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A(nother) measurement of Cardiac parameters P. Campana

A(nother) measurement of Cardiac parameters P. Campana (thanks to Paolo, Rossano and Mario for help and ideas on the setup) July 16th, 2010. Method described in LHCb-2007-122 (OT FEE calibration) Inject a calibrated charge through a small capacitance (delta charge)

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A(nother) measurement of Cardiac parameters P. Campana

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  1. 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. 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 C=25-175 pF 4.2 pF pulser Atten. Cardiac+SPB True triggers 50 W Q=4.5-25 fC Fake triggers delay

  3. Fitting the data points we can deduce the position of the Vthr for which P=50% and the width of the noise (gaussian) distribution (ENC) Furthermore, we can determine the channel offset efficiency Register units Noise rate ... and substracting the fake triggers, study the shape of the efficiency below the offset Register units

  4. Check with Threshold Scan (“A”) that system is not perturbed by measurement setup Channel 16 under test

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

  6. Noise scan • 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)

  7. P50% P50% Input Charge (fC) Input Charge (fC) P50% P50% Input Charge (fC) Input Charge (fC) Example: channel 10 of a Positive (shielded) Cardiac

  8. Resume’ no. 1 – Gain vs capacitance curve (comparison with Werner data) Gain (mV/fC) Input capacitance (pF)

  9. Resume’ no. 2 – ENC vs capacitance curve (comparison with Werner data) Noise (electrons) Input capacitance (pF)

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

  11. Positive cardiac (unshielded) Positive cardiac (shielded)

  12. Cardiac dead time Injection on the same channel of 2 delta charges separated by a variable Dt Delta = 35 ns Cardiac input Cardiac output Delta = 35 ns 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

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

  14. Conclusions • Measurements on Cardiac boards show reasonable agreement with Werner • old 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”...)

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