Lect_06 - ECE!442 Solid"State!Devices!&!Circuits...

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1 Jose E. Schutt " Aine " ECE 442 ECE 442 Solid " State Devices & Circuits 6. Bipolar Transistors Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu
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2 Jose E. Schutt " Aine " ECE 442 Bipolar Junction Transistor (BJT) – First Introduced in 1948 (Bell labs) – Consists of 2 pn junctions – Has three terminals: emitter, base, collector Bipolar Junction Transistor
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3 Jose E. Schutt " Aine " ECE 442 BJT – Modes of Operation Forward Forward Saturation Forward Reverse Rev. Active Reverse Forward Forw. Active Reverse Reverse Cutoff CBJ EBJ Mode
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4 Jose E. Schutt " Aine " ECE 442 BJT in Forward Active Mode (NPN)
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5 Jose E. Schutt " Aine " ECE 442 Electrons are minority carriers in the base (p-type) / (0) BE T VV p po n n e ! ( ) (0) pp n E n E n dn x n I A qD A qD dx W "# ! ! $ %& ’( i C is independent of v CB Collector current: Minority electrons will diffuse in the p-type base Operation: Current Flow / BE T vV C n S i I I e !! 2 E ni S A A qD n I NW ! A E : cross section area of BEJ W : Effective width of base N A : doping concentration base D n : electron diffusivity q : electron charge
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6 Jose E. Schutt " Aine " ECE 442 Operation: Current Flow / 2 1 BE T vV E p i B Dp A qD n e i NL ! D p : hole diffusivity in emitter L p : hole diffusion length in emitter N D : doping concentration of emitter Base current : Two components – Hole injection into emitter ! i B1 – Electron recombination in base ! i B2 2 n B b Q i ) !
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Lect_06 - ECE!442 Solid"State!Devices!&!Circuits...

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