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1、EECS140ANALOGCIRCUITDESIGNMOREONOPAMPSTELESCOPICANDFOLDEDCASCODEUniversityofCaliforniaBerkeleyCollegeofEngineeringDepartmentofElectricalEngineeringandComputerScienceRobertW.BrodersenEECS140Fall,2002AnalogCircuitDesignMoreonOpAmpsTELESCOPICandFOLDEDCASCODEROBERTW.BRODERSENLE
2、CTURE22EECS140ANALOGCIRCUITDESIGNMOREONOPAMPSTELESCOPICANDFOLDEDCASCODEVddMOA-1M3M4M9I121¤21¤I21¤2Telescopic-OPAMPM5VG6M6Circuit1(PoorBiasM1021¤21¤21¤Strategy)nOUTM7VG8M821¤M1121¤21¤VidVid------------n1-+22+-IREFM1M2RC101¤101¤n2+-VicM13M1241¤21¤–V–VddddROBERTW.BRODERSENLECT
3、URE22EECS140ANALOGCIRCUITDESIGNMOREONOPAMPSTELESCOPICANDFOLDEDCASCODECircuit1:MOA-2TelecopicOPAMPwith“BAD”Biasofcascode:Thecurrentsarebalancedsothatalltransistorshave,IDS=IREFexceptforM13whichhas,IDS13=2×IREFSince,I1==I2IREfthen,VGS3==VGS4VGS9(allW/L’sareequalalso)Thisalsoi
4、mpliesthat,VDS4=VDS3similarily,VDS5=VDS6Soiftheinputhas,Vid=0ROBERTW.BRODERSENLECTURE22EECS140ANALOGCIRCUITDESIGNMOREONOPAMPSTELESCOPICANDFOLDEDCASCODEthen,MOA-3VOUT=VDD–2×VTo–2×VDSAT==VG6(ifg0)ThegateofM8isalsoat,VDD–2×VTo–2×VDSATduetoitsconnectiontoM11,so,VOUT==VG6VG8Thes
5、winginthepositivedirectionwillbe,VOUT,MAX+=VG6+VTButsince,VOUT=VG6thismeanstheswingisonly1VTinthepositivedirection.Inthenegativedirection,VOUT,MIN--=VG8–VTbutsince,VOUT=VG8theswingisonlyVTagain.ROBERTW.BRODERSENLECTURE22EECS140ANALOGCIRCUITDESIGNMOREONOPAMPSTELESCOPICANDFOL
6、DEDCASCODEMOA-4Thusthetotalswingisonly2VT...nottoogood.Inthepositivedirectionwecoulduseahighswingconfigurationaswasdescribedforthecascodedcurrentsource.Onthelowsidewecanuseabettercircuit.Circuit2:Telescopicwithacascodebiasthatgivesabetterswinginthenegativedirection.Maximumv
7、oltageinthepositivedirectionisgivenbyM6goinglinearwhen,VOUT,MAX+>VDD–VGS3–VDSAT6NegativeswingislimitedbyM8goinglinear,VOUT,MIN--=VA–VT8SetVAsothatM1&M2areattheedgeofsaturationROBERTW.BRODERSENLECTURE22EECS140ANALOGCIRCUITDESIGNLECTURESONMOSDEVICEMODELSVdd=5VMOA-5M3M421¤21¤d
8、3d4Telescopic-OPAMPM5M621¤21¤Circuit2(BetterBias)d5IbnOUTIREFIREF--------------22d
