Università degli studi di Torino

Tesi di Laurea Triennale“Characterization of front-end electronics boards for ionization chambers used to

monitor hadrontherapy beams”

di RIVERO FABIO

RELATORE: PROF. CRISTIANA PERONICO-RELATORE: DOTT. ALESSANDRO LA ROSA

September 2007 Fabio Rivero 2

KEY WORDS:• Hadrontherapy: Hadrons' beam for cancer treatment

Low dose on surface

High dose in depth

High precision on dose delivery

Minimal lateralscattering

• Monitoring and control of hadrontherapy beams

• Front-end electronics (TERA 06 Chip)

September 2007 Fabio Rivero 3

MY WORK FOR THE CNAO OF PAVIA

DETECTORSWITH THE

FRONT-END ELECTRONICS TESTED

Laboratorio Tecnologico (Via 7 Comuni, To)

Centro Nazionale Adroterapia Oncologica

September 2007 Fabio Rivero 4

THE PIXEL DETECTORSSTRUCTURE:

DEVELOPED FROM:

CHIP TERA 05 CHAMBERS(older

version)

MOPI (at Marie Curie

Institute, Orsay)

• Cathode - gap 5 mm – Anode• Anode subdivided in 1024 pixel• Pixel = 5 x 5 mm2

• Active area = 160 x 160 mm2

• Read-out: ASIC Tera06

September 2007 Fabio Rivero 5

THE ASIC TERA 06• Recycling integrator architecture

• 0.8 µm AMS CMOS

• 64 channel/chip

• 100 fC minimum detectable charge

• 1 µA maximum input current

• 200 fA background current

• 16 bit counters

designed by the INFN Torino Division

materially produced by the IBA Group, Belgium

• No dead-time in read-out

September 2007 Fabio Rivero 6

HOW THE CHIPS WORKI to f converter

QIN= 5us x 1uA= 5 pC

Qread= 8 x 600 fC = 4.8 pC

N = 8

∆V = 3 V;

Csub = 200 fF;Ch. Q = Csub*∆V = 600 fC

OTA_ref

SINGLE CHANNEL:

September 2007 Fabio Rivero 7

HOW EVERY CHANNEL WORKSEvery channel has:

• a converter, that converts current into frequency;

• a counter, of 16 bits;• a latch, that allows the

saving of the counts of every channel at the same time;

• a multiplexer, that unify all the 64 channels in order to allow the reading of the selected channel.

I→f converter 16 bit counter

I→f converter 16 bit counter

I→f converter 16 bit counter

I→f converter 16 bit counter

I→f converter 16 bit counter

... ...

in0

in1

in2

in62

in63

16

16

16

16

16

16

OTA

ref

Vpul

se+

Vpul

se-

A_re

set

latc

h

chan

nel

sele

ct6

MUX

D_r

eset

rstA : analogical reset signal;rstD : digital reset signal;

September 2007 Fabio Rivero 8

THE FRONT-END TERA 06: BOARDSTOP-SIDE: BOTTOM-SIDE:

SixLayers:Top layer

Layer 2

Layer 3 OTA

Layer 4 GND

Layer 5 Vcc

Bottom layer

CHIP 1

CHIP 0

September 2007 Fabio Rivero 9

HOW THE BOARDS WORK

September 2007 Fabio Rivero 10

TESTS DONE• PART 1: on all 60 boards

1. PEDESTALS: channel counts

2. CHARGE QUANTUM: quantization error

• PART 2: on few boards1. LINEARITY: variation of current into

channel2. STABILITY IN TIME: different

measurements at different times

September 2007 Fabio Rivero 11

Before testing…cleaning!ULTRASOUND CLEANER: BOARDS CLEANED

DRYING:

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EXPERIMENTAL SET UP

•Power supply card voltage fixed at 6 V;•Vota = 2.05 V, fixed reference voltage;•V th = 2.5 V, threshold comparator voltge;•V p+ = 3.12 V•V p- = 2.12 V( V p = V p+ - V p- = 1.0 V, Q = Csub x Vp )

•two comunication boards LA TxRx;•a computer with the necessary LabViewsoftware

POWER SUPPLY

the first to convert the TTL signal in RS422 long-distance standard, the second to convert RS422 in TTL

September 2007 Fabio Rivero 13

On all 60 boards PEDESTALS

Pedestal Spread

0,60

0,80

1,00

1,20

1,40

1,60

1,80

2,00

0 50 100

Channel

Pede

stal

(Hz)

FE_057_029FE_111_086FE_005_050

chip counting without current injected inFound by measuring the counts of the chips with every channel floating

<PED> ~ 1.2 Hz

September 2007 Fabio Rivero 14

On all 60 boards CHARGE QUANTUM:

Charge Quantum Spread

164166168170172174176178180182

0 50 100Channel

Cha

rge

Q.(f

C)

FE_044_024FE_090_076FE_084_015

Found by injecting manually current of 100 nAinto every channel of the chips with a injector

<C.Q.> ~ 173.26 fC and Stand. Dev of 2.26 fC or 1.3%

September 2007 Fabio Rivero 15

BACKGROUND CURRENTBackground Current Spread

100

150

200

250

300

350

0 50 100Channel

I(fA

)

057_029052_046005_050

On all 60 boards

I = Background Current;

f = Frequency

Q = Charge Quantum

PEDESTALS BACKGROUND CURRENT

<Ibk> ~ 195 fA

September 2007 Fabio Rivero 16

LINEARITYMeasuring the charge quantum at

different currentvalues (from 5 nA

to 1,5 µA)

On few boards

I = f * q

( I = current q = charge f = frequency )

0,00E+00

1,00E+06

2,00E+06

3,00E+06

4,00E+06

5,00E+06

6,00E+06

0 200 400 600 800 1000 1200 1400

Input Current (nA)

Out

put f

requ

ency

(Hz)

SATURATION FROM 850nA

RELATIVE DEVIATION UNDER 1%Verify the fit:

September 2007 Fabio Rivero 17

STABILITY IN TIME On few boards

Measuring the charge quantum at different times

A = taken on 12/07/07B = taken on 17/07/07 at

14:50C = taken on 17/07/07 at

16:12D = taken on 18/07/07 at

14:12

ratio A/B, A/C, A/D and the corrispondent percentual

relative deviation The test showed a perfect

constancy of measurements in time

Allunder 4 ‰

% Deviation FE_010_009

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0 20 40 60 80 100 120

Channel

% D

evia

tion

FE_010_009 AB% deviation

FE_010_009 AC% deviationFE_010_009 AD% deviation

September 2007 Fabio Rivero 18

SUMMARY57 of them worked out correctlyThere had to be tested

60 boards3 with different

problems

On few boards :• the linear behaviour with the increase of current is confirmed, with a saturation after at least 850 nA of current;• there is no instability of measurements with time.

The working chips on board for the TERA 06 electronic front-end tested are ready to be mounted on the detector.

Our work on TERA 06 will be submitted in NIM A

September 2007 Fabio Rivero 19

THANKS TO:

Torino Group of Medical Physics• my parents

• Dott. Alessandro La Rosa

• my relator Prof. Cristiana Peroni and all the Torino Group of Medical Physics

September 2007 Fabio Rivero 20

Thanks for your attention!