Download - ATLAS SCT powering issues
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Total power is 50 kW of which 50% are dissipated in cables
ATLAS SCT powering issuesATLAS SCT powering issues
SLHC tracker will require even more channels and thus more cables, more cooling and more material
Material in radiation length is dominated by power supply and cooling services
Innovative powering system design is needed
Nearly 2000 m
ore cables n
eeded
Nearly 2000 m
ore cables n
eeded
in th
e final a
ssembly
in th
e final a
ssembly
ATLAS SCT Barrel 3 at CERN (192 cables visible) Material in radiation length
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Conventional scheme: Independent PoweringConventional scheme: Independent Powering
Pc = nIm2 Rc
* PM = n ImVm
N modules are powered N modules are powered independently by by NN constant voltage constant voltage power suppliespower supplies
Im
Im
Im
For For ATLAS SCT: R = 3.5 SCT: R = 3.5 ΩΩ, V = 4 V, I = 1.3 A => x ≈ 1.14 , V = 4 V, I = 1.3 A => x ≈ 1.14
Power efficiencyPower efficiency η ≈ 50% 50%
Define efficiency η = PM/(PM + Pc)
η = 1/(1 + IMRC/VM) = 1/(1+x)
x = IM RC/Vm = voltage drop in cable/ module voltage
η decreases with increasing IM and RC
and with decreasing Vm
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Proposed scheme: Serial PoweringProposed scheme: Serial Powering
I Supply
Module 1
Module 2
Module n
Power cable
Power cable
Im
Im
Pc = Im2Rc* PM = nImVm
N modules are powered in series by N modules are powered in series by one one constant current source; current source;local regulators provide supply voltage to the moduleslocal regulators provide supply voltage to the modules
η = 1/(1 + IR/nV) = 1/(1+x/n)
Efficiency increases if number of modules n increases
Concept never practically implemented
For For ATLAS SCT: R = 3.5 SCT: R = 3.5 ΩΩ, V = 4 V, I = 1.3 A , V = 4 V, I = 1.3 A N = 10N = 10 => x ≈ 1.14 => x ≈ 1.14
Power efficiencyPower efficiency η ≈ 90% 90%
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Advantages of serial poweringAdvantages of serial powering
Much less power cables
Much less material (less cables, less cooling)
Improved power efficiency
Significant cost savings
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Much less cablesMuch 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)
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
Module 1
Module 2
Module n
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Improved power efficiencyImproved power efficiency
nxx
1
1
||
Overall efficiency increases with increasing number of modules N
Reduction of load to cooling system by tens of kW inside the tracker volume are possible
X = 1.14
X = 4.5
Efficiency of serial powering normalized to independent powering vs. number of modules n for various x factors
*SCT*
*SLHC*
m
mC
V
IRx
*
n
Future readout chips require reduced operation voltage (due to reduced feature
size) x increases
Independent powering η ≈ 18%Serial powering (n = 10) η ≈ 69%Serial powering (n = 20) η ≈ 81%
For a future SLHC detector x ≈ 4.5:
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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
Cost savingsCost savings
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Miles stones of serial powering R&DMiles 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 modulesStep 1: Test with ATLAS SCT modules
Photograph of test setup with 4 ATLAS SCT modules, serial powering scheme implemented on PCB.
Current sourceCurrent source
SCT4SCT4
SP4SP4
SCT3SCT3
SCT2SCT2
SCT1SCT1
SP3SP3
SP2SP2
SP1SP1
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
Detailed set of reference measurements with up to 6 modulesMeasure power saving and compare with predicted valuesNoise spectrum study: introduce high frequency noise Deadtime-less operation
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Step 2: Grounding and interference in a Step 2: Grounding and interference in a densely- packed detector systemdensely- 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 well-understood and documented
M. Weber et. al., NIM A556 (2006) 459-481 and
R. Ely, M. Weber et al., IEEE Trans. Nucl. Sci NS-52 (5) (2005) in press.
CDF Run IIb stave
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Step 4: Serial Powering circuitry integrationStep 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 -Appendix - connection diagram -
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
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.
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Appendix - TX/RX diagram -Appendix - TX/RX diagram -
Figure A1: Simplified TX/RX connection diagram. The connections are Figure A1: Simplified TX/RX connection diagram. The connections are differential. Termination and feed-back resistors are omitted for differential. Termination and feed-back resistors are omitted for clarity.clarity.
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 AC-coupling of LVDS signals
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Figure A5: Consumption in power cablesFigure A5: Consumption in power cables
Appendix - Power consumption in power cables-Appendix - Power consumption in power cables-
one-way cable length from power supply to detector: up to 160 mone-way cable length from power supply to detector: up to 160 m
cable resistance (including return): cable resistance (including return): 3.5 3.5 ΩΩ; ; ~1.5 ~1.5 ΩΩ in active volume in active volume
Power Consumption in power cablesONLY power supply lines are considered
BarrelDigital Idd(A) = 1.290 Analogue Icc(A) = 0.900Length(m) Ohms/m Ohms Vdrop(V) Power(W) Length(m) Ohms/m Ohms Vdrop(V) Power(W)(one way) (plus return)(plus return) (one way) (plus return)(plus return)
Hybrid Traces (half of total) NA 0.062 0.080 0.103 NA 0.052 0.047 0.042Hybird/Dogleg Connector NA 0.006 0.008 0.010 NA 0.007 0.006 0.006Dog-leg NA 0.024 0.031 0.040 NA 0.024 0.022 0.019Dogleg/LMT50 Connection NA 0.022 0.028 0.037 NA 0.022 0.020 0.018LMT-Al50 1.6 0.275 0.440 0.568 0.732 1.6 0.275 0.440 0.396 0.356PPB1 NA 0.088 0.114 0.146 NA 0.068 0.061 0.055VeryThinConventional 9.1 0.080 0.728 0.939 1.211 9.1 0.080 0.728 0.655 0.590PPB2 NA 0.0150 0.019 0.025 NA 0.0150 0.014 0.012ThinConventional 23 0.047 1.079 1.392 1.795 23 0.047 1.079 0.971 0.874PP3 NA 0.1600 0.206 0.266 NA 0.1600 0.144 0.130ThickConventional 100 0.009 0.938 1.210 1.561 100 0.009 0.938 0.844 0.760Cable/PS Connector NA 0.000 0.000 NA 0.000Total per module 3.562 4.595 5.927 3.533 3.180 2.862Total cable power per barrel module [W] 8.789
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Appendix - Material overhead -Appendix - Material overhead -
Figure A7: Material in radiation lengthFigure A7: Material in radiation length
DiscsBarrelInteraction point
CablesService gap
Figure A6: Generic tracker layout with barrel and discsFigure A6: Generic tracker layout with barrel and discs
in ATLAS SCT, particles cross in ATLAS SCT, particles cross (0.1 to 0.45%) x √2 of R.L. of cables in (0.1 to 0.45%) x √2 of R.L. of cables in service gap alone service gap alone (dep. on polar angle) (dep. on polar angle)
a ten-fold increase of cables is prohibitivea ten-fold increase of cables is prohibitive
Reduction of detector material in the tracking volume: less multiple Reduction of detector material in the tracking volume: less multiple scattering and creation of secondary particles, leading to improved tracking scattering and creation of secondary particles, leading to improved tracking efficiency and resolutionefficiency and resolution