Basic Amplifiers and Differential Amplifier

1 Basic Amplifiers and Basic Amplifiers and Differential Amplifier Differential Amplifier CSE 577 Spring 2011 Insoo Kim, Kyusun ChoiMixed Signal CHIP Design of Computer Science & EngineeringThe Penn State UniversityIn today s analog design, simulation of circuits is essential because the behavior of short-channel MOSFETs cannot be predicted accurately by hand calculations. Nonetheless, if the designer avoids a simple and intuitive analysis of the circuits and hence skips the task of gaining insight, then he/she Don t let the computer think for youDon t let the computer think for youInsoo Kim2/22/2011and hence skips the task of gaining insight, then he/she cannot interpret the simulation results intelligently. For this reason, we say, Don t let the computer think for you. Don t let the computer think for you. - Behzad RazaviContentsContents Fundamentals Basic Amplifiers : Low Frequency Analysis Basic Amplifiers : High Frequency AnalysisInsoo Kim2/22/2011 Differential Amplifier FeedbackFundamentalsFundamentals Definitions DC Operating Point & Load line Large Signal Analysis vs.

2 Small Signal Analysis MOSFET intrinsic CapacitancesDefinitionsDefinitionsInsoo Kim2/22/2011mbmbmbmbDC Operating Point & Load LineDC Operating Point & Load LineInsoo Kim2/22/2011 Large Signal Analysis vs. Small Signal AnalysisLarge Signal Analysis vs. Small Signal Analysis Large Signal AnalysisInsoo Kim2/22/2011 Large Signal Analysis vs. Small Signal AnalysisLarge Signal Analysis vs. Small Signal Analysis Small Signal AnalysisInsoo Kim2/22/2011 How convenient !! How convenient !! How convenient !! How convenient !! How convenient !! How convenient !! How convenient !! How convenient !! MOSFET Intrinsic CapacitancesMOSFET Intrinsic CapacitancesInsoo Kim2/22/2011(cont d) MOSFET Intrinsic Capacitances(cont d) MOSFET Intrinsic CapacitancesInsoo Kim2/22/2011 Basic Amplifiers : Low Frequency Basic Amplifiers : Low Frequency AnalysisAnalysis Single Stage Amplifiers Multi Stage AmplifiersSingle Stage Amplifiers : CS, CD, and CG StageSingle Stage Amplifiers : CS, CD, and CG StageInsoo Kim2/22/2011 Common Source Stage : voltage GainCommon Source Stage : voltage GainInsoo Kim2/22/2011 Common Drain Stage: Output ResistanceCommon Drain Stage: Output ResistanceInsoo Kim2/22/2011 Common Gate Stage : Input ResistanceCommon Gate Stage : Input ResistanceInsoo Kim2/22/2011 SummarySummaryInsoo Kim2/22/2011 QuizQuiz CD stage Amplifier is suitable for output stage of OPAmp due to its low output impedance and large bandwidth.

3 However, in CMOS analog IC, CS stage is more widely used for output stage OPAmp than CD stage. Why?Insoo Kim2/22/2011 Loads for Basic amplifiersLoads for Basic amplifiersInsoo Kim2/22/2011(cont d) Loads for Basic Amplifiers (cont d) Loads for Basic Amplifiers Diode Connected LoadmmbmombmombmXXgggrggrggIV11||111 + +=++= 11ggAmv =XRInsoo Kim2/22/20112121)/()/(LWLW gmmv (cont d) Loads for Basic Amplifiers (cont d) Loads for Basic Amplifiers Source degenerationSmmmRggG+ 1 Insoo Kim2/22/2011]1)([]1)[(2222++ +++ =mbmSooombmSoutggRrrrggRRCascode StageCascode Stage Small Signal Analysis)||()||(1inmDoutoutRRgAVgRRV = =Insoo Kim2/22/2011 Rout)||(1 DoutmvRRgA =]1)([]1)[(221222221++ +++ =mbmoooombmooutggrrrrggrRFolded Cascode StageFolded Cascode Stageom1R||RRRgA==Insoo Kim2/22/2011()[] []( )LLm1 DtoLDo3o4Cm4Co7o2o2Cm2Co4Co2Co2I/CSR/CgA RC/1rrg||r||rrg R||RR====== (cont d) Folded Cascode Stage(cont d) Folded Cascode Stage What are the advantages of folded cascode Amplifier ?

4 Insoo Kim2/22/2011 Disadvantages: Limited Output swing Large voltage Headroom Large Power ConsumptionBasic Amplifiers : High Frequency Basic Amplifiers : High Frequency AnalysisAnalysis Frequency Analysis Dominant Pole ApproachFrequency AnalysisFrequency AnalysisInsoo Kim2/22/2011(cont d) Frequency Analysis(cont d) Frequency Analysis Bode PlotInsoo Kim2/22/2011 Dominant Pole ApproachDominant Pole ApproachInsoo Kim2/22/2011BW Estimation by Dominant Pole ApproachBW Estimation by Dominant Pole ApproachInsoo Kim2/22/2011 Bandwidth ComparisonBandwidth ComparisonInsoo Kim2/22/2011 QuizQuiz Design an Amplifier which satisfy following features using Basic single-stage Amplifiers . High gain Large Bandwidth High input impedance Low output impedanceInsoo Kim2/22/2011 Differential AmplifierDifferential Amplifier Single Stage Amplifiers Multi Stage AmplifiersWhy Differential Amplifier ?Why Differential Amplifier ? Single Ended Signal can be easily contaminated A Differential Signal can be cleaned upInsoo Kim2/22/2011 Power Supply noise can be reducedDifferential Amplifier AnalysisDifferential Amplifier Analysis Classic Diff AmpInsoo Kim2/22/2011(cont d) Differential Amplifier Analysis(cont d) Differential Amplifier AnalysisInsoo Kim2/22/2011 Diff Amp with Current Mirror LoadDiff Amp with Current Mirror Load)||(||424,2424,2oomvoooutmmrrgArrRgG = =Insoo Kim2/22/2011 Common Mode Input voltage RangeVSS+VTN1+VDSAT5+VDSAT1< VIC< VDD |VDSAT3| |VTP3|+| VTN1|)||()()||()2(31331351oomoomomrrgloa dRCMRR rrgrgCMRR = =1.

5 What is CM Input voltage ?1. What is CM Input voltage ?1. What is CM Input voltage ?1. What is CM Input voltage ?2. How do we prove this equation?2. How do we prove this equation?2. How do we prove this equation?2. How do we prove this equation?(Std. Library) Design Exercise(Std. Library) Design Exercise Design Flow Determine Specifications Power Consumption (ex. 1mW) voltage Gain (ex. >30) Active Common Mode Input range (as large as possible) Others: slew rate, CMRR, PSRR, etc. Determine minimum channel lengthInsoo Kim2/22/2011 Determine channel width Determine W1,2from voltage gain spec. Determine W5 & Bias voltage from power consumption & CM min. Determine W3,4from CM max. Determine Bias Level of current source tr. Check other specificationsFeedbackFeedback Feedback & Stability voltage Amplifier Model Common Mode FeedbackFeedback & StabilityFeedback & StabilityInsoo Kim2/22/2011 voltage Amplifier ModelVoltage Amplifier Model ModelsInsoo Kim2/22/2011(cont d) voltage Amplifier Model(cont d) voltage Amplifier Model 1stOrder ModelInsoo Kim2/22/2011(cont d) voltage Amplifier Model(cont d) voltage Amplifier Model 2ndOrder ModelInsoo Kim2/22/2011(cont d) voltage Amplifier Model(cont d) voltage Amplifier Model Time Response of the 2ndOrder ModelInsoo Kim2/22/2011(cont d) voltage Amplifier Model(cont d) voltage Amplifier ModelInsoo Kim2/22/2011 Feedback CharacteristicsFeedback Characteristics Gain desensitizationBand width extensionAAA11 AAA)(1 AAA1 AxxAff2fsofdddd +=+=+= Noise Reduction2ns211n2121soAVVNSAA1 AVAA1 AAVV=+++= nsVVNS=Insoo Kim2/22/2011 Band width extension)A1(/s1)A1/(A A(s)1A(s))s(As/1AA(s)

6 MHMMfHM +++=+=+= Non-linearity Reduction(a)(a)(a)(a) w/o feedbackw/o feedbackw/o feedbackw/o feedback(b)(b)(b)(b) w feedbackw feedbackw feedbackw feedbackCommon Mode FeedbackCommon Mode Feedback Why is CMFB circuit needed? Due to TR mismatch, TRs may not be in saturation region at operating point. DM Gain decreases and CM gain increases Since output CM level is sensitive to device properties and mismatches, it cannot be stabilized by means of Differential feedback. General Topology of CMFB CircuitInsoo Kim2/22/2011(cont d) Common Mode Feedback(cont d) Common Mode Feedback Examples of CMFBI nsoo Kim2/22/2011 Useful for low gain applicationsUseful for low gain applicationsUseful for low gain applicationsUseful for low gain applicationsFolded cascode Amplifier with CMFBF olded cascode Amplifier with CMFBF olded cascode Amplifier with CMFBF olded cascode Amplifier with CMFB)||||(4,32,12,1 FOOmvRrrgA =ReferencesReferences Joongho Choi, CMOS analog IC Design, IDEC Lecture Note, Mar.

7 1999. B. Razavi, Design of Analog CMOS Integrated Circuits, McGraw-Hill, 2001. Hongjun Park, CMOS Analog Integrated Circuits Design, Sigma Press, 1999. Insoo Kim2/22/2011