1  Total power is 50 kW of which 50% are dissipated in cables ATLAS 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 more cables needed in the final assembly ATLAS SCT Barrel 3 at CERN (192 cables visible)Material in radiation length

2 Conventional scheme: Independent Powering P c = nI m 2 R c * P M = n I m V m N modules are powered by N modules are powered independently by N constant voltage power supplies N constant voltage power supplies ImIm ImIm ImIm  For SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A => x ≈ 1.14  For ATLAS SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A => x ≈ 1.14  Power efficiency 50%  Power efficiency η ≈ 50%  Define efficiency η = P M /(P M + P c )  η = 1/(1 + I M R C /V M ) = 1/(1+x)  x = I M R C /V m = voltage drop in cable/ module voltage  η decreases with increasing I M and R C and with decreasing V m

3 Proposed scheme: Serial Powering I Supply Module 1 Module 2 Module n Power cable ImIm ImIm P c = I m 2 Rc * P M = nI m V m N modules are powered in series by one current source; N modules are powered in series by one constant current source; local 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 SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A N = 10 => x ≈ 1.14  For ATLAS SCT: R = 3.5 Ω, V = 4 V, I = 1.3 A N = 10 => x ≈ 1.14  Power efficiency 90%  Power efficiency η ≈ 90%

4 Advantages of serial powering  Much less power cables  Much less material (less cables, less cooling)  Improved power efficiency  Significant cost savings

5 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)  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 efficiency  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*  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 savings

8 Miles stones of serial powering R&D Noise occupancy with 1 fC discriminator threshold for standard (left) and serial (right) power scheme. No added noise introduced by the alternative scheme is seen.  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 modules Noise occupancy with 1 fC discriminator threshold for standard (left) and serial (right) power scheme. No added noise introduced by the alternative scheme is seen. Photograph of test setup with 4 ATLAS SCT modules, serial powering scheme implemented on PCB. Current source SCT4 SP4 SCT3 SCT2 SCT1 SP3 SP2 SP1 Noise performance with 4 SCT modules in series are very satisfactory. See talk M. Weber at LECC 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 modules  Measure power saving and compare with predicted values  Noise spectrum study: introduce high frequency noise  Deadtime-less operation

10 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 well- understood and documented M. Weber et. al., NIM A556 (2006) 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 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 μ m CMOS RDIC

12 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 - Figure A1: Simplified TX/RX connection diagram. The connections are differential. Termination and feed-back resistors are omitted for 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 cables Appendix - Power 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  cable resistance (including return): 3.5 Ω; ~1.5 Ω in active volume

15 Appendix - Material overhead - Figure A7: Material in radiation length DiscsBarrel Interaction point CablesService gap Figure A6: Generic tracker layout with barrel and discs 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)  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 efficiency and resolution  Reduction of detector material in the tracking volume: less multiple scattering and creation of secondary particles, leading to improved tracking efficiency and resolution