hw05 - ECE 315 Homework 5 Due 11:15am Sept 28 2007 in the...

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Unformatted text preview: ECE 315 Homework 5 Due 11:15am, Sept. 28, 2007, in the drop box 1. (BJT large-signal and small-signal characteristics in realistic designs) For a 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) To evaluate the current at the BE junction (i.e., the emitter current I F0 ), what is the largest current component among electron/hole drift/diffusion in emitter/base (8 current components) and recombination in emitter/hole (two current components)? Briefly explain. (4 pts). (b) Find I F0 in the Ebers-Moll model (notice that this only needs to include the largest current component above. Please notice that this is a short-base diode case). (4 pts) (c) 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...
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