121B_1_bjt

W w qdb nb 0 qvbe qv coth b exp 1 csch

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Unformatted text preview: JTs, WB LB and VBC < 0 VBE > 0 under nomal mode operation, expanding the hyperbolic functions using Taylor series, 3 1 WB - qDB N B 0 LB / qVBE -J E = 1 + exp - 1 LB 3 LB / kT WB qDE pE 0 qVBE - exp kT - 1 + J rec * WE 2 qDB nB 0 LB qV 1 WB 1- exp BE - 1 JC = kT LB WB 6 LB / DC pC 0 * +q - J rec LC Jason Woo 16 EE121B Spring 2010 From PN junctions' recombination currents under forward bias and the generation currents under reversed bias, we have: qVBE qni exp nkT W J rec rec DBE with 1 < n < 2 J * rec = - J gen - qni g W DBC with g n + p Jason Woo 17 EE121B Spring 2010 Current Gain Common emitter current gain: I C I B = Common base current gain I C 0 = I E 1 I B Since I B = - I C + I E = = -1 + I C 0 1 i.e., Jason Woo 0 = 1 - 0 18 EE121B Spring 2010 Now, using chain rule I C I nE I nC I C 0 = = I E I E I nE I nC We shall look at these terms one by one First I nE I nE = = I E I nE + I pE + I rec ( ) = 1+ I p ( - x E ) I n ( 0 ) 1 + I n ( 0 ) I rec Jason Woo 19 EE121B Spring 2010 Now I p ( - x E ) I n ( 0 ) DEWB N AB DBW E N DE Since typically WB<<LB and WE<<LE and I rec = I n ( 0 ) WDBEWB N AB exp DB ni rec - qVBE kT n - 1 n is sm...
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