Novel Powering Schemes for the CMS Tracker at SLHC
description
Transcript of 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
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
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
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
• 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
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
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
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
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
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
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
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
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
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
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
Katja Klein R&D in Aachen on New Powering Schemes for SLHC 16
Combination of Measures
Can get as good as without converter when toroidal coils are shielded and combined with an LDO.
zoom on edge channels
System Test with DC-DC Converters
Katja Klein 17R&D in Aachen on New Powering Schemes for SLHC
Measurements with custom DC-DC converters
Katja Klein R&D in Aachen on New Powering Schemes for SLHC 18
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
Katja Klein 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
Simulated components: Kapton substrate with 4 copper layers Copper wire toroid Resistors & capacitors Chip
TEC, 1 converter/module
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:
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
Back-up Slides
Katja Klein 22R&D in Aachen on New Powering Schemes for SLHC
The APV25
Katja Klein 23System Test Measurements with DC-DC Converters
f = 1/(250nsec) = 3.2MHz
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
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
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
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
• 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.
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
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)