CMOS Current Amplifiers: Speed versus Nonlinearity

305 Pages·2000·2.78 MB·English

by  Kimmo Koli

HelsinkiUniversityofTechnologyElectronicCircuitDesignLaboratory
Report30,Espoo2000
CMOS Current Amplifiers: Speed versus Nonlinearity
KimmoKoli
DissertationforthedegreeofDoctorofScienceinTechnologytobepresentedwithdueper-
mission of the Department of Electrical and Communications Engineering for public exami-
nationanddebateinAuditoriumS1atHelsinkiUniversityofTechnology(Espoo,Finland)on
the13thofNovember,2000,at12o’clocknoon.
HelsinkiUniversityofTechnology
DepartmentofElectricalandCommunicationsEngineering
ElectronicCircuitDesignLaboratory
Teknillinenkorkeakoulu
Sähkö-jatietoliikennetekniikanosasto
Piiritekniikanlaboratorio
Distribution:
HelsinkiUniversityofTechnology
DepartmentofElectricalandCommunicationsEngineering
ElectronicCircuitDesignLaboratory
P.O.Box3000
FIN-02015HUT
Finland
Tel. [phone]
Fax: [phone]
ISBN951-22-5193-0
ISSN1455-8449
OtamediaOy
Espoo2000
Abstract
The tradition of implementing analogue circuits by means of voltage amplifiers is al-
mostasoldastheconceptofelectroniccircuitdesign. Theintegratedelectroniccircuit,
however, is a relatively new concept. Furthermore, integrated electronic circuits have
significantlydifferentlimitationsandstrengthstotheconventionaldiscreteelectronic
circuitshave. Sincetheactivedevicesinintegratedcircuitsamplifycurrentratherthan
voltage,variouscurrent-modecircuitideashaveemergedaftertheintroductionofthe
integratedcircuit.
This work deals with analogue integrated circuit design using various types of
current-modeamplifiers. ThesecircuitsareanalysedandrealisedusingmodernCMOS
integrationtechnologies. Thedynamicnonlinearitiesofthesecircuitsarediscussedin
detailasintheliteratureonlylinearnonidealitiesandstaticnonlinearitiesareconven-
tionallyconsidered.
The most important open-loop current-mode amplifier is the second-generation
current-conveyor (CCII). For this amplifier, a macromodel is derived that accurately
describes all linear nonidealities. Unlike other reported macromodels, this model can
accuratelypredictthecommon-modebehaviourofdifferentialcurrent-conveyorappli-
cations. The accuracy of the model is experimentally verified in the case of current-
mode instrumentational amplifiers. This model is also used to describe the nonide-
alities of several other current-mode amplifiers because circuit structures similar to
second-generationcurrent-conveyorsarecommoninsuchamplifiers.
Push-pullclass-ABrealisationsofthesecond-generationcurrent-conveyorandthe
current-feedbackoperationalamplifierperformefficientlywhenimplementedincom-
plementarybipolarintegrationtechnologies. However,inmodernlow-voltageCMOS
integrationtechnologiesbothamplifiertypessufferfromlimitedinputandoutputvolt-
age swing. Similarly, adequate distortion and input impedance levels are difficult to
reach. Therefore,othercurrent-modeamplifiers,suchasthecurrent-modeoperational
amplifier and the high-gain current-conveyor (CCII¥ ), are more suitable for modern
CMOS-processes. Simple calculations show that, unlike with conventional voltage-
modeoperationalamplifiers,thelarge-signalsettlingbehaviourofthesetwoamplifier
typesdoesnotdegradeasCMOSintegrationtechnologiesarescaleddown.
ii Abstract
Twoillustrativeapplicationsofcurrent-modecircuitsareinvestigated: continuous-
rd
time analogue filters and logarithmic amplifiers. Two 1 MHz 3 -order low-pass
continuous-time filters are designed and fabricated with a 1.2 µm CMOS-process.
These filters use differential high-gain conveyors with linearised, dynamically biased
output stages resulting in performance superior to most OTA-C filter realisations re-
ported. Additionally, a current reference is designed that reduces the temperature de-
pendencyofthefiltercornerfrequencydownto-100ppm/K.
Similarly, two logarithmic amplifier chips are designed and fabricated. The first
circuit, implemented with a 1.2 µm BiCMOS-process, uses again a CCII¥ . The op-
eration of this circuit relies on the logarithmic behaviour of the pn-junction used as
a feedback element. With a CCII¥ the constant gain-bandwidth product, typical of
voltage-mode operational amplifiers, is avoided resulting in a constant 1 MHz band-
widthwitha60dBsignalamplituderange.
The second current-mode logarithmic amplifier is realised in a standard 1.2 µm
CMOS-process. In this case, a piece-wise linear approximation of the logarithmic
function is realised with a cascade of limiting current amplifier stages. The limiting
level in these current amplifiers is less sensitive to process variation than in limiting
voltageamplifiersresultinginexceptionallylowtemperaturedependencyoftheloga-
rithmicoutputsignal. Additionally,alongwiththislogarithmicamplifieranewcurrent
peakdetectorisdeveloped.
Keywords: analogueintegratedcircuit,CMOS,currentamplifier,current-mode,am-
plifierdistortion,nonlinearity,continuous-timefilter,logarithmicamplifier.
Preface
Writing this thesis has been a lengthy process. It is difficult to estimate how long
this process exactly was, since the beginning is almost impossible to pinpoint. How-
ever, this event may even be traced back to my first conference presentation in 1991
(ECCTD’91 in Copenhagen), when I first realised that even my research may have
anaudience. ThewritingprocesswasfurtherprolongedbecauseIpreferredwritinga
book which could additionally be used as a handbook on current-mode analogue in-
tegrated circuit design to writing exclusively a doctoral thesis. I hope that this book
servesatleastoneofthesepurposes.
IwouldliketoexpressmygratitudetomysupervisorProfessorKariHalonenfor
recruitingmetoElectronicCircuitDesignLaboratoryandintroducingtotheintriguing
field of analogue integrated circuit design, otherwise I might have ended up doing
something less imaginative. In addition, I would like to thank both Professor Kari
HalonenandProfessorVeikkoPorraforthevariousinterestingprojectsandthestate-
of-the-art design and measurement facilities in the laboratory, an effort that was not
easytoachieveparticularlyintheearlyyearsofthelaboratory,inlate1980’sandearly
1990’s.
Although work is often hard and even unsolvable problems are occasionally en-
countered,notadaygoesbywithoutlaughteratElectronicCircuitDesignLaboratory.
For that I owe my gratitude to the entire staff at the laboratory. In addition, during
thesealmostelevenyearsatthelaboratoryIhavehadnumerouscolleagueswhohave
similarlyhelpedmeinvariousotherways. Sincethislistofacknowledgementswould
be extremely long and I would unavoidably miss a name or two, as a compromise,
I must thank You all collectively and name individually here only persons who have
directly contributed to the content of this thesis. Esa Tiiliharju Tero Wahlroos have
helpedmeinvariousfiltersynthesisrelatedproblems. Similarly,MarkoKosunenand
Tero Wahlroos have made excellent continuous-time filter implementations using the
filter building blocks described in this thesis. The experience gained in projects with
Harri Kimppa, Harri Riihihuhta, Esa Rantanen, Jarkko Routama and Pasi Ruhanen
has also been valuable in writing this thesis. In addition, I have had numerous fruit-
ful discussions involving circuit theory and distortion calculations in particular with
iv Preface
Saska Lindfors. These discussion have given my ideas which otherwise would not
have ended up in this thesis. Finally, without several long discussion about effective
and accurate layout design with Jukka Riihiaho, Jukka Wallinheimo, Tero Sillanpää,
OlliSalminenandKariHalonen, afewdesibelsworseperformancefiguresmayhave
resultedinthechipsIhavedesigned.
Professors Chris Toumazou and Gordon Roberts are acknowledged for reviewing
mythesis. Iwouldliketoexpressmywarmestthanksfortheirencouragingcomments.
The thesis is based on research financed by Technology Development Centre of
Finland,AcademyofofFinland,NokiaNetworksandNokiaMobilePhones. Inaddi-
tion, Foundation for Financial Aid at the Helsinki University and Wihuri Foundation
havegivensignificantsupportforthiswork. Allofthemaregratefullyacknowledged.
KimmoKoli
Espoo,October2000
Contents
1 Introductiontocurrent-modecircuittechniques 1
1.1 Developmentofintegrationtechnologies . . . . . . . . . . . . . . . . 1
1.2 Motivationforcurrent-modecircuitdesign . . . . . . . . . . . . . . . 2
1.3 Evolutionofcurrent-modebuildingblocks . . . . . . . . . . . . . . . 3
1.4 Adjointprinciple . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Scopeofthisbook . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.6 Contributionsbytheauthor . . . . . . . . . . . . . . . . . . . . . . . 8
2 Basiccurrentamplifiers 15
2.1 Current-mirror . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.1 Nonidealitiesduetothechannellengthmodulation . . . . . . 17
2.1.2 Nonidealitiesduetothethresholdvoltagemismatch . . . . . 20
2.1.3 Highfrequencynonidealities . . . . . . . . . . . . . . . . . 22
Lineareffects . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Nonlineareffects . . . . . . . . . . . . . . . . . . . . . . . . 24
2.1.4 Distortionreductionmethods . . . . . . . . . . . . . . . . . . 30
Transconductancelinearisation . . . . . . . . . . . . . . . . . 30
Nonlinearcurrentreduction . . . . . . . . . . . . . . . . . . 31
Nonlinearcurrentcancellation . . . . . . . . . . . . . . . . . 31
2.1.5 Noiseanddynamicrange . . . . . . . . . . . . . . . . . . . . 33
2.1.6 Othermirrortopologies . . . . . . . . . . . . . . . . . . . . 36
Accuratecurrent-mirrortopologiesforlargesignalamplitudes 36
Resistivelycompensatedmirror . . . . . . . . . . . . . . . . 38
2.2 Currentbuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.2.1 Linearnonidealities . . . . . . . . . . . . . . . . . . . . . . . 41
2.2.2 Nonlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.2.3 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.2.4 Alternativetopologies . . . . . . . . . . . . . . . . . . . . . 44
vi Contents
3 Open-loopcurrentamplifiers 49
3.1 Firstgenerationcurrent-conveyorCCI . . . . . . . . . . . . . . . . . 49
3.1.1 Linearnonidealities . . . . . . . . . . . . . . . . . . . . . . . 50
3.1.2 Nonlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.1.3 ApplicationsoftheCCI . . . . . . . . . . . . . . . . . . . . 53
3.1.4 Push-pullCCItopologies . . . . . . . . . . . . . . . . . . . 54
3.1.5 LowvoltageCCItopologies . . . . . . . . . . . . . . . . . . 58
3.2 Secondgenerationcurrent-conveyorCCII . . . . . . . . . . . . . . . 59
3.2.1 Linearnonidealities . . . . . . . . . . . . . . . . . . . . . . . 61
3.2.2 CCIImacromodel. . . . . . . . . . . . . . . . . . . . . . . . 63
3.2.3 ApplicationsoftheCCII . . . . . . . . . . . . . . . . . . . . 65
3.2.4 Nonlinearityoftheclass-ACCII . . . . . . . . . . . . . . . . 71
3.2.5 Alternativeclass-ACCIItopologies . . . . . . . . . . . . . . 72
3.2.6 Push-pullCCIItopologies . . . . . . . . . . . . . . . . . . . 76
Basicoperationofapush-pullCCII+ . . . . . . . . . . . . . 76
Basicoperationofapush-pullCCII- . . . . . . . . . . . . . . 78
X-terminalimpedance . . . . . . . . . . . . . . . . . . . . . 79
Currentgainnonlinearity . . . . . . . . . . . . . . . . . . . . 80
3.3 Thirdgenerationcurrent-conveyorCCIII . . . . . . . . . . . . . . . . 84
4 Current-modefeedbackamplifiers 89
4.1 Current-feedbackoperationalamplifier . . . . . . . . . . . . . . . . 89
4.1.1 Closedloopbandwidth . . . . . . . . . . . . . . . . . . . . . 91
4.1.2 Integratorimplementations . . . . . . . . . . . . . . . . . . . 94
4.1.3 Self-compensationofvoltagefollowers . . . . . . . . . . . . 96
4.1.4 Common-moderejection . . . . . . . . . . . . . . . . . . . . 97
4.1.5 CMOSimplementations . . . . . . . . . . . . . . . . . . . . 99
4.2 Operationalfloatingconveyor . . . . . . . . . . . . . . . . . . . . . 101
4.2.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.2.2 Compositeconveyors . . . . . . . . . . . . . . . . . . . . . 103
4.3 Current-modeoperationalamplifiers . . . . . . . . . . . . . . . . . . 105
4.3.1 Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.3.2 Slewrateandfullpowerbandwidth . . . . . . . . . . . . . . 108
4.3.3 Alternativetopologies . . . . . . . . . . . . . . . . . . . . . 109
4.4 High-gaincurrent-conveyor . . . . . . . . . . . . . . . . . . . . . . . 111
4.4.1 Linearnonidealities . . . . . . . . . . . . . . . . . . . . . . . 112
4.4.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.4.3 Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.4.4 Designexample . . . . . . . . . . . . . . . . . . . . . . . . . 119
Contents vii
5 Systemaspectsofcurrent-modecircuits 127
5.1 Inputvoltage-to-currentconversion . . . . . . . . . . . . . . . . . . . 127
5.2 Outputcurrent-to-voltageconversion . . . . . . . . . . . . . . . . . . 130
5.3 Differentialvoltageinputstructures . . . . . . . . . . . . . . . . . . 133
5.3.1 CMRRenhancementtechniques . . . . . . . . . . . . . . . . 134
Common-modebootstrapping . . . . . . . . . . . . . . . . . 135
Outputcurrentsubtraction . . . . . . . . . . . . . . . . . . . 135
Compositeconveyors . . . . . . . . . . . . . . . . . . . . . . 139
5.4 Differentialcurrentinputstructures . . . . . . . . . . . . . . . . . . . 141
5.5 Single-endedtodifferentialconversion . . . . . . . . . . . . . . . . . 142
5.6 Noiseincurrent-modecircuits . . . . . . . . . . . . . . . . . . . . . 145
5.6.1 Class-ACMOSCCII+ . . . . . . . . . . . . . . . . . . . . . 145
5.6.2 Otherlow-gainconveyortopologies . . . . . . . . . . . . . . 149
5.6.3 High-gaincurrent-conveyor . . . . . . . . . . . . . . . . . . 149
5.6.4 Othercurrent-modefeedbackamplifiers . . . . . . . . . . . . 152
5.6.5 Generalnotesoncurrentamplifiernoise . . . . . . . . . . . . 153
6 Current-modecontinuous-timefilters 157
6.1 Integratorqualityfactor . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.2 Voltage-modeactive-RCintegrators . . . . . . . . . . . . . . . . . . 159
6.3 OTA-basedintegrators . . . . . . . . . . . . . . . . . . . . . . . . . 161
6.3.1 Theeffectsofprocessvariationandtemperaturedrift . . . . . 162
6.3.2 Transconductancelinearity . . . . . . . . . . . . . . . . . . . 164
6.4 IntegratorswithMOS-resistors . . . . . . . . . . . . . . . . . . . . . 166
6.5 Current-conveyorbasedfilters . . . . . . . . . . . . . . . . . . . . . 167
6.6 Current-mirrorbasedfilter . . . . . . . . . . . . . . . . . . . . . . . 171
6.7 High-gaincurrent-conveyorbasedfilters . . . . . . . . . . . . . . . . 176
6.8 Multi-outputcurrentintegratorwithalinearisedtransconductor . . . . 180
6.8.1 Linearizationbydraincurrentdifference. . . . . . . . . . . . 181
6.8.2 Linearisationbydynamicbiasing . . . . . . . . . . . . . . . 185
6.9 Designcase: A1MHzcurrent-modelow-passfilter . . . . . . . . . 187
6.9.1 Filterbuildingblocks . . . . . . . . . . . . . . . . . . . . . . 187
Thetransimpedancedriveramplifier . . . . . . . . . . . . . . 188
Multiple-outputlinearisedtransconductanceelement . . . . . 191
Temperaturedriftcompensationoftheintegratortimeconstant 191
6.9.2 Thefirstfilterrealisation . . . . . . . . . . . . . . . . . . . . 194
IntegratorQ-enhancement . . . . . . . . . . . . . . . . . . . 196
Experimentalresults . . . . . . . . . . . . . . . . . . . . . . 199
6.9.3 Thesecondtestchip . . . . . . . . . . . . . . . . . . . . . . 202
viii Contents
Alternatedriverimplementation . . . . . . . . . . . . . . . . 205
Experimentalresults . . . . . . . . . . . . . . . . . . . . . . 209
6.10 Finalremarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7 Current-modelogarithmicamplifiers 217
7.1 Diode-feedbacklogarithmicamplifiers . . . . . . . . . . . . . . . . 218
7.1.1 Voltage-modeoperationalamplifierbasedrealizations . . . . 218
7.1.2 Designcase: High-gainconveyorbasedlogamp . . . . . . . . 220
BiCMOSimplementationofaCCII¥ . . . . . . . . . . . . . 221
Logarithmicpeakdetectorimplementation . . . . . . . . . . 221
Postprocessingofthelogarithmicoutputvoltage . . . . . . . 226
Finalremarksonthedesign . . . . . . . . . . . . . . . . . . 233
7.2 Pseudologarithmicamplifiers . . . . . . . . . . . . . . . . . . . . . . 234
7.2.1 LimitingCMOSvoltageamplifiers . . . . . . . . . . . . . . 235
7.2.2 LimitingCMOScurrentamplifiers . . . . . . . . . . . . . . . 237
7.2.3 Accuracyofthepseudologarithmicamplifier . . . . . . . . . 239
7.2.4 Amplitudedetectioninpseudologarithmicamplifiers . . . . . 240
CMOSrectifiers . . . . . . . . . . . . . . . . . . . . . . . . 240
CMOSsquarers . . . . . . . . . . . . . . . . . . . . . . . . . 242
CMOSpeakdetectors . . . . . . . . . . . . . . . . . . . . . 242
7.2.5 Design case: A 2.5 V CMOS pseudologarithmic current am-
plifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Limitingamplifier . . . . . . . . . . . . . . . . . . . . . . . 247
Currentreference . . . . . . . . . . . . . . . . . . . . . . . . 249
Currentpeakdetector . . . . . . . . . . . . . . . . . . . . . . 251
Experimentalresults . . . . . . . . . . . . . . . . . . . . . . 251
7.3 Otherapproaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
Current peak detector with enhanced discharging time con-
stantadjustment . . . . . . . . . . . . . . . . . . . 256
Conclusions 263
A Basicdistortiondefinitions 265
A.1 Harmonicdistortion . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
A.2 Intermodulationdistortion . . . . . . . . . . . . . . . . . . . . . . . 266
A.3 Distortioninfeedbackamplifiers . . . . . . . . . . . . . . . . . . . . 267
A.3.1 Distortioninquasi-staticfeedbackamplifiers . . . . . . . . . 267
A.3.2 Distortionindynamicfeedbackamplifiers . . . . . . . . . . . 268