Welcome

28.09.2011 Jan Sammet - 1 -

A DC-DC converter based powering schemefor the upgrade of the CMS pixel detector

TWEPP-11, Wien28.09.2011

Arndt Schultz von Dratzig, Lutz Feld, Waclaw Karpinski, Katja Klein,

Jennifer Merz, Jan Sammet, Oliver Scheibling, Michael Wlochal

Welcome Outline

28.09.2011 Jan Sammet - 2 -

• Introduction

• Implementation into CMS

• Challenges…

• … and how we address them

• Conclusions & Outlook

WelcomeUpgrade of the CMS Pixel Detector

28.09.2011 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

28.09.2011 Jan Sammet - 4 -

• Increase efficiency of power transmission

• Ploss=Rcable·I2

supply power at higher voltage r·U i.e. lower current I/r (Conversion ratio r >1)

power losses Ploss=R·(I/r)2 are reduced by factor r2!

DC-DC poweringModuleDC-DC

ModuleDC-DCPower suppy

Conventional poweringModule

ModulePower supply

How it works

• Frequently connect and disconnect source and load

• Duty cycle D = ton/T

• Conversion ratio r = Vin/Vout = 1/D (ideal converter)

Welcome DC-DC Buck Converters

28.09.2011 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 http://indico.cern.ch/contributionDisplay.py?contribId=21&confId=120853]

• Radiation tolerance of many semi-conductor technologies evaluated AMIS I3T80 0.35µm (ON Semiconductor, US) - functional up to dose of 300Mrad & fluence of 51015 p/cm2

[F. Faccio, TWEPP-10, Development of custom radiation-tolerant DCDC converter ASICs]

Advantages

• Output regulation by pulse width modulation Vout is regulated

• Provide high currents with high efficiency

Welcome Aachen DC-DC Converter

28.09.2011 Jan Sammet - 6 -

PCB:2 copper layers a 35µm0.3mm thickLarge ground area on backside for cooling

Toroidal inductor:L = 450nHRDC = 40m

Shield/heat sinkA = 28 x 16 mm2

M 2.5g3.8% of a radiation length

“PIX_V7“:

Design guidelines from CERN grouphave been implemented.

Pi-filters at in- and output

ASIC prototype: AMIS2 by CERNIout < 3AVin < 12VVout configurable; (here: 2.5V & 3.3V)fs configurable, e.g. 1.3MHz

Welcome Challenges

28.09.2011 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

28.09.2011 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

28.09.2011 Jan Sammet - 9 -

2.2m

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)

• CO2 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

• 2 000 DC-DC converters required in total

Pixel detector

Welcome Implementation into CMS

28.09.2011 Jan Sammet - 10 -

CAENA4603

PSU

PSU

Vana

Vdig

6 - 7 converters

1 - 4 pixel modules per converter

DC-DCdig

DC-DCana

6 - 7 converters

• Two CAEN power supply units (PSU) per supply tube channel• Power supplies need modification • I < 2.8A per converter (for L = 2 x 1034 cm-2 s-1)

Vout = 2.5V

Vout = 3.3V

Vin 12V

1 - 4 pixel modules per converter

50m

Welcome Challenges

28.09.2011 Jan Sammet - 11 -

• 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

28.09.2011 Jan Sammet - 12 -

• 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

28.09.2011 Jan Sammet - 13 -

R&D on Shielding

Welcome

28.09.2011 Jan Sammet - 14 -

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

BZ

Welcome

28.09.2011 Jan Sammet - 15 -

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

offsetmean

noShieldmean

offsetmean

shieldmean

BBBB

Welcome

28.09.2011 Jan Sammet - 16 -

Thermal FE-Simulation• Cooling bridges clamp around CO2 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

-20

-10

-15

-6°C

Shielding simulated,but not displayed

0.5 1 1.5 2 2.5 30

20

40

60

80

100

120

60µm Cu.30µm Cu.Alu shieldingNo shielding

Welcome

28.09.2011 Jan Sammet - 17 -

Thermal Measurements

PIX_V7, 450nH, 1.3MHzVin = 10V, Vout = 3.3V

Output current [A]

Coi

l tem

pera

ture

[°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

28.09.2011 Jan Sammet - 18 -

• 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

28.09.2011 Jan Sammet - 19 -

• 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 - 20 -

Efficiency

28.09.2011

• Phase 1 conditions: Vout = 3.3V or 2.5V, Iout < 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, Vout too low]

PIX_V7, Vout = 2.5V PIX_V7, Vout = 3.3V Efficiency [%] Efficiency [%]

Copper Aluminium

Photo

Inductance L [nH] ~450 ~450

Resistance RDC [m] 40 55

Height h [mm] 6 6Diameter d [mm] 7 9

Mass m [mg] 660 370

Welcome

Jan Sammet - 21 -

Choice of Inductor

28.09.2011

10 20 30 40 50 60 70 80 906668707274767880

Efficiency (R4) vs. Inductor DC resistance

Iout = 3A

Iout = 1A

RDC [mOhm]

Effic

ienc

y [%

]• 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

28.09.2011 Jan Sammet - 22 -

• 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

28.09.2011 Jan Sammet - 23 -

• 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

28.09.2011 Jan Sammet - 24 -

SpectrumAnalyzer

Load

LISN = Line ImpedanceStabilization Network

GND

Differential Mode (DM), “ripple“ Common Mode (CM)

Noise through cables (conductive noise) was studied with EMC set-upEMC = electromagnetic compatibility

Welcome Conductive Noise

28.09.2011 Jan Sammet - 25 -

Differential Mode, no shield Common Mode, no shield

Differential Mode, with shield Common Mode, with shield

Large reduction of CM above 2 MHz due to shield

PIX_V7output noiseVout = 3.3VVin = 10Vfs = 1.3MHzL = 450nH

WelcomeSystem Tests with CMS Pixel Modules

28.09.2011 Jan Sammet - 26 -

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

VA

Connectorboard

Moduleadapter

PC interface „Advanced Test Board“

DAQ PC Module

DC-DCconverter

s

CAEN Pixel PSU multi-service cables (40m)

VD

EASY4000

SY1527+ Branch

Controller

PSMA4603

Original pixel powersupply unit

HV(150V)

WelcomePowering with DC-DC Converters

28.09.2011 Jan Sammet - 27 -

• DC-DC converters cause no significant increase of noise

powering with DCDC

conventional powering

Welcome

28.09.2011 Jan Sammet - 28 -

Impact of Orbit Gaps• Orbit gaps of LHC beam no collisions for 3µs every 89µs Pixel digital current drops within 25..100ns (1..4 bunches, depending on the occupancy) Worst case for 2×1034cm-2s-1:

• ID_high = ~ 2.7A (86µs) ID_low = ~1A (3µs)

Stability Test of the whole power supply chain:

Also check impact of “inverted orbit gaps”

• ID_high = ~ 2.7A (3µs) ID_low = ~1A (86µs) (LHC fill with only a few intense bunches)

VA

Connectorboard

Moduleadapter

PC interface „Advanced Test Board“

DAQ PCModule

HV(150V)

DC-DCconverter

s

CAEN Pixel PS multi-service cables (40m)

VD

Dynamic Load Box

EASY4000

SY1527+ Branch

Controller

PSMA4603

ID

t

ID

t

Welcome Impact of Orbit Gaps

28.09.2011 Jan Sammet - 29 -

• 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

WelcomeInfluence of the Switching Frequency

28.09.2011 Jan Sammet - 30 -

0.5 1.0 1.5 2.0 2.5 3.0 3.5123.5

124

124.5

125

125.5

126

126.5

127

Orbit gaps

2A add. load

Module only

Frequency [MHz]

Noi

se [e

]

Slight reduction ( < 1e ) at 2 MHz Not significant yet Might become relevant in larger system

é Not directly comparable to previous measurements

(slightly different cabling, no copper plate here)

0.5 1.0 1.5 2.0 2.5 3.0 3.50

50

100

150

Frequency [MHz]

Noi

se [e

]

Welcome Different Sensing Points

28.09.2011 Jan Sammet - 31 -

Dynamic Load

DC-DCconverter

CAEN PSmulti-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

28.09.2011 Jan Sammet - 32 -

• 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

28.09.2011 Jan Sammet - 33 -

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

28.09.2011 Jan Sammet - 34 -

Welcome The CMS Pixel Detector

28.09.2011 Jan Sammet - 35 -

• Pixel size: (100 x 150) µm²

Present barrel New barrel

Welcome Aachen DC-DC Converter

28.09.2011 Jan Sammet - 36 -

Design guidelines from CERN grouphave been followed.

Welcome

28.09.2011 Jan Sammet - 37 -

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

09.09.2011 Jan Sammet - 38 -

Welcome

28.09.2011 Jan Sammet - 39 -

Conductive Noise with Shielding

No shield Milled shield, 90µm Cu galvanic, 60µm Cu galvanic, 30µm0

2

4

6

8

10

12

14

16

18

20

DMCM

Qua

drati

c su

m o

f noi

se p

eaks

[dBµ

A]

Welcome Set-Up for System Tests

28.09.2011 Jan Sammet - 40 -

Original pixel powersupply system

Pixel module

DC-DCconverters

WelcomePowering with DC-DC Converters 2

28.09.2011 Jan Sammet - 41 -

• Variations with different but identical converters ~2e

• Reproducibility of measurements ~1e

VD = 3.2V, VA= 2.5V

VD = 3.2V, VA= 2.5V

WelcomeInfluence of the Switching Frequency

28.09.2011 Jan Sammet - 42 -

With inverted orbit gaps With simulated orbit gaps

Additional 2A const. Load No additional load (VD = 3.2V, VA= 2.5V)

(VD = 3.2V, VA= 2.5V)

(VD = 3.2V, VA= 2.5V)

(VD = 3.2V, VA= 2.5V)

WelcomeDifferent sensing points, w/o Add. Load

28.09.2011 Jan Sammet - 43 -

Powering with DC-DC converters

DC-DCconverter

sCAEN 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

WelcomeDifferent sensing points, w/o Add. Load

28.09.2011 Jan Sammet - 44 -

Powering with DC-DC convertersConventional powering

No increase of noise due to sensing at PS No increase of noise due to sensing at PS

DC-DCconverter

sCAEN PS

multi-service cables (40m)ModuleSensing 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

WelcomeDifferent sensing points with Orbit Gaps

28.09.2011 Jan Sammet - 45 -

Dynamic Load Box

DC-DCconverter

sCAEN 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

WelcomeDifferent sensing points with Orbit Gaps

28.09.2011 Jan Sammet - 46 -

Noise increases if voltages are senses at PS No increase of noise due to sensing at PS

Dynamic Load Box

DC-DCconverter

sCAEN PS

multi-service cables (40m)ModuleSensing 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)