Characterization of an ADC

78 Pages·2017·2.25 MB·English

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