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ATLAS SCT powering issues
ATLAS SCT Barrel 3 at CERN (192 cables visible)
Material in radiation length
 Total power is 50 kW of which 50% are dissipated in cables
 Material in radiation length is dominated by power supply and cooling
services
 SLHC tracker will require even more channels and thus more cables, more
cooling and more material
Innovative powering system design is needed
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Conventional scheme: Independent Powering
N modules are powered independently by
N constant voltage power supplies
 Define efficiency η = PM/(PM + Pc)
Im
 η = 1/(1 + IMRC/VM) = 1/(1+x)
 x = IM RC/Vm = voltage drop in cable/
module voltage
Im
 η decreases with increasing IM and RC
and with decreasing Vm
Im
Pc = nIm2 Rc*
PM = n ImVm
 For ATLAS SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A => x ≈ 1.14
 Power efficiency η ≈ 50%
2
Proposed scheme: Serial Powering
N modules are powered in series by one constant current source;
local regulators provide supply voltage to the modules
Im
Module 1
 η = 1/(1 + IR/nV) = 1/(1+x/n)
Module 2
 Efficiency increases if number of
modules n increases
Power cable
I Supply
 Concept never practically implemented
Power cable
Module n
Im
Pc = Im2Rc*
PM = nImVm
 For ATLAS SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A N = 10 => x ≈ 1.14
 Power efficiency η ≈ 90%
3
Advantages of serial powering
 Much less power cables
 Much less material (less cables, less cooling)
 Improved power efficiency
 Significant cost savings
4
Much less cables
 for
a detector with N modules with local regulators, the number of
cables is reduced by a factor of up to 2N (analogue and digital power no
longer separated)
Module 1
Module 2
Module n
Reduction of detector material in the tracking volume: less multiple scattering
and creation of secondary particles, leading to improved track finding efficiency
and resolution
Cable volume reduction is mandatory for an SLHC tracker, where increased
luminosity would require an increased detectors granularity by a factor of 5 to 10.
It is even challenging to squeeze the current number of cables in the available space
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Improved power efficiency
 Future readout chips require reduced
operation voltage (due to reduced feature
size)
x increases
 1  x

|| 1  x
X = 4.5
*SLHC*
X = 1.14
*SCT*
n
*
 Overall efficiency increases with increasing
number of modules N
 For a future SLHC detector x ≈ 4.5:
Independent powering η ≈ 18%
Serial powering (n = 10) η ≈ 69%
Serial powering (n = 20) η ≈ 81%
R I
x C m
Vm
n
Efficiency of serial powering normalized to independent
powering vs. number of modules n for various x factors
 Reduction of load to cooling system by
tens of kW inside the tracker volume are
possible
6
Cost savings
 Reduced number of cables and remote power supplies results in
major cost savings;
electricity bill is reduced as well.
Take ATLAS SCT as an example:
4088 power supply modules cost ≈ 1.5 MCHF;
Cabling cost
≈ 2 MCHF
For an SLHC tracker with independent powering, the power supplies and
cables would cost tens of MCHF; a serial powering approach would reduce this
by a large factor, implying a saving of many MCHF
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Miles stones of serial powering R&D
 Tests with ATLAS SCT modules (well advanced and promising)
 Grounding and interference issues in a realistic densely-packed
detector system (first implementation and test in July 2006)
 Development of a redundancy and failure protection scheme
 Serial Powering circuitry integration into ABC_Next chip
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Step 1: Test with ATLAS SCT modules
Detailed set of reference measurements with up to 6 modules
Measure power saving and compare with predicted values
Noise spectrum study: introduce high frequency noise
Deadtime-less operation
Noise performance with 4 SCT modules in series are very satisfactory. See talk M.
Weber at LECC 2006. Have meanwhile rebuilt and streamlined hardware. Tests
with 6 SCT modules will start in June 2006
Current source
SP1
SCT1
SP2
SCT2
Photograph of test setup with 4
ATLAS SCT modules, serial
powering scheme implemented
on PCB.
SP3
SCT3
SP4
SCT4
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Step 2: Grounding and interference in a
densely- packed detector system
 Tests with independent modules are sensitive to “pick-up” through the
serial power line (conductive interference)
 In an integrated detector arrangement, there are additional pick-up mechanisms
e.g. capacitive and inductive interference between nearby components
(bus cable/hybrids/sensors)
 This will be investigated, understood and eliminated using a CDF Run IIb type stave
built by Carl Haber at LBNL (first tests are scheduled for July 2006)
 This stave is a most compact
package and thus the ultimate test
bed
 Its electrical performance and
interference mechanisms are wellunderstood and documented
M. Weber et. al., NIM A556 (2006) 459-481
and
CDF Run IIb stave
R. Ely, M. Weber et al., IEEE Trans. Nucl.
10 Sci
NS-52 (5) (2005) in press.
Step 4: Serial Powering circuitry integration
 Stave noise tests will be performed with bare-die commercial regulators
 Final implementation requires radiation-hard ASICs
Noise and redundancy studies will, however, lead to regulator specifications for a
dedicated ASIC or a silicon strip readout chip (RDIC)
 output impedance of regulators, max. current
 PSRR of RDIC
 current sensing features of RDIC/regulators
 controlled short
 voltage adjustment features
 Design of an RDIC with serial powering features is discussed with CERN
MIC group in the context of the proposed ABC-Next chip, a 0.25 μm CMOS
RDIC
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Appendix - connection diagram  Serial Powering reduces the number of power cables by up to 2n, instead of n,
when analogue module power is obtained from digital power.
 The final number of modules n will depend on several factors
e.g. maximum allowed voltage, failure probability, readout architecture and
mechanical considerations.
 The rapidly shrinking feature size in microelectronics, implies a decrease in x;
We thus expect the number of modules powered in series to be higher than 10.
The maximum voltage difference depends on the voltage
required by each module. The latter is expected to be of the
order of 1.2 – 2.5V maximum
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Appendix - TX/RX diagram -
 Modules are referenced
to different “ground”
levels than DAQ
 Modules have to send
data signals to DAQ and
receive
clock
and
command signals from
DAQ
 This is achieved by ACcoupling of LVDS signals
Figure A1: Simplified TX/RX connection diagram. The connections are
differential. Termination and feed-back resistors are omitted for clarity.
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Appendix - Power consumption in power cablesPower Consumption in power cables
ONLY power supply lines are considered
Barrel
Digital
Idd(A) =
1.290
Length(m) Ohms/m
Ohms Vdrop(V) Power(W)
(one way)
(plus return)
(plus return)
Hybrid Traces (half of total)
NA
0.062
0.080
0.103
Hybird/Dogleg Connector
NA
0.006
0.008
0.010
Dog-leg
NA
0.024
0.031
0.040
Dogleg/LMT50 Connection
NA
0.022
0.028
0.037
LMT-Al50
1.6
0.275
0.440
0.568
0.732
PPB1
NA
0.088
0.114
0.146
VeryThinConventional
9.1
0.080
0.728
0.939
1.211
PPB2
NA
0.0150
0.019
0.025
ThinConventional
23
0.047
1.079
1.392
1.795
PP3
NA
0.1600
0.206
0.266
ThickConventional
100
0.009
0.938
1.210
1.561
Cable/PS Connector
NA
0.000
0.000
Total per module
3.562
4.595
5.927
Total cable power per barrel module [W]
8.789
Analogue
Icc(A) =
0.900
Length(m) Ohms/m Ohms Vdrop(V) Power(W)
(one way)
(plus return)
(plus return)
NA
0.052
0.047
0.042
NA
0.007
0.006
0.006
NA
0.024
0.022
0.019
NA
0.022
0.020
0.018
1.6
0.275
0.440
0.396
0.356
NA
0.068
0.061
0.055
9.1
0.080
0.728
0.655
0.590
NA
0.0150
0.014
0.012
23
0.047
1.079
0.971
0.874
NA
0.1600
0.144
0.130
100
0.009
0.938
0.844
0.760
NA
0.000
3.533
3.180
2.862
Figure A5: Consumption in power cables
 one-way cable length from power supply to detector: up to 160 m
 cable resistance (including return): 3.5 Ω; ~1.5 Ω in active volume
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Appendix - Material overhead Service gap
Interaction
point
Barrel
Cables
Discs
Figure A6: Generic tracker layout with barrel and discs
Figure A7: Material in radiation length
 in ATLAS SCT, particles cross (0.1 to 0.45%) x √2 of R.L. of cables in service
gap alone (dep. on polar angle)
 a ten-fold increase of cables is prohibitive
 Reduction of detector material in the tracking volume: less multiple
scattering and creation of secondary particles, leading to improved tracking
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efficiency and resolution