4.3 - 4.3 BJT Non Idealities 4.3.1 Base Width Modulation...

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ECE3080, Chapter 4.3 1 June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 1 of 19 4.3 BJT Non Idealities 4.3.1 Base Width Modulation 4.3.2 Breakdown 4.3.3 Geometrical Effects 4.3.4 Graded Base Pierret, Chapter 11, page 407-426 June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 2 of 19 Common-Base: Ideal vs. Real Base Width Modulation Breakdown Pierret, Fig. 11.4
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ECE3080, Chapter 4.3 2 June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 3 of 19 Common-Emitter: Ideal vs. Real Base Width Modulation Breakdown Pierret, Fig. 11.5 June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 4 of 19 Real BJT Characteristics Common-Base Configuration Common-Emitter Configuration Sze, Fig. 5.10 Sze, Fig. 5.8
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3 June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 5 of 19 4.3.1 Base Width Modulation Assumption in ideal BJT: W is independent of applied voltages Reality: W increases/decreases with applied E-B and B-C voltages because of changes in the depletion layer widths Base-width modulation or Early effect (named after J. Early, who first recognized the effect) June 21, 2005 ECE 3080: Chapter 4.3 – BJT O. Brand, 6 of 19 Base Width Modulation Common-Base Configuration • Emitter current for (i) W << L B and (ii) –V CB > few kT: • W decreases with increasing reverse bias –V CB of the B-C junction; thus, at a given V EB , I E increases with increasing reverse bias –V CB I E = qA D B W p B0 ! " # $ % e qV EB /kT = I Ep ! " ### $ ### + qA D E L E n E0 ! " # $ % e qV EB /kT 1 ( ) = I En << I Ep ! " #### $ #### ( qA D B W p B0 ! " # $ % e
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This note was uploaded on 08/28/2010 for the course ECE 3080 taught by Professor Staff during the Spring '08 term at Georgia Tech.

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4.3 - 4.3 BJT Non Idealities 4.3.1 Base Width Modulation...

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