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Unformatted text preview: 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 381 Lecture 38 Bipolar Junction Transistor (cont.) May 9, 2007 Contents: 1. Nonideal effects in BJT in FAR Reading material: del Alamo, Ch. 11, 11.5 ( 11.5.1, 11.5.3, 11.5.4, 11.5.5 but only qualitatively) Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 382 Key questions Why are the output characteristics of a BJT in FAR not perfectly at? What is the maximum voltage that the collector of a BJT can sustain in FAR? What are the key design issues for the break down voltage? Why does the performance of a BJT degrade at high collector current? How does one model the base resistance in a BJT? Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 383 1. Nonideal effects in BJT Basewidth modulation V BE and V BC affect x BE and x BC , respectively W B = f ( V BE , V BC ). log N log N N E N E N B N C x BE x BC x thermal equilibrium (V BE =V BC =0) forward active (V BE >0, V BC <0) N B N C x BE x BC Early effect : impact of V BC on W B  V BC  x BC W B I C , I B unchanged Reverse Early effect : impact of V BE on W B V BE x BE W B smaller I C than ideal F , I B unchanged x Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 384 Early effect : impact of V BC on W B I C = f ( V BC ) n W B (V BC ) n B (0) n B (x) I C n B (W B )=0 n i 2 N B x V BC more negative W B ( V BC ) I C ( V BC ) To capture firstorder impact, linearize W B ( V BC ): V BC W B ( V BC ) W B ( V BC = 0)(1 + ) V A V A is Early voltage : qN B W Bo V A = C jco Impact on I C : I C ( V BC = 0) V BC I C ( V BC ) I C ( V BC = 0)(1 ) 1 + V BC V A V A Also, since I B unchanged: F ( V BC = 0) V BC F ( V BC ) = F ( V BC = 0)(1 ) 1 + V BC V A V A Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J Integrated Microelectronic Devices Spring 2007 Lecture 385 Manifestation of Early effect in output characteristics: V CEV A I C I B I B =0 0 Main consequence of Early effect: finite slope in output characteris tics in FAR: output conductance.conductance....
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This note was uploaded on 09/24/2010 for the course EECS 6.720J taught by Professor Jesúsdelalamo during the Spring '07 term at MIT.
 Spring '07
 JesúsdelAlamo
 Transistor

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