Signal Processing Techniques Enabling Wideband A/D Converters PDF
Preview Signal Processing Techniques Enabling Wideband A/D Converters
UCLA UCLA Electronic Theses and Dissertations Title Signal Processing Techniques EnablingWideband A/D Converters Permalink https://escholarship.org/uc/item/4335n0zt Author Ghosh, Abhishek Publication Date 2013 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA LosAngeles Signal Processing Techniques Enabling Wideband A/D Converters Adissertationsubmittedinpartialsatisfaction oftherequirementsforthedegree DoctorofPhilosophyinElectricalEngineering by Abhishek Ghosh 2013 ©Copyrightby AbhishekGhosh 2013 ABSTRACT OF THE DISSERTATION Signal Processing Techniques Enabling Wideband A/D Converters by Abhishek Ghosh DoctorofPhilosophyinElectricalEngineering UniversityofCalifornia,LosAngeles,2013 ProfessorSudhakarPamarti,Chair With an ever-widening signal spectrum and incorporation of multiple standards that share the availablespectrumatthesametime,researchtowardsbuildingwidebandanalog-to-digitalconvert- ers (ADCs) has gained significant momentum. Furthermore, with an aim to improve spectral effi- ciency, increasingly complex modulation schemes are being invoked having high peak-to-average ratios, the latter translating to high dynamic ranges for the received signals. Consequently, the ADCs deployed in these receivers need to be of quite high precision as well. With these two pri- marygoalsforADCs(highbandwidth,highresolution)inmind,thisthesispresentsafewdifferent techniquesforachievingthem. Inthefirstpartofthisthesis,weshallexploretheartofditheringtolinearizeanA/Dconverter system. Inparticular,adigital-signalconditioningtechnique(usingsubtractivedither)isdeveloped asastepping-stoneforahighresolutionsystem. Theeffectsoffilteringthedithersignaltoshapeits spectralcontentoutsidethesignalbandwhilemaintainingitsbenefitsarestudiedindetail. Design ii strategiesforfiniteimpulseresponse(FIR)filtersthataccomplishspectralshapingaswellasallay quantizernon-linearityarederivedtheoretically. In the second part of this thesis, the proposed dithering technique is used for linearizing an ADC system that is intrinsically non-linear, namely a VCO-based ADC. Ring voltage-controlled oscillator(VCO)-basedADCshavesurfacedaselegantalternativestothetraditional∆−Σmodu- latorsprimarilyduetotheirmostlydigitalnature. Theyofferlowpower,lowareaandsimplicityof designbenefits. However,theyareknowntobenotoriouslynon-linearthatcanbeattributedtothe non-linear nature of the frequency-voltage tuning curve of the VCO. In the proposed scheme, the ring VCO-based ADC is preceded by a coarse flash ADC. The former processes the quantization error(residue),asignalwithmuchsmallerdynamicrange,fromthecoarseADCtherebylessening the impact of the non-linearity. The proposed dithering technique further helps in alleviating the non-linearity. IthelpsconditionthesignaltotheVCOinputtoappearaswhitenoisetherebyelim- inating spurious signal content arising out of the VCO nonlinearity. The technique, thus obviates theneedforpower-hungrydigitalcalibrationtechniquesorexpensivefront-endloop-filters. Apro- totypeimplementation(in65nmCMOS)basedonthetechniqueachieves10-bENOBindigitizing signalswith50MHzbandwidthconsuming8.2mWatanFoMof90fJ/conv.step. In the third part of this thesis, a very popular technique of bandwidth enhancement through time-interleaving multiple A/D converters is examined. Time-interleaved A/D converters enable high conversion bandwidths with quite high precisions. However, inevitable mismatch errors typ- ical of any integrated circuit fabrication process degrades the achievable dynamic range of such A/D converters. Multiple techniques have been proposed over the past two decades to alleviate the problems of mismatch errors. This chapter takes a detailed look at most of these techniques iii bringing out their strengths and weaknesses. The chapter provides a hitherto unavailable common platform to look at analog and digital intensive techniques towards solving this issue motivating thedevelopmentofanovelsolutiontothisprobleminthesubsequentsection. In the fourth chapter, a power-efficient technique to combat mismatches for time-interleaved systems is proposed. The proposed technique adaptively selects finite impulse response filters that take advantage of the signal characteristics. The sub-band outputs from the ADC are passed through these filters to correct for errors at a minimal hardware expense. Simulation results sub- stantiating the claims and thorough analyses of the technique are subsequently presented to high- lighttheefficacyofthetechnique. Chapter1ofthisthesishasbeenpublishedinfullintheInternationalConferenceonAcoustics, Speech and Signal Processing(ICASSP), 2013. The dissertation author is the primary investigator andauthorofthispaper. ProfessorSudhakarPamartisupervisedtheresearchwhichformsthebasis forthispaper. Chapter 2 of this thesis is a reprint of a paper under preparation to be submitted in part or in full to the IEEE Journal of Solid-States Circuits (JSSC). The dissertation author is the primary investigatorandProfessorSudhakarPamartisupervisedtheresearchwhichformsthebasisforthis paper. By the virtue of being (or to be) independent papers, there is a slight degree of overlap in contentbetweenChapters1and2,butthisisessentialtomaintainthecontinuityofthechapters. Chapter 3 of this thesis is a reprint of a paper under preparation to be submitted in part or in full to the IEEE Transactions of Circuits and Systems-1 (TCAS-1). The dissertation author is the primary investigator and Professor Sudhakar Pamarti supervised the research which forms the iv basisforthispaper. Chapter 4 of this thesis is also a reprint of a paper under preparation to be submitted in part or in full to the IEEE Transactions of Circuits and Systems-1 (TCAS-1). The dissertation author is the primary investigator and Professor Sudhakar Pamarti supervised the research which forms the basisforthispaper. v ThedissertationofAbhishekGhoshisapproved. MilosErcegovac ChihKongKenYang SudhakarPamarti,CommitteeChair UniversityofCalifornia,LosAngeles 2013 vi ToMaandBaba vii TABLE OF CONTENTS 1 Filteringofsubtractivediscreteditherinquantizers: somenewresults . . . . . . . 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 Ditheredquantization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.2 Prior-art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.3 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Behavioralmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Mainresult: theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 Mainresults: simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2 Linearization through dithering: A 50MHz bandwidth, 10-b ENOB, 8.2mW VCO- basedADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2 RingoscillatorbasedVCO-ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.3 Prior-art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3.1 FeedbackLoop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3.2 ForegroundCalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 viii
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