英文翻译及文献 单片机 LCDLED AD转换.docx

英文翻译及文献 单片机 LCDLED AD转换.docx

《英文翻译及文献 单片机 LCDLED AD转换.docx》由会员分享，可在线阅读，更多相关《英文翻译及文献 单片机 LCDLED AD转换.docx（17页珍藏版）》请在冰豆网上搜索。

英文翻译及文献单片机LCDLEDAD转换

Digit,LCD/LEDDisplay,A/DConverters

Abstract:

TheIntersilICL7106andICL7107arehighperformance,lowpower,

digitA/Dconverters.Includedaresevensegmentdecoders,displaydrivers,areference,andaclock.TheICL7106isdesignedtointerfacewithaliquidcrystaldisplay（LCD）andincludesamultiplexedbackplanedrive;theICL7107willdirectlydriveaninstrumentsizelightemittingdiode（LED）display.

TheICL7106andICL7107bringtogetheracombinationofhighaccuracy,versatility,andtrueeconomy.Itfeaturesautozerotolessthan10μV,zerodriftoflessthan1μV/℃,inputbiascurrentof10pA（Max）,androllovererroroflessthanonecount.Truedifferentialinputsandreferenceareusefulinallsystems,butgivethedesigneranuncommonadvantagewhenmeasuringloadcells,straingaugesandotherbridgetypetransducers.Finally,thetrueeconomyofsinglepowersupplyoperation（ICL7106）,enablesahighperformancepanelmetertobebuiltwiththeadditionofonly10passivecomponentsandadisplay.

Keyword:

DigitLCD/LEDDisplayA/DConverters

1Features

（1）GuaranteedZeroReadingfor0VInputonAllScales

（2）1pATypicalInputCurrent

（3）TrueDifferentialInputandReference,DirectDisplayDrive-LCDICL7106,LEDLCL7107

（4）LowNoise-LessThan15μVP-P

（5）OnChipClockandReference

（6）LowPowerDissipation-TypicallyLessThan10mW

（7）NoAdditionalActiveCircuitsRequired

2DetailedDescription

2.1AnalogSection

Figure1showstheAnalogSectionfortheICL7106andICL7107.Eachmeasurementcycleisdividedintothreephases.Theyare

（1）auto-zero（A-Z）,

（2）signalintegrate（INT）and（3）de-integrate（DE）.

FIGURE1ANALOGSECTIONOFICL7106ANDICL7107

2.2Auto-ZeroPhase

Duringauto-zerothreethingshappen.First,inputhighandlowaredisconnectedfromthepinsandinternallyshortedtoanalogCOMMON.Second,thereferencecapacitorischargedtothereferencevoltage.Third,afeedbackloopisclosedaroundthesystemtochargetheauto-zerocapacitorCAZtocompensateforoffsetvoltagesinthebufferamplifier,integrator,andcomparator.Sincethecomparatorisincludedintheloop,theAZaccuracyislimitedonlybythenoiseofthesystem.Inanycase,theoffsetreferredtotheinputislessthan10μV.

2.3SignalIntegratePhase

Duringsignalintegrate,theauto-zeroloopisopened,theinternalshortisremoved,andtheinternalinputhighandlowareconnectedtotheexternalpins.TheconverterthenintegratesthedifferentialvoltagebetweenINHIandINLOforafixedtime.Thisdifferentialvoltagecanbewithinawidecommonmoderange:

upto1Vfromeithersupply.If,ontheotherhand,theinputsignalhasnoreturnwithrespecttotheconverterpowersupply,INLOcanbetiedtoanalogCOMMONtoestablishthecorrectcommonmodevoltage.Attheendofthisphase,thepolarityoftheintegratedsignalisdetermined.

2.4De-IntegratePhase

Thefinalphaseisde-integrate,orreferenceintegrate.InputlowisinternallyconnectedtoanalogCOMMONandinputhighisconnectedacrossthepreviouslychargedreferencecapacitor.Circuitrywithinthechipensuresthatthecapacitorwillbeconnectedwiththecorrectpolaritytocausetheintegratoroutputtoreturntozero.Thetimerequiredfortheoutputtoreturntozeroisproportionaltotheinputsignal.Specificallythedigitalreadingdisplayedis:

DISPLAYCOUNT=

2.5DifferentialInput

Theinputcanacceptdifferentialvoltagesanywherewithinthecommonmoderangeoftheinputamplifier,orspecificallyfrom0.5Vbelowthepositivesupplyto1Vabovethenegativesupply.Inthisrange,thesystemhasaCMRRof86dBtypical.However,caremustbeexercisedtoassuretheintegratoroutputdoesnotsaturate.Aworstcaseconditionwouldbealargepositivecommonmodevoltagewithanearfullscalenegativedifferentialinputvoltage.Thenegativeinputsignaldrivestheintegratorpositivewhenmostofitsswinghasbeenusedupbythepositivecommonmodevoltage.Forthesecriticalapplicationstheintegratoroutputswingcanbereducedtolessthantherecommended2Vfullscaleswingwithlittlelossofaccuracy.Theintegratoroutputcanswingtowithin0.3Vofeithersupplywithoutlossoflinearity.

2.6DifferentialReference

Thereferencevoltagecanbegeneratedanywherewithinthepowersupplyvoltageoftheconverter.Themainsourceofcommonmodeerrorisaroll-overvoltagecausedbythereferencecapacitorlosingorgainingchargetostraycapacityonitsnodes.Ifthereisalargecommonmodevoltage,thereferencecapacitorcangaincharge（increasevoltage）whencalleduptode-integrateapositivesignalbutlosecharge（decreasevoltage）whencalleduptode-integrateanegativeinputsignal.Thisdifferenceinreferenceforpositiveornegativeinputvoltagewillgivearoll-overerror.However,byselectingthereferencecapacitorsuchthatitislargeenoughincomparisontothestraycapacitance,thiserrorcanbeheldtolessthan0.5countworstcase.

2.7AnalogCOMMON

Thispinisincludedprimarilytosetthecommonmodevoltageforbatteryoperation（ICL7106）orforanysystemwheretheinputsignalsarefloatingwithrespecttothepowersupply.TheCOMMONpinsetsavoltagethatisapproximately2.8Vmorenegativethanthepositivesupply.Thisisselectedtogiveaminimumend-of-lifebatteryvoltageofabout6V.However,analogCOMMONhassomeoftheattributesofareferencevoltage.Whenthetotalsupplyvoltageislargeenoughtocausethezenertoregulate（>7V）,theCOMMONvoltagewillhavealowvoltagecoefficient（0.001%/V）,lowoutputimpedance（≅15Ω）,andatemperaturecoefficienttypicallylessthan80ppm/×℃.

Thelimitationsoftheonchipreferenceshouldalsoberecognized,however.WiththeICL7107,theinternalheatingwhichresultsfromtheLEDdriverscancausesomedegradationinperformance.Duetotheirhigherthermalresistance,plasticpartsarepoorerinthisrespectthanceramic.ThecombinationofreferenceTemperatureCoefficient（TC）,internalchipdissipation,andpackagethermalresistancecanincreasenoisenearfullscalefrom25μVto80μVP-P.Alsothelinearityingoingfromahighdissipationcountsuchas1000（20segmentson）toalowdissipationcountsuchas1111（8segmentson）cansufferbyacountormore.DeviceswithapositiveTCreferencemayrequireseveralcountstopulloutofanover-rangecondition.Thisisbecauseover-rangeisalowdissipationmode,withthethreeleastsignificantdigitsblanked.Similarly,unitswithanegativeTCmaycyclebetweenover-rangeandanon-overrangecountasthediealternatelyheatsandcools.Alltheseproblemsareofcourseeliminatedifanexternalreferenceisused.

TheICL7106,withitsnegligibledissipation,suffersfromnoneoftheseproblems.Ineithercase,anexternalreferencecaneasilybeadded,asshowninFigure2.

AnalogCOMMONisalsousedastheinputlowreturnduringauto-zeroandde-integrate.IfINLOisdifferentfromanalogCOMMON,acommonmodevoltageexistsinthesystemandistakencareofbytheexcellentCMRRoftheconverter.However,insomeapplicationsINLOwillbesetatafixedknownvoltage（powersupplycommonforinstance）.Inthisapplication,analogCOMMONshouldbetiedtothesamepoint,thusremovingthecommonmodevoltagefromtheconverter.Thesameholdstrueforthereferencevoltage.IfreferencecanbeconvenientlytiedtoanalogCOMMON,itshouldbesincethisremovesthecommonmodevoltagefromthereferencesystem.

WithinthelC,analogCOMMONistiedtoanN-ChannelFETthatcansinkapproximately30mAofcurrenttoholdthevoltage2.8Vbelowthepositivesupply（whenaloadistryingtopullthecommonlinepositive）.However,thereisonly10μAofsourcecurrent,soCOMMONmayeasilybetiedtoamorenegativevoltagethusoverridingtheinternalreference.

FIGURE2USINGANEXTERNALREFERENCE

2.8TEST

TheTESTpinservestwofunctions.OntheICL7106itiscoupledtotheinternallygenerateddigitalsupplythrougha500Ωresistor.ThusitcanbeusedasthenegativesupplyforexternallygeneratedsegmentdriverssuchasdecimalpointsoranyotherpresentationtheusermaywanttoincludeontheLCDdisplay.Figures3and4showsuchanapplication.Nomorethana1mAloadshouldbeapplied.

Thesecondfunctionisa“lamptest”.WhenTESTispulledhigh（toV+）allsegmentswillbeturnedonandthedisplayshouldread“1888”.TheTESTpinwillsinkabout15mAundertheseconditions.

FIGURE3SIMPLEINVERTERFORFIXEDDECIMALPOINT

FIGURE4EXCLUSIVE‘OR’GATEFORDECIMALPOINTDRIVE

2.9DigitalSection

Figures5and6showthedigitalsectionfortheICL7106andICL7107,respectively.IntheICL7106,aninternaldigitalgroundisgeneratedfroma6VZenerdiodeandalargeP-Channelsourcefollower.Thissupplyismadestifftoabsorbtherelativelargecapacitivecurrentswhenthebackplane（BP）voltageisswitched.TheBPfrequencyistheclockfrequencydividedby800.Forthreereadings/sec.,thisisa60Hzsquarewavewithanominalamplitudeof5V.ThesegmentsaredrivenatthesamefrequencyandamplitudeandareinphasewithBPwhenOFF,butoutofphasewhenON.InallcasesnegligibleDCvoltageexistsacrossthesegments.

Figure6istheDigitalSectionoftheICL7107.ItisidenticaltotheICL7106exceptthattheregulatedsupplyandbackplanedrivehavebeeneliminatedandthesegmentdrivehasbeenincreasedfrom2mAto8mA,typicalforinstrumentsizecommonanodeLEDdisplays.Sincethe1000output（pin19）mustsinkcurrentfromtwoLEDsegments,ithastwicethedrivecapabilityor16mA.

Inbothdevices,thepolarityindicationis“on”fornegativeanaloginputs.IfINLOandINHIarereversed,thisindicationcanberev