1EE105 - Fall 2005Microelectronic Devices and CircuitsLecture 12MOS Current SourcesTwo-port Models2AnnouncementsHomework 6 due next TuesdayLab 4 this weekReading: Chapters 9.4, 8 (MOS only)Midterm 1 next weekOctober 13, 6:30-8pm, SibleyReview session on TuesdayOctober 11, 6:30-8pm, 277 Cory23Lecture MaterialLast lectureMOSFET small-signal modelThis lectureMOS current sourcesGeneralized two-port models4Voltage ReferencesFirst topic: voltage and current references (9.4)Generating a voltage: use a current source to set VGS35Modeling the Voltage SourceFind iOUTversus vOUTMOSFET is off or saturated: why?()REFDSnTnGSoxnREFSATDOUTIvVvLWCIii −+−⎟⎠⎞⎜⎝⎛=−= )1(22,λµ vOUT iOUT Typical operating point:iOUT= 0 A6Small-Signal Source ResistancettIOUTOUTSivdvdiROUT=⎟⎟⎠⎞⎜⎜⎝⎛=−=10Equivalent Circuit: RS+ - iOUT + - VSvOUT47Creating a Current Source859Equivalent Circuit for I-SourceFind the DC current for “gray circle” equivalent circuit()222TnREFoxnOUTVVLWCI −⎟⎠⎞⎜⎝⎛=µSubstitute for VREF10Small-Signal Resistance of I-Source611Current Sinks and SourcesSink: output current goesto groundSource: output current comesfrom voltage supply12Current MirrorsIdea: we only need one reference current to set up all the currentsources and sinks needed for a multistage amplifier.71314Application of Current Mirrors:Digital-to-Analog ConverterRREFMREFVDDRLvOUTD0D1D2D4Digital input: word D0D1D2D3 Æ voltages are either VDDor 0 V.Transistors M0, M1, M2, M3 have binary-weighted (W/L) ratiosM0M1M2M3iDoiD1iD2iD381516ExampleInput word D0D1D2D3 = 0101IREF= 100 µA (W/L)REF= (W/L)0(W/L)1= 2(W/L)0(W/L)2= 2(W/L)1(W/L)3= 2(W/L)2Output voltage is vOUT= VDD– RL(iD0+ iD2)= VDD– RL(IREF+ 4 IREF)Sources of error: fab imprecision, channel-lengthmodulation, …917Generalized AmplifiersvSBIASsvV v=+ovBIASVDDVSSVBIASIsiSRDDILDDDiI i=−()Dinifv=LRinvActive Device18Amplifier TerminologySources: Signal, its source resistance, and bias voltage or currentLoad: Use resistor/current source or in Chap. 8, but could be a general impedancePort: A pair of terminals across which a voltage andan associated current are definedSource, Load: “one port”Amplifier: “two port”1019One-Port Models (EECS 40)A terminal pair across which a voltage and associated current are
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