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

Timepix Studies:Medipix Collaboration Summary and More Timewalk Plots

Alessandra BorgiaMarina ArtusoSyracuse UniversityGroup Meeting – Thursday20 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 timepixshutter

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 2010 Alessandra Borgia -- Medipix Mtg 3

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


ResultsNumber of Pixels Mean of sum of TOT counts over all pixels

(i.e. Offset)

1 128.6 ± 0.2

2 147.3 ± 0.1

4 201.8 ± 0.1


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

Entr

ies

TOT Counts

Same Effect Seen inTimepix TestBeam 2009

Testbeam response of the timepix assembly showed that the total charge in theclusters created by minimum ionizing particles had a clear dependence on the number ofpixels 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


Investigation of offsetwith Test Pulses

Test Pulse Charge (arbitrary scale)

TO

T C

ounts

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.


Pixel to Pixel Uniformity:Method

Aim: To measure several pixels for uniformity.

1. Chose 10 random pixels 2. Ensured laser located in center of pixel3. Measure TOT for each over 100 frames4. Re-measure first pixel at end of run for drift check

x

y

1

4

2

9

7

56

3

8

Timepix

10


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


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 responseMean % = 4.23%

Over 10 pixels, the variation in the measured TOT never exceeds 5.5 counts.


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


Laser Stability

X, pixel number

Y,

pix

el num

ber

Alessandra Borgia -- Medipix Mtg 12

All laser signal within shutter time

Result

+*o

Preamp DAC 140Preamp DAC 200Preamp DAC 255

There is no change with respect to Preamplifier setting.

*Plot at multiple preamp values with proper chess board correction

1 MIP!


Ikrum = 10



Close up of the Timewalk Measurement

Preamp DAC setting 255 is unstable.

x+*o

Preamp DAC 140 – Test PulsePreamp DAC 140Preamp DAC 200Preamp DAC 255

+*o

Preamp DAC 140Preamp DAC 200Preamp DAC 255



Ikrum = 10


Timewalk result with Test Pulse

x+

Preamp DAC 140 – Test PulsePreamp DAC 140

**Difference still needs to be understood.20 May 2010 Alessandra Borgia -- Medipix Mtg 15

Settings for Laser data:THL = 411 59 DACs above noise 1475 e-s above noiseIkrum = 10


Settings for Test Pulse data:THL = 410 43 DACs above noise 1075e-s above noiseIkrum = 10


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


Conclusion and Future Studies

• Important measurements can be done with laser

• A new 660nm laser now in use– Smaller penetration depth


Back Up Slides


All DAC settings for all datai.e. Test Beam settings

Setting DAC Value

Ikrum 10 (5 for data on slide 17)

Disc 127

Preamp 140, 200 or 255 (nominal here is 140)

Buff. Analog A 127

Buff. Analog B 127

Hist 0

THL 411

Vcas 7

FBK 130

GND 128

THS 80

Bias LVDS 68

RefLVDS 128


Timewalk measurement without chessboard correction

+ Preamp DAC 140


Ikrum = 10

All others same as test beamAll values in this

area are below 0.

Chessboard Correction:Method

1. Central pixel known2. 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)

A A A

A A

A A A

A A

A AA

B

B

B

B B

B B

B B

B

B

B


More Timewalk plots

All with TB settings except for:1. THL2. Preamp3. Ikrum

22

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 16000

25

50

75

100

125

150

175

200

225

250 TimewalkPreamp: 140 DAC

Ikrum: 5 DACTHL: 411 DAC

==>59 DACs above noise ==>1475 e-s above noise

700mV - ChessBoardCorr - B770mV - ChessBoardCorr- B800mV - ChessBoardCorr900mV - ChessBoardCorr - B1000mV - ChessBoardCorr - B1 MIP1 MIP+offset

TOT Counts

TOA

(ns)

23

Close up

0 10 20 30 40 50 60 70 80 90 1000

25

50

75

100

125

150

175

200

225




700mV - ChessBoardCorr - B770mV - ChessBoardCorr- B800mV - ChessBoardCorr900mV - ChessBoardCorr - B1000mV - ChessBoardCorr - B1 MIP1 MIP+offset

TOT Counts

TOA

(ns)

24

Test Pulse by Veerle (on 19 May 2010 yesterday)

0 50 100 150 200 250 300 350 400 4500

10

20

30

40

50

60

70

80

90

100ToA vs ToT Preamp 140

Ikrum: 10 DACTHL: 410

--> 43 DACs above noise --> 1075e-s above noise

Series1

Qin [mV](Or Test Pulse voltage (mV) )

ToA[

ns]

According to Xavi, at the TB DAC settings Ikrum=10, 1 MIP ≈ ~50 TOT counts

25

Timewalk comparison: TP and laser

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 16000

25

50

75

100

125

150

175

200

225




700mV - ChessBoardCorr - B

770mV - ChessBoardCorr- B

800mV - ChessBoardCorr



Veerle's TP data -Preamp140 -Ikrum10-1050e's above noise floor

1 MIP (Ikrum5)

1 MIP(Ikrum5) + offset

1 MIP (Ikrum10)

TOT Counts

TOA

(ns)

26

Documents

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