Design of Switched-Capacitor Filter Circuits using Low Gain Amplifiers

101 Pages·2015·7.14 MB·English

by  Hugo Alexandre de Andrade Serra

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Hugo Alexandre de Andrade Serra • Nuno Paulino
Design
of Switched-Capacitor Filter
Circuits using Low Gain
Amplifiers
2123
HugoAlexandredeAndradeSerra NunoPaulino
FaculdadedeCiênciaseTecnologia DepartmentofElectricalEngineering
UNINOVA UNINOVA
Caparica Caparica
Portugal Portugal
ISSN2191-8112 ISSN2191-8120(electronic)
SpringerBriefsinElectricalandComputerEngineering
ISBN978-3-319-11790-4 ISBN978-3-319-11791-1(eBook)
DOI10.1007/978-3-319-11791-1
LibraryofCongressControlNumber:2014954623
SpringerChamHeidelbergNewYorkDordrechtLondon
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Preface
Analogfiltersareextremelyimportantblocksinseveralelectronicsystemssuchas
RF transceivers or sigma delta modulators. They allow selecting between signals
withdifferentfrequencyandeliminatingunwantedsignals.
Inmoderndeep-submicronCMOStechnologiestheintrinsicgainofthetransistors
is low and has a large variability, making the design of moderate and high gain
amplifiersextremelydifficult.
Theobjectiveofthisbookistostudyswitched-capacitor(SC)circuitsbasedonthe
low-passandband-passSallen-Keytopologies,sincetheydonotrequirehighgain
amplifiers. Thestrategyusedtoachievethisobjectiveistoreplacetheoperational
amplifier (opamp) with a voltage buffer. Doing this simplifies the design of the
amplifieralthoughitalsoeliminatesthevirtualgroundnodefromthecircuit.Without
thisnodeparasiticinsensitiveSCnetworkscannotbeused.Duetomodernparasitic
extractionsoftwarethatcanreliablypredictthevaluesofparasiticcapacitances,the
historicaldisadvantageofparasiticsensitiveSCnetworks(parallelSC)isnolonger
critical,allowingitsinfluencetobecompensatedduringthedesignprocess.
Different types of switches were simulated to determine the one with the least
non-linear effects. Two techniques (common mode voltage adjustment and source
degeneration)wereusedtoreducethedistortionintroducedbythebuffers.
Low-pass(secondandsixthorder)andband-pass(secondandfourthorder)SC
filtersweresimulatedindifferentialconfigurationinstandard130nmCMOStech-
nology,havingobtainedforthelow-passfilteradistortionof−62dBforthebiquad
sectionand−54dBforthesixth-orderfilter,foracutofffrequencyof1MHzand
whenoperatingat100MHzofclockfrequency.Thetotalpowerconsumptionwas
986μW(i.e.986×10−6)and5.838mW,respectively.
v
Acknowledgements
This work was supported by projects DISRUPTIVE (EXCL/EEI-ELC/0261/2012)
andPEST(PEst-OE/EEI/UI0066/2014).
vii
Contents
1 Introduction................................................... 1
2 Switched-CapacitorCircuits..................................... 3
2.1 Switched-CapacitorFiltersBuildingBlocks .................... 3
2.1.1 OperationalAmplifiers................................ 3
2.1.2 Switches............................................ 3
2.1.3 Capacitors .......................................... 5
2.1.4 Non-OverlappingClockPhases ........................ 5
2.2 Switched-CapacitorResistorEmulationNetworks ............... 5
2.2.1 Parasitic-SensitiveIntegrator........................... 7
2.2.2 Parasitic-InsensitiveIntegrator ......................... 8
2.2.3 SignalFlowGraphAnalysis ........................... 10
2.3 Sallen-KeyTopology........................................ 11
2.3.1 Low-PassSallen-KeyTopology ........................ 12
2.3.2 Band-PassSallen-KeyTopology........................ 13
3 Low-PassFilterTopologies ...................................... 15
3.1 Continuous-TimeSallen-KeyLow-PassFilter................... 15
3.2 Switched-CapacitorLow-PassFilter........................... 16
3.2.1 Single-EndedSwitched-CapacitorLow-PassFilter ........ 16
3.2.2 DifferentialSwitched-CapacitorLow-PassFilter .......... 18
3.3 Switched-CapacitorFiltersUsingCascadedSections............. 19
3.4 Conclusions ............................................... 22
4 Band-PassFilterTopologies ..................................... 23
4.1 Continuous-timeSallen-KeyBand-PassFilter................... 23
4.2 Switched-CapacitorBand-PassFilter .......................... 24
4.2.1 Single-EndedSwitched-CapacitorBand-PassFilter........ 24
4.2.2 DifferentialSwitched-CapacitorBand-PassFilter ......... 26
4.3 Switched-CapacitorFiltersUsingCascadedSections............. 26
4.4 Conclusions ............................................... 28
ix
x Contents
5 Non-IdealEffects............................................... 29
5.1 Non-linearEffectsduetoRealSwitches........................ 29
5.1.1 FilterAnalysis....................................... 29
5.1.2 SimulationResults ................................... 30
5.2 ClockBoostCircuit......................................... 33
5.2.1 ClockBoostCircuitAnalysis .......................... 33
5.2.2 SimulationResults ................................... 36
5.3 Low-VoltageClockBoostCircuit ............................. 37
5.3.1 Low-VoltageClockBoostCircuitAnalysis ............... 37
5.3.2 SimulationResults ................................... 38
5.4 SourceFollowerwithg Compensation ....................... 41
ds
5.4.1 SourceFollowerwithg Compensation ................. 41
ds
5.4.2 ComplementarySourceFollowerwithg Compensation... 45
ds
5.4.3 SourceFollowerwithg andBodyEffectCompensation... 47
ds
5.4.4 SimulationResults ................................... 50
5.5 Low-VoltageFully-DifferentialVoltage-Combiner ............... 52
5.5.1 Fully-DifferentialVoltageCombiner .................... 53
5.5.2 ComplementaryFully-DifferentialVoltage-Combiner ...... 57
5.5.3 SimulationResults ................................... 59
6 SwitchedCapacitorFilterImplementation ........................ 63
6.1 Second-OrderLow-PassSCFilter............................. 63
6.1.1 Filter using Clock Boost and Complementary Source
Followerwithg Compensation....................... 64
ds
6.1.2 FilterUsingLow-VoltageClockBoostandVoltageCombiner
at1.2V............................................ 65
6.1.3 FilterUsingLow-VoltageClockBoostandVoltageCombiner
at0.9V............................................ 67
6.2 Sixth-OrderLow-PassSCFilter .............................. 67
6.2.1 SectionwithLowQualityFactor ....................... 68
6.2.2 SectionwithMediumQualityFactor .................... 68
6.2.3 SectionwithHighQualityFactor ....................... 70
6.2.4 CascadedSections ................................... 71
6.3 Second-OrderBand-PassSCFilter ............................ 72
6.4 Fourth-OrderBand-PassSCFilter............................. 74
6.4.1 FirstFilterSection ................................... 75
6.4.2 SecondFilterSection ................................. 75
6.4.3 CascadedSections ................................... 78
7 Conclusion .................................................... 79
AppendixAButterworthFilteringTransferFunction.................. 83
A.1 Continuous-TimeLow-PassButterworthTransferFunction........ 83
A.1.1 First-OrderPrototypeTransferFunction ................. 84
A.1.2 Second-OrderPrototypeTransferFunction ............... 84
Contents xi
A.2 Discrete-TimeLow-PassButterworthTransferFunction .......... 85
A.2.1 First-OrderPrototypeTransferFunction ................. 85
A.2.2 Second-OrderPrototypeTransferFunction ............... 86
A.3 Continuous-TimeBand-PassButterworthTransferFunction....... 86
A.4 Discrete-TimeBand-PassButterworthTransferFunction.......... 87
A.4.1 Second-OrderPrototypeTransferFunction ............... 87
AppendixBImpulseResponseSimulationandBodeDiagramPlotting 89
References........................................................ 91