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03_exam2fall

# 03_exam2fall - Page 1 of 9 YOUR NAME Department of...

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Page 1 of 9 YOUR NAME________________________________ Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 6.012 Electronic Devices and Circuits Exam No. 2 Notes: 1. Unless otherwise indicated, assume room temperature and that kT/q is 0.025 V. You may also approximate [(kT/q) ln 10] as 0.06 V. 2. Closed book; one sheet (2 pages) of notes permitted (to be handed in with exam). 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 you do make. 5. Be careful to include the correct units with your answers when appropriate. 6. Be certain that you have all nine (9) pages of this exam booklet and the formula sheet, and make certain that you write your name at the top of this page in the space provided. 6.012 Staff Use Only PROBLEM 1 (out of a possible 35) PROBLEM 2 (out of a possible 35) PROBLEM 3 (out of a possible 30) TOTAL

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Page 2 of 9 Problem 1 (35 points) You are given a packaged npn silicon bipolar junction transistor (BJT) and are told that it is a well-designed, high performance device with w E = 2w B and w C = 10w B , long minority carrier diffusion lengths, and N DE >> N AB >> N DC . You are told which lead is the base, but you are not told which is the emitter lead and which is the collector lead. This problem concerns a number of possible measurements you might do to distinguish between the emitter lead and the collector lead. (a) [4 pts] Which BJT junction, emitter-base or collector base, if any, has the smallest reverse-bias breakdown voltage and why? o Emitter-base junction o Collector-base junction o No difference because (b) [4 pts] Which BJT junction, if any, has the largest zero-bias depletion capacitance and why? Assume comparable junction areas. o Emitter-base junction o Collector-base junction o No difference because (c) (i) [4 pts] At which BJT junction, if any, is there more reduction of the effective base width (i.e. base width modulation) when the junction isreverse biased, and why? o Emitter-base junction o Collector-base junction o No difference because Problem 1 continues on the next page
Page 3 of 9 Problem 1 continued (ii) [3 pts] If the junction you identified Part (c) (i) is used as the collector-base junction, would one find an Early voltage that is larger or smaller in magnitude

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03_exam2fall - Page 1 of 9 YOUR NAME Department of...

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