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APPLICATIONINFORMATION
TheoryofOperation
DACTransferFunction
I
OUTFS
I
OUT1
I
OUT2
(1)
I
OUT1
I
OUTFS
代号
4096
(2)
I
OUT2
I
OUTFS
4095
代号
4096
(3)
I
OUTFS
32
I
REF
32
V
REF
R
设置
(4)
V
OUT1
I
OUT1
R
加载
(5)
V
OUT2
I
OUT2
R
加载
(6)
DAC5662
SLAS425–JULY2004
ThearchitectureoftheDAC5662usesacurrentsteeringtechniquetoenablefastswitchingandhighupdate
比率.thecoreelementwithinthemonolithicdacisanarrayofsegmentedcurrentsourcesthataredesignedto
deliverafull-scaleoutputcurrentofupto20ma.aninternaldecoderaddressesthedifferentialcurrentswitches
eachtimetheDACisupdatedandacorrespondingoutputcurrentisformedbysteeringallcurrentstoeither
outputsummingnode,iout1andiout2.thecomplementaryoutputsdeliveradifferentialoutputsignal,这个
improvesthedynamicperformancethroughreductionofeven-orderharmonics,一般-modesignals(噪音),
anddoublethepeak-至-peakoutputsignalswingbyafactoroftwo,comparedtosingle-endedoperation.
thesegmentedarchitectureresultsinasignificantreductionoftheglitchenergy,improvesthedynamic
效能(sfdr),anddnl.thecurrentoutputsmaintainaveryhighoutputimpedanceofgreater
than300k
Ω
.
whengsetishigh(oneresistormode),thefull-scaleoutputcurrentforbothdacsisdeterminedbytheratioof
theinternalreferencevoltage(1.2v)andanexternalresistorrsetconnectedtobiasj_一个.whengsetislow
(tworesistormode),thefull-scaleoutputcurrentforeachdacsisdeterminedbytheratiooftheinternal
referencevoltage(1.2v)andseparateexternalresistorsrsetconnectedtobiasj_aandbiasj_b.这
resultingIREFisinternallymultipliedbyafactorof32toproduceaneffectiveDACoutputcurrentthatcanrange
from2mato20ma,dependingonthevalueofrset.
thedac5662issplitintoadigitalandananalogportion,eachofwhichispoweredthroughitsownsupplypin.
thedigitalsectionincludesedge-triggeredinputlatchesandthedecoderlogic,whiletheanalogsection
comprisesthecurrentsourcearraywithitsassociatedswitches,andthereferencecircuitry.
eachofthedacsinthedac5662hasasetofcomplementarycurrentoutputs,iout1andiout2.thefull-规模
outputcurrent,ioutfs,isthesummationofthetwocomplementaryoutputcurrents:
theindividualoutputcurrentsdependonthedaccodeandcanbeexpressedas:
wherecodeisthedecimalrepresentationofthedacdatainputword.additionally,ioutfsisafunctionofthe
referencecurrentiref,whichisdeterminedbythereferencevoltageandtheexternalsettingresistor(rset).
inmostcases,thecomplementaryoutputsdriveresistiveloadsoraterminatedtransformer.asignalvoltage
developsateachoutputaccordingto:
thevalueoftheloadresistanceislimitedbytheoutputcompliancespecificationofthedac5662.tomaintain
specifiedlinearityperformance,thevoltageforiout1andiout2shouldnotexceedthemaximumallowable
compliancerange.
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