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Implementation of DC-DC Converters into the CMS Tracker at Super-LHC

Implementation of DC-DC Converters into the CMS Tracker at Super-LHC. Katja Klein 1. Physikalisches Institut B RWTH Aachen University. ATLAS / CMS Power Working Group CERN, March 31st, 2010. Outline. DC-DC converters for CMS phase-1 pixel upgrade CMS track trigger layers

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Implementation of DC-DC Converters into the CMS Tracker at Super-LHC

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  1. Implementation of DC-DC Converters into the CMS Tracker at Super-LHC Katja Klein 1. Physikalisches Institut B RWTH Aachen University ATLAS / CMS Power Working Group CERN, March 31st, 2010

  2. Outline • DC-DC converters for • CMS phase-1 pixel upgrade • CMS track trigger layers • CMS outer tracker upgrade Caveat: can present only a snap shot of current ideas; outcome of Chamonix Workshop and consequences are still being discussed... DC-DC Conversion for CMS Tracker Upgrade

  3. Powering the CMS Tracker Upgrade • In 2008 a task force, led by Peter Sharp, was set up to look into the two options: Serial Powering and DC-DC conversion. • As a result of this review process, the CMS tracker has chosen DC-DC conversion as baseline solution, and maintains Serial Powering as back-up (January 2009). • Reasons: • closer to today‘s parallel powering scheme (modularity, failure modes, grounding & shielding, ...) • only one new component required (the DC-DC converter) • less consequences on system design (classical grounding, no AC-coupling etc.) DC-DC Conversion for CMS Tracker Upgrade

  4. CMS Pixel Upgrade The easy application DC-DC Conversion for CMS Tracker Upgrade

  5. Phase-1 Pixel Upgrade Current pixel detector: Cell size: 100µm x 150µm FPIX: 2 x 2 disks  2 x 3 (larger) disks (3rd disk had been staged) BPIX: 3 barrel layers  4 layers r = 3.9, 6.8, 10.9, 16.0cm • Number of ROCs increases: BPIX: 11 520  19 456; FPIX: 4 320  10 756 • Modifications to PSI46 ROC to reduce data losses (buffer size ...) • Reduction of material (light-weight mechanics, CO2 cooling ...) • DC-DC conversion • ... more radical changes are under discussion DC-DC Conversion for CMS Tracker Upgrade

  6. Pixel Power System • PSI46 ROC needs two supply voltages: Vana1.5V and Vdig 2.5V • On-chip voltage regulators compensate for differences in supply voltage due to voltage drops on cables, and improve power noise rejection • Supplied by 56 CAEN A4603 power supply modules (EASY 4000 system) • Want to keep power supplies, if possible (perhaps with light modifications) • 40m + 5m long multi-service cables to pixel supply tube – cannot be exchanged • Cables run along supply tube to pixel detector pixel det. Pixel PowerSystem Developments

  7. Why DC-DC Converters? • More readout chips per cable and per power supply • FPIX: might cope without DC-DC converters (cables for 3rd disk already installed) • BPIX: • Increase of heat load in cable channels by a factor of 3 • Required power cannot be delivered by todays’ power supplies • Need to reduce supply currents and thus power losses in supply cables • Decision in June 09 to go for buck converters, located on far end of supply tube • Low conversion ratio (~ 2:1) to be compatible with voltage specification of PS • Note: DC-DC converters needed even if PS would be replaced, to reduce heat load in cable channels Pixel PowerSystem Developments

  8. DC-DC Converters: BPIX Scheme A4603 4-5 converters 4 barrel modules per converter DC-DC analog PSU Vana 4-5 converters 4 barrel modules per converter DC-DC digital Vdig PSU FPIX: 2 blades per DC-DC converter Pixel PowerSystem Developments

  9. Converter Integration - BPIX Silvan Streuli, 28/10/2009 0 1 2 3 4 • Multiservice cables arrive at point 0 • PCB with DC-DC converters in region 1 • Embedded standard cables in region 2 • PCB in region 3 & thin wires to modules at 4 • Mock-up in preparation Pixel PowerSystem Developments

  10. “Specs“ for Pixel DC-DC Converters (I) Numbers are still subject to changes. Converter type: Inductor-based non-isolated step-down converter, probably of buck-type, integrated on a separate PCB. • Conversion ratio Vin/Vout:2 - 3 Output voltage Vout: Vana = 2.3V Vdig = 3.5V Input voltage Vin (for 1:2): Vana = 4.6V Vdig = 7.0V • Output current Iout:< 2.8A (in some detector regions up to 4.9A – adapt modularity?) Switching frequency: 1 - 2 MHz Low frequency to maximize the efficiency. • Efficiency: 80% Pixel PowerSystem Developments

  11. “Specs“ for Pixel DC-DC Converters (II) Dissipated power: 2-3W per converter for 80% efficiency.Active cooling has to be foreseen. • Dimensions of PCB: Length = 3.2cm , width = 2cm, height <1.4cm • Small piggy-board with board-to-board connectors Material budget / Weight: Since these converters are at z = 2.0-2.3m and r ~ 19cmthey are absolutely outside of the tracking region and therefore uncritical in mass and material budget. The only concern is the use of material with little activation. Output voltage ripple: Since the PSI46 ROC has rather fast on-chip regulators, the requirements for ripple are very relaxed. Radiation environment: 19cm radius, z = 2.3m, 700fb-1, safety factor = 2:Fast hadrons fluence: 6-7 x 1014 /cm2Dose: 200kGy Specific requirements: Behaviour for very fast load variations due to orbit gaps. Stability of operation together with long pixel cables and the CAEN A4603 power supply modules. Pixel PowerSystem Developments

  12. Prototype: AC_PIX_V4 Buck Converter PCB: 2 copper layers a 35m FR4 1mm A = 18mm x 25mm for QFN32 m = 2.7g 18mm Chip: AMIS2 by CERN VIN< 12V IOUT< 3A VOUT = 3.3V fS ≈ 1.3MHz 25mm Air-core toroid: Custom-made toroid,   6mm, height = 7mm, L = 600nH, RDC= 80mΩ Input and output π-filters L = 12.1nH, C = 22µF Cooling contact Pixel PowerSystem Developments

  13. AC_PIX_V4 Efficiency PIX_V4, Vout = 3.3V, f = 1.3MHz • ~ 75% for 3A and conv. ratio of 2-3 • Res. losses (Ron, wire bonds, coil ) ~ 1/fs; switching & driving losses ~ fs • Further improvements are expected: • Move from 1.3MHz to 1.0MHz • Gain few % with cooling • Move to flip-chip package • On-chip routing? • PCB layout, capacitors etc.? Pixel PowerSystem Developments

  14. AC_PIX_V4 Noise Behaviour Vin = 10V, Vout = 3.3V, Iout = 1.4A, fs = 1.3MHz Differential Mode Common Mode L = 12.5nH C = 22µF fcut  600kHz • On-board pi-filter DM noise reduced wrt. CM • However, performance of filter to be improved • Recall: PSI46 has Linear Regulators • Tests with real pixel modules in preparation for FPIX (Fermilab) and BPIX (Aachen) Enpirion withexternal pi-filter Pixel PowerSystem Developments

  15. System Aspects • Operation with 40m long cables and A4603 CAEN power supplies • Remote sensing of CAEN power supplies at input of DC-DC converters • Stability of Vout (both from converter & CAEN PS) during fast load variations on digital line • Digital activity lower during orbit gaps (3µs) • Idig = 2.7A  1.9A for L = 21034/cm2/s • Changes within one to few bunch crossings • Current supplied by capacitors on pixel module? • System test activities & simulations started (FNAL, Aachen) Pixel PowerSystem Developments

  16. CMS Track Trigger Layers The most demanding application DC-DC Conversion for CMS Tracker Upgrade

  17. Track Trigger Layers • Tracking information needed in L1 trigger, to preserve trigger rate at nominal value • All ideas based on discrimination between low and high pT tracks due to bending • Cluster width approach OR stacked, closely spaced, pixelated layers • Worst case in terms of power consumption: “Long Barrel Double Stack“ layout whole tracker constructed out of double-stacked layers (~ 300m2) J. Jones (~2005) CMS Tracker SLHC Upgrade Workshops α The “Long Barrel Double Stack“ layout 4 layers DC-DC Conversion for CMS Tracker Upgrade

  18. Track Trigger Power Requirements • Estimates for stacked layers FE power consumption from CMS: • Power/channel: 0.1mW for 100µm x ~2mm pixel • Power per unit area: ~100mW/cm2 • Power per double module: 2W – 9W • More relevant: supply currents • 130nm or 90nm technology: 1.2V (analogue) or 0.9V (digital) • Total current at 1.2V: 1.6 ... 8A. Note: buck supply current 3-4A. • Digital power consumption ~ 50-75% of total; lowering Vdig to 0.9V halfes Pdig • Need up to 2 x 2A at 1.2V and2 x 2A at 0.9Vper double module • Two buck converters (1 x 1.2V, 1 x 0.9V) per double module • Currents at 0.9V too large for switched capacitors • Linear regulator for 0.9V: efficiency = 0.75% DC-DC Conversion for CMS Tracker Upgrade

  19. Link Power Requirements • Power per GBT link: 2W • Power per pixel (50% usage of bandwidth): 150µW • 1 GBT per double module for trigger data: 2W • Separate GBT links for readout • GBTIA, GB Laser Driver: 280mA at 2.5V • GBTX: 1.0A at 1.5V • Various options: • One buck (1.5V) plus one step-up switched capacitor conv. (2.5V) per GBT • As 1), but 1.5V buck converter delivers in addition Vana to module (25% more P) • Two buck converters (1.5V, 2.5V) per 1-3 GBT(s) P. Moreira, GBTX SPECIFICATIONS V1.2 DC-DC Conversion for CMS Tracker Upgrade

  20. Requirements for CMS Stacked Layers DC-DC Conversion for CMS Tracker Upgrade

  21. Prototypes: AC_AMIS2 and AC2 Chip: AMIS2 by CERN (QFN48) VIN = 3 - 12V IOUT< 3A VOUT = 1.2V (also 2.5V) fS ≈ 1.3MHz (V1) or programmable (V2) 19mm Input and output π-filters L = 12.1nH, C = 22µF 25mm m = 1.1g Chip: EnpirionEQ5382D Vin = 2.4-5.5V(rec.)/7.0V(max.) Iout 0.8A fs 4MHz 12mm Standard filters (C1||C2) 19mm Air-core toroid (both converters):   6mm, height = 7mm, L = 600nH, RDC= 80mΩ DC-DC Conversion for CMS Tracker Upgrade

  22. Power Efficiency Pout/Pin AMIS2, Vout = 1.2V, fs = 1.3MHz Enpirion chip, Vout = 1.3V • Efficiency drops with conversion ratio and current • Efficiency not yet sufficient • Ohmic losses in transistor, wire bonds, PCB, coil; switching losses etc. • Improvements possible, but need to be careful not to add more material... DC-DC Conversion for CMS Tracker Upgrade

  23. Noise • Noise of prototypes has been studied in system test with current strip modules •  Noise increases with conversion ratio • Noise increases for lower switching frequency (as required for efficiency) • Further R&D required to make noise emissions compatible with trigger layers  DC-DC Conversion for CMS Tracker Upgrade

  24. Space Requirements • AMIS2 (QFN32) with input & output pi-filter: 25mm x 18mm • ... but LDO for 3.3V and some passives will vanish • Enpirion converter: 19mm x 12mm • ... but pi-filter at output desirable • Height ~ 10mm, dominated by inductor (to be optimized) • Final size will be inbetween • Will be hard to squeeze below 2cm2 without compromising performance • Trade-off between redundancy and size (e.g. input pi-filter) • If two converters (1.2V/0.9V) needed per double module: • can of course be installed on one PCB • size increases by a factor of  1.5 18mm 25mm DC-DC Conversion for CMS Tracker Upgrade

  25. Space Requirements pT-module by Geoff Hall et al. 26mm pT-module by Sandro Marchioro 80mm Enpirion converter, to scale DC-DC Conversion for CMS Tracker Upgrade

  26. A Possible Implementation • Converters could be integrated into support structure: • no space on hybrid required • height/shape of coil no issue • larger distance  less magnetic field • easier shielding (e.g. by existing Carbon Fibre structures) • much easier cooling • Kapton bus between converter and modules - needed anyway: GBT, by-pass caps • decoupling of module & converter R&D, QA etc. • straight-forward in double-stack proposal (less obvious in others) Marvin Johnson, CMS Upgrade WS, 2009 Per 100cm2 double-module: 1 GBT 1 DC-DC a 1.2V for module power 1 DC-DC a 0.9V for module power 1 DC-DC a 1.5V for GBT 1 DC-DC a 2.5V for GBT  2 PCBs a  4cm2 ~ ok 100cm2 1 PCB 1 PCB 20cm A lot of space inside – is it usable? DC-DC Conversion for CMS Tracker Upgrade

  27. CMS Outer Tracker Upgrade The classical application DC-DC Conversion for CMS Tracker Upgrade

  28. Outer Tracker Upgrade • Some proposals combine a minimalistic trigger configuration with a “classical“ outer strip tracker • Successor of APV25, the CMS Binary Chip (CBC), foreseen as readout ASIC (under development) • 1 CBC (128 channels) needs P = 64mW (for 1.2V supply voltage) Tracking layers 2.5/5.0cm strips 85m2 active area 10kW FE-power (0.5mW/strip) R [cm] single-sided double-sided Two stacked trigger layers R = 25cm & 35cm 27m2 active area 12kW FE-power (0.1mW/pixel) Pixel z [cm] Upgrade of the CMS Tracker for SLHC

  29. DC-DC Converters for Outer Tracker • Power requirements: only 1.5W per module • Idea: use 1.2V buck converter (requ. conv. ratio ~ 4) plus maybe on-chip charge pump (currents are low) • Space is again tight – various ideas: • move into 3rd dimension • integrate into support structure • Tests have to wait for CBC and module prototypes Top Bottom sensor CBC DC-DC converter TPG strips cooling block hybrid DC-DC Conversion for CMS Tracker Upgrade

  30. Summary • Earliest and best understood application: pixel detector at “phase-1“ • Some noise tolerable, due to on-chip regulators • Space and mass not so critical ( 4) • Most demanding and most speculative application: stacked layers for trigger • Large currents at high conversion ratio with high efficiency required • No space available and material budget very critical • Converters for trigger layers probably also fine for Outer Tracker layers • On-chip charge pump is an option to be explored • After Chamonix workshop upgrade plans need to be refined, but R&D on DC-DC conversion will for sure stay on the agenda DC-DC Conversion for CMS Tracker Upgrade

  31. Back-up Slides DC-DC Conversion for CMS Tracker Upgrade

  32. AC_AMIS2 Schematics W. Karpinski, I. Özen (RWTH Aachen) DC-DC Conversion for CMS Tracker Upgrade

  33. On-Chip Common Mode Subtraction • 128 APV inverter stages powered from 2.5V via common resistor (historical reasons)  mean common mode (CM) of all 128 channels is effectively subtracted on-chip • Works fine for regular channels which see mean CM • CM appears on open channels which see less CM than regular channels • CM imperfectly subtracted for channels with increased noise, i.e. edge channels pre-amplifier inverter V250 R (external) V250 V125 vCM strip vIN+vCM vOUT = -vIN VSS Node is common to all 128 inverters in chip DC-DC Conversion for CMS Tracker Upgrade

  34. Module Edge Strips APV25 pre-amplifier V250 V125 strip bias ring VSS=GND [Mark Raymond] • Edge strips are capacitively coupled to bias ring • Bias ring is AC coupled to ground • Pre-amplifier is referenced to 1.25V • If V125 is noisy, pre-amp reference voltage fluctuates against input • This leads to increased noise on edge channels [Hybrid] DC-DC Conversion for CMS Tracker Upgrade

  35. Material Budget (MB) Motivation for new powering schemes is to save material inside the tracker • Detailed study of Enpirion-converter, 1 per Tracker End Cap module, located on FE-hybrid • Assumptions: 80% efficiency, r = 8, Iout = 2A per module, Uout = 1.2V • Simulation of current tracker layout with CMS software based on GEANT4  Converter adds 10% of strip module, but still saves 30% in electronics & cables MB of End Cap buck converters Chip C‘s & R‘s Toroid Copper layers Connector FR4 of PCB MB of electronics & cables Without DC-DC With DC-DC - 30.9% DC-DC Conversion for CMS Tracker Upgrade

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