A102-dB-SNRmixedCT/DT†󰂁ADCwithcapacitordigitalself-calibrationforRCspreadcompensationLiuYan(刘岩)󰂁,HuaSiliang(华斯亮),WangDonghui(王东辉),andHouChaohuan(侯朝焕)InstituteofAcoustics,ChineseAcademyofSciences,Beijing100190,ChinaAbstract:Thispaperprovidesamixedcontinuous-time/discrete-time,single-loop,4th-order,4-bitaudio-bandsigmadeltaADCwithcapacitordigitalself-calibrationforRCspreadcompensation.ThisADCcombinesthebenefitsofCTandDTcircuits,andtheself-calibrationcontrolcircuitscompensateforthevariationoftheRCproductinthecontinuous-timeintegratorandforvariationinthesamplingfrequency.MeasurementresultsshowthatthepeakSNRofthisADCreaches102dBandthetotalpowerconsumptionislessthan30mW.Keywords:continuous-time;discrete-time;self-calibration;sigmadeltaADCDOI:10.1088/1674-4926/32/8/085004EEACC:1265H;61301.IntroductionSigmadelta(†󰂁/ADCsprovideameanstoachievehighresolutionandlowdistortionatarelativelylowcostcomparedtoNyquistconverters.Thehighresolutionisachievedbyover-samplingtheinputsignalandshapingthequantizationnoiseinthebandofinterestintoahigherfrequencyregion.Thehigherfrequencynoisecanthenbedigitallyfilteredoutbythesubse-quentdigitalfilterstages.Theresultingdataisthendownsam-pledtothedesiredsamplerateattheoutputoftheconverterŒ1󰂁.Typically,anaudio-bandsigmadeltaADCisimplementedusingdiscrete-time(DT)circuitssuchasswitchedcapaci-tors,becauseswitchedcapacitorcircuitsofferlowsensitiv-itytoclockjitterandarereadilyscalablewiththesamplingrateŒ2󰂁.However,duetothenatureofDT,theconvertersuf-fersfromharmonicdistortionprimarilycausedbysignal-dependentglitchescapturedbythesamplingcapacitorsofthefirstintegrator.Furthermore,forhighperformanceconverters,thesamplingcapacitorsofthefirstintegratorhavetobelargeinordertoreducethethermalnoiseandthereforeneedadriverinfrontofthefirstintegratortoloadthesamplingcapacitors.Insteadofimplementationbyswitchedcapacitors,thefirstin-tegratorcanbeimplementedusingacontinuous-time(CT)in-tegrator.ACTintegratorhassignificantadvantagesoveraDTintegrator,notablyanimplicitanti-aliasingfilter,nofront-endsampleandholdS/H,andtheabsenceofkT/CnoiseŒ3󰂁.AmajordrawbackassociatedwiththecombinationofCTandDTimplementationisthattheRCtimeconstantinthecontinuous-timeintegratorvariessignificantlywithprocess,temperatureandpowersupplyvariation.VariationintheRCproductchangesthenoisetransferfunctionoftheloopandleadstoadegradationinperformanceoftheconverter.AnotherdisadvantageisthattheRCtimeconstantalsochangeswiththeperiodofthemasterclockoftheconverter.Thisessentiallylimitstheconverteroperationtooneparticularsamplingrate.SothispaperprovidesamixedCT/DTaudio-bandsigmadeltaADCwithcapacitordigitalself-calibrationforRCspreadcompensation.ThisADCcombinesthebenefitsofCTandDTcircuits,andtheself-calibrationcontrolcircuitscompensateforthevariationoftheRCproductinthecontinuous-timeinte-gratorandforvariationinthesamplingfrequency.TheADCuseschopperstabilization;theIDACcanbeconnectedtothebranchesviachoppingswitchesandtheintegratoramplifiercanalsobechopper-stabilized.Chopperstabilizationcanre-movetheflickernoiseespeciallyproblematicindeepsubmi-cronMOSdevicesŒ4󰂁.2.MixedCT/DTaudio-bandsigmadeltaADCAnaudio-band†󰂁ADCrequiresasetoftwotransferfunctions:high-passnoisetransferfunction(NTF)andlow-passsignaltransferfunction(STF).ThearchitectureofthemixedCT/DT,single-loop,4th-order,4-bit,audio-band†󰂁A...