Novel Powering Schemes for the CMS Tracker at SLHC

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

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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:. - PowerPoint PPT Presentation

Transcript of Novel Powering Schemes for the CMS Tracker at SLHC

Page 1: Novel Powering Schemes for the  CMS Tracker at SLHC

Novel Powering Schemes for the CMS Tracker at SLHC

2nd Helmholtz Alliance Workshop, AachenNovember 27th, 2008

Katja Klein (Detector Fellow)1. Physikalisches Institut B

RWTH Aachen University

Page 2: Novel Powering Schemes for the  CMS Tracker at SLHC

Katja Klein R&D in Aachen on New Powering Schemes for SLHC 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

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New Powering Schemes

Katja Klein 3R&D in Aachen on New Powering Schemes for SLHC

Vdrop = RI0

Pdrop = RI02

+ 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

Serial powering Parallel powering with DC-DC conversion

Conversion ratio r = Vout / Vin << 1 Pdrop = RI0

2n2r2

+ 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

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The Buck Converter (Inductor-Based)

Katja Klein 4R&D in Aachen on New Powering Schemes for SLHC

The “buck converter“ is the simplest inductor-based step-down converter:

Switching frequency fs:fs = 1 / Ts

• 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

Convertion ratio r < 1:r = Vout / Vin

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• Tracker end-cap (TEC) “petal“ with four modules powered & read out

• APV25: analogue readout pre-amp – inverter – CR-RC shaper ( = 50nsec) – analogue pipeline – 128:1 multiplexer

• Optical readout & control communication

The System Test

• 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 6.16.4 6.3 6.2

Katja Klein 5R&D in Aachen on New Powering Schemes for SLHC

Petal

Motherboard(ICB)

Ring 6 modules

Goal: Understand if and how DC-DC conversion could be used to power the upgrade strip tracker; identify potential show-stoppers

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System Test with DC-DC Converters

Katja Klein 6R&D in Aachen on New Powering Schemes for SLHC

Measurements with commercial buck converters

with internal ferrite-core inductor

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EN5312QI & Its Integration

• Enpirion EN5312QI: 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, ...)

Katja Klein 7R&D in Aachen on New Powering Schemes for SLHC

VinL type S type

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Katja Klein 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

Spectrum analyzer

Load

Line impedance stabilization network

Copper ground plane Current probe

SpectrumAnalyzer

Load

Enpirion2.5V at loadCommon mode

fs

Enpirion2.5V at loadDifferential Mode

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Raw Noise with DC-DC Converter

Pos. 6.4

No converter

Type L

Type S

• Raw noise increases by up to 10%

• Large impact of PCB design and connectorization

Katja Klein 9R&D in Aachen on New Powering Schemes for SLHC

Pos. 6.4

No converter

Type L

Type S

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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

Katja Klein 10R&D in Aachen on New Powering Schemes for SLHC

Pos. 6.4

No converter

Type L

Type S

inverter

V125V250

VSS

V250R (external)

vIN+vCM

vCM

vOUT = -vIN

Node is common to all 128 inverters in chip

pre-amplifier

strip

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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

Katja Klein 11R&D in Aachen on New Powering Schemes for SLHC

No converter

Type L without LDO

Type L with LDO, dropout = 50mV

No converter

Type L without LDO

Type L with LDO, dropout = 50mV

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System Test with DC-DC Converters

Katja Klein 12R&D in Aachen on New Powering Schemes for SLHC

Measurements with commercial buck converters with external air-core inductor

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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

Katja Klein 13R&D in Aachen on New Powering Schemes for SLHC

Air-core solenoid

6.6

0m

m

10.55mm

5.97mm

Pos. 6.4

Pre

limin

ary

Toroid wound from copper wire

Toroid wound from copper strip

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External Air-Core Inductor

Pos. 6.2

• 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

Katja Klein 14R&D in Aachen on New Powering Schemes for SLHC

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

conductive part

radiative part

No converter

Solenoid

Wire toroid

Strip toroid

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Shielding the DC-DC Converter

• Enpirion with air-core solenoid wrapped in copper or aluminium foil

• Skin depth at 4MHz: Cu = 33m; Al = 42m

No further improvement for > 30m, thinner foils should be tried

• No diff. betw. floating / grounded shield magnetic coupling• Shielding increases the material budget

Contribution of 3x3x3cm3 box of 30m Al for one TEC: 1.5kg (= 2 per mille of a TEC)

Katja Klein 15R&D in Aachen on New Powering Schemes for SLHC

No converter No shielding 30 m aluminium 35 m copper

No converter Copper shield Aluminium shield

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Combination of Measures

Can get as good as without converter when toroidal coils are shielded and combined with an LDO.

zoom on edge channels

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System Test with DC-DC Converters

Katja Klein 17R&D in Aachen on New Powering Schemes for SLHC

Measurements with custom DC-DC converters

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The CERN SWREG2 Buck Converter

No converter2.5V via S type0.60 MHz0.75 MHz1.00 MHz1.25 MHz

Output DM

fs = 1MHz

Vin = 5.5V

• 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 – 20Vfs = 250kHz – 3MHz

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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

Simulated components: Kapton substrate with 4 copper layers Copper wire toroid Resistors & capacitors Chip

TEC, 1 converter/module

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Simulation of a DC-DC Converter

R&D in Aachen on New Powering Schemes for SLHCKatja Klein 20

Total gain for TEC assuming a conversion ratio of 8; with power cables and motherboards modified accordingly:

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Katja Klein 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

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Back-up Slides

Katja Klein 22R&D in Aachen on New Powering Schemes for SLHC

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The APV25

Katja Klein 23System Test Measurements with DC-DC Converters

f = 1/(250nsec) = 3.2MHz

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Katja Klein R&D in Aachen on New Powering Schemes for SLHC 24

Comparison between Supply Voltages

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

No converter L10 L11 L10, 1.25V from converter L11, 2.5V from converter

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Reference without converter

Katja Klein R&D in Aachen on New Powering Schemes for SLHC 25

Radiative Noise from Air-Core Coil

• Increase of mean noise even if converter is not plugged noise is radiated• Noise pick-up not in sensor but close to APVs

Mean noise of 6.4[ADC counts]

• Module “irradiated“ with detached converter board

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Katja Klein R&D in Aachen on New Powering Schemes for SLHC 26

Correlations

Per APV: two halfs of 64 strips strips within each half are highly correlated (90%) but two halfs are strongly anti-correlated (-80%) linear, see-saw like CM

50% correlations also on module 6.3 (no converter)

corrij = (<rirj> - <ri><rj>) / (ij)

Pos. 6.3 (no conv.)

Pos. 6.4 (with conv.)

APV 4

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Distance to FE-Hybrid

Pos. 6.4

• 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?

Katja Klein 27R&D in Aachen on New Powering Schemes for SLHC

Type S‘ with Solenoid Type S‘ 4cm further away

No converter

Type L

Type S‘

Type S‘ + 1cm

Type S‘ + 4cm

Type L with Solenoid

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• Simple capacitor-based step-down converter: capacitors charged in series and discharged in parallel → Iout = nIin, 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 1F flying capacitors has been developed (0.5A, 0.5MHz)

Katja Klein System Test Measurements with DC-DC Converters 28

The LBNL Charge Pump

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.

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The LBNL Charge Pump

Katja Klein 29System Test Measurements with DC-DC Converters

• 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

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Summary of Power WG Activities

Katja Klein 30R&D in Aachen on New Powering Schemes for SLHC

Scheme Electronics development System tests Material budget

DC-DC conversion Non-isolated inductor-based:CERN (technology, chip development, simulation);Aachen (PCB);Bristol (air-core coil)

Aachen (strips) Aachen

Transformer-based:Bristol

Fermilab, Iowa, Mississippi (pixels)

Charge pump:PSI

Piezo-electric transformer: -

Serial powering Fermilab, Iowa, Mississippi (pixels)

Aachen

Others Karlsruhe (Powering via cooling pipes)