ts

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

R = 100W

88

70

56

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

R = 100W + 0.1F

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

R = 50W

5002500time [nsec]

111

140

175

222

279

350

442

500

630

794

1111

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


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

1600

1400

1200

1000

800

600

400

200

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


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



R = 100W + 0.1F

12008004000



R = 50W

12008004000



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


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


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


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


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)

[email protected] tracker week, january 20021 lab measurements and simulations of hips...

Documents

hip signal size

localised hip signal

hip channel big signal

hip signals

assumed signal

signal result

hip signal spice simulations

saturated channels