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Unformatted text preview: ECE3050 Homework Set 6 The f gures show a common-emitter ampli f er, a common-collector ampli f er, and a common-base ampli f er. For each circuit, it is given that R tb = 1k , R te = 100 , and R tc = 10k . The transis- tors have the values I E = 1 . 5mA , V T = 25mV , = 99 , r x = 50 , and r = . 1. For each transistor, show that g m = 59 . 4mS , r = 1 . 667k , = 0 . 99 , and r e = 16 . 67 . 2. For the common-emitter ampli f er of Figure (a): (a) Replace the BJT with the model. Label the controlled source in the collector i c , the base current i c / , and the emitter current i c / . Let the voltage across r be written v = i c /g m . Write a loop equation around the base-emitter loop and solve for i c . Use the circuit to show that i c v tb = 1 R tb + r x + 1 g m + R te = 7 . 785mS v o v tb = R tc R tb + r x + 1 g m + R te = 77 . 85 Label the base current i b and the emitter current (1 + ) i b . Write the loop equation and show that r in = v tb i b = R tb + r x + r + (1 + ) R te = 12 . 72k Show that r out = R tc = 10k (b) Replace the BJT with the T model. Label the controlled source in the collector i c , the base current i c / , and the emitter current...
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