# U of U ECE 2280 - Homework 8 (2 pages)

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## Homework 8

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## Homework 8

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Pages:
2
School:
University of Utah
Course:
Ece 2280 - Fundamentals of Engineering Electronics
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ECE2280 Homework 8 Spring 2007 1 Assume the transistors at the right have a finite and an infinite Early voltage Write an expression for the input resistance Rin in the circuit shown below Your expression should include only real resistances R1 R2 R3 R4 or a subset of these and possibly re1 or r 1 and re2 or r 2 Assume all transistors have the same Circle your answer VCC R2 VCC VCC vO R1 Q2 Q1 2 The transistors below are identical use VBE 0 7 100 gm 80m A V r 1250 C1 C2 100 F a Find the complete frequency response for Vo Vsig ignore ro and the parasitic capacitors b Find the low frequency pole values RSig 100 Vsig Rin R3 R4 VCC Vo C2 C1 3 Use the following circuit for both problems 3 and 4 100 VBE 0 7 Find VE1 VC1 VC2 VE2 VE3 VC3 IE1 IE2 and IE3 4 Analyze the circuit to find the midband gain Vo Vsig Rin ignore input source Vsig and Rout ignore RL 1k 10V 4 7k 2k 5 1k C2 Vout Q2 Q1 1n Q3 Rout RL 1k C1 Vsig Rin 1n 3k 4 7k 1 3k 10V 1 5 The input and output curves vs time are are shown below Explain in detail why this circuit is not amplifying the signal and is instead 0V VCE SAT 0 2V VBE 0 7V and 100 1mV 1 0mV 0 5mV 0 5mV 0V 0V 0 5mV R2 1k 0 5mV V4 10V C3 1 0mV 1mV 0s V R4 2 0 5ms V C5 1 1 0ms 1 5ms 2 0ms 2 5ms 3 0ms Time 3 5ms C5 Time V9 R5 10m VOFF 0 VAMPL 1m FREQ 1k 4 0ms 1k V8 V 4V Q1 100m 5k R4V Q2N3904 6 can range from 40 to 200 For the two extreme values of 40 and 200 find IE VE VB Rin ignore the source resistance 10k and the midband voltage gain Vout Vsig 9V C1 Vsig 100k Q1 10k C2 Rin 1k Vout 1k 2

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