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Unformatted text preview: ECE3050 Homework Set 6 The f gures show a commonemitter ampli f er, a commoncollector ampli f er, and a commonbase ampli f er. For each circuit, it is given that R tb = 1k Ω , R te = 100 Ω , and R tc = 10k Ω . The transis tors have the values I E = 1 . 5mA , V T = 25mV , β = 99 , r x = 50 Ω , and r = ∞ . 1. For each transistor, show that g m = 59 . 4mS , r π = 1 . 667k Ω , α = 0 . 99 , and r e = 16 . 67 Ω . 2. For the commonemitter ampli f er of Figure (a): (a) Replace the BJT with the π model. Label the controlled source in the collector i c , the base current i c /β , and the emitter current i c /α . Let the voltage across r π be written v π = i c /g m . Write a loop equation around the baseemitter loop and solve for i c . Use the circuit to show that i c v tb = 1 R tb + r x β + 1 g m + R te α = 7 . 785mS v o v tb = − R tc R tb + r x β + 1 g m + R te α = − 77 . 85 Label the base current i b and the emitter current (1 + β ) i b . Write the loop equation and show that r in = v tb i b = R tb + r x + r π + (1 + β ) R te = 12 . 72k Ω Show that r out = R tc = 10k Ω (b) Replace the BJT with the T model. Label the controlled source in the collector i c , the base current i c /β , and the emitter current...
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This note was uploaded on 05/25/2011 for the course ECE 3050 taught by Professor Hollis during the Summer '08 term at Georgia Tech.
 Summer '08
 HOLLIS
 Amplifier, Transistor

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