Lecture26-BJT-smallsignal-2up.pdf

Lecture26-BJT-smallsignal-2up.pdf - EE105 Fall 2005...

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1 EE105 - Fall 2005 Microelectronic Devices and Circuits Lecture 26 Bipolar Junction Transistor Large and Small Signal Models 2 Announcements Homework 11 due today Homework 12 (the last one!) due next Tuesday Lab 9 (the last one!) this week Reading: Chapter 7 (7.1-3.)
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2 3 Lecture Material Last lecture Finished cascode amplifier Bipolar junction transistor This lecture Bipolar junction transistor Large and small-signal models 22 Small-Signal Models Analogy from MOSFET s.s. model: ( ) BS DS GS D v v v f i , , = ( ) CE BE C v v f i , =
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3 23 Transconductance g m The transconductance is analogous to diode conductance 24 Transconductance (cont) Forward-active large-signal current: / (1 ) BE th v V C S CE A i I e v V = + Differentiating and evaluating at Q = ( V BE, V CE ) / (1 ) BE qV kT C S CE A BE Q di q I e V V dv kT = + C C m BE Q di qI g dv kT = =
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4 25 Comparison with MOSFET Typical bias point: drain/coll. current = 100 μ A; Select ( W/L ) = 8/1, μ n C ox = 100 μ A/V 2 BJT: MOSFET: 100 μ 4mS 25m C m th I g V = = = 2 D m GS T I g V V = C C m th qI I g kT V = = 2 2 2 100 μ 8 100 μ 400 μ D m ox D GS T I W g C I S V V L μ = = = × × × = 26 BJT Base Currents Unlike MOSFET, there is a DC current into the base terminal of a bipolar transistor:
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  • Spring '12
  • cengizbeşikçi
  • Transistor, Bipolar junction transistor, Early effect

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