EE105 Fall 2005 Microelectronic Devices and Circuits Lecture 28 BJT Amplifiers Announcements Homework 12 due today Lab 9 reports due Thursday 3 30pm in the drop box Reading Chapter 8 8 2 8 6 8 7 8 8 1 8 9 1 2 1 Lecture Material Last lecture Bipolar junction transistor Small signal models This lecture BJT amplifiers common emitter common collector common base 3 Bipolar Amplifiers Common emitter amplifier Biasing adjust VBIAS VBE so that IC ISUP Note this could be tricky 4 2 Small Signal Two Port Model Parameters Rin Rout Gm 5 6 3 Common Base Amplifier To find IBIAS note that IBIAS IE 1 F IC Common base current gain Ai F 7 CB Input Resistance Rin 8 4 CB Output Resistance put roc back in after finding vt it note polarity Same topology as CG amplifier but with r RS rather than RS Rout 9 Common Base Two Port Model Why is it a current amp 10 5 Common Collector Amplifier DC Bias output is one VBE drop down from input 11 Common Collector Input Resistance note that o gmr Rin 12 6 Common Collector Output Resistance Divider between vt and v 13 Common Collector Voltage Gain KCL at the output node note v vt vout 14 7 Common Collector Two Port Model 15 Common Collector Summary Typo in Fig 8 47 in text Rin can t depend upon RS Input and output resistances depend on load and source resistances respectively See Appendix to Chapter 8 for limits to using this model with very low values of RL 16 8 Summary of Two Port Parameters for CE CS CB CG CC CD 17 Common Emitter with Emitter Degeneration 1 What is it 2 DC Bias 3 Small signal 2 port model 4 Output swing 18 9 DC Bias for CEdeg 19 Two Port Model for CEdeg Input looks like CC Rin Output looks like CB see p 504 for details Rout Transconductance Gm 20 10 Two Port Model for CEdeg cont Find Gm Voltage Gain Is it a good voltage amplifier vs CE 21 11
View Full Document
Unlocking...