Signal Processing Techniques Enabling Wideband A/D Converters

120 Pages·2013·3.03 MB·English

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
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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
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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
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