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A(nother) measurement of Cardiac parameters

P. Campana

(thanks to Paolo, Rossano and Mario for help and ideas on the setup)

July 16th, 2010

2

pulser

4.2 pF

50 W

Cardiac+SPB True

triggers

Q=4.5-25 fC

C=25-175 pF

Atten.

Method described in LHCb-2007-122 (OT FEE calibration)

Inject a calibrated charge through a small capacitance (delta charge)Capacitance carefully (error 10%) measured with 1 GHz Lecroy Oscilloscope (P. Ciambrone)

Deduce from Efficiency vs Threshold curves all Cardiac parameters (gain slope, noise) at various capacitance values (0 pf, 50pF, 100pF, 150pF + SPB [25pF])

Measurements performed on several channels of a Negative, a Positive and (the same) a Positive Shielded CARDIAC board

delayFake

triggers

3

effici

ency

Register units

Fitting the data points we can deduce the position ofthe Vthr for which P=50% and the width of the noise (gaussian) distribution (ENC)Furthermore, we can determine the channel offset

Noi

se ra

te

Register units

... and substracting the faketriggers, study the shapeof the efficiency below the offset

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Check with Threshold Scan (“A”) that system is not perturbed by measurement setup

Channel 16 under test

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Previous measurement of sensitivity (to my knowledge): Riegler, sept. 2003on a prototype board

Presentconfiguration

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• Spectra obtained with noise scan + 5 set of charge injection: 4.5, 7.5, 10.5, 15, 25 fC• ONE channel under charge injection, all the others at “reasonable” threshold [8 fC] (anyhow no effect on efficiency found if this threshold was raised/lowered)

Noise scan

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0.0 5.0 10.0 15.0 20.0 25.00

50

100

150

200

250

300

350

400

450

f(x) = 9.48642424242424 x + 175.937309090909

P10-175pF (mV)

0 5 10 15 20 250

50

100

150

200

250

300

350

400

450

f(x) = 11.4347272727273 x + 168.515272727273P10-125pF (mV)

0 5 10 15 20 250

100

200

300

400

500

600

f(x) = 14.3146666666667 x + 164.212

P10-75pF (mV)

0 5 10 15 20 250

100

200

300

400

500

600

f(x) = 17.9672727272727 x + 156.346327272727

P10-25pF (mV)

P50% P50%

P50% P50%

InputCharge (fC)

InputCharge (fC)

InputCharge (fC)

InputCharge (fC)

Example: channel 10 of a Positive (shielded) Cardiac

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0 50 100 150 200 2505

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P_RieglerN_RieglerP_this_measPolynomial (P_this_meas)N_this_measPolynomial (N_this_meas)

Input capacitance (pF)

Gai

n (m

V/fC

)Resume’ no. 1 – Gain vs capacitance curve (comparison with Werner data)

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Resume’ no. 2 – ENC vs capacitance curve (comparison with Werner data)

0 20 40 60 80 100 120 140 160 180 2000

2000

4000

6000

8000

10000

12000

14000

P_Riegler

N_Riegler

P_this_meas

N_this_meas

P_this_meas_Noshield

Input capacitance (pF)

Noi

se (e

lect

rons

)

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Summary data table

Capacitance (pF) Gain (mV/fC) Bias (fC) ENC (fC) Comparison with ENC

from Thr. Scan Data *

Negative Cardiac 25 16,8 3,2 0,63

75 12,6 3,5 0,80 M2R1W (75 pF) 0,60

125 9,7 3,1 1,17 M1R4W (100 pF) 0,89

175 7,9 3,2 1,48 M2R4W (192 pF) 1,59

Pos. Cardiac (shielded) 25 18,6 2,4 0,64

75 14,4 2,4 0,91 M2R3C (89 pF) 0,81

125 11,7 2,7 1,36 M3R2C (122 pF) 1,09

175 9,7 2,5 1,90 M5R3C (167 pF) 1,41

Pos. Cardiac (unshielded) 25 17,9 2,4 0,60

125 11,5 2,6 1,86

* From Burkhard’s table (I ignore if these are the latest data)

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Positive cardiac (unshielded)

Positive cardiac (shielded)

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Cardiac dead timeInjection on the same channel of 2 delta charges separated by a variable Dt

Delta = 35 ns

Delta = 35 ns

Cardiac input

Cardiac output

Cardiac is “blind” below 35ns. This time value is not affected by the amount of charge injected(over a very wide range) and by the duration of Cardiac shaping

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This result seems in contradiction with data obtained with Am241 and – probably – by GIF data,where dead time is correlated to signal amplitude

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Conclusions

Measurements on Cardiac boards show reasonable agreement with Wernerold measurements, although I noticed:

• boards show higher gain at low capacitance (in particular for positive one)

• ENC trend is confirmed, but noise in unshielded positive boards at high capacitance is much higher(note: all INFN chambers with pad readout are equipped with shielded FEE. M2R1-C, M2R2-C,M3R1-C, M3R2-C chamber capacitances are in the range of 110-140 pF and equipped with unshielded FEE. Is this effect noticed in the data from threshold scan?)

• ENC from threshold scan appears smaller than the one evaluated with this method (done in “perfect conditions”)

Measurements were consistent and stable among several channels of the same board. A more extensive campaign of measurements (on several boards) would have been desirable...but out of the reach of my patience (all data taken “by hand”...)