1EE105 - Fall 2005Microelectronic Devices and CircuitsLecture 11MOS TransistorSmall-Signal ModelCurrent Sources2AnnouncementsHomework 5 due todayHomework 6 due next TuesdayLab 4 this weekReading: Chapter 4 (4.5-4.6), 8.3Midterm 1 in nine daysOctober 13, 6:30-8pm, Sibley23Lecture MaterialLast lectureMOS amplifier exampleMOSFET small-signal modelThis lectureFinish MOSFET small-signal modelMOS current sources15Voltage ReferencesFirst topic: voltage and current references (9.4)Generating a voltage: use a current source to set VGS316Modeling the Voltage SourceFind iOUTversus vOUTMOSFET is off or saturated: why?()REFDSnTnGSoxnREFSATDOUTIvVvLWCIii −+−⎟⎠⎞⎜⎝⎛=−= )1(22,λµ vOUT iOUT Typical operating point:iOUT= 0 A17Small-Signal Source ResistancettIOUTOUTSivdvdiROUT=⎟⎟⎠⎞⎜⎜⎝⎛=−=10Equivalent Circuit: RS+ - iOUT + - VSvOUT418Creating a Current Source19Equivalent Circuit for I-SourceFind the DC current for “gray circle” equivalent circuit()222TnREFoxnOUTVVLWCI −⎟⎠⎞⎜⎝⎛=µSubstitute for VREF520Small-Signal Resistance of I-Source21Current Sinks and SourcesSink: output current goesto groundSource: output current comesfrom voltage supply622Current MirrorsIdea: we only need one reference current to set up all the currentsources and sinks needed for a multistage
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