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98_finalexamfall

# 98_finalexamfall - YOUR NAME Department of Electrical...

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YOUR NAME________________________ Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 6.012 Electronic Devices and Circuits FINAL EXAMINATION Open book. Notes: 1. Unless otherwise indicated, assume room temperature and that kT/q is 0.025 V, kT/q ln 10 = 60 mV, and n i = 10 10 cm -3 for Si. 2. This test is designed to that most parts can be worked independently of the others. 3. All of your answers and any relevant work must appear on these pages. Any additional paper you hand in will not be graded. 4. Make reasonable approximations and assumptions. State and justify any such assumptions and approximations. 5. Be certain that you have all thirteen (13) lucky pages of this exam booklet and make certain that you write your name at the top of this page in the space provided. 6. For staff use only Problem 1 Problem 2 Problem 3 Problem 4 Problem 5 TOTAL You may see your final exam beginning January 4, 1999.

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Page 2 of 13 Problem 1 (20 pts total) Parts (a) thru (f) of this problem concern two npn silicon bipolar junction transistors, A and B. All of the dimensions of these two devices, and the magnitudes of all of the doping levels in these two devices are identical, except that the base width, w B , of Transistor A is twice that of Transistor B. (a) Which transistor, if either, has the larger dc current gain, b F ? Explain your answer and estimate the ratio of the two b F 's. o Transistor A o Transistor B o neither, because Ratio, b F,A / b F,B = (b) Which transistor, if either, has the larger emitter-base junction saturation current, I ES ? Explain your answer and estimate the ratio of the two I ES 's. o Transistor A o Transistor B o neither, because Ratio, I ES,A /I ES,B = (c) With the base-collector junctions of both transistors reverse biased with the same values of base-collector junction voltage, V BC , which transistor, if either, has the largest small-signal base-collector junction capacitance, C µ ? Explain your answer and estimate the ratio of the two C µ 's. o Transistor A o Transistor B o neither, because Ratio, C µ,A /C µ,B = (d) With both transistors biased at the same quiescent current level, I C , which transistor, if either, has the largest small-signal transconductance, g m ? Explain your answer and estimate the ratio of the two g m 's. o Transistor A o Transistor B o neither, because Ratio, g m,A /g m,B = Problem 1 continues on the next page
Page 3 of 13 Problem 1 continued (e) Which transistor, if either, has a larger unity short-circuit current gain frequency, w T , at large collector current bias levels? Explain you answer and estimate the ratio of the two w T 's. o Transistor A o Transistor B o neither, because Ratio, w T,A / w T,B = (f) Which transistor, if either, has a larger Early voltage, V A ? Explain your answer. o Transistor A o Transistor B o neither, because Parts (g) thru (j) deal with an n-channel silicon MOSFET and a p-channel silicon MOSFET which are identical in all dimensions and doping level magnitudes except that the gate length, L, of one of the devices is twice that of the other. The K-factors

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98_finalexamfall - YOUR NAME Department of Electrical...

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