Transcript Bias setting scan

Beetle; a front-end chip for LHCb VELO
A collaboration between the ASIC-lab Heidelberg,
NIKHEF Amsterdam and the University of Oxford
ASIC lab
Heidelberg
10/09/2002
IWoRID; Niels van Bakel
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Outline
•Vertex detector
•Silicon strip detectors
•Beetle architecture
•Radiation hardness
•Measured characteristics
•Conclusions
25 stations (50 Si planes)
10/09/2002
IWoRID; Niels van Bakel
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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 < 900 ns per event
•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
10/09/2002
Decay distance resolution  120 m
IWoRID; Niels van Bakel
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Silicon strip detector
•Detector capacitance 5-30 pF
•Yearly radiation dose at 8 mm
~11014 [1 MeV neutrons/cm2]
5 cm
•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
10/09/2002
IWoRID; Niels van Bakel
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Beetle architecture
test channel
dummy channel
128 channels
pipeline
readout
Pipeline 128186
preamp
shaper
multiplexer
324
Readout via 2 m twisted-pair cable, repeater card
10/09/2002
IWoRID; Niels van Bakel
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
•< 0.1 % dead pipeline cells
pipeline
pipeline
readout control
10/09/2002
I2C
IWoRID; Niels van Bakel
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Radiation hard design
Tolerable irradiation
dose > 10 Mrad in 5 years
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
Gate oxide
Field
oxide
Leakage current
Single event upset (SEU) triggered by
single particles; tests needed
Control logic protected by SEU: use
triple redundant flip-flops with majority
encoding
10/09/2002
IWoRID; Niels van Bakel
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Radiation tests (TID)
Vout [V]
Test with X-ray
facility at CERN
Total ionizing dose
results in gate bias
voltage shifts
time [ns]
Beetle1.1 showed full functionality
up to 30 Mrad (15 LHCb years):
full trigger / readout functionality
full slow control functionality
performance degradations are small
10/09/2002
IWoRID; Niels van Bakel
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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
10/09/2002
IWoRID; Niels van Bakel
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Pulse shape
Measured
• 15 ns rise time
• 20 % spillover
HSPICE calculated
pulse (solid line)
10/09/2002
IWoRID; Niels van Bakel
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The Beetle in a Testbeam
Beetle
•Scintillator trigger
•Tracks used
•40 MHz sampling rate
•Two Beetle chips bonded
•Aligned with ~30 m
precision
Track
10/09/2002
IWoRID; Niels van Bakel
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Testbeam results
17.5 ns rise time
21.3 % spill over
Preliminary
Sstrip/Nstrip = 13.3
Scluster/Nstrip = 15.3
10/09/2002
IWoRID; Niels van Bakel
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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)
10/09/2002
IWoRID; Niels van Bakel
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Residuals
10/09/2002
IWoRID; Niels van Bakel
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Landau?
10/09/2002
IWoRID; Niels van Bakel
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RF tests?
10/09/2002
IWoRID; Niels van Bakel
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Analogue readout?
10/09/2002
IWoRID; Niels van Bakel
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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
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IWoRID; Niels van Bakel
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