CBC2: CMS microstrip readout for HL-LHC
[D. Braga], G. Hall , M. Pesaresi, M. Raymond (Imperial College) D. Braga, L. Jones, P. Murray, M. Prydderch (RAL)
D. Abbaneo, G. Blanchot, A. Honma, M. Kovacs, F. Vasey (CERN)
HSDT9 Sep 2013 2
Background
• CMS upgrade under consideration for many years– objective to reach 3000 fb-1 in next decade or so– High Luminosity LHC (Phase II) requires new Tracker around 2023– Requirements:
• lower material budget• increased granularity• enhanced radiation tolerance• tolerable power consumption• affordable cost• all compatible with physics objectives –some of which remain
uncertain– e.g. will new physics be discovered in next running period?– but solid long term programme of Higgs & top studies, searches, etc…
Geoff Hall
HSDT9 Sep 2013 3
Evolution of objectives
• Original goal– new – improved - tracker with similar angular coverage, constrained by
re-using existing services– provide some part of tracker data to L1 trigger to contain rate to 100 kHz
• More recent developments– Baseline Tracker design now adopted
• “conventional” barrel-endcap layout looks optimal– but CMS exploring enhancing forward region physics as well as standard
physics programme– uncertainty if L1-track triggering will reduce rate to 100 kHz in 6.4µs
• ideas (and detector requirements) not yet validated by simulations• possible objective of L1 readout up to 1 MHz/10-20µs• both approaches require on-detector data reduction
Geoff Hall
HSDT9 Sep 2013 4
Baseline tracker layout (pixels not shown)
• Double layer readout compatible with trigger• Geometry compatible with forward extension
Geoff Hall
2S short strip double-layers(~7500 modules)
PS strip-strixel double-layers (~10,000 modules)
HSDT9 Sep 2013 5
ASIC development
• Earliest developments foresaw conventional outer tracker, plus some dedicated trigger (and pixel) layers– 128 channel CMS Binary Chip (CBC) produced and proven 2011– Readout architecture followed original tracker, using APV25– Analogue data abandoned for practical reasons
• digital optical link components now standard, ADC power, 130 nm CMS harder to implement analogue cells
• Subsequently, outer modules with trigger capability– 254 CBC2 successfully developed – delivered 2012 – optimised for new assembly method with mass production in mind
Geoff Hall
HSDT9 Sep 2013 6
Present CMS Tracker architecture
• Analogue unsparsified readout– APV25 in 0.25µm commercial CMOS– synchronous – occupancy independent data volume– 2.7mW/chan for 10-20cm µstrips
– analogue data transmission to external ADC & zero-suppression, clusters
• semi-custom optical links @ 40Msps• 1310 nm single-mode Fabry-Perot lasers• very successful• reflected state of technology at the time
– benefits• simple and easy to debug/evaluate• robust against noise
Geoff Hall
pipeline
128x192
128
x pr
eam
p/sh
aper
APSP
+ 1
28:1
MU
X
pipe logicbias gen. controllogic
7.1
mm
8.1 mm
Analogue Optical Hybrid
HSDT9 Sep 2013 7
Basic trigger module concept
• Compare binary pattern of hit pixels on upper and lower sensors
Geoff Hall
High pT tracks can be identified if hits lie within a search window in R-f (rows) in second layer
~200μm
Upper Sensor
Lower Sensor
Pass Fail
~100μm
1-2 mm
R
f~mm-cm
f (rows)
z (columns)
Sensor separation and search window determines pT cutz-segmentation determines vertex capability
HSDT9 Sep 2013 8
2S PT-module with CBC2
• Track & trigger µstrip module for outer tracker region– CBC2 logic correlates hits on two sensors to reject those from low pT tracks
Geoff Hall 8
8 x 254 channel chipsbump-bonded to hybrid
8 x 254 channel chipsbump-bonded to hybrid
chips on top surface onlysignals from lower sensor
via’d through substrate
~5 cm
90 µm pitch strips
sensors wire-bondedabove and below
~5 cm
concentrator&
controller
two layers of sensorslow mass, high density interconnect layer
HSDT9 Sep 2013 9
CBC main features
– IBM 130nm CMOS process
– binary, unsparsified architecture• retains chip and system simplicity• but no pulse height data
– designed for ~2.5 - 5cm µstrips < ~ 10 pF
– 128 channels, 50 mm pitch wire-bond• either polarity input signal
– not contributing to L1 trigger
– powering test features: • 2.5 -> 1.2 DC-DC converter• LDO regulator (1.2 -> 1.1) feeds analogue FE
– fast (SLVS) and slow (I2C) control interfaces
Geoff Hallam
plifi
ers &
com
para
tors
256 deep pipeline +32 buffers
128
chan
nel i
nput
2.5->1.25DC-DC converter
bias generator linear
drop out regulator
7 m
m
4 mm
HSDT9 Sep 2013 10
CBC measured performance
Geoff Hall
115k
80f1p
VPLUS
Vdda
16k
200k
100f
60k 92k
VCTH 2k
4k
8k
16k
500k
preamp
postamp
comparator
– analogue• 130 + (21 x C [pF]) µW/chan
– digital• < 50 µW/chan
– total• 180 + (21 x C[pF]) µW/chan e.g. < 300 µW /channel for C = 5 pF
1200
1000
800
600
400
200
0
nois
e [rm
s el
ectro
ns]
121086420
external capacitance [pF]
400
350
300
250
200
150
100
power per channel [uW
]
holes mode
noisepower
simulation: open circles
1200
1000
800
600
400
200
0
nois
e [rm
s el
ectro
ns]
121086420
external capacitance [pF]
400
350
300
250
200
150
100
power per channel [uW
]
electrons mode
noisepower
simulation: open circles
HSDT9 Sep 2013 11
CBC comparator
Geoff Hall
• thresholds adjusted satisfactorily
• timewalk within spec
720700680660640
720700680660640
even
ts a
bove
thre
shol
dcomparator global threshold [mV]
128 channelsbefore tuning
after
threshold uniformity
VCTH
timew
alk
[ 1ns
ec /
divi
sion
]
109876543210
charge injected [fC]
added capacitance 1.8 pF 3.8 pF 5.8 pF 8.1 pF 10.7 pF
timewalk: threshold at 1 fC
VDDA
postamp O/PO/S adjust8-bit value
(per channel)
16k VCTH
hysteresis
2k
4k
8k
16k
16k
500k
postampO/P
comparator
HSDT9 Sep 2013 12
Beam telescope• Based on CMS Tracker DAQ readout hardware, software (used for UA9 studies)
• FED, APV25s, 100m fibres, custom control system, multi-core PCs• 50 kHz data taking during 10s spill, 10 kHz to disk,
Geoff Hall
Goniom
eter
p+ beam
upstream downstream
XY
Plane 1
XY
Plane 2
XY
Plane 3
UV
Plane 4
XY
Plane 5
Crystal
Granite Table
10,289mm
295mm
416mm
214mm
9,960mm
Trigger Scintillators
spatial resolution: 6.8-7.0 µm
angular resolution: 5.2 µrad
HSDT9 Sep 2013 13
APV plane
CBC sensor
5 mV / division
beam profileCBC beam tests 2011
• CERN H8 beam line– 400 GeV/c protons
Geoff Hall
5 cm
p-on-n150 mm pitch320 µm thick
64 strips bonded to 5 cm p-on-n sensorno pitch adaptor150 µm pitch 320 µm thickness fan shaped
160x103
140
120
100
80
60
40
20
0nu
mbe
r of r
aw d
ata
even
ts
900850800750700650600
comparator threshold [mV]
raw data landau dist. (arb. scale) fit to raw data using landau
HSDT9 Sep 2013 14
CBC performance in beam
• Successful operation• Digital logic works well
– no pipeline errors– no CBC errors in > 30M events
Geoff Hall
use telescope to select events at CBC module- single track events only (pileup eliminated)- incident on CBC sensor (transverse to strips)- incident in 3mm along strips (const p=134um)- events within 7ns of sampling clock
measure resolution of CBC module from residual- using telescope for track extrapolation- factoring out telescope spatial resolution
resolution: 29.4 um
better than pitch/√12 due to contribution from 2 strip clusters
close to binary resolution from 1 strip clusters
HSDT9 Sep 2013 15
CBC -> CBC2: New features
• 250µm pitch C4 layout• aim for commercially assembled module• some gains in bond inductance• back edge wire-bond pads for wafer probe
• 254 channels for 127 + 127 strips• correlation logic for stub formation
• between top & bottom strips• vetoes wide clusters
• Test pulse• no time to implement on CBC• & other minor circuit improvements
• Improved DC-DC (CERN)• received Jan 2013 – fully functional
DC-D
C
LDO
pipeline+
buffering
254
ampl
ifier
/com
para
tor c
hann
els
CWD,
offs
et co
rrec
tion
and
colle
ralti
on lo
gic
band
gap
bias
gen
.
254inputs
5 mm
11mm
inter-chip
signals
inter-chip
signalsGeoff Hall
16
notch
wafer name:A4PNFAH
CBC2
reticle
CBC2 C4 wafers (shared with RAL XFEL ASIC)
Geoff Hall HSDT9 Sep 2013
Offset+
correlation
DFront End Ch. Mask CWDB
Front End Ch. Mask CWDA C
254
253
127
Front End Ch. Mask CWDB
Front End Ch. Mask CWD
252
251
Front End Ch. Mask CWD
Front End Ch. Mask CWDB’
250
249
2
A
B
A
Front End Ch. Mask CWD
Front End Ch. Mask CWDB’
2
1
B
A
22
22
22
22
22
2
2
22
2
Offset+
correlation
D
C
126
Offset+
correlation
D
C
125
Offset+
correlation
D
C
1
11
11
11
11
11
11
11
11
127
254
To pipeline RAM
4 4
fast
OR
11 11
4 4 11 11
EN
MUX toSR
Stub finding Logic
Stub
s shi
ft re
gist
er
latch
@40MHz
Individual mask for noisy channels→254b from I2C reg.(can be also used to inhibit coincidence logic)
Need to be able to inhibit stub shift register operation→1b EN from I2C reg.
254-OR of channel outputs to signal any activity on chip
127-OR of stubs to control the stubs SR readout
HSDT9 Sep 2013 18
Stub logic features
• Cluster width– exclude clusters wider than 3 strips
• Offset correction and correlation– programmable window, selects pT
• up to +/-8 channels– programmable offset, adjust lateral displacement
• up to +/-3 channels
Geoff Hall
n
n+1
n-1
1/2/3 stripcluster onchannel n
channelcomparator
outputs
p = ∞
IP
R-f view
offset
19
first wafer probed manually
selection of chips for module assembly
Geoff Hall HSDT9 Sep 2013
20
CBC2
bad chip112 reticles108 good chips4 bad chips
reticle
final yield for 1st wafer
bad chips duesolely to physicaldamage fromprobecard
supply current - all chips
no defective channel found on any of112 chips tested on this first wafer
=> 100% yield
perhaps not too surprising if overall wafer yield highCBC2 is relatively small area of reticle& significant fraction of CBC2 area notoccupied by active circuitry
Geoff Hall HSDT9 Sep 2013
HSDT9 Sep 2013 21
2S module
• Development with CMS team• Substrate development mainly by CERN
– Hybrid procured and assembled commercially• First version: 2 chip hybrid
– electrical validation
Geoff Hall
mount capacitors here to simulate interstrip capacitance
small pitch adapter board(wire-bond pitch to 1.27mm connector)
calibratedcharge injection(both sensor layers)
HSDT9 Sep 2013 22
Result with test pulse
– Proves basic functionality but need real data for better test
Geoff Hall
1234567891011121314151617181920212223
11
22
33
44
55
66
77
88
99
1010
1111
12
channelon chip
channelon layer 1
channelon layer 2
8 testgroups
HSDT9 Sep 2013 23
2S mini-module
• Prototype assembled with two sensors– Now under test in lab
Geoff Hall
beta source
data frame width
scope in persistence modeSr-90 sourcescintillator signal
CBC2 trigger output
hits in thedata stream
24Geoff Hall HSDT9 Sep 2013
CBC2 triggered data output
CBC2 trigger output
scintillator/PM signal
hits in the data stream
25Geoff Hall HSDT9 Sep 2013
CBC2 triggered data output
2 consecutive hits=> track passed throughstrips directly aboveeach other
50 ns
26Geoff Hall HSDT9 Sep 2013
single strip clustersoffset by 1 strip
75 nsec
27Geoff Hall HSDT9 Sep 2013
single strip clustersoffset by 3 strips
175 nsec
28Geoff Hall HSDT9 Sep 2013
single strip clustersoffset by 4 strips
225 nsec
29Geoff Hall HSDT9 Sep 2013
2 strip cluster in one planecorrelates with 1 strip clusterin the other
30Geoff Hall HSDT9 Sep 2013
2 strip cluster in one planecorrelates with 1 strip clusterin the other
31Geoff Hall HSDT9 Sep 2013
2 strip cluster in lower sensorcorrelates with 1 strip clusterin the other, offset by 7 strip
375 nsec
32Geoff Hall HSDT9 Sep 2013
127
33
CBC3 - the “final prototype”
bottom
top
8 bits to describe clusteraddress in bottom layer
5 bits to describe correlating clusteraddress in top layer window
1 or 3 stripcluster centredon channel n
2 strip clustercentred onn and n+1
n
n+1
n-1
next version of chip should incorporate all features required for HL-LHC
• final choices for front end½ strip cluster resolution
2 strip cluster position assigned to mid-point
• stub data definition8 bits address (for ½ strip resolution) of cluster in bottom layer5 bit bend information
address of correlating cluster in top layer
• stub data formatting & transmission to concentrator13 bit / stub, up to 3 stubs/BX => 39 bits+1 bit unsparsified L1 triggered readout data=> 40 bits / 25 nsec
e.g. 10 lines at 160 Mbps (per chip)
• other useful featurese.g. slow ADC to monitor bias levels…
concentrator
CBCCBC
CBCCBC
CBCCBC
CBCCBC
10 lines / CBC25 ns
S1 S1 S1 S1 S1 S1 S1 S1 B1 B1B1 B1 B1S2 S2 S2 S2 S2 S2 S2S2 B2 B2 B2 B2 B2S3 S3 S3 S3S3 S3 S3 S3 B3 B3 B3 B3 B3 R
25 ns
CBC data to concentrator
Geoff Hall HSDT9 Sep 2013
HSDT9 Sep 2013 34
Rough road map
Geoff Hall
CBC1
- analogue front end in 130nm- wirebonded- binary logic- L1 triggered readout only, non-sparsified
CBC2
- C4 bump-bonded- full hit correlation logic- L1 triggered non-sparsified
readout, fast trigger OR
CBC3
- full readout architecture defined
- additional correlation logic
CBC4
- optimisation- final version
2011
2012
2014
2016
2S-Pt prototype module studies
2S-Pt final module studies
start production2017
2015
2013
HSDT9 Sep 2013 35
Summary & conclusions
• Two successful iterations of new outer Tracker ASIC
• First prototype version of 2S module in hand– functions well in lab environment– first beam tests foreseen late 2013
• Road map for future developments– detailed schedule depends on complete upgrade plan and HL-LHC
approval process
Geoff Hall
Backup slides
37
CBC power featuresDC-DC switched capacitor converter(CERN)
converts 2.5 -> ~ 1.2works well: ~ 90% efficiency
but switch noise produces differencebetween internal and external grounds
=> interference depending on CEXT
improved circuit on CBC2, and bump-bondingshould help
1.111.101.091.081.071.061.051.04
LDO
out
put [
V]
1.201.151.101.05
LDO input voltage [V]
30mA load 60mA load
LDO dropout 40 mVGNDEXT
GNDINT
CEXT
Cf
vnoise
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Vol
ts
353025201510502.52 Volt supply current [mA]
DC-DC Vout vs. load
LDO linear regulator
provides clean, regulated rail to analog FE(uses CERN 130 nm bandgap)
~ 1.2 Vin, 1.1 Vout
dropout ~ 40 mV for 60 mA load
provides > 30dB supply rejection up to 10 MHzGeoff Hall HSDT9 Sep 2013
WIT 2012Mark Pesaresi (IC-CMS) CBC Readout Chip for LHC Phase II
digital logic
38
no correlation/trigger logic in this iteration- triggered readout only (~270kHz max sustained)
hit detect logic in two modes – single/variable
output from each channel stored in a 256 sample deep pipeline RAM (6.4us latency max)
32 trigger FIFO buffer
unsparsified readout (140-to-1 shift register)
40MHz clock
hit detect -variable mode
hit detect -single mode
comparator output
WIT 2012Mark Pesaresi (IC-CMS) CBC Readout Chip for LHC Phase II
CBC performance in beam
39
cluster width, resolution and efficiency will be affected by threshold setting
- expecting to operate at 1fC level (~640mV)- important to get rough estimations for tuning
stub/tracklet simulations- study of noise occupancy with threshold required
efficiency drop due to charge sharing
2 strip clusters originate from interstrip region
CBC2 architecture
pipe. control
FE amp comp. pipeline shift reg.
vth
vth
vth
vth
256 deeppipeline
+32 deepbuffer
testpulse
biasgen.
fastcontrol
slow control
stub
shi
ft re
gist
er
offs
et c
orre
ctio
n &
cor
rela
tion
clus
ter w
idth
di
scrim
inat
ion
1
254 40 MHz diff.clock
all signals in blue are single-ended -only travel shortdistance on hybrid
trig’d data outstub shift reg. O/Ptrigger O/PI2C
front end, pipeline, L1 triggered readout, biasing~ same as prototype (some bug fixes) twice as many channelsnew blocks associated with Pt stub generationchannel mask: block problem channels (not from L1 pipeline)cluster width discrimination: exclude wide clusters > 3offset correction and correlation: correct for phi offset across module and correlate between layersstub shift register: test feature - shift out result of correlation operation at 40 MHztrigger O/P: in normal operation 1 bit per BX indicates presence of high Pt stubtest pulsecharge injection to all channels (8 groups of ~32), programmable timing and amplitude
nearest neighbour signals
T1 triggerfast resettest pulseI2C refresh
4 4 11 11
chan
. m
ask
4 4 11 11
nearest neighbour signals
reset
OR_254
OR_stubs
Ck
From F.Vasey: Electronic System for 2S-Pt modules System Architecture and Data Formats, CMS Tk Week
@160MHz
(@160MHz)
42
HSDT9 Sep 2013 43
Comparison logic
Geoff Hall
• Modules are flat, not arcs• Compensate for Lorentz drift• Orientation of module => position dependent logicd
Luminous region (large!)
R-z view
• z offset h dependent• search window to allow for luminous region and quantization => 3 pixels (if not tiny)
p = ∞
IP
R-f view
~200µm ~12mmh = 2.5
• Family of modules with offsets in z