Tests of AGATA preamplifiers and hints to improve their performance

Transcription

1 Tests of AGATA preamplifiers and hints to improve their performance A. Pullia on behalf of preamplifier team AGATA Digital Processing workshop Milano, Italy, September 2005

2 Outline Tests of segment preamps at IKP Tests of built-in fast-reset device Tests of a digital deoscillator filter Tests of a digital baseline controller Conclusions

3 Outline Tests of segment preamps at IKP Tests of built-in fast-reset device Tests of a digital deoscillator filter Tests of a digital baseline controller Conclusions

4 AGATA Detector CSP Set ( 12 Segments + 1 Core) new solid GND concept for the mother board of 12+1 CSPs / Agata_Detector MDR26 connectors GND_Layer Top_Layer Segment preamplifiers Core preamplifier Segment preamplifiers

5 Tests made with one segmented detector housed in triple cryostat March 2005: GANIL preamps succesful after damping of a 75 MHz oscillation by increasing the compensation capacitance. Detailed report available upon request April 2005: MILANO preamps succesful after damping of a 120 MHz oscillation by reducing bias current of FET and increasing the compensation capacitance. Detailed report available upon request.

6 Comparison of Milano and Ganil preamplifiers 1,20 FWHM of 122keV-line Measurements made by D. Weisshaar (April 2005) FWHM [kev] 1,00 0,80 0,60 0,40 GANIL Reihe1 Milano Reihe2 FWHM of 59.5keV-line Mean FWHM is 1 kev with GANIL and Milano preamplifiers 1,20 0,20 1,00 0, ,80 Segment index FWHM [kev] 0,60 0,40 GANIL Reihe1 Milano Reihe2 Mean FWHM is 0.94 kev with GANIL and Milano preamplifiers 0,20 0, segment index

7 FWHM of Core with segments equipped with preamplifiers from Ganil Milano 122keV: 1.15keV 1.15keV 1.3MeV: 2.14keV 2.15keV Some segment resolutions: Ganil Milano C2 122keV 0.91keV 0.92keV 1.3MeV 1.85keV 1.83keV C3 122keV 0.90keV 0.90keV 1.3MeV 1.81keV 1.81keV D5 122keV 1.02keV 1.04keV 1.3MeV 1.99keV 1.97keV D6 122keV 1.07keV 1.12keV 1.3MeV 1.93keV 1.92keV

8 Absolute best result Energy resolution of 1.71/1.77 kev fwhm on 60 Co lines (12 April 2005) is one of the best ever obtained with Ge detectors!

9 Outline Tests of segment preamps at IKP Tests of built-in fast-reset device Tests of a digital deoscillator filter Tests of a digital baseline controller Conclusions

10 Tests made with MILANO preamplifiers Negative tails Inh signals Reset time Random arrival of MeV events provided by a poissonian pulser BNC mod. DB-2 An accidental AC-coupling in the pulser module causes the output signal to have a zero DC component and so to assume also negative values The random distribution of negative tails yields a random distribution of reset times, each of which is smaller than that obtained with no tail

11 Measurements of the event energy from the reset time S ( V1 V ) EO 2 E b T + b T k + = correction of the tail of the previous events E S = photon energy (or equivalent) T = reset time b 1, b 2, k 1, E 0 = fitting parameters V 1, V 2 = pre- and post-pulse pulse baselines Francesca Zocca, A A new low-noise preamplifier for γ-ray sensors with smart device for large signal management, Laurea Degree Thesis,, University of Milano, October 2004 (in Italian), topserver.mi.infn.it/mies/labelet_iii/download_file/capitolo6.doc

12 Energy resolution in auto-reset mode Event count rate Energy MeV in HPGe (fwhm) 140 Hz 0.26 % 470 Hz 0.29 % 1.14 khz 0.30 % 1.44 khz 0.30 % 2.65 khz 0.34 % 4.87 khz 0.44 %

13 Outline Tests of segment preamps at IKP Tests of built-in fast-reset device Tests of a digital deoscillator filter Tests of a digital baseline controller Conclusions

14 A simple approach exists to improve the preamplifier response PREAMP ADC NUMERICAL DEOSCILLATOR FILTER (FIR) Insufficient compensation capacitance The filter goal is to eliminate the ringings while preserving the high-frequency content of the preamplifier output signal

15 Weights of the numerical deoscillator filter as obtained from the DECONVOLUTION between the oscillating signal of the preamplifier and the wanted ideal response

16 Example: deoscillator filter removes ringings from a disturbed pulse shape

17 Outline Tests of segment preamps at IKP Tests of built-in fast-reset device Tests of a digital deoscillator filter Tests of a digital baseline controller Conclusions

18 Tests of a digital BL controller In XILINX Spartan 3 in out 200 mv / in ADC input out ADC input 1 µs / 12 bit 100 MHz 14 bit 100 MHz in out 0.5 V / A. Pullia, S. Riboldi, G.M. Franchi, F. Zocca Active control of the baseline of digitized preamplifiers with sliding-scale correction 2004 IEEE Nucl. Sci. Symp. Conference Record, Rome, ITALY, Oct out - in 0.5 ms /

19 The baseline can now walk across the preamplifier full range without causing ADC saturation!

20 Analysis of observed signals Noise of output signal is 0.85 mv (1.75 LSB) r.m.s. For slow input signals an amplitudefolding effect occurs, which yields an extended input dynamic range

21 ...which in turn yields an extended range on the individual signals The extended range (bit gain) increases as the input signal gets slower

22 Conclusion Full sets of Ganil and Milano segment preamplifiers have been installed in triple cryostat and operated succesfully in conjunction with one segmented detector All preamplifiers are equipped with over-threshold fast-reset device. Energy measurements are still possible in reset mode (up to 50 MeV) and energy resolution is good (0.26 to 17 MeV) Techniques to improve integrity and reduce random walks of preamplifier signals are available