Electronics status
• Measurements on CARIOCA (Johan)
– Gain
– First qualitative results on crosstalk
• Estimates on CARIOCA and discrete performance
– Charge used
– Noise analysis
– Time resolution
• Readout
– TDC implementation in FPGA (Andrea)
CARIOCA
•
Sensitivity
–
–
–
–
–
–
The delta charge injection with known capacitor
Injection capa much smaller than virtual input capacitance (<<100pF)
Various values of injection capa
Charge should be the same (up to certain limit)
With and without straw capacitance
Measure threshold for 50% counts
Carioca Threshold Sensitivity
1.200
1.150
1.100
Threshold Value (V)
1.050
1.000
1.9pF Carioca 2 no cap in //
0.950
1.3pF with 27pF run 3
1.9pF with 27pF run 1
0.900
0.850
0.800
3
8
13
Input charge (fC)
18
23
Summary of measurements
Carioca Sensitivity
Sensitivity 13.8 mV/fC
1.200
1.150
1.100
Threshold (V)
1.050
27pF in //
1.000
0pF in //
y = 0.0138x + 0.7478
R² = 0.9961
0.950
Linear (27pF in //)
0.900
0.850
0.800
0.000
5.000
10.000
15.000
Charge (fC)
20.000
25.000
Crosstalk on 64-straw prototype
•
•
•
•
•
FE boards removed
Injection from the far end
Measurements on the near end
Only qualitative
Looking for crosstalk
– Capacitive
– Inductive
– conductive
Crosstalk examples
“Close” straw
- on the same cutout
“far” straw
Crosstalk summary
1V step
generator
56 Ohm
Differential
probe
300 Ohm
1nF
A
>15%
<15%
<10%
<5%
<2%
injection straw
E
F
G
A
H
20%
10%
5%
2%
1%
2
1
injection straw
B
C
D
E
F
G
2
1
A
B
C
D
E
F
G
2
1
A
>15%
<15%
<10%
<5%
<2%
4
3
2
1
B
C
D
E
F
G
H
B
C
D
E
F
G
H
B
C
D
E
F
G
H
B
C
D
E
F
G
H
3
1
4
3
2
1
A
H
>15%
<15%
<10%
<5%
<2%
injection straw
G
2
A
injection straw
F
4
>15%
<15%
<10%
<5%
<2%
3
E
1
H
4
D
3
A
injection straw
C
2
>15%
<15%
<10%
<5%
<2%
3
B
4
H
4
>15%
<15%
<10%
<5%
<2%
injection straw
D
3
A
injection straw
C
4
>15%
<15%
<10%
<5%
<2%
injection straw
B
4
3
2
1
Estimates on frontend performance
• CARIOCA model, best reconstruction
• Response to delta pulse
Estimates on frontend performance
• Discrete FE model
• Response to delta pulse
4
R2 
( 1  s  tauc1)  ( 1  s  tauc2)
s
2  

  Rf  taub
6
1  s  taub
 R1 
( 1  s  taui)
5
How much charge do we use?
• Integrate complete charge from straw
– Inject as a delta
– Inject in the correct form 1/(t+t0)
– Compare amplitudes
• FE response is a convolution of straw current and
FE transfer function
t

1
1
out( t)   pash ( tau ) 
d tau

t0 t  tau  t0

0
CARIOCA uses ~10% of total charge for Ar:CO2
out_car( tmaxcar)
q_max_car( tmaxcarq )
 0.105
How much charge do we use?
• For discrete electronics we can adjust shaping
How much charge do we use?
• Charge estimates for Ar:CO2
–
–
–
–
–
–
–
Mobility 1.6*10**-4
Average number of secondary electrons 1.5
Total electrons starting cluster 2.5
Gas gain 10**5
Total charge in average cluster 40 fC
CARIOCA uses 4 fC from 1 cluster
Discrete uses 6 fC from 1 cluster for taui=5ns
• Measured sensitivity is ~ 14 mV/fC
– We should see ~60 mV output signal (scope on analog
output or threshold scan) for single cluster
Frontend noise
• Noise from the electronics
– CARIOCA 2000+42*Cd electrons = ~3000 e (0.5fC)
– Discrete 500+31*Cd electrons = ~1300e (0.2fC)
• Noise from the detector
– Resistivity of cathode and anode
– Protection resistor
2
ENCdet  4 kB Te ( Rd  Rp)  Cd 
Ks
n  taui
 16
 3.754287701847413  10
– ~3000 electrons (0.5fC) for CARIOCA shaping
– ~2300 electrons (0.37fC) for discrete electronics
(taui=5ns)
Frontend noise
• Noise from termination resistor far end (300 Ohms)
4 kB Te
Rterm
•
•
•
•
 16
 Kp  n  taui  7.032425188291864  10
0.6 fC CARIOCA
0.7 fC discrete (longer integration)
Better to avoid !!!
Straw near end terminated with protection resistor
and preamp input impedance
– Discrete electronics can be tuned to ~300 Ohms
Signal to noise ratio
• Total noise CARIOCA
– 0.7 fC without termiantion
– 1 fC with termination
• Total noise discrete
– 0.42 fC without termination
– 0.81 fC with termination
• Noise in the system
– Well designed system exhibits 1.5-2 times intrinsic noise of the frontend
– CARIOCA
• 1 fC – 1.4 fC
• 1.5 fC – 2 fC (term)
– Discrete
• 0.63 fC – 0.84 fC
• 1.2 fC – 1.6 fC (term)
• Measured sensitivity is ~ 14 mV/fC
– We should see ~10-20 mV output noise (scope or threshold scan)
Signal to noise ratio
• CARIOCA uses 4 fC from single cluster
– S/N = 4/(1-2) <4
– Can’t work with single clusters
• Discrete uses 6 fC (taui=5ns) from single
cluster
– S/N= 6/(0.63-1.6) < 10
– Depends on system performance and termination
Time resolution
• Time resolution caused by noise
– Slope at output signal linear region compared with noise
sigma 
n  taui ENCtotcar
2 Ne  cur0 t0 ln  1 

n  taui 
2 t0


• CARIOCA
– Sigma 0.5ns
– 0.66ns with termination
• Discrete
– Function of the shaping time
– 0.35ns for taui=5ns
– 0.78ns for taui=5ns with termination
Discrete electronics time resolution
Without termination
With termination
large series noise increase with integration
Time resolution- Limit by cluster
arrivals and pulse height, CARIOCA
Dependence on cluster arrival
time
Mean 8ns for Ar:CO2
Dependence on threshold (% of
single cluster amplitude)
Plans
• Till now
– Study of single cluster
• CARIOCA with slow gas?
• Even some hints for CARIOCA with Ar:CO2
• Reality
– Multiple clusters
• Trailing edges not touched
• Impossible to solve analytically
• Monte-Carlo in preparation
TDC study
•
•
•
•
•
Andrea has started TDC design
We want to try few different schemes
Collaboration with Heidelberg
Already at second scheme
Need to fix pinout for FPGA to be able to start
PCB (cover) design
• Need to start backend board soon