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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