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Novel Powering Schemes for the CMS Tracker at SLHC

Novel Powering Schemes for the CMS Tracker at SLHC. Katja Klein (Detector Fellow) 1. Physikalisches Institut B RWTH Aachen University. 2 nd Helmholtz Alliance Workshop, Aachen November 27 th , 2008. Motivation. Powering the frontend-electronics is an issue for silicon trackers at SLHC:.

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Novel Powering Schemes for the CMS Tracker at SLHC

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  1. Novel Powering Schemes for the CMS Tracker at SLHC Katja Klein (Detector Fellow) 1. Physikalisches Institut B RWTH Aachen University 2nd Helmholtz Alliance Workshop, Aachen November 27th, 2008

  2. Motivation Powering the frontend-electronics is an issue for silicon trackers at SLHC: • The granularity must increase • The complexity must increase (track trigger) • New cables cannot be added (no space, no access) • The material budget shall be decreased  New powering schemes must be deployed: Serial Powering or parallel powering with DC-DC conversion CMS Strip tracker with cables R&D in Aachen on New Powering Schemes for SLHC

  3. New Powering Schemes Serial powering Parallel powering with DC-DC conversion Vdrop = RI0 Pdrop = RI02 Conversion ratio r = Vout / Vin << 1 Pdrop = RI02n2r2 + Many modules can easily be chained + No noise problems observed so far – Each module has its own ground potential – All communication must be AC-coupled – Shunt regulator and transistor to take excess current and stabilize voltage Significant local inefficiency – Safety issues + Classical grounding, readout & communication + Flexible: different voltages can be provided + Several conversion steps can be combined – Radiation-hard, HV and magnetic field tolerant DC-DC converter to be developed – Converter efficiency 70-90% – Converters are switching devices  noise – Inductors must have air-cores  noise R&D in Aachen on New Powering Schemes for SLHC

  4. The Buck Converter (Inductor-Based) The “buck converter“ is the simplest inductor-based step-down converter: Switching frequency fs: fs = 1 / Ts Convertion ratio r < 1: r = Vout / Vin • Can provide relatively large currents (several Amps) • Technology must work in a 4T magnetic field  since ferrites saturate at lower fields, air-core inductors must be used • Need to find compromise between high efficiency (low fs) and low noise (high fs) • Discrete components (coil, capacitors, ...) need space and contribute to material R&D in Aachen on New Powering Schemes for SLHC

  5. The System Test Goal: Understand if and how DC-DC conversion could be used to power the upgrade strip tracker; identify potential show-stoppers • Prototypes of tracker upgrade readout chips, modules or substructures do not yet exist current tracker hardware must be used! • Avoid to “tune“ R&D to current system • Still a lot can be learned with current system Ring 6 modules 6.4 6.3 6.2 6.1 • Tracker end-cap (TEC) “petal“ with four modules powered & read out • APV25: analogue readoutpre-amp – inverter – CR-RC shaper ( = 50nsec) – analogue pipeline – 128:1 multiplexer • Optical readout & control communication Motherboard (ICB) Petal R&D in Aachen on New Powering Schemes for SLHC

  6. System Test with DC-DC Converters Measurements with commercial buck converterswith internal ferrite-core inductor R&D in Aachen on New Powering Schemes for SLHC

  7. EN5312QI & Its Integration • EnpirionEN5312QI:switching frequency fs 4 MHz, Vin<5.5V, I = 1A with integrated planar ferrite inductor • Mounted onto 4-layer adapter PCB • 2 converters provide 1.25V and 2.5V for FE-hybrid • Input and output filter capacitors on-board • Various designs (L, S, ...) L type Vin S type R&D in Aachen on New Powering Schemes for SLHC

  8. Frequency Spectrum Standardized EMC set-up to measure Differential & Common Mode noisespectra (similar to set-up at CERN) PS Line impedance stabilization network Load Load Spectrum analyzer SpectrumAnalyzer Copper ground plane Current probe Enpirion 2.5V at load Common mode Enpirion 2.5V at load Differential Mode fs R&D in Aachen on New Powering Schemes for SLHC

  9. Raw Noise with DC-DC Converter  No converter  Type L  Type S  No converter  Type L  Type S Pos. 6.4 Pos. 6.4 • Raw noise increases by up to 10% • Large impact of PCB design and connectorization R&D in Aachen on New Powering Schemes for SLHC

  10. Open and Edge Channels • 128 APV inverter stages powered via common resistor  on-chip common mode subtraction • Common mode in noise distributions coupled in after inverter (via 2.5V) • “Real“ CM appears on open channels that do not see the mean CM • Edge channels are special: coupled to bias ring which is AC referenced to ground  strong noise if pre-amp reference (1.25V) fluctuates wrt ground  this is not subtracted pre-amplifier inverter V250  No converter  Type L  Type S R (external) V250 V125 Pos. 6.4 vCM strip vIN+vCM vOUT = -vIN VSS Node is common to all 128 inverters in chip R&D in Aachen on New Powering Schemes for SLHC

  11. Combination with Low DropOut Regulator • Low DropOut Regulator (LDO) connected to output of EN5312QI DC-DC converter • Linear technology VLDO regulator LTC3026 • LDO reduces voltage ripple and thus noise significantlyNoise is mainly conductive and differential mode • Would require a rad.-hard LDO with very low dropout  No converter  Type L without LDO  Type L with LDO, dropout = 50mV  No converter  Type L without LDO  Type L with LDO, dropout = 50mV R&D in Aachen on New Powering Schemes for SLHC

  12. System Test with DC-DC Converters Measurements with commercial buck converters with external air-core inductor R&D in Aachen on New Powering Schemes for SLHC

  13. External Air-Core Inductor • Enpirion EN5382D (similar to EN5312QI) operated with external inductor: • Air-core inductor Coilcraft 132-20SMJLB; L = 538nH • Self-made toroids; L  600nH Toroid wound from copper wire Air-core solenoid Pos. 6.4 10.55mm Toroid wound from copper strip 6.60mm 5.97mm Preliminary R&D in Aachen on New Powering Schemes for SLHC

  14. External Air-Core Inductor  No converter  Internal inductor  External ferrite inductor  External air-core inductor •  No converter •  Internal inductor •  External ferrite inductor • External air-core solenoid • Ext. air-core inductor + LDO Pos. 6.2 radiative part conductive part  No converter  Solenoid  Wire toroid  Strip toroid • Huge wing-shaped noise induced by air-core inductor, even on neighbour-module • Conductive part increases as well • LDO improves only conductive part • Less noise observed with toroids R&D in Aachen on New Powering Schemes for SLHC

  15. Shielding the DC-DC Converter • Enpirion with air-core solenoid wrapped in copper or aluminium foil • Skin depth at 4MHz: Cu = 33m; Al = 42m • No further improvement for > 30m, thinner foils should be tried • No diff. betw. floating / grounded shield magnetic coupling • Shielding increases the material budget • Contribution of 3x3x3cm3 box of 30m Al for one TEC: 1.5kg (= 2 per mille of a TEC)  No converterNo shielding  30 m aluminium  35 m copper • No converter Copper shield •  Aluminium shield R&D in Aachen on New Powering Schemes for SLHC

  16. Combination of Measures zoom on edge channels Can get as good as without converter when toroidal coils are shielded and combined with an LDO. R&D in Aachen on New Powering Schemes for SLHC

  17. System Test with DC-DC Converters Measurements with custom DC-DC converters R&D in Aachen on New Powering Schemes for SLHC

  18. The CERN SWREG2 Buck Converter • Buck controller chip “SWREG2“ dev. by CERN electronics group (F. Faccio et al.) in HV compatible AMIS I3T80 technology (not yet rad-hard) • PCB designed and manufactured by Aachen • Measured the conductive noise on 2.5V • 8-strip ripple structure understood to be artefact of strip order during multiplexing; converter affects readout stages of APV Vin = 3.3 – 20V fs = 250kHz – 3MHz No converter2.5V via S type 0.60 MHz 0.75 MHz 1.00 MHz 1.25 MHz Output DM Vin = 5.5V fs = 1MHz R&D in Aachen on New Powering Schemes for SLHC

  19. Simulation of a DC-DC Converter • DC-DC converter simulated in CMS geometry software based on GEANT4 • Understand order-of-magnitude of contribution to material budget, compare with SP TEC, 1 converter/module • Simulated components: • Kapton substrate with 4 copper layers • Copper wire toroid • Resistors & capacitors • Chip R&D in Aachen on New Powering Schemes for SLHC

  20. Simulation of a DC-DC Converter Total gain for TEC assuming a conversion ratio of 8; with power cables and motherboards modified accordingly: R&D in Aachen on New Powering Schemes for SLHC

  21. Summary • First system tests have revealed several issues with the operation of DC-DC converters close to CMS tracker FE-electronics • Several measures to reduce the noise from converters have been tested • Results have been presented at TWEPP-2008:System Tests with DC-DC Converters for the CMS Silicon Strip Tracker at SLHC , K. Klein et al., TWEPP-08 • Interesting meeting with Bonn group (N. Wermes) working on Serial Powering for Atlas pixels was useful to understand where we can collaborate (and where not) • Well integrated and visible in CMS Tracker Upgrade Power Working Group • Next steps: • Finish up these first system test measurements (e.g. noise injection) • Continue material budget simulation • Optimize converter integration Many thanks to host group: Prof. Lutz Feld, Waclaw Karpinski, Rüdiger Jussen, Jennifer Merz, Jan Sammet R&D in Aachen on New Powering Schemes for SLHC

  22. Back-up Slides R&D in Aachen on New Powering Schemes for SLHC

  23. The APV25 f = 1/(250nsec) = 3.2MHz System Test Measurements with DC-DC Converters

  24. Comparison between Supply Voltages •  No converter • L10 • L11 • L10, 1.25V from converter • L11, 2.5V from converter zoom on edge channels • Either 2.5V or 1.25V line powered via converter; other line powered normally • Overall noise increases when converter powers 2.5V • 1.25V powers ~only pre-amp; noise on 1.25V subtracted by CM subtraction • 2.5V used also after inverter stage; this contribution cannot be subtracted • Edge strip noise increases more if converter powers 1.25V R&D in Aachen on New Powering Schemes for SLHC

  25. Radiative Noise from Air-Core Coil • Module “irradiated“ with detached converter board Mean noise of 6.4 [ADC counts] Reference without converter • Increase of mean noise even if converter is not plugged noise is radiated • Noise pick-up not in sensor but close to APVs R&D in Aachen on New Powering Schemes for SLHC

  26. Correlations corrij = (<rirj> - <ri><rj>) / (ij) APV 4 • Per APV: • two halfs of 64 strips • strips within each half arehighly correlated (90%) • but two halfs are strongly anti-correlated (-80%) linear, see-saw like CM • 50% correlations also on module 6.3 (no converter) Pos. 6.4 (with conv.) Pos. 6.3 (no conv.) R&D in Aachen on New Powering Schemes for SLHC

  27. Distance to FE-Hybrid •  No converter •  Type L •  Type S‘ • Type S‘ + 1cm • Type S‘ + 4cm • The distance between converter and FE-hybrid has been varied using a cable between PCB and connector • Sensitivity to distance is very high • Conductive noise is decreased as well due to filtering in the connector/cable • Place converter at substructure edge? Pos. 6.4 Type L with Solenoid Type S‘ with Solenoid Type S‘ 4cm further away R&D in Aachen on New Powering Schemes for SLHC

  28. The LBNL Charge Pump • Simple capacitor-based step-down converter: capacitors charged in series anddischarged in parallel → Iout = nIin, with n = number of parallel capacitors • At LBNL (M. Garcia-Sciveres et al.) a n = 4 prototype IC in 0.35 m CMOS process (H35) with external 1F flying capacitors has been developed (0.5A, 0.5MHz) P. Denes, R. Ely and M. Garcia-Sciveres (LBNL), A Capacitor Charge Pump DC-DC Converter for Physics Instrumentation, submitted to IEEE Transactions on Nuclear Science, 2008. System Test Measurements with DC-DC Converters

  29. The LBNL Charge Pump • Two converters connected in parallel: tandem-converter • fs = 0.5MHz (per converter) • In-phase and alternating-phase versions • Tandem-converter connected either to 2.5V or 1.25V • Noise increases by about 20% for alternating phase  No converter  In-phase on 2.5V  Alt-phase on 2.5V System Test Measurements with DC-DC Converters

  30. Summary of Power WG Activities R&D in Aachen on New Powering Schemes for SLHC

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