Serial Powering vs. DC-DC Conversion -

Serial Powering vs. DC-DC Conversion -

A First Comparison

Tracker Upgrade Power WG Meeting

October 7

th

, 2008

Katja Klein

1. Physikalisches Institut B

RWTH Aachen University

Katja Klein

Serial Powering vs. DC-DC Conversion

2

Outline

Compare Serial Powering & DC-DC conversion under various aspectsPower loss in cablesLocal efficiencyCompatibility with servicesPower suppliesBias voltage

SafetySlow controlStart-up ScalabilityFlexibilityPotential

to deliver different voltagesProcess considerations & radiation hardnessInterplay with FE-chipInterplay with readout & controlsNoise

Material budgetSpaceTest systemsDiscussion

The Basic IdeasKatja Klein

Serial Powering vs. DC-DC Conversion3

Conversion

ratio r:

r = Vout / Vin ! << 1 Pdrop

= RI02n2

r2

Vdrop = R

I0Pdrop = RI0

2

Serial powering

Powered from constant

current source

Each module is on different ground potential

 AC-coupled communication

Shunt regulator and transistor to take

excess current and stabilize voltage

Voltages are created locally via shunt

and linear regulators

Parallel

powering with

DC-DC

conversion

Need

radiation-hard magnetic field tolerant

DC-DC converter

One converter per module or parallel scheme 1-step or 2-step conversion

Katja Klein

Serial Powering vs. DC-DC Conversion

4

The Buck Converter

Convertion ratio g > 1

:g = Vin / Vout

Switching frequency fs:fs = 1 / Ts

The “Buck converter“ is simplest inductor-based step-down converter:

Katja Klein

Serial Powering vs. DC-DC Conversion

5

The Charge Pump

Capacitor-based design

Step-down: capacitors charged in series and discharged in parallel Conversion ration = 1 / number of parallel capacitors

Low currents

Implementation ExamplesKatja Klein

Serial Powering vs. DC-DC Conversion6

PP

with DC-DC conversion:

Serial powering:

Atlas pixels, Tobias Stockmanns

Stefano Michelis, TWEPP2008

Two-stage system Diff. technologies proposed for the two stages

Analogue and digital power fully separated

Power for optical links ~ integrated

HV not integrated

Regulators on-chip or on the hybrid

AC-coupled communication with off-module

electronics

Power for optical links not integrated

HV not integrated

What Conversion Ratio do we need?Katja Klein

Serial Powering vs. DC-DC Conversion7

Total tracker current estimate

Current strip tracker: 15kA; current pixel: 1.5kA Geoffs Strawman: strips: 25kW/1.2V = 21kA; pixels: 3.2kA; trigger layers: 10kA

Currents increase roughly by factor of 2 in this strawman Power loss in cables

Goes with I2  increase by factor of 4 for same number of cables (2000) T

otal power loss inverse proportional to number of power groups Can compensate with (conversion ratio)2 Material budget

Saving in cable x-section scales with I Total material independent of segmentation

Of course want to reduce as much as possibleConversion ratio needed for parallel powering with DC-DC converters?With conversion ratio of ¼ we would be as good as or better than today.SP: current fixed; cable material & power loss depends only on # of cables!

Power Losses in CablesKatja Klein

Serial Powering vs. DC-DC Conversion8

Consider

system

with n modules: P

det = n

I0V0

Voltage drop on cables & power loss P

cable calculated within each scheme Efficiency = Pdet

/ Ptotal = Pdet

/ (Pdet + P

cable)

Power losses in cables lead to decrease of overall power efficiency

 expensive

... increase the heat load within the cold volume  cooling capacity must be higher

SP

DC-DC,

r = 1/10

DC-DC, r = 1/5

Serial powering

Eff

. increases with n.

Since

10-20

modules can be chained

,

efficiency

can be very high!PP with DC-DC

conversion

E

ff

. goes down with n. Need

more

cables

or lower

conversion

ratio

Equal to SP if

conversion ratio

=

1/n

Local EfficiencyKatja Klein

Serial Powering vs. DC-DC Conversion9

Serial powering

Constant current source  total power consumption is contant!

Current of chain is fixed to highest current needed by any member Current not used by a module flows

through shunt regulator Linear regulator: voltage difference between dig. & analog drops across it

Local power consumption is increased! Estimated increase for - Atlas pixels (NIM A557): 35%

- Atlas strips (NIM A579, ABCD): 18%

PP with DC-DC conversion All DC-DC converters have inefficiencies switching losses ESR of passive components

Ron of transistor etc. Typical values (e.g. comm. buck): 80-95%

Efficiency goes down for low conv. ratio! Trade-off betw. eff. & switching frequency

In two-step schemes, efficiencies multiply Estimates (St. Michelis, TWEPP2008):

Step-1: 85-90% Step-2: 93%

Total: 80-85% This needs to be demonstrated

Compatibility with LIC Cables

Katja Klein

Serial Powering vs. DC-DC Conversion

10PP

with DC-DC conversion 30V is largely enough

For any reasonable segmentation and conv. factor currents should be lower e.g. 20 chips a 53mA per module  1.2A / module

20 modules per rod  24A /rod r = ¼  I = 6A looks compatible

Serial powering

Current is small 30V allows for chains with more than 20 modules looks compatibleConstraints from recycling of current services:

2000 LICs with two LV conductors & common return each  Not realistic to split return to obtain 4000 lines

 Stay with 2000 LV power lines (“power groups“) LV conductors certified for 30V and 20A Twisted pairs (HV/T/H/sense) certified for 600V

256 PLCC control power cables Adapt at PP1 to (lower mass) cables inside tracker

Power SuppliesKatja Klein

Serial Powering vs. DC-DC Conversion11

PP with

DC-DC conversion

Standard PS: ~15V, ~10A (radiation & magnetic field tolerant?) Any sensitivity of converter to input voltage ripple?

No sensing needed (local regulation)?

Serial powering Constant current source Not so common in industry (e.g. CAEN) Atlas: PSs developed by Prague group

(developed already their current PSs) No sensing

Assume that power supplies will be exchanged after 10 years

Bias VoltageKatja Klein

Serial Powering vs. DC-DC Conversion12

PP

with DC-DC conversion

Same options as for SP

Serial powering Not yet well integrated into concept

Derive on-module via step-up converters? In Atlas, piezo-electric transformers are discussed. Or independent delivery using todays cables

Power is not a problem (currents are very low)

Up to now: independent bias lines for 1-2 modules Might not be possible anymore when current cables are re-used Note: T/H/sense wires are equal to HV wires

Safety (I)Katja Klein

Serial Powering vs. DC-DC Conversion13

PP with

DC-DC conversion

Open connections Converter itself can break Shorts between converter and module If PP of several mod.s by one converter:

risk to loose several modules at once

Serial powering Open leads to loss of whole chain Shunt regulators/transistors to cope with this

Several concepts are on the market (next page) Connection to module can break

 bypass transistor on mothercable - high V, high I  rad.-hardness? - must be controlable from outside Real-time over-current protection? Real time over-voltage protection?

Fermilab expressed interest to perform a systematic failure analysis

Safety (II)Katja Klein

Serial Powering vs. DC-DC Conversion14

One shunt regulator + transistor per module

+ no matching issue- no redundany- needs high-current shunt transistor- must stand total voltage

One reg. per module + distributed transistors

+ no matching issue+ some redundancy- feedback more challenging

Shunt regulators + transistors parallel on-chip

(Atlas pixels)

+ redundancy- matching issue at start-up Regulator with lowest threshold voltage conducts first  all current goes through this regulator

 spread in threshold voltage and internal resistance must be small

Slow ControlKatja Klein

Serial Powering vs. DC-DC Conversion15

PP

with DC-DC conversion

Slow control IC or block on hybrid For on-chip charge pump: would be useful to have SC information

from individual chips Could be used to set converter output voltage and switch on/off converters

Serial powering Slow control IC or block on hybrid

Could be used to communicate with linear regulator and turn to stand-by Ideas to sense module voltage in

Atlas pixels: - sense potential through HV return - sense through AC-coupled data-out termination - sense from bypass transistor gate Module voltage(s) Module current(s)?

Bias current

Start-up & Selective PoweringKatja Klein

Serial Powering vs. DC-DC Conversion16

PP

with DC-DC

conversion If converter output can be switched on/off, then easy and flexible: - controls can be switched on first - bad modules (chips?) can be switched off

- groups of chips/modules can be switched on/off for tests This should be a requirement!

Serial powering If controls powered from separate line,

it can be switched on first Devices in chain switched on together (both module controller and FE-chips)

Can take out modules only by closing bypass transistor from outside

ScalabilityKatja Klein

Serial Powering vs. DC-DC Conversion17

Serial powering

Current is independent on # of modules

Number of modules reflected in maximal voltage within chain; relevant for capacitors for AC-coupling

constant current source bypass / shunt transistors

PP with DC-DC conversion

If one converter per module: perfect scalability PP of

several mod. by one converter: current depends on # of modules, must be able to power largest group Should specify soon what we need current per chip # of chips per module

# of modules per substructure Otherwise we will be constraint by currents that devices can provide

Consequences if more modules are powered per chain or in parallel? E.g. barrel vs. end caps: different # of modules per substructure

FlexibilityKatja Klein

Serial Powering vs. DC-DC Conversion18

PP

with DC-DC conversion

If one converter per module: very flexible, do not care! If PP of several modules by one converter: distribution between modules arbitrary

Serial powering

Current of chain is equal to highest current needed by any member  chains with mixed current requirements are inefficient!

Flexibility with respect to combination of devices with different currents E.g. trigger vs. standard module (or 4 / 6-chips)

Potential to Provide Different VoltagesKatja Klein

Serial Powering vs. DC-DC Conversion19

PP

with DC-DC

conversion With charge pumps, only integer conversion ratios are possible With inductor-based designs, arbitrary Vout

< Vin can be configured (but feedback circuit optimized for a certain range)

Only hard requirement: Vin >= Vopto Analogue and digital voltage can be supplied independently 

no efficiency loss

Serial powering Needed voltage created by regulators ~1.2V by shunt regulator Lower voltage derived from this via linear regulator  efficiency loss Technically could power opto-electronics

and controls via own regulators, but inefficient to chain devices with different current consumption D

ecouple from chain (Atlas: plan to power separately from dedicated cables)

Chip supply voltage(es): ~ 1.2V (Atlas: 0.9V for digital part to save power) Opto-electronics supply voltage: 2.5 – 3V

Process Considerations & Radiation HardnessKatja Klein

Serial Powering vs. DC-DC Conversion

20

Serial powering Regulators must be rad.-hard

Standard CMOS process can be used; but... HV tolerant components (up to nU0):

- capacitors for AC-coupling - bypass transistor Shunt transistors must stand high currents (~2A) if one per module

PP with

DC-DC conversion Commercial devices are not rad.-hard

Apparent exception: Enpirion EN5360 (S. Dhawan, TWEPP2008) Standard 130nm CMOS: 3.3V maximal For high conversion ratio transistors must tolerate high Vin , e.g. 12V Several “high voltage“ processes exist

Rad.-hard HV process not yet identified This is a potential show stopper

For r = ½ (e.g. charge pump) can use 3.3V transistors - radiation hardness?

Interplay with FE-ChipKatja Klein

Serial Powering vs. DC-DC Conversion21

Serial powering

Several options for shunt - Regulator and transistor on-chip

- Only shunt transistor on-chip - Both external Linear regulators typically on-chip Next Atlas strip FE-chip (ABCnext):

- linear regulator - shunt regulator circuit - shunt transistor circuit Next Atlas pixel chip (FE-I4):

- Shunt regulator - LDO DC-balanced protocol

PP with DC-DC

conversion Ideally fully decoupled Not true anymore in two-step approach with on-chip charge pump Next Atlas strip FE-chip (ABCnext): - linear regulator to filter switching noise

Next Atlas pixel chip (FE-I4): - LDO - Charge pump (r = ½) No influence on protocol

Readout & ControlsKatja Klein

Serial Powering vs. DC-DC Conversion22

PP

with DC-DC conversion

Nothing special: electrical transmission of data and communication signals to control ICs No DC-balanced protocol needed

Serial powering

Modules are on different potentials  AC-coupling to off-module electronics needed Decoupling either on the hybrid

(needs space for chips & capacitors) or at the end of the rod (Atlas strips, P. Phillips, TWEPP08) Needs DC-balanced protocol

 increase of data volumeAtlas pixels, NIM A557

NoiseKatja Klein

Serial Powering vs. DC-DC Conversion23

Serial powering

Intrinsically clean - current is kept constant

- voltages generated locally Main concerns: - pick-up from external source - pick-up from noisy module in chain Tests by Atlas pixels (digital) and strips

(binary) revealed no serious problems - noise injection - modules left unbiased - decreased detection thresholds - external switchable load in parallel to one

module (changes potential for all modules): some effect (Atlas pixels, NIM A557)

PP with DC-DC conversion

Switching noise couples conductively into FE Radiated noise (actually magnetic near-field) is picked up by modules Details depend on FE, distances, filtering, coil type & design, switching frequency, conversion ratio, ... Shielding helps against radiated noise,

but adds material, work and cost LDO helps against conductive noise, but reduces efficiency

Surprises might come with bigger systems Not good to start already with shielding and system-specific fine-tuning

Material BudgetKatja Klein

Serial Powering vs. DC-DC Conversion24

Serial powering

Regulators ~ one add. chip per hybrid

Components for AC-coupling - HV-safe capacitors (might be big!) - LVDS chip Flex for discrete components

Cable cross-section from PP1 to detector (rest stays) scales with current - One cable must carry I0 - Total mass depends on modules / cable

Motherboard/-cable: power planes can be narrow, small currents & voltages created locally

PP with DC-DC

conversion Converter chip(s) Discrete components - air-core inductor (D = 1-2cm!) - output filter capacitor(s) Flex for discrete components

One cable must carry I0nr  total mass depends only on conv. ratio

Motherboard/-cable - buck converter can tolerate certain voltage drop since input voltage must not be exact  low mass

- charge pumps have no output regulation: need exact Vin

Shielding?

SpaceKatja Klein

Serial Powering vs. DC-DC Conversion25

Serial powering

Different options are discussed, but regulators + shunt transistors are either

in readout chip or in a separate chip  ~ one additional chip per hybrid Components for AC-coupling - LVDS buffers - HV-safe capacitors (might be big)

Bypass transistor?

PP with DC-DC conversion

Charge pump in readout chip or in a separate chip

Buck converter: - controller chip - discrete air-core inductor (D = 1-2cm!) - discrete output filter capacitor(s) - more?  very unlikely to be ever fully on-chip In all other inductor-based topologies more components (inductors!) needed

Test Systems for Construction PhaseKatja Klein

Serial Powering vs. DC-DC Conversion26

PP

with DC-DC

conversion Electrical readout of single modules possible with adapter PCB needed

Serial powering If AC-coupling at end of stave, a decoupling board is necessary to read out single modules

Adapter PCB needed anyway for electrical readout

RWTH Aachen (L. Feld)

– proposal acceptedSystem

test measurements with commercial and custom DC-DC (buck) converters

Simulation of material budget of powering schemesRad.-hard magnetic-field tolerant buck converter

in collaboration with CERN groupBristol university (C. Hill)

– proposal accepted

Development of PCB air-core toroid DC-DC converter designs with air-core

transformerPSI (R. Horisberger)

– no proposal, but private communicationDevelopment of on-chip CMOS step-down converter (charge pump)IEKP Karlsruhe (W. de Boer) – proposal under review

Powering via cooling pipesFermilab / Iowa / Mississippi (S. Kwan)

– proposal under review System test measurements focused on pixel modules (DC-DC conversion & SP)

Power distribution simulation software

Katja Klein

Serial Powering vs. DC-DC Conversion

27

Work on Powering within CMS Tracker

Both schemes have their pros and cons – how to weigh them?

SP is complicated, but I do not see a real show stopper DC-DC conversion is straighforward, but two potential show stoppersnoise, radiation-hardness of HV-tolerant process

Need to understand SP better

In particular safety, slow controlsUp to now, we focus on DC-DC

conversion – should we start on SP? Who?Both Atlas pixels and strips integrate power circuitry in their new FE-chips: shunt regulators, charge pump, LDO

Seems to be a good approach - can we do the same?

Katja Klein

Serial Powering vs. DC-DC Conversion

28Summary