Lect_06-1 - ECE 442 ECE 442 SolidState Devices Circuits 6 Bipolar Transistors p Jose E Schutt-Aine Electrical Computer Engineering University of

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CE 442 ECE 442 Solid State Devices & Circuits 6. Bipolar Transistors Jose E. Schutt-Aine lectrical & Computer Engineering Electrical & Computer Engineering University of Illinois [email protected] ECE 442–Jose Schutt Aine 1
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Bipolar Junction Transistor Bipolar Junction Transistor (BJT) – First Introduced in 1948 (Bell labs) onsists of 2 pn junctions Consists of 2 pn junctions – Has three terminals: emitter, base, collector ECE 442–Jose Schutt Aine 2
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BJT – Modes of Operation Mode EBJ CBJ Cutoff Reverse Reverse Forw. Active Forward Reverse Rev. Active Reverse Forward aturation orward orward Saturation Forward Forward ECE 442–Jose Schutt Aine 3
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BJT in Forward Active Mode (NPN) ECE 442–Jose Schutt Aine 4
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lectrons are minority carriers in the base (p- pe) Operation: Current Flow Electrons are minority carriers in the base (p type) / (0) BE T VV pp o nn e Minority electrons will diffuse in the p-type base () ( 0 ) nE n E n dn x n IA q D A q D dx W     A E : cross section area of BEJ W : Effective width of base N A : doping concentration base Collector current: / BE T vV CnS iII e D n : electron diffusivity q : electron charge independent of B 2 E ni S A A qD n I NW ECE 442–Jose Schutt Aine 5 i C is independent of v CB
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Operation: Current Flow Base current : Two components – Hole injection into emitter i B1 – Electron recombination in base i B2 / 2 1 BE T vV Ep i B Dp AqDne i NL Base p n p (0) D p : hole diffusivity in emitter L p : hole diffusion length in emitter N D : doping concentration of emitter n p (ideal) 2 n B b Q i Q n : minority carrier charge in base effective b : minority carrier lifetime 2 1 ) E T V i AqWn A W base width From area under triangle ECE 442–Jose Schutt Aine 6 / (0) 22 BE Ei nE p A QA qn e N 
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BJT Operation: Current Gain 12 BB B ii i Total Base current : 2 / 1 BE T p vV A D NW W I e  is the common-emitter current gain order to achieve a high gain e need
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This note was uploaded on 05/05/2010 for the course ECE 329 taught by Professor Franke during the Spring '08 term at University of Illinois at Urbana–Champaign.

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Lect_06-1 - ECE 442 ECE 442 SolidState Devices Circuits 6 Bipolar Transistors p Jose E Schutt-Aine Electrical Computer Engineering University of

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