Timepix Studies: Medipix Collaboration Summary and More Timewalk Plots Alessandra Borgia Marina Artuso Syracuse University Group Meeting – Thursday 20 May 2010

Medipix Collaboration slides 2

Lab Setup Thanks to Jan and Richard! 1060nm laser via Maurice Glaser 2 attenuators Many degrees of freedom for motion NIM to TTL 3Hz clk Trig for timepix shutter Trig for laser Laser width = 20ns 3Hz laser pulse Rising edge of Timepix shutter triggers the start of the delay for the laser pulse. ~6.5μs delay 20 May 2010Alessandra Borgia -- Medipix Mtg3

Investigation of Cluster Charge as a Function of Number of Pixels 1 pixel cluster 2 pixel cluster 4 pixel cluster 2 Dim Spread of hits in pixels separately Spread of hits in all pixels summed 20 May 2010Alessandra Borgia -- Medipix Mtg4

Results Number of PixelsMean of sum of TOT counts over all pixels (i.e. Offset) ± ± ± May 2010Alessandra Borgia -- Medipix Mtg5 Note on Settings: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 5 All others same as test beam – see backup slide 27

Entries TOT Counts Same Effect Seen in Timepix TestBeam 2009 Testbeam response of the timepix assembly showed that the total charge in the clusters created by minimum ionizing particles had a clear dependence on the number of pixels in the clusters: for each extra pixel in the cluster, an extra ~25 counts were seen. 1 Pixel ~125 2 Pixels ~150 4 Pixels ~200 DUT at 0º 20 May 2010Alessandra Borgia -- Medipix Mtg6

Investigation of offset with Test Pulses Test Pulse Charge (arbitrary scale) TOT Counts Test Pulse Data Data and fits thanks to Atreyi, Paula and Richard. Using the new test pulse facility, we can show that this is an intrinsic property of the Timepix response: *There is an offset in the relationship between deposited charge and pixel response. This could be digitally removed in a future version of the chip, in order to optimize our use of the bits available. 20 May 2010Alessandra Borgia -- Medipix Mtg7

Pixel to Pixel Uniformity: Method Aim: To measure several pixels for uniformity. 1.Chose 10 random pixels 2.Ensured laser located in center of pixel 3.Measure TOT for each over 100 frames 4.Re-measure first pixel at end of run for drift check x y Timepix May 2010Alessandra Borgia -- Medipix Mtg8

Results *Small change in the TOT, gives a handle on the measurement accuracy *Fit indicates any drift - more linear than expected. * Note: scale set from 60 to 120 to show small difference in each point Same pixel 20 May 2010Alessandra Borgia -- Medipix Mtg9 Settings: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 10 All others same as test beam

Results Each individual measurement shows a spread of about 5%. This comes from a combination of variation in laser power, and variation in pixel response Mean % = 4.23% Over 10 pixels, the variation in the measured TOT never exceeds 5.5 counts. 20 May 2010Alessandra Borgia -- Medipix Mtg10

Timewalk: Laser Method Y-Axis TOA: Method of extraction 1.Get TOA of each pixel 2.Subtract it from the central pixel to get a ΔrawTOA per pixel. 3.Mean of this ΔrawTOA*25ns is y-axis quantity. 1. Use the laser to illuminate a group of pixels. 2. Ensure that over 100 events the TOT is stable to ~5%. 3. Switch to TOA mode. 4. Look at timewalk as a function of input charge 5. Chessboard correction needed 20 May 2010Alessandra Borgia -- Medipix Mtg11

Laser Stability X, pixel number Y, pixel number Alessandra Borgia -- Medipix Mtg12 All laser signal within shutter time

Result +*o+*o Preamp DAC 140 Preamp DAC 200 Preamp DAC 255 There is no change with respect to Preamplifier setting. *Plot at multiple preamp values with proper chess board correction 1 MIP! Settings: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 10 All others same as test beam 20 May 2010Alessandra Borgia -- Medipix Mtg13

Close up of the Timewalk Measurement Preamp DAC setting 255 is unstable. x+*ox+*o Preamp DAC 140 – Test Pulse Preamp DAC 140 Preamp DAC 200 Preamp DAC 255 +*o+*o Preamp DAC 140 Preamp DAC 200 Preamp DAC May 2010Alessandra Borgia -- Medipix Mtg14 Settings: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 10 All others same as test beam

Timewalk result with Test Pulse x+x+ Preamp DAC 140 – Test Pulse Preamp DAC 140 **Difference still needs to be understood. 20 May 2010Alessandra Borgia -- Medipix Mtg15 Settings for Laser data: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 10 All others same as test beam Settings for Test Pulse data: THL = 410  43 DACs above noise  1075e - s above noise Ikrum = 10 All others same as test beam

Conclusions The offset of multiple pixel clusters exists and is consistent between all measurements, but not necessarily a constant Pixel to pixel variation is very small ~5.5 TOT counts The timewalk is visible at the minimum ionization particle energy (~50 TOT counts) Preamplifier DAC value does not seem to effect the timewalk Preamplifier DAC value 255 seems unstable in laser measurements Timewalk slightly off between test pulse and laser data 20 May 2010Alessandra Borgia -- Medipix Mtg16

Conclusion and Future Studies Important measurements can be done with laser A new 660nm laser now in use – Smaller penetration depth 20 May 2010Alessandra Borgia -- Medipix Mtg17

Back Up Slides 20 May 2010Alessandra Borgia -- Medipix Mtg18

All DAC settings for all data i.e. Test Beam settings SettingDAC Value Ikrum10 (5 for data on slide 17) Disc127 Preamp140, 200 or 255 (nominal here is 140) Buff. Analog A127 Buff. Analog B127 Hist0 THL411 Vcas7 FBK130 GND128 THS80 Bias LVDS68 RefLVDS May 2010Alessandra Borgia -- Medipix Mtg19

Timewalk measurement without chessboard correction +Preamp DAC 140 Settings: THL = 411  59 DACs above noise  1475 e - s above noise Ikrum = 10 All others same as test beam All values in this area are below 0.

Chessboard Correction: Method 1.Central pixel known 2.Call this A (white square) 3.Create the chessboard pattern with the remaining pixels (whether they have been illuminated or not) 4.Add ½ clock cycle (12.5ns) from those marked B (white square) AAA A A AA A A A AAA B B B B B BB B B B B B 20 May 2010Alessandra Borgia -- Medipix Mtg21

More Timewalk plots All with TB settings except for: 1.THL 2.Preamp 3.Ikrum 22

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Close up 24

Test Pulse by Veerle (on 19 May 2010 yesterday) According to Xavi, at the TB DAC settings Ikrum=10, 1 MIP ≈ ~50 TOT counts 25

Timewalk comparison: TP and laser 26