ASSOCIATE PROF FRANCOIS RIGAUT & MARKUS DIRNBERGER ADVANCED INSTRUMENTATION TECHNOLOGY CENTRE

AUSTRALIAN NATIONAL UNIVERSITY WORK DONE WITHIN THE FRAMEWORK OF A COLLABORATION WITH PSL (D.GRATADOUR) AND SUBARU (Y.MINOWA)

ROLLING SHUTTER: THE GOOD, THE BAD& THE UGLY

BANDWIDTH, BANDWIDTH, BANDWIDTH.(Bob Fugate, circa 1990)

LATENCY, LATENCY, LATENCY.

▸ Latencyisnoteverything,butcano3endoorundoasystem▸ …especiallyifnoiseinatplay(integra;on;me)▸ …and/orifyouarehun;ngplanets

WFSing in the ELT era, Padova, 2-4 October 2017

WHAT IS ROLLING SHUTTER ANYWAY?

CCD VS CMOS▸ CCD▸ Interline,frametransfer(regularorEMCCD)▸ Transferintostorageareahappensinnanoseconds▸ Readoutoccursthroughoneorseveralamplifiers▸ Becausenoisegrowswithreadoutspeed,atmaxCCDsreadoutspeed,readout;mes=integra;on;me

▸ Rela;velycostly▸ CMOS(sCMOS)▸ Oneamplifier/ADCperpixel.BecausethereisnonecessitytogofastthroughtheADCs,andbecausethereisveryliMleopportunitytopickupnoise(shortdistancepixelrecep;veareatoADC),verylownoisecanbereached(<<forCCDs,typicalsCMOSmediannoise1.0e-)

▸ ADCsyieldnotperfect,soasmallfrac;onofthepixelshavelargertomuchlargernoise(2-10e-).No;onofaveragevsmediannoise.

▸ Rela;velyinexpensive

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WFSing in the ELT era, Padova, 2-4 October 2017

WHAT IS ROLLING SHUTTER ANYWAY?

CCD READ OUT DIAGRAM

Pixel 1Pixel 2

Last pixel

}Integration Transfer }Read-out

▸ Integra;onissimultaneous▸ Readoutanddataaccessisnot▸ Earlydatau;lisa;onwouldmeanvariabledelayacrosstheframe

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Pixel 1Pixel 2

Last pixel

Com

pute

Com

man

d

WFSing in the ELT era, Padova, 2-4 October 2017

} }

WHAT IS ROLLING SHUTTER ANYWAY?

SCMOS READ OUT DIAGRAM (ROLLING SHUTTER)

Pixel 1Pixel 2

Last pixel

Pixel 1Pixel 2

Last pixel

Integration Read-out

▸ Integra;onofallpixelsisNOTsimultaneous▸ Lastpixelalmostonefullframelatewithrespecttofirstpixel

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Pixel 1 (next frame)

WFSing in the ELT era, Padova, 2-4 October 2017

WHAT IS ROLLING SHUTTER ANYWAY?

ROLLING SHUTTER IMAGES CAN BE SOMEWHAT SICKENING

▸ …anddonotappeartogiveresultspar;cularlyusefulfordoingphysics…

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Global shutter Rolling shutter

WFSing in the ELT era, Padova, 2-4 October 2017

} }

WHAT IS ROLLING SHUTTER ANYWAY?

BUSINESS AS USUAL: WAIT FOR THE LAST PIXEL IN

Pixel 1Pixel 2

Last pixel Integration Read-out

▸ Integra;onofallpixelsisNOTsimultaneous▸ Lastpixelalmostonefullframelatewithrespecttofirstpixel

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Com

pute

Com

man

d

Pixel 1Pixel 2

Last pixelPixel 1 (next frame)

WFSing in the ELT era, Padova, 2-4 October 2017

WHAT IS ROLLING SHUTTER ANYWAY?

BUSINESS AS USUAL: WAIT FOR THE LAST PIXEL INWFS DM

Latency = l0

Latency = l0+τ

▸ Thisisbadnews:differentlatencymeandifferenttransferfunc;ons▸ worsebandwidthforpartofthepupil▸ resonance,noiseamplifica;on,etc…

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Latency = l0+τ

Latency = l0

WFSing in the ELT era, Padova, 2-4 October 2017

WHAT IS ROLLING SHUTTER ANYWAY?

NEW APPROACH: PROCESS AS IT COMES IN

▸ Thisisgoodnews:▸ Samelatencyforallpoints▸ Minimallatencyforeveryone

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} }

Pixel 1Pixel 2

Last pixel

Pixel 1Pixel 2

Last pixel

Integration Read-out

Pixel 1 (next frame)

ComputeCommand

WFSing in the ELT era, Padova, 2-4 October 2017

NEW APPROACH: PROCESS AS IT COMES IN

THE GOOD

▸ ProposedbyR.ConaninGMTLTAOPDR(perhapsbyotherspriortothat),revivedrecentlyforSubaruUl;mateGLAO

▸ Inthispresenta;on,I’mjustgoingabitfurther▸ Typicallycutfullframein4sub-frames▸ Updatecommandsforeachsub-frames(4xfaster)▸ Reducelatencyby3/4frames▸ Nominallatencyofe.g.1.4framesinmostop;misedsystems(in

addi;onto1frameZoH,POLL):▸ 1framereadout▸ 0.4framesmatrixmul;ply,driversoverhead,mechBW

▸ Poten;altoreducetoe.g.0.25+0.2=0.45frames

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WFSing in the ELT era, Padova, 2-4 October 2017

THE GOOD

IT DOUBLES THE BANDWIDTH▸ Examplewith▸ 1kHzsampling▸ 1frameZoH▸ 1.40vs0.45latency▸ BW:48➜102Hz.▸ Maxgain:0.33➜0.73forovershoot=2.5dB

▸ Noise:BWdoublingmeansonecansampletwiceasslowandgettwicethenumberofphotons(0.7maggain)

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laten

cy 1.

40lat

ency

0.45

WFSing in the ELT era, Padova, 2-4 October 2017 14

▸ Examplewith▸ 1kHzsampling▸ 1frameZoH▸ 1.40vs0.45latency▸ BW:48➜67Hz.▸ Noisevariance÷2

THE GOOD

… AND/OR REDUCES NOISE PROPAGATION

laten

cy 1

.40

laten

cy 0.

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WFSing in the ELT era, Padova, 2-4 October 2017

THE BAD

THE BAD

▸ Amorecomplexcontrolscheme,▸ …butnotnecessarilymuchmorecalcula;ons(nextslides)

▸ Needse.g.4xthebandwidthtotheDM(compa;bledrivers)

▸ Needdiggingintoframegrabber/CCDcontrollercode▸ Needgoodcontrolofallotherlatencyterms,butrewardishigh

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WFSing in the ELT era, Padova, 2-4 October 2017

NOT MANY MORE FLOPS

ONE MATRIX MULTIPLY, GLOBAL APPROACH

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RECONSTRUCTOR

ACTUATOR ERROR = RECONSTRUCTOR ⊗ MEASUREMENTS

NMES

NAC

T

MEASUREMENTS

ACT ERROR =

WFSing in the ELT era, Padova, 2-4 October 2017

RECONSTRUCTOR

NOT MANY MORE FLOPS

ONE MATRIX MULTIPLY, GLOBAL APPROACHACTUATOR_ERRORS = RECONSTRUCTOR ⊗ MEASUREMENTS

NMES

NAC

T= MEASUREMENTS

ACT_ERROR

▸ OnceyouhaveACT_ERROR,youcanproceedasusual:controllaw,POLC,etc,toupdatetheDMcommands

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ACT_ERROR =

WFSing in the ELT era, Padova, 2-4 October 2017

NOT MANY MORE FLOPS

…SPLIT TO PREPARE PARTIAL UPDATES

=

ACT_ERROR + + +N

ACT

REC1

NMES÷4

MES1

}ACT_ERROR 1

REC4

MES4

NMES÷4}

ACT_ERROR 4

REC2

MES2

NMES÷4

}ACT_ERROR 2

REC3MES3

NMES÷4

}ACT_ERROR 3

▸ Each1/4frame,computenewACT_ERRORi(1/4FLOPS)▸ Ifusingasinglematrixmul;plyandasimpleintegratorwithgain thenit’salllinearandthereisnothingtodo(justaddACT_ERRORiinsteadofACT_ERROR,just4;mesaso3en)

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=

ACT_ERROR

Cnew = Cold + gE |wi

WFSing in the ELT era, Padova, 2-4 October 2017

NOT MANY MORE FLOPS

…SPLIT TO PREPARE PARTIAL UPDATES

=

ACT_ERROR + + +N

ACT

REC1

NMES÷4

MES1

}ACT_ERROR 1

REC4

MES4

NMES÷4}

ACT_ERROR 4

REC2

MES2

NMES÷4

}ACT_ERROR 2

REC3MES3

NMES÷4

}ACT_ERROR 3

▸ Each1/4frame,computenewACT_ERRORi(1/4FLOPS)▸ IfusingaPOLCormorecomplexcontrolscheme,thenupdatethe

newACT_ERRORvectorbyreplacingACT_ERRORivaluesbynewones(NACTsubtrac;ons,NACTaddi;ons).

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=

ACT_ERROR

WFSing in the ELT era, Padova, 2-4 October 2017

THE UGLY

THE UGLY▸ Usualassump;onson simultaneityofmeasurementaredead▸ Proper;esofphase, e.g.donotapply

▸ FilteringofTTandothermodeswillbehavedifferently

▸ CouplingfromTT(vibra;ons) intoothermodes!Couplingof ;meandspace*

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* no, not like wormholes

grad(rot(~')) = 0

Extreme example of how Tilt may be seen through a rolling shutter

WFSing in the ELT era, Padova, 2-4 October 2017

CONCLUSION

ROLLING SHUTTER IS NOT YOUR ENEMY▸ sCMOShavegreatpoten;alforWFS(lowcost,lownoise,goodQE)▸ sCMOScameraimplementarollingshuMermode▸ Strategyofcommandcanbechangedtotakeadvantageofthis▸ Poten;allyallowsreduc;onoflatencybyafactor2-4▸ whichtranslateintobandwidthgain(typ.2x)▸ buthasimplica;onsoncontrolschemes▸ andhardware(e.g.DMdriversandBW)

▸ S;llneedquiteabitofworktoworkoutthedetailsofthemaths(compa;bilitywithKalmanetc,cleanupprocess,etc).

▸ Simula;onsneededforafullendtoendinves;ga;on▸ Poten;alapplica;onsforUl;mateGLAO,GMTLTAO,etc▸ DemonstratorbeingputtogetheratANU(MarkusDirnberger)ona

HamamatsuORCAFlash4

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