malte backhaus - fe-i4 testing, 07.02.20111 calibration constant measurements malte backhaus,...
TRANSCRIPT
Malte Backhaus - FE-I4 testing, 07.02.2011 1
Calibration Constant Measurements
Malte Backhaus, University of Bonn
Malte Backhaus - FE-I4 testing, 07.02.2011 2
Problem
• Problem:can not measure C_inj
• Idea:use known input charge from γ in sensor: #e = Eγ / 3.61 and compare with measured threshold
• How to do this?
Vth
Eγ
#e-h = Eγ/3.61
Vcal
C_inj
Malte Backhaus - FE-I4 testing, 07.02.2011 3
Idea
• Measure hit rate in dependency of threshold. Expected result:
Rate
threshold
At „50%-value“: Threshold [e] = Eγ / 3.61 [e]
Malte Backhaus - FE-I4 testing, 07.02.2011 4
Idea
• Measure hit rate in dependency of threshold. Expected result:
• Example measurement: Am241 how to know „50%-value“?
Rate
threshold
At „50%-value“: Threshold [e] = Eγ / 3.61 [e]
Malte Backhaus - FE-I4 testing, 07.02.2011 5
Idea
• Measure hit rate in dependency of threshold. Expected result:
• Example measurement: Am241 how to know „50%-value“? Derivative of rate is spectrum!
Rate
threshold
At „50%-value“: Threshold [e] = Eγ / 3.61 [e]
Malte Backhaus - FE-I4 testing, 07.02.2011 6
Measurement plan
• Use variable x-ray source to have different Eγ with known energies.
• Iterative process for four energies: - Search for „peak energy [VthinDAC]“ with untuned chip. - Set peak VthinDAC, measure „mean threshold“. - Tune chip to „mean threshold“.- Measure „peak energy [VthinDAC]“ with tuned chip.- Peak position [VthinDAC] moved (dominated by some pixels) need to retune chip… - Set (new) peak VthinDAC, measure „mean threshold“. - Tune chip to „mean threshold“.- finally measure peak position [VthinDAC].- Measure threshold [e] with this settings, compare with expected #e = Eγ / 3.61.
• Calculate correction for calibration constant…
• Problems: Measurement loop implemented in USBpixTest, but USBpixTest can not tune the chip / load a tuning need to run Stcontrol and USBpixTest in parallel, which is dangerous…
• Only „final“ measurements for Mo, Ag, Ba and Tb are shown in next slides…
Malte Backhaus - FE-I4 testing, 07.02.2011 7
Mo
• Eγ: 17.44 keV and 19.63 keV• Expected #e-h pairs: 4831 and 5438
Malte Backhaus - FE-I4 testing, 07.02.2011 8
Ag
• Eγ: 22.1 keV and 24.99 keV• Expected #e-h pairs: 6122 and 6922
Malte Backhaus - FE-I4 testing, 07.02.2011 9
Ba
• Eγ: 32.06 keV and 36.55 keV• Expected #e-h pairs: 8881 and 10125
Malte Backhaus - FE-I4 testing, 07.02.2011 10
Tb
• Eγ: 44.23 keV and 50.65 keV• Expected #e-h pairs: 12252 and 14030
Malte Backhaus - FE-I4 testing, 07.02.2011 13
Quick result
• Calibration constant correction factor: K = 1 / slope of fit = 1 / 0.6443 = 1.55
• # e_injected = (V_cal * C_inj) * 1.55 = ((PulserDAC * slope + offset) * C_inj) * 1.55
• slope of PulserDAC can be measured (was assumed to be 1.5 mV/DAC) Thresholds measured using Stcontrol have to be multiplied with 1.55
Noise: ~90e * 1.55 = ~140 e, close to expected noise value with sensor…
• Test this correction factor with Kβ-peak…
Malte Backhaus - FE-I4 testing, 07.02.2011 15
PulserDAC calibration
• Vcal [mV] = PulserDAC [DAC] * 2.06 [mV/DAC] K splits to K_plsr and K_inj
Malte Backhaus - FE-I4 testing, 07.02.2011 16
Result + Outview
• K_plsr = slope_measured / slope_assumed = 2.06 / 1.5 = 1.37• K = K_plsr * K_inj K_inj = K / K_plsr = 1.55 / 1.37 = 1.13
C_inj = C_assumed * K_inj = 5.9 fF * 1.13 = 6.7 fF
• Still to do:
- Think carefully about uncertainties:does splitting charge cloud lower rate? (Remark from Maurice...)width of photo-peak in Si, Threshold, ...
- Redo this procedure with second pixel flavour (result should be the same...)
- Redo this procedure with CAP0 and CAP1 independendly value of CAP0 and CAP1
- Crosscheck result with 2nd method...