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
• 1060nm laser
• via Maurice
Glaser
•Laser width = 20ns
•2 attenuators
•Rising edge of
Timepix shutter
triggers the start of
the delay for the
laser pulse.
•~6.5μs delay
•3Hz laser pulse
• Many degrees of
freedom for motion
Thanks to Jan and
Richard!
3Hz
clk
Trig for
timepix
shutter
20 May 2010
Alessandra Borgia -- Medipix Mtg
Trig
for
laser
NIM
to
TTL
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
20 May 2010
Alessandra Borgia -- Medipix Mtg
4
Results
Number 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
20 May 2010
Alessandra Borgia -- Medipix Mtg
5
Entries
Same Effect Seen in
Timepix TestBeam 2009
1 Pixel ~125
2 Pixels ~150
DUT at 0º
4 Pixels ~200
TOT Counts
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.
20 May 2010
Alessandra Borgia -- Medipix Mtg
6
Investigation of offset
with
Test
Pulses
Test Pulse Data
TOT Counts
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.
Test Pulse Charge (arbitrary scale)
This could be digitally removed in a
future version of the chip, in order
to optimize our use of the bits
available.
Data and fits thanks to Atreyi,
Paula and Richard.
20 May 2010
Alessandra Borgia -- Medipix Mtg
7
Pixel to Pixel Uniformity:
Method
Aim: To measure several pixels for uniformity.
1.
2.
3.
4.
Chose 10 random pixels
Ensured laser located in center of pixel
Measure TOT for each over 100 frames
Re-measure first pixel at end of run for drift check
Timepix
10
9
1
2
3
4
y
5
6
7
8
x
20 May 2010
Alessandra Borgia -- Medipix Mtg
8
Results
Settings:
Same pixel
* Note: scale set
from 60 to 120
to show small
difference in
each point
20 May 2010
*Small change in the TOT, gives a handle on the
measurement accuracy
*Fit indicates any drift - more linear than expected.
Alessandra Borgia -- Medipix Mtg
THL = 411
59 DACs above
noise
1475 e-s above
noise
Ikrum = 10
All others same
as test beam
9
Results
Over 10 pixels, the variation in the measured
TOT never exceeds 5.5 counts.
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%
20 May 2010
Alessandra Borgia -- Medipix Mtg
10
Timewalk:
Laser Method
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
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.
20 May 2010
Alessandra Borgia -- Medipix Mtg
11
Y, pixel number
Laser Stability
X, pixel number
All laser signal within shutter time
Alessandra Borgia -- Medipix Mtg
12
Result
+ Preamp DAC 140
* Preamp DAC 200
o Preamp DAC 255
*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
There is no change with respect to Preamplifier setting.
20 May 2010
Alessandra Borgia -- Medipix Mtg
All others same
as test beam
13
Close up of the Timewalk
Measurement
x
+
*
o
Preamp DAC 140 – Test Pulse
Preamp
DAC 140
+ Preamp
DAC 140
Preamp DAC 200
* Preamp DAC 200
Preamp DAC 255
o Preamp DAC 255
Preamp DAC
setting 255
is unstable.
Settings:
THL = 411
59 DACs
above noise
1475 e-s
above noise
Ikrum = 10
All others same
as test beam
20 May 2010
Alessandra Borgia -- Medipix Mtg
14
Timewalk result with Test Pulse
Settings for
Laser data:
THL = 411
59 DACs
above noise
1475 e-s
above noise
Ikrum = 10
x Preamp DAC 140 – Test Pulse
+ Preamp DAC 140
All others same
as test beam
Settings for
Test Pulse
data:
THL = 410
43 DACs
above noise
1075e-s above
noise
Ikrum = 10
**Difference still needs to be understood.
20 May 2010
Alessandra Borgia -- Medipix Mtg
All others same
as test beam 15
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 2010
Alessandra Borgia -- Medipix Mtg
16
Conclusion
and Future Studies
• Important measurements can be done
with laser
• A new 660nm laser now in use
– Smaller penetration depth
20 May 2010
Alessandra Borgia -- Medipix Mtg
17
Back Up Slides
20 May 2010
Alessandra Borgia -- Medipix Mtg
18
All DAC settings for all data
i.e. Test Beam settings
20 May 2010
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
Alessandra Borgia -- Medipix Mtg
19
Timewalk measurement without
chessboard correction
+ Preamp DAC 140
Settings:
THL = 411
59 DACs
above noise
1475 e-s
above noise
Ikrum = 10
All values in this area
are below 0.
All others same
as test beam
Chessboard Correction:
Method
A
B
A
B
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
A
B
A
B
A
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)
20 May 2010
Alessandra Borgia -- Medipix Mtg
21
More Timewalk plots
All with TB settings except for:
1. THL
2. Preamp
3. Ikrum
22
Timewalk
250
700mV - ChessBoardCorr - B
Preamp: 140 DAC
Ikrum: 5 DAC
THL: 411 DAC
225
200
770mV - ChessBoardCorr- B
800mV - ChessBoardCorr
==>59 DACs above noise
==>1475 e-s above noise
175
900mV - ChessBoardCorr - B
1000mV - ChessBoardCorr - B
1 MIP
1 MIP+offset
TOA (ns)
150
125
100
75
50
25
0
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
TOT Counts
23
Close up
700mV - ChessBoardCorr - B
Timewalk
250
225
770mV - ChessBoardCorr- B
Preamp: 144 DAC
800mV - ChessBoardCorr
Ikrum: 5 DAC
900mV - ChessBoardCorr - B
1000mV - ChessBoardCorr - B
THL: 411 DAC
200
1 MIP
==>59 DACs above noise
==>1475 e-s above noise
175
1 MIP+offset
TOA (ns)
150
125
100
75
50
25
0
0
10
20
30
40
50
60
70
80
90
100
TOT Counts
24
Test Pulse by Veerle
(on 19 May 2010 yesterday)
ToA vs ToT Preamp 140
Ikrum: 10 DAC
THL: 410
--> 43 DACs above noise
--> 1075e-s above noise
100
90
80
70
ToA[ns]
60
Series1
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
Qin [mV]
(Or Test Pulse voltage (mV) )
According to Xavi, at the TB DAC settings Ikrum=10, 1 MIP ≈ ~50 TOT counts
25
Timewalk comparison:
TP and laser
Timewalk
250
700mV - ChessBoardCorr - B
Preamp: 144 DAC
225
770mV - ChessBoardCorr- B
Ikrum: 5 DAC
THL: 411 DAC
200
800mV - ChessBoardCorr
==>59 DACs above noise
==>1475 e-s above noise
175
900mV - ChessBoardCorr - B
1000mV - ChessBoardCorr - B
TOA (ns)
150
Veerle's TP data -Preamp140 -Ikrum101050e's above noise floor
1 MIP (Ikrum5)
125
100
1 MIP(Ikrum5) + offset
75
1 MIP (Ikrum10)
50
25
0
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
TOT Counts
26