# hw05 - ECE 3150 Homework 5 Due 1(BJT large-signal and...

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ECE 3150 Homework 5 Due 2/27/2009 1. (BJT large-signal and small-signal characteristics one more time) For an npn transistor in the forward active mode with emitter area A E =100 μ m 2 , N E = 10 20 cm -3 , N B = 10 17 cm -3 , N C =10 15 cm -3 , the base width W B =0.5 μ m, the emitter width W E =0.1 μ m, V bi =0.96V for the BE junction, the electron mobility μ n =1000cm 2 /Vs, the hole mobility μ p =400cm 2 /Vs, and the minority lifetime τ n = τ p =10 -7 s, (a) Find I F0 in the Ebers-Moll model. Please notice that this is a short-base diode case). (4 pts) (b) The base current contains two components: the recombination current and the hole back injection into emitter. If we assume that back injection dominates and both emitter and base are “short-based”, the current gain β can be estimated by (D nB N E W E )/(D pE N B W B ). Calculate β and α F (4 pts). (c) If we ignore the Early effect now (i.e., current mostly independent of the reverse-biased V CB ), for a bias condition of V BE =0.7V and V CE =3.0V, verify that this is in the forward active mode

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