1Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34Lecture 34: Designing amplifiers, biasing, frequency responseProf J. S. SmithDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithContextWe will figure out more of the design parameters for the amplifier we looked at in the last lecture, and then we will do a review of the approximate frequency analysis of circuits which have a single dominant pole.Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithReadingzChapter 9, multi-stage amplifiers. The frequency analysis is in the first section of chapter 10, but we won’t go farther into chapter 10 for a while.zThe Lectures on Wednesday and Friday will be given by Joe and Jason, respectively. They will be doing several example problems.Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithLecture OutlinezExample 1: Cascode Amp DesignzExample 2; CS NMOS->CS PMOSzReview of frequency analysis (with a dominant pole)2Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithAmplifier SchematicNote that the backgateconnection for M2is notspecified: ignore gmbDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithComplete Amplifier SchematicGoals: gm1= 1 mS,Rout=10 MΩBias voltagesderived fromtransistors undersimilar operatingconditions tothe transistorsthey supplyCascode current sourceFor high rocCS input, with low voltagegainCG outputDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithCurrent Supply DesignOutput resistance goal requires large rocfor high gainÆso we used a cascodecurrent sourceHigh impedance current source means all of thesmall signal current goes to the load resistance,giving more SS voltage gainDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithTotem Pole Voltage SupplyDC voltages must be set for the cascode current supply transistors M3and M4, as well as the gate of M2.M2Bsupplies the Bias quiescent voltageFor the CG stage3Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithMiller Capacitance of Input StageFind the Miller capacitance for Cgd1Input resistance to common-gatesecond stage is low Æ gain acrossCgd1 is small.gdCDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithTwo-Port Model with CapacitorsMiller capacitance:1)1(1gdvCMCACgd−=211mmvCggAdg−≅Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithSchematicGoals: gm1= 1 mS,Rout=10 MΩDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithDevice SizesM1: select (W/L)1= 200/2 to meet specified gm1= 1 mSÆ find VBIAS= 1.2 VCascode current supply devices: select VSG= 1.5 V(W/L)4= (W/L)4B= (W/L)3= (W/L)3B = 64/24Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithDevice SizesM2: select (W/L)2= 50/2 to meet specified Rout=10 MΩÆ find VGS2= 1.4 VMatch M2with diode-connected device M2B.Assuming perfect matching and zero input voltage,what is VOUT?Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithOutput (Voltage) SwingMaximum VOUTMinimum VOUTDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithTwo-Port ModelFind output resistance Routλn= (1/20) V-1, λn= (1/50) V-1at L = 2 µm Æron= (100 µA / 20 V-1)-1 = 200 kΩ, rop= 500 kΩ()( )()1223332221||11||omoSmoSmoocoutrgrRgrRgrrR++=+=SVVAVVIgTnGSDmµµ50014.1)100(22222=−=−=SVVAVVIgTpSGDmµµ40015.1)100(2)(2333=−=+−=Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithVoltage Transfer CurveOpen-circuit voltage gain: Av = vout/ vin= - gm1Rout vOUT vIN 341 2 1 0 3 4 2000,10101073−≈=×−=Qinoutdvdv5Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithMultistage Amplifier Design ExampleStart with basic two-stage transconductance amplifier:Why do this combination?Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithQuiescent level shiftsPMOSNMOS⇑(known shift)⇓(known shift)CDSource follower⇓⇑CG⇓(typical)⇑(typical)CSDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithCS→CS AmplifierDirect DC connection: use NMOS then PMOSDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithCurrent Supply DesignAssume that the reference is a “sink” set by a resistorMust mirror the reference current and generate a sink for iSUP 26Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithUse Basic Current SuppliesDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithComplete Amplifier TopologyWhat’s missing? The device dimensions,the bias voltage and reference resistorDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithDC Bias: Find Operating PointsFind VBIASsuch that VOUT= 0 VDevice parameters: =oxnCµ50 µA/V2=oxpCµ25 µA/V2λn= 0.05 V-1λp= 0.05 V-1VTn= 1 V VTp= -1 VDevice dimensions (for “lecture” design): (W/L)n= 50/2 (W/L)p= 80/2Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithFinding RREF V+ V+ V- RREFM3 Require IREF= - ID3= 50 µA333)/(2LWCIVVoxpDTpSGµ−+−=[][]refSGREFRVVVAI−+−−==350µVAAVVSG32.14041)2/80(25502)1(3=+=×−+−−=µµ[][ ]Ω=⇒−−−= kRRArefref745.232.15.250µ7Department of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithDC Operating PointIREF=50 µAVVAALWCIVVVoxnDtnGSBIAS79)2/50)(/(501001)/(2211≈+=+==−µµµDepartment of EECS University of California, BerkeleyEECS 105 Spring 2004, Lecture 34 Prof. J. S. SmithSmall-Signal Device Parametersgm1= 350 µSgm2= 315 µSro1= 400 kΩro2= 400 kΩTransistors M1and M2Current supplies iSUP1and iSUP2roc1= ro4=400 kΩroc2= ro6=400 kΩDepartment of
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