Beetle; a front-end chip for LHCb VELO
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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
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10/09/2002 IWoRID; Niels van Bakel 2
Outline
25 stations (50 Si planes)
•Vertex detector•Silicon strip detectors•Beetle architecture•Radiation hardness•Measured characteristics•Conclusions
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10/09/2002 IWoRID; Niels van Bakel 3
•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
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10/09/2002 IWoRID; Niels van Bakel 4
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
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10/09/2002 IWoRID; Niels van Bakel 5
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
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10/09/2002 IWoRID; Niels van Bakel 6
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
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10/09/2002 IWoRID; Niels van Bakel 7
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
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10/09/2002 IWoRID; Niels van Bakel 8
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
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10/09/2002 IWoRID; Niels van Bakel 9
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
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10/09/2002 IWoRID; Niels van Bakel 10
Pulse shape
Measured
• 15 ns rise time
• 20 % spillover
HSPICE calculated
pulse (solid line)
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10/09/2002 IWoRID; Niels van Bakel 11
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
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10/09/2002 IWoRID; Niels van Bakel 12
Preliminary
Testbeam results
Sstrip/Nstrip = 13.3
Scluster/Nstrip = 15.3
17.5 ns rise time
21.3 % spill over
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10/09/2002 IWoRID; Niels van Bakel 13
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)
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10/09/2002 IWoRID; Niels van Bakel 14
Residuals
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10/09/2002 IWoRID; Niels van Bakel 15
Landau?
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10/09/2002 IWoRID; Niels van Bakel 16
RF tests?
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10/09/2002 IWoRID; Niels van Bakel 17
Analogue readout?
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10/09/2002 IWoRID; Niels van Bakel 18
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?