lec18 - 6.012 - Microelectronic Devices and Circuits - Fall...

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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-1 Lecture 18 - The Bipolar Junction Transistor (II) Regimes of Operation November 10, 2005 Contents : 1. Regimes of operation. 2. Large-signal equivalent circuit model. 3. Output characteristics. Reading assignment: Howe and Sodini, Ch. 7, §§ 7.3, 7.4 Announcements: Quiz 2: 11/16, 7:30-9:30 PM, open book, must bring calculator; lectures #10-18.
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-2 Key questions What other regimes of operation are there for the BJT? What is unique about each regime? How do equivalent circuit models for the BJT look like?
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-3 1. Regimes of operation saturation reverse cut-off forward active V BC V BC V CE V BE V BE B C E + - + - + - forward active : device has good isolation and high gain; most useful regime; saturation : device has no isolation and is Fooded with minority carriers takes time to get out of satura- tion; avoid reverse : poor gain; not useful; cut-off : negligible current: nearly an open circuit; useful.
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-4 ± Forward-active regime : V BE > 0, V BC < 0 n-Emitter p-Base n-Collector I E <0 I B >0 I C >0 V BE > 0 V BC < 0 Minority carrier profles ( not to scale ): n pB p nE p nC n pBo p nEo p nCo 0 W B - X BE W B +X BC -W E -X BE W B +X BC +W C x emitter base collector
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 18-5 Emitter injects electrons into base, collector collects electrons from base: I C = I S exp qV BE kT Base injects holes into emitter, recombine at emitter contact: I B = I S
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lec18 - 6.012 - Microelectronic Devices and Circuits - Fall...

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