Master of Science Thesis in Electrical Engineering Department of Electrical Engineering, Linköping University, 2017 Characterization of an ADC Carl-Fredrik Tengberg MasterofScienceThesisinElectricalEngineering CharacterizationofanADC Carl-FredrikTengberg LiTH-ISY-EX–17/5065–SE Supervisor: Dr.ErikBackenius Examiner: Dr.JJacobWikner isy,Linköpingsuniversitet DivisionofIntegratedCircuitsandSystems DepartmentofElectricalEngineering LinköpingUniversity SE-58183Linköping,Sweden Copyright©2017Carl-FredrikTengberg Abstract Analog-to-Digitalconverters,ADCs,introducesthepossibilityofperformingdig- italcomputationonrealworldanalogsignalsbybeingtheinterfacebetweenthe twodomains.ThedemandsontheperformanceoftheADCissteadilyincreasing, whichalsocomeswithanincreaseddifficultyofactuallybeingabletoguarantee thefunctionalityofthedevice. Therefore,theartofestimatingthecharacteristics oftheADChasflourishedovertheyearswhereresearchershassugestedwaysof performingdifferenttestprocedurestoarriveatthemostaccuratemethodsuited foraspecificapplication. Inthisthesis,ameasurementdevicecontaininganADCisthesubjectofinvesti- gation. SomeofthestaticcharacteristicsoftheADCwereestimatedbyisolating the ADC in the circuit and putting it through a set of tests developed in a lab environmentandanalyzingthe resultingdataoffline. By thenalsocarryingout measurementsofthewholesystem,theamountofinputreferrednoiseaddedby theADCcouldbeestimated. iii Contents ListofFigures vii ListofTables ix Notation xi 1 Introduction 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.2 Problemstatements . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Analog-to-DigitalConverter . . . . . . . . . . . . . . . . . . . . . . 4 1.3.1 RegistersintheADC . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Offsetmode . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.3 ADCgain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3.4 Commonmodeadjust . . . . . . . . . . . . . . . . . . . . . 9 1.3.5 Settingsinsidethecomparator. . . . . . . . . . . . . . . . . 9 1.4 CharacteristicsoftheADC . . . . . . . . . . . . . . . . . . . . . . . 11 1.4.1 Commonmodeinputrange . . . . . . . . . . . . . . . . . . 11 1.4.2 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.4.3 Inputreferredshiftandoffset . . . . . . . . . . . . . . . . . 13 1.4.4 Inputreferrednoise . . . . . . . . . . . . . . . . . . . . . . . 14 2 Method 17 2.1 Thetestsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.1.1 TheLabViewSoftware . . . . . . . . . . . . . . . . . . . . . 20 2.2 Registercombinations. . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.3 EstimatingthecharacteristicsoftheADC . . . . . . . . . . . . . . 26 2.3.1 Commonmodeinputrange . . . . . . . . . . . . . . . . . . 28 2.3.2 Gainestimation . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.3 Inputreferredshiftandoffsetestimation . . . . . . . . . . 30 2.3.4 Noiseestimation. . . . . . . . . . . . . . . . . . . . . . . . . 30 2.3.5 Nonlinearityestimation . . . . . . . . . . . . . . . . . . . . 31 v vi Contents 2.4 InputreferrednoiseestimationofcircuitA . . . . . . . . . . . . . 31 3 Results 33 3.0.1 Commonmoderange . . . . . . . . . . . . . . . . . . . . . . 33 3.1 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.1 Combinationstwo . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.2 Combinationsthree . . . . . . . . . . . . . . . . . . . . . . . 38 3.1.3 Individualregistersweep . . . . . . . . . . . . . . . . . . . 39 3.1.4 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2 Offsetandshift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2.1 Combinationstwo . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2.2 Combinationsthree . . . . . . . . . . . . . . . . . . . . . . . 41 3.2.3 Individualregistersweep . . . . . . . . . . . . . . . . . . . 42 3.2.4 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3 Inputreferrednoise . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3.1 Combinationstwo . . . . . . . . . . . . . . . . . . . . . . . . 45 3.3.2 Combinationsthree . . . . . . . . . . . . . . . . . . . . . . . 47 3.3.3 Individualregistersweep . . . . . . . . . . . . . . . . . . . 49 3.3.4 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.4 Quantizationnoise . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.4.1 Combinationstwo . . . . . . . . . . . . . . . . . . . . . . . . 52 3.4.2 Combinationsthree . . . . . . . . . . . . . . . . . . . . . . . 53 3.4.3 Individualregistersweep . . . . . . . . . . . . . . . . . . . 54 3.4.4 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.5 INL/DNL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.5.1 Combinationstwo . . . . . . . . . . . . . . . . . . . . . . . . 57 3.5.2 Combinationsthree . . . . . . . . . . . . . . . . . . . . . . . 58 3.5.3 Individualregistersweep . . . . . . . . . . . . . . . . . . . 59 3.5.4 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.6 InputreferrednoiseofcircuitA . . . . . . . . . . . . . . . . . . . . 62 4 Conclusions 63 4.1 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Bibliography 65 List of Figures 1.1 Roughoverviewofthemeasurementdevice. . . . . . . . . . . . . . 1 1.2 ExampleofadifferentialSARADC. . . . . . . . . . . . . . . . . . . 4 1.3 TransfercurveofadifferentialADC. . . . . . . . . . . . . . . . . . 5 1.4 Capacitorswitchessetdependingonthecomparatordecision. . . 6 1.5 Principleofoperationforoffsetmode. . . . . . . . . . . . . . . . . 8 1.6 TransfercurveswithdifferentvaluesofVoffset. . . . . . . . . . . . . 8 1.7 TransfercurveswithdifferentvaluesofV . . . . . . . . . . . . . 9 high 1.8 Principleofoperationofcommonmodeadjust. . . . . . . . . . . . 9 1.9 Roughblockdiagramofthecomparator. . . . . . . . . . . . . . . . 10 1.10 Twowaysofdetermeningthecommonmodeinputrange. . . . . . 11 1.11 Thresholdsofthecommonmodeinputrange. . . . . . . . . . . . . 12 1.12 DifferentinputrangesforasetofdifferentADCs. . . . . . . . . . . 12 1.13 Offseterror. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.14 Jitteringcodetransitionsduetothepresenceofnoise. . . . . . . . 14 1.15 DNLandINL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1 Testsetup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2 ConnectingtheKeithley2701viaethernet[2]. . . . . . . . . . . . . 18 2.3 UsingtheKeithley2701multimeterwithLabView. . . . . . . . . . 18 2.4 ReadingtheIPaddressoftheKeithley2701[2]. . . . . . . . . . . . 19 2.5 Measuringtheaccuracyofthetwovoltagesources. . . . . . . . . . 19 2.6 PinoutofthePXIe6361[4]. . . . . . . . . . . . . . . . . . . . . . . 20 2.7 Flowchartofthelabviewprogram. . . . . . . . . . . . . . . . . . . 21 2.8 Exampleofthetestsignalbehaviour. . . . . . . . . . . . . . . . . . 22 2.9 Exampleofalistofregisterwritesusedforsweepingregistervalues. 23 2.10 Extractingthemeasurementdataforeachinputvoltage. . . . . . . 23 2.11 Organizingthedata.. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.12 Cell array containingthe filenames together withthe currentset- tingcombination,idealinputvoltagesandmeasuredvoltagediffer- ence.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.13 Conversiondatastoredinmatrixes. . . . . . . . . . . . . . . . . . . 27 2.14 PlottingthemeanvalueoftheNconversionsforeachinputvoltage. 27 2.15 Interpolatingthedatatofindthetransitions. . . . . . . . . . . . . 28 2.16 Findingthecommonmoderangeintermsoflostcodes. . . . . . . 29 2.17 Inputreferrednoiseofthesignalchain. . . . . . . . . . . . . . . . 31 vii viii LISTOFFIGURES 3.1 SweepingvaluesofLatchcurrentandcomparatorstart. . . . . . . 34 3.2 Sweepingtwoofthefiltercoefficients. . . . . . . . . . . . . . . . . 35 3.3 Sweeping values of Pre-amp current, common mode adjust and ADCgain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.4 Inputrangesofcombinationsettwo. . . . . . . . . . . . . . . . . . 37 3.5 Inputrangesofcombinationsetthree. . . . . . . . . . . . . . . . . 38 3.6 InputrangesoftheADCwhensweepingthroughthesettingsindi- vidually.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.7 Inputrangesfordifferentfiltersettings. . . . . . . . . . . . . . . . 40 3.8 Inputreferredshiftandoffsetforcombinationstwo. . . . . . . . . 41 3.9 Inputreferredshiftandoffsetforcombinationsthree. . . . . . . . 41 3.10 Inputreferredshiftandoffsetforindividualregistersweeps. . . . 42 3.11 Inputreferredshiftandoffsetforindividualregistersweeps. . . . 43 3.12 Shiftandoffsetfordifferentfiltersettings. . . . . . . . . . . . . . . 44 3.13 Input referred noise distributed over the full input range of the ADC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.14 Inputreferrednoise(codes)ofcombinationstwo. . . . . . . . . . . 45 3.15 Inputreferrednoise(volts)ofcombinationstwo. . . . . . . . . . . 46 3.16 Inputreferrednoise(codes)ofcombinationsthree. . . . . . . . . . 47 3.17 Inputreferrednoise(volts)ofcombinationsthree. . . . . . . . . . 48 3.18 Inputreferrednoiseofindividualregistersweeps. . . . . . . . . . 49 3.19 Inputreferrednoiseofindividualregistersweeps. . . . . . . . . . 50 3.20 Inputreferrednoisefordifferentfiltersettings. . . . . . . . . . . . 51 3.21 Quantizationnoiseofcombinationstwo. . . . . . . . . . . . . . . . 52 3.22 Quantizationnoiseofcombinationsthree. . . . . . . . . . . . . . . 53 3.23 Quantizationnoiseindividualregistersweep. . . . . . . . . . . . . 54 3.24 Quantizationnoisefordifferentfiltersettings. . . . . . . . . . . . . 55 3.25 Fitteddata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.26 DNLandINLforcombinationstwo. . . . . . . . . . . . . . . . . . 57 3.27 DNLandINLforcombinationsthree.. . . . . . . . . . . . . . . . . 58 3.28 DNLandINLforindividualregistersweeps. . . . . . . . . . . . . 59 3.29 DNLandINLforindividualregistersweeps. . . . . . . . . . . . . 60 3.30 DNLandINLfordifferentfiltercombinations. . . . . . . . . . . . 61 List of Tables 2.1 Registersettingsforindivudualsweeps. . . . . . . . . . . . . . . . 24 2.2 Registersettingsforcombinationtwosweep. . . . . . . . . . . . . 25 2.3 Registersettingsforcombinationthreesweep. . . . . . . . . . . . . 25 2.4 CombinationsofpreampcurrentandfiltercoefficientA. . . . . . 25 3.1 InputreferrednoiseofcircuitA . . . . . . . . . . . . . . . . . . . . 62 ix