24 - BJT non-ideal - EECS 320 Base-Width Modulation Early...

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EECS 320 Bipolar Junction Transistor Non-Ideal Characteristics J. Phillips EECS 320 R-G In Depletion Region For BJT in Common Emitter Configuration kT qV nr d i scr BE e x n q J 2 2 τ = Similar expression for BC depletion region, however insignificant for rev bias junction SCR Ep En E I I I I + + = Revise Emitter and Base Current Expressions ( ) ( ) Cp Cn SCR Ep En C E B I I I I I I I I + + + = = SCR in BE depletion region Significant in fwd bias, but significance decreases at large fwd bias
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J. Phillips EECS 320 Equilibrium Carrier Densities Base typically formed (in Si) using implant/diffusion fabrication processes Our assumptions of uniform doping not true Base current dependent on charge stored in base Impurity Conc. (cm -3 ) Emitter Base Collector τ B B Q I J. Phillips
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Unformatted text preview: EECS 320 Base-Width Modulation Early effect Base width changes with bias E C B In FA, significant change in collector current with bias Analogous to channel length modulation in FET Early voltage at y-intercept I C V BE V A V CE J. Phillips EECS 320 Base Pushout Kirk Effect At high injection, minority charge in base comparable to B-C space charge E C B B-C depletion region decreased Base width increased Opposite effect of Early effect J. Phillips EECS 320 Breakdown In BJT Punch-through Base fully depleted E C B Diode Reverse Breakdown F r Avalanche Tunneling E V E C E fp E fn-V B I V a...
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24 - BJT non-ideal - EECS 320 Base-Width Modulation Early...

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