1

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

2

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

3

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%

4

Advantages of serial poweringAdvantages of serial powering

Much less power cables

Much less material (less cables, less cooling)

Improved power efficiency

Significant cost savings

5

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

6

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:

7

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

8

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

9

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

10

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

11

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

12

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.

13

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

14

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

15

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