Beetle; a front-end chip for LHCb VELO

10/09/2002 IWoRID; Niels van Bakel 1

A collaboration between the ASIC-lab Heidelberg, NIKHEF Amsterdam and the University of Oxford

Beetle; a front-end chip for LHCb VELO

ASIC lab

Heidelberg


Outline

25 stations (50 Si planes)

•Vertex detector•Silicon strip detectors•Beetle architecture•Radiation hardness•Measured characteristics•Conclusions


•Required S/N > 14 (10 pF load)•Power consumption < 6 mW/channel •Peaking time 25 ns•Pulse spill-over < 30 % after 25 ns•Dynamic range ± 10 MIP

The Vertex detector

•Provide production and decay vertex information•Detector resolution ~8 m•200000 strip lines•Sampling frequency 40 MHz•1 MHz accepted triggers; no dead time if readout < 900 ns per event

Decay distance resolution 120 m


Silicon strip detector

•Detector capacitance 5-30 pF•Yearly radiation dose at 8 mm ~11014 [1 MeV neutrons/cm2] •300 (200) m thick•40-60 m inter strip distance•1 MIP creates ~22000 electrons•LHCb requirements depend on efficiency, technical limits, costs

5 cm

•Energy loss distribution obeys

a Landau function

•Non ionizing energy loss is expected to

be the major source of radiation damage

of the Silicon detector

•Fully depleted


Beetle architecture

Readout via 2 m twisted-pair cable, repeater card

preamp shaper

Pipeline 128186

pipelinereadout

multiplexer324

test channel 128 channelsdummy channel

Multi event buffer


Beetle layout

•Dimensions 6.1 mm 5.5 mm•Pitch input pads 41.2 m•Positive supply 2.5 V•Analog output driver ~ 50 mV/MIP•No dead channels allowed•< 0.1 % dead pipeline cells

pipeline

I2C

pipelinereadout control

fron

t-en

d am

pli

fier

s

128

anal

ogu

e in

pu

ts

pip

elin

e re

adou

t am

plif

iers

mu

ltip

lexe

rs

4 ou

tpu

ts


Radiation hard design

Tolerable irradiation dose > 10 Mrad in 5 years

Field

oxide

Leakage current

Gate oxide

Obtain radiation hardness with:•Tox < 10 nm : tunneling decreases the

trapped ions in the gate-oxide

•Enclosed nMOS prevents large

leakage currents

•Guardrings around nMOS

Single event upset (SEU) triggered by

single particles; tests needed

Control logic protected by SEU: use triple redundant flip-flops with majority encoding


Beetle1.1 showed full functionality up to 30 Mrad (15 LHCb years):

full trigger / readout functionalityfull slow control functionalityperformance degradations are small

Radiation tests (TID)

time [ns]

Vou

t [V

]

Test with X-ray

facility at CERN

Total ionizing dose

results in gate bias

voltage shifts


ENC behaviour of the new Beetle front end (measured on a test chip):

449 e- + 46.8 e-/pF

The channel thermal noise dominates the noise for an input transistor with a large area:

45.3 e-/pF (calculated)

1 MIP in the detector generates 22000 electrons

ENC measurements


Pulse shape

Measured

• 15 ns rise time

• 20 % spillover

HSPICE calculated

pulse (solid line)


The Beetle in a Testbeam

40 mm

80 mm

130 mm

Beam telescope

R and Phi

Beetle

Track

•Scintillator trigger

•Tracks used

•40 MHz sampling rate

•Two Beetle chips bonded

•Aligned with ~30 m

precision


Preliminary

Testbeam results

Sstrip/Nstrip = 13.3

Scluster/Nstrip = 15.3

17.5 ns rise time

21.3 % spill over


Conclusions and outlook

The Beetle1.1 fulfills the LHCb requirements: •rise time •spillover•S/N•sample frequency•radiation hardness

•Additional data with 16 Beetle1.1 chips on a VELO Beetle hybrid bonded to a silicon detector•Improved Beetle1.2 available since July (see LEB)•Beetle also considered for the Inner tracker, RICH detector and the pile-up veto detector (LHCb)


Residuals


Landau?


RF tests?


Analogue readout?


track mode

pulse mode

left: - signal pulse shape- comparator output

right: - binary readout (4 consecutive BX)

Comparator output level shifter is too slow

causes spill-over tothe second BX

Beetle 1.2: has nowan output buffer

Comparator?

Documents

Beetle; a front-end chip for LHCb VELO