Front End Electronics for the ALICE TPC TPC SYMPOSIUM Berkeley, October 17, 2003

117 October 2003 Luciano Musa

Front End Electronics for the ALICE TPC

TPC SYMPOSIUM

Berkeley, October 17, 2003

Luciano Musa – CERN

[email protected]

http://ep-ed-alice-tpc.web.cern.ch/ep-ed-alice-tpc/

TPC FEE Collaboration

Bergen, CERN, Darmstadt TU

Frankfurt, Heidelberg, Lund, Oslo


FEE for the ALICE TPC

OUTLINE

• How to measure in high track density environment?

• The pile-up (ion-tail) problem in MPW

• Signal conditioning (pre-processing) in the front-end components

• Architecture and main components

• Measured performance


How to Measure in a High Track Density Environment?

ALICE TPC LAYOUT

510 cm

EE

88us

GAS VOLUME88 m3

DRIFT GAS90% Ne - 10%CO2

400 V / cm

88s

ALICE TPC CHALLENGES

up to 2x104 charged particles in TPC

LARGE DATA VOLUME

• 570 132 (pads) x 1000 (time bins)

• 712 Mbytes / event

• Pb – Pb (@200 Hz) 142 Gbyte / sec

• p-p (@1KHz) 710 GByte / sec


370

380

390

400

pad number

1015

2025

3035

am

pli

tud

e

0

50

100

150

How to Measure in a High Track Density?

TPC OCCUPANCY(*) IN THE PAD-TIME SPACE:

INNERMOST PAD ROW: 50% OUTERMOST PAD ROW: 17% AVERAGE OCCUPANCY: 25%

CLUSTER AT THE INNERMOST PAD ROW OF THE TPC

Occupancy figure for an idealcancellation of the ion tail!

(*)Occupancy = NABOVE / NALL

40% occupancy!


0 100 200 300 400 500 600 700

0

100

200

300

400

500

600

700

800

900

1000cluster peaks montecarlo data

Pad Row: 9

Nr samples after zero suppression: 310

Nr clusters: 76

Mean time between clusters: 1.2 s

Aliroot: Montecarlo with microscopic TPC simulation


Ionization in gas Generation of secondary electrons Diffusion of electrons Electron attachment E x B effect near the anode wires Avalanche of the anode wire Charge induced on pads and pad response function Shaping and sampling time signal

Physics of the Aliroot Monte Carlo


The Ion–Tail Problem

Test of Inner Readout Chamber with final FEE in Field Cage prototype

Ionization from 83Kr Decay

Ion tail


Aliroot: Montecarlo with microscopic TPC simulation

0 100 200 300 400 500 600 700

0

100

200

300

400

500

600

700

800

900

1000cluster peaks montecarlo data

Pad Row: 9

Nr samples after zero suppression: 310

Nr clusters: 76

Mean time between clusters: 1.2 s


0 100 200 300 400 500 600 700

0

100

200

300

400

500

600

700

800

900

1000Montecarlo data through NA49-FTPC amplifier

cluster peaks NA49-FTPC amplifier response

Aliroot data convoluted with measured signal



0 100 200 300 400 500 600 700-50

0

50

100

150

200Montecarlo data through NA49-FTPC amplifier

cluster peaks NA49-FTPC amplifier response

Aliroot data convoluted with measured signal

Signal corresponding to 1 MIP


_1μ10.1%_afterF(t)*R(t)

The measured TPC signal is approximated by the sum of exponential terms:

and processed by a linear network that cancels all but the fastest terms:

R(t)iταt

en

1i iA0Iis(t)

F(t)*R(t))0t/α/exp(F(t)*is(t)

F(t): impulse response function of the networkis(t): current induced on the pad

Ion Tail Cancellation

• Can the algorithm be implemented with sufficient accuracy by an hardwired circuit?

• Is the shape of the signal the same for all avalanches ?

• NA49, NA45 and STAR: 1st order analog filter (two exponential terms)

• ALICE: 3rd order digital filter (four exponential terms)

• Can the algorithm be implemented with sufficient accuracy by an hardwired circuit?

• Is the shape of the signal the same for all avalanches ?

• NA49, NA45 and STAR: 1st order analog filter (two exponential terms)

• ALICE: 3rd order digital filter (four exponential terms)

Digital Conditioning of the TPC Signal


0 100 200 300 400 500 600 700-50

0

50

100

150

200filter inputthreshold

0 100 200 300 400 500 600 700-50

0

50

100

150

200Filtered data and fixed threshold

filter outputthreshold

AD

C c

ou

nts

Time samples (170 ns)

filter off

AD

C c

ou

nts


filter on


0 100 200 300 400 500 600 700-50

0

50

100

150

200filter inputthreshold

0 100 200 300 400 500 600 700-50

0

50

100

150

200Filtered data and fixed threshold

filter outputthreshold

AD

C c

ou

nts


filter off

AD

C c

ou

nts


filter on


DIGITAL TAIL CANCELLATION PERFORMANCE




ALIROOT CLUSTERS +

BASELINE PERTURBATIONS

ALIROOT CLUSTERS +

BASELINE PERTURBATIONS

EVENT 1

EVENT 2

EVENT 3

time samples

AD

C c

ou

nts

Baseline perturbations:• temp. variation (ramp-up)• gating grid switching• power supply instability• pick-up noise



EV 1 EV 2

EV 3

EV 1 EV 2

EV 3

EV 1 EV 2EV 3

EV 1 EV 2

EV 3

ADC BC I

TCF BC II


Architecture and Main Components

anode wire

pad plane

drift region88s

L1: 5s 200 Hz

PASA ADC DigitalCircuit

RAM

8 CHIPS x

16 CH / CHIP

8 CHIPSx

16 CH / CHIP

CUSTOM IC(CMOS 0.35m) CUSTOM IC (CMOS 0.25m )

DETECTOR FEC (Front End Card) - 128 CHANNELS(CLOSE TO THE READOUT PLANE)

FEC (Front End Card) - 128 CHANNELS(CLOSE TO THE READOUT PLANE)

570132 PADS

1 MIP = 4.8 fC

S/N = 30 : 1

DYNAMIC = 30 MIP

CSA SEMI-GAUSS. SHAPER

GAIN = 12 mV / fCFWHM = 190 ns

10 BIT

< 10 MHz

• GAIN EQUALIZ.

• LINEARIZATION

• BASELINE CORR.

• TAIL CANCELL.

• ZERO SUPPR.

MULTI-EVENT

MEMORY

L2: < 100 s 200 Hz

DDL(3200 CH / DDL)

Powerconsumption:

< 40 mW / channel

Powerconsumption:

< 40 mW / channel

gat

ing

gri

d

analog memory in front of the ADC readout time independent of the occupancy

no zero suppression in the FEE high data throughput on the detector data links

ALTRO

FEE FOR THE NA49 AND STAR TPCs


PRE-AMPLIFIER SHAPING AMPLIFIER (PASA)

CfRf

(RC)4

+-

Q

Q/Cf

Q

Noise < 103 e < 1mV

MIP = 3x104 e 30mV

PASA RESPONSE FUNCTION

Gain: 12mV / fC (@ 12pF)

FWHM: 190ns

Noise: 566e (@ 12pF)

INL: < 1%

Crosstalk: < 0.1%

Power: 11 mW / ch

OPA OPA OPA

Cf // Rf

CSA SHA OA

MAIN CHARACTERISTICS

FWHM = 190 ns

Q = 149 fC

A(t / )4e-4(t/)


ALICE TPC READOUT CHIP (ALTRO)

010011010001011101010011010001011110010011010001011010

01001101000110111010110011000111001010011010 010011010001101110010 010011010001101110010 010011010001101110010

BaselineCorrection

I

+

–

TailCancellation

BaselineCorrection

II

ZeroSuppression

010011010001101110010010011010001101110010010011010001101110010

DataFormat

Memory+

Multi-EventBuffer

010011010001011101010011010001011110010011010001011010

01001101000110111010110011000111001010011010 010011010001101110010 010011010001101110010 010011010001101110010

BaselineCorrection

I

+

–

TailCancellation

BaselineCorrection

II

ZeroSuppression

010011010001101110010010011010001101110010010011010001101110010

DataFormat

Memory+

Multi-EventBuffer

MAX SAMPLING CLOCK 40 MHz

MAX READOUT CLOCK 60 MHz

HCMOS7 0.25 mm (ST)

area: 64 mm2

power: 16 mW / ch

ADC ENOB: 9.5 (@ 10MHz)

Data memory: 800 kbit

output bandwidth: 300MB/s

10- bit20 MSPS

11- bit CA2arithmetic

18- bit CA2arithmetic

11- bitarithmetic

40-bitformat

40-bitformat

10-bitarithmetic

16-CH Signal Digitizer and Processor


Front End Card: Layout, Cooling and Mounting

COOLING PLATES(COPPER)

WATER COOLING PIPE

INNER READOUT CHAMBER

Shaping AmplifiersALTROs

current monitoring & supervision

voltageregulators

powerconnector

control bus connector

readout busconnectors

GTL transceivers(back side)

155 mm

190

mm


0.9 ADC count = 1000 e

TESTS WITH ALICE TPC PROTOTYPE

SYSTEM NOISE



IONIZATION WITH COSMIC RAYS

10 MIP

1 MIP

Arrival of the ions to the

Cathode wires

INPUTAFTER TCF+MAF



IONIZATION WITH COSMIC RAYS

OCCUPANCY ~ 50%

INPUTAFTER TCF+MAF


Summary and Conclusions

ALICE TPC FEEALICE TPC FEE

• New electronics for on detector digital signal conditioning and high readout rate

• High resolution can be preserved, in presence of fast switching digital electronics, with proper time scheduling of digital processing and analogue to digital conversion

• Tests show an accurate (~0.1%) ion-tail cancellation and baseline

restoration when applied to the ALICE conditions

• Perturbations of the baseline and gain dispersion are corrected with digital

filtering techniques

• Production of the main components is well advanced and on schedule for the detector commissioning in middle of 2004


ALICE TPC READOUT CHIP (ALTRO)

Effective Number of Bits vs Input Frequency

7

7.5

8

8.5

9

9.5

10

0.00 1.00 2.00 3.00 4.00 5.00

Fin (MHz)

EN

OB

ALTRO16

ADS-901

AD9200

TDA8766

HI5710

Quartz Jitter:

25ps r.m.s.

BW at PASA output

Amplitude Uncertainty:

102 jitterf4 in

0.5 bits at 4.8 MHz

0.5 LSB

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 1 2 3 4 5

f (MHz)

dB

c

HD2 HD3HD4

ALTRO: a 16-channel A/D converter and digital processor chip

L. Musa et al. - ESSCIRC – June 2002


TPC READOUT PARTITION


Loc

al

Con

trol

ler

DD

L - IN

TS

low-C

ontrolInterface

TTC-RX

BOARDCTRL

RCU

Ethernet

Detector Link(100 MB / s)

(#216)

COUNTING ROOM

1

2

25

Each TPC Sector is served by 6 Readout Subsystems

Front-end bus(200 MB / sec)

LocalSlow- Control

Serial link

ON DETECTOR

Overall TPC: 4356 Front End Card 216 Readout Control Unit

FEC128 ch

DataCompr.

FEC128 ch

FEC128 ch

PASA – ADC – DIG.

Global Architecture


36 trapezoidal sectors

Inner chamberInner chamber

Outer chamberOuter chamber

FEC

C1 : 18 FECs

C6 : 20 FECs

C4 : 20 FECs

C3 : 18 FECs

C2 : 25 FECs

FRONT VIEWFRONT VIEW

C5 : 20 FECs

SIDE VIEWSIDE VIEW

128 channels Front End Card (FEC)

Capton Cable

140mm

190m

m

FEE POWER:

CHANNEL: 40 mW BOARD: 6.9 W

SECTOR: 832 W TOTAL: 30.2 KW

MOUNTING

Connection to the pad plane


ALTRO EVOLUTION

4cards16 ch

13

5 m

m

1998

CHANNELS / CHIP: 1

POWER / CH: 120mW

PRICE / CH: 50CHF

Integrated ADCs2

0 m

m

4 PQFP 100

8 SSOP 28

24 mm

1999

CHANNELS / CHIP: 4

POWER / CH: 80mW

PRICE / CH: 8CHF

2001

CHANNELS / CHIP: 1

POWER / CH: 16mW

PRICE / CH: 5CHF


240 mm

300

mm

155 mm

190

mm

FIRST PROTOTYPE

NEW DESIGN

FRONT END CARD



ALICE CHALLENGEThe ALICE Event Display

Nch(-0.5<<0.5) = 8000 slice: 2o in

Projection of a slice (2o in )

dNch / dy = 8000

Nr Pixels

570132 pads x 500 time bins

Projection of the drift volume into the pad plane

Nr hits = 19431047

pad row


• Z (time direction): fewer time bins

limitations:

– signal/noise gets critical for FWHM < 200 ns

– temporal signal is diffusion limited

oversampling

• R- (pad direction): smaller pads

limitations: – # of channels (cost!)

– HV-GND gets critial

– PRF is diffusion limited

oversampling

• Conclusion choose the time/pad area which yields still

reasonable signal (S/N > 20) for a given pad area optimize aspect ratio

minimize diffusion: “cold gas”, use high drift field

0 50 100 150 200 250 300 350 4000

0.2

0.4

0.6

0.8

1TPC Signal

D( )t

t

FWHM = 200 ns

Single avalanche



TPC WORKING PRINCIPLE


Signal induced by a single electron-ion pair



Signal induced by a single electron-ion pair Signal induced by a single avalanche

• In the readout chamber multiplication starts at 400 m from the anode wires

• The electron induced current growth in 5-10 ps from 10% to 90% of its final value

• Ions move slowly and need 30 -110s to reach their destination

• The ion induced current has a long tail with a rather complex shape

AVALANCHE PROCESS




Alignment for Pulses in a single channel

Results: Cosmic Run

0.1%



ALTRO Block Diagram

Input Signal

0

Readout bus

40-bit wide busBandwidth: 300 Mbyte/s

Trigger signals

L1: acquisition

L2: event freeze

Data Processor

Correction of:• Slow drifts and systematic effects• Non-systematic effects

Tail filteringData compression

40-bit backlinked format

•Channel address

•Time stamp

5 kbyte4 or 8 buffers

Memory

10-bit25 MSPS40 MSPS

TSA1001


Baseline Correction 1

Systematic perturbationBaseline drift

Fixed pedestal Slow drifts Systematic perturbation Combination

fpd = 0


Input Output

Tail Cancellation Filter

11 bit 11 bit

18 bit

Z-1 L1

K1

Z-1 L2

K2

Z-1 L3

K3

Base Range

211121617

DecimalsOverflowSign

1 0

2’s Complement

din

010

dout

10

Fixed-Point

Arithmetic

9

1 0

2’s Complement

2’s Complement


Filter Operation

Compensates Undershoot

Filter

Narrows the pulse

Filter

Improves cluster separation when pile-up occurs

Filter

Gain equalization


Characteristics:• Corrects non-systematic perturbations during the

processing time• Moving Average Filter (MAF)• Double threshold scheme (acceptance window)

After Tail Cancellation Filter After Baseline Correction II

BC II

Double threshold

A fixed threshold can

now be applied safely

din - bsl + offset , 0 dout

1023

0 , dout < 0

din - bsl + offset - 1024 , dout > 1023

Unsigned 11-bit FIR system

1. Slow variations of the signal Baseline updated

2. Fast variations of the signal Baseline value frozen

Operation

bsl frozen

8

ndin8

1bsl

bsl calculation

Baseline Correction 2


A fixed threshold for Zero Supression is not a suitable solution

Filter does not remove the perturbation because it is not related to the tail

The BC1 cannot correct non-systematic perturbations

Every sample within this window will be averaged and used to calculate next sample’s window

Perturbation has been removed

A fixed threshold can now be applied safely



Zero Suppression

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

Z-1

a

ba b

din

thr0

dout

glitchfilter

pre-samplespost-samples

clustermerger

flag

11 Z-1

4 Z-1 4 Z-1 3 Z-1

10

10


Zero Suppression Operation

above-threshold samples

pre-samples

post-samples

fill-in samples

rejected glitches

dismissed samples

discarded glitches

adjoined pre and post samples merged clusters

Documents

Front End Electronics for the ALICE TPC TPC SYMPOSIUM Berkeley, October 17, 2003