Beetle; a front-end chip for LHCb VELO

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Beetle a front-end chip for LHCb VELO
A collaboration between the ASIC-lab Heidelberg,
NIKHEF Amsterdam and the University of Oxford
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Outline

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

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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 lt 900 ns per event

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

Decay distance resolution ? 120 ?m
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Silicon strip detector

• Detector capacitance 5-30 pF
• Yearly radiation dose at 8 mm
• 1?1014 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

• 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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Beetle architecture
128 channels
test channel
dummy channel
pipeline readout
Pipeline 128?186
preamp
shaper
multiplexer 32?4
Readout via 2 m twisted-pair cable, repeater card
Multi event buffer
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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
• lt 0.1 dead pipeline cells

4 outputs
front-end amplifiers
pipeline
multiplexers
pipeline readout amplifiers
128 analogue inputs
pipeline readout control
I2C
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Radiation hard design
Tolerable irradiation dose gt 10 Mrad in 5 years

• Obtain radiation hardness with
• Tox lt 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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Radiation tests (TID)
Test with X-ray facility at CERN
Total ionizing dose results in gate bias
voltage shifts
Beetle1.1 showed full functionality up to 30 Mrad
(15 LHCb years) full trigger / readout
functionality full slow control
functionality performance degradations are small
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ENC measurements
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
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Pulse shape

• Measured
• 15 ns rise time
• 20 spillover
• HSPICE calculated
• pulse (solid line)

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The Beetle in a Testbeam

• Scintillator trigger
• Tracks used
• 40 MHz sampling rate
• Two Beetle chips bonded
• Aligned with 30 ?m
• precision

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Testbeam results
17.5 ns rise time 21.3 spill over
Preliminary
Sstrip/Nstrip 13.3 Scluster/Nstrip 15.3
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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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Residuals
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Landau?
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RF tests?
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Analogue readout?
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Comparator?
left - signal pulse shape - comparator
output right - binary readout (4
consecutive BX)
track mode
Comparator output level shifter is too
slow ? causes spill-over to the second
BX ? Beetle 1.2 has now an output buffer
pulse mode