1EE105 - Fall 2005Microelectronic Devices and CircuitsLecture 28BJT Amplifiers2AnnouncementsHomework 12 due todayLab 9 reports due Thursday 3:30pm in the drop boxReading: Chapter 8 (8.2, 8.6, 8.7, 8.8.1, 8.9.1)23Lecture MaterialLast lectureBipolar junction transistorSmall-signal modelsThis lectureBJT amplifiers: common emitter, common collector, common base4Bipolar AmplifiersCommon-emitter amplifier: Biasing: adjustVBIAS= VBEsothat IC= ISUP.(Note: this could be tricky!)35Small-Signal Two-Port ModelParameters:Rin= Rout= Gm= 647Common-Base AmplifierTo find IBIAS, note that IBIAS= IE= - (1/αF)ICCommon-base currentgain Ai= - αF8CB Input ResistanceRin:59CB Output Resistancenotepolarityput rocback inafter finding vt/ itSame topology as CG amplifier, but with rπ|| RSrather than RSRout= 10Common-Base Two-Port ModelWhy is it a current amp?611Common-Collector AmplifierDC Bias:output is one“VBEdrop” downfrom input12Common-Collector Input Resistancenote thatβo= gmrπRin=713Common-Collector Output ResistanceDivider between vtand vπ14Common-Collector Voltage GainKCL at the output node: note vπ= vt- vout815Common-Collector Two-Port Model16Common-Collector SummaryTypo in Fig. 8.47 in text … Rincan’t depend upon RS!Input and output resistances depend on load and source resistances, respectivelySee Appendix to Chapter 8 for limits to using this model with very low values of RL917Summary of Two-Port Parameters for CE/CS, CB/CG, CC/CD18Common-Emitter with Emitter Degeneration1. What is it?2. DC Bias3. Small-signal 2-portmodel4. Output swing1019DC Bias for CEdeg20Two-Port Model for CEdegInput looks like CC Æ Rin=Output looks like CB (see p. 504 for details) Æ Rout= Transconductance: Gm=1121Two-Port Model for CEdeg(cont.)Find GmVoltage Gain: Is it a good voltage amplifier (vs.
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