Welcome Jan Sammet- 1 - A DC-DC converter based powering scheme for the upgrade of the CMS pixel detector TWEPP-11, Wien Arndt Schultz von Dratzig, Lutz Feld, Waclaw Karpinski, Katja Klein, Jennifer Merz, Jan Sammet, Oliver Scheibling, Michael Wlochal

Welcome Outline Jan Sammet- 2 - Introduction Implementation into CMS Challenges… … and how we address them Conclusions & Outlook

Welcome Upgrade of the CMS Pixel Detector Jan Sammet- 3 - CMS pixel detector is going to be replaced during shut down of LHC in ~2016  Additional layer of pixel modules  Number of readout chips (ROCs) increases by factor of 1.9 (16k  30k)  Present powering scheme cannot supply sufficient power through existing cables  Use DC-DC converters to reduce power losses  Aachen develops, tests and produces converters, to be used by CMS 93 cm 53 cm The CMS pixel detector

Welcome Strategy Jan Sammet- 4 - Increase efficiency of power transmission P loss =R cable ·I 2  supply power at higher voltage r·U i.e. lower current I/r (Conversion ratio r >1)  power losses P loss =R·(I/r) 2 are reduced by factor r 2 !

How it works Frequently connect and disconnect source and load Duty cycle D = t on /T Conversion ratio r = V in /V out = 1/D (ideal converter) Welcome DC-DC Buck Converters Jan Sammet- 5 - ASIC includes transistors and voltage regulation circuit ASIC is being developed within CERN electronics group (F. Faccio et al.) [see talk by S. Michelis Radiation tolerance of many semi-conductor technologies evaluated  AMIS I3T µm (ON Semiconductor, US) - functional up to dose of 300Mrad & fluence of 5  p/cm 2 [F. Faccio, TWEPP-10, Development of custom radiation-tolerant DCDC converter ASICs] Advantages Output regulation by pulse width modulation  V out is regulated Provide high currents with high efficiency

Welcome Aachen DC-DC Converter Jan Sammet- 6 - PCB: 2 copper layers a 35µm 0.3mm thick Large ground area on backside for cooling Toroidal inductor: L = 450nH R DC = 40m  Shield/heat sink A = 28 x 16 mm 2 M  2.5g 3.8% of a radiation length “PIX_V7“: Design guidelines from CERN group have been implemented. Pi-filters at in- and output ASIC prototype: AMIS2 by CERN I out < 3A V in < 12V V out configurable; (here: 2.5V & 3.3V) f s configurable, e.g. 1.3MHz

Welcome Challenges Jan Sammet- 7 - Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions  (covered by CERN group)

Welcome Challenges Jan Sammet- 8 - Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions 

Welcome Implementation into CMS Jan Sammet m Mockup Integration for pixel barrel onto supply tube Large distance of converters to pixel modules (  ~ 4) (goal is to be able to power detector, NOT to reduce material) CO 2 cooling available 26 DC-DC converters per channel Power dissipation ~ 40W per channel Full channel (PCB, cooling pipes & bridges, 26 converters) weighs 200g and corresponds to 7% of a radiation length DC-DC converters required in total Pixel detector

Welcome Implementation into CMS Jan Sammet CAEN A4603 PSU Vana Vdig converters pixel modules per converter DC-DC dig DC-DC ana converters Two CAEN power supply units (PSU) per supply tube channel Power supplies need modification I < 2.8A per converter (for L = 2 x cm -2 s -1 ) V out = 2.5V V out = 3.3V V in  12V pixel modules per converter  50m

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions  

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions  

Electrical shielding: Acts also as cooling contact for coil Shape optimized to fit into edge channels of supply tube Several technologies are under investigation: Hydroformed/deep drawn aluminium Ruled out; required shape not feasible in mass production Plastic shields coated with a metal layer Different materials, thicknesses and depositing techniques have been tested Milled Aluminium shields 120µm of Aluminium etched down to 90µm+ 15 µm of Nickel + 15 µm of Copper Welcome Jan Sammet R&D on Shielding

Welcome Jan Sammet Effectiveness of Shielding Measure z-component of magnetic field of DC-DC converter Automated x-y table allows high spatial resolution Many different materials and thickness have been tested  focus on thinnest and lightest functional shieldings here Scanning table BZBZ

Welcome Jan Sammet Effectiveness of Shielding 90µm milled Aluminium Magnetic field reduced to 15% Price per piece ~ 25 € Plastic shield coated with 30 µm Cu Magnetic field reduced to 30% Price per piece: ~ 13 € Plastic shield coated with 60 µm Cu Magnetic field reduced to 5% Price per piece: ~ 13 € Roughly 56% higher contribution to MB No shield 90µm AL 60µm Cu 30µm Cu

Welcome Jan Sammet Thermal FE-Simulation Cooling bridges clamp around CO 2 pipes Chip cooled through PCB backside Shield (soldered to PCB) acts as cooling contact for inductor Temperature of cooling bridge T = -20°C  Chips are at -7°C (  T = 13K)  Coils are at -6°C (  T = 14K)  For room temperature (20°C) operation, both stay below 40°C °C Shielding simulated, but not displayed

Welcome Jan Sammet Thermal Measurements PIX_V7, 450nH, 1.3MHz V in = 10V, V out = 3.3V Output current [A] Coil temperature [°C] Converter on cooling bridge at 20°C  Good agreement with Finite Element simulations  Shielding fulfils task of cooling contact for coil  Cooling of chips via backside of PCB is very effective

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions    

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions    

Welcome Jan Sammet Efficiency Phase 1 conditions: V out = 3.3V or 2.5V, I out < 2.8A, conversion ratio of 3-4  75% - 80% efficiency: ok – still expected to increase further with new version of AMIS chip [White regions: regulation not working properly, V out too low] PIX_V7, V out = 2.5V PIX_V7, V out = 3.3V Efficiency [%]

CopperAluminium Photo Inductance L [nH]~450 Resistance R DC [m  ] 4055 Height h [mm]66 Diameter d [mm]79 Mass m [mg] Welcome Jan Sammet Choice of Inductor Optimal coil shape has been calculated for different wire types and thicknesses In the available space, copper offers higher efficiency For pixel upgrade, favour efficiency over material budget (due to high  )

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions      

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions      

Welcome Conductive Noise Jan Sammet Spectrum Analyzer Load LISN = Line Impedance Stabilization Network GND Differential Mode (DM), “ripple“Common Mode (CM) Noise through cables (conductive noise) was studied with EMC set-up EMC = electromagnetic compatibility

Welcome Conductive Noise Jan Sammet Differential Mode, no shieldCommon Mode, no shield Differential Mode, with shieldCommon Mode, with shield  Large reduction of CM above 2 MHz due to shield PIX_V7 output noise V out = 3.3V V in = 10V f s = 1.3MHz L = 450nH

Welcome System Tests with CMS Pixel Modules Jan Sammet DC-DC converter on bus board Pixel module System tests with original pixel PSU from CAEN and module qualification set-up One full module (16 ROCs, each containing 4160 pixels) is read out S-curve noise of each pixel is measured Many thanks to PSI for hardware and advice VAVA Connector board Module adapter PC interface „Advanced Test Board“ DAQ PC Module DC-DC converters CAEN Pixel PSU multi-service cables (40m) VDVD EASY 4000 SY Branch Controller PSM A4603 Original pixel power supply unit HV (150V)

Welcome Powering with DC-DC Converters Jan Sammet DC-DC converters cause no significant increase of noise powering with DCDC conventional powering

Welcome Jan Sammet Impact of Orbit Gaps Orbit gaps of LHC beam  no collisions for 3µs every 89µs  Pixel digital current drops within ns (1..4 bunches, depending on the occupancy)  Worst case for 2×10 34 cm -2 s -1 : I D_high = ~ 2.7A (86µs)  I D_low = ~1A (3µs)  Stability Test of the whole power supply chain:  Also check impact of “inverted orbit gaps” I D_high = ~ 2.7A (3µs)  I D_low = ~1A (86µs) (LHC fill with only a few intense bunches) VAVA Connector board Module adapter PC interface „Advanced Test Board“ DAQ PC Module HV (150V) DC-DC converters CAEN Pixel PS multi-service cables (40m) VDVD Dynamic Load Box EASY 4000 EASY 4000 SY Branch Controller SY Branch Controller PSM A4603 PSM A4603 IDID t IDID t

Welcome Impact of Orbit Gaps Jan Sammet Without DC-DC converters  Load variations cause moderate increase of noise With DC-DC converters  Sensitivity is reduced due to filtering components and regulation of DC-DC converter Powering with DC-DC convertersConventional powering

Welcome Influence of the Switching Frequency Jan Sammet  Slight reduction ( < 1e ) at 2 MHz  Not significant yet  Might become relevant in larger system  Not directly comparable to previous measurements   (slightly different cabling, no copper plate here) 

Welcome Different Sensing Points Jan Sammet Dynamic Load DC-DC converter CAEN PS multi-service cables (40m) Module Powering with DC-DC converters Sensing at PS Sensing at DC-DC converter  No increase of noise due to sensing at PS  Sensing at DC-DC converters not necessary DC-DC converter is seen by PS as negative impedance  Sensing at converter could cause instabilities  Modifications of PS would be more complex and costly  Measure influence of sensing point in system tests

Welcome Challenges Jan Sammet Ensure radiation tolerance of high voltage (~15V) power transistors Implement DC-DC converters into CMS Provide magnetic field tolerance  air-core inductor  risk of radiated noise Provide good shielding and cooling Provide high conversion efficiency Provide compact device with small impact on material budget Reduce and control noise emissions       

Welcome Conclusions & Outlook Jan Sammet Conclusions Good progress has been made towards a DC-DC converter based powering scheme Plans for implementation are far advanced Efficiency and noise performance of our DC-DC converters are satisfactory Outlook Improve system tests with more modules, cold temperatures… Perform thermal cycling to simulate accelerated aging and to ensure reliable operation in the long term Implement new versions of the AMIS chip (AMIS4 expected soon) Implement control scheme for DC-DC converters

Welcome Back-Up Slides Jan Sammet- 34 -

Welcome The CMS Pixel Detector Jan Sammet Pixel size: (100 x 150) µm² Present barrel New barrel

Welcome Aachen DC-DC Converter Jan Sammet Design guidelines from CERN group have been followed.

Welcome Jan Sammet Mechanical & Thermal Integration cooling pipes lower part of cooling bridge upper part of cooling bridge chip area Cooling bridge clamps around pipe Area reduced to reduce material Aluminium (could be Graphite, but gain for material budget is low)

Welcome Effectiveness of Shielding Jan Sammet- 38 -

Welcome Jan Sammet Conductive Noise with Shielding

Welcome Set-Up for System Tests Jan Sammet Original pixel power supply system Pixel module DC-DC converters

Welcome Powering with DC-DC Converters Jan Sammet Variations with different but identical converters ~ 2e Reproducibility of measurements ~ 1e VD = 3.2V, VA= 2.5V

Welcome Influence of the Switching Frequency Jan Sammet With inverted orbit gapsWith simulated orbit gaps Additional 2A const. LoadNo additional load (VD = 3.2V, VA= 2.5V)

Welcome Different sensing points, w/o Add. Load Jan Sammet Powering with DC-DC converters DC-DC converters CAEN PS multi-service cables (40m) Module Sensing at PS Sensing at DC-DC (VD = 3.2V, VA= 2.5V) µ-twisted pair cables DC-DC converter is seen by PS as negative impedance  Sensing at converter could cause instabilities  Modifications of PS would be complex and costly Test influence of sensing point in system tests  No increase of noise due to sensing at PS

Welcome Different sensing points, w/o Add. Load Jan Sammet Powering with DC-DC convertersConventional powering  No increase of noise due to sensing at PS DC-DC converters CAEN PS multi-service cables (40m) Module Sensing at PS (with voltage divider) Sensing at DC-DC/load (with and w/o voltage divider) (VD = 3.5V, VA= 2.7V) (VD = 3.2V, VA= 2.5V) µ-twisted pair cables

Welcome Different sensing points with Orbit Gaps Jan Sammet Dynamic Load Box DC-DC converters CAEN PS multi-service cables (40m) Module Powering with DC-DC converters (VD = 3.2V, VA= 2.5V) Sensing at PS Sensing at DC-DC/load µ-twisted pair cables Test influence of sensing point in system tests  No increase of noise due to sensing at PS  Simplifies modifications of PS by CAEN

Welcome Different sensing points with Orbit Gaps Jan Sammet  Noise increases if voltages are senses at PS  No increase of noise due to sensing at PS Dynamic Load Box DC-DC converters CAEN PS multi-service cables (40m) Module Sensing at PS (with voltage divider) Sensing at DC-DC/load (with and w/o voltage divider) Powering with DC-DC convertersConventional powering (VD = 3.5V, VA= 2.7V) (VD = 3.2V, VA= 2.5V)