4902C2009hw1

# 4902C2009hw1 - EE4902 C2009 HW Set 1 Due in class Friday...

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EE4902 C2009 HW Set 1 Due in class Friday January 23. To make life easier on the grader: Be sure your NAME and ECE MAILBOX NUMBER are prominently displayed on the upper right of what you hand in. When appropriate, indicate answers with a box or underline Work as neatly as possible You may assume T = 300K unless otherwise indicated. 1) [Capacitance of reverse biased PN junction] Given a step PN junction with the following characteristics at T=300K: Doping on P side: N A = 3.0 x 10 23 acceptor / m 3 Doping on N side: N D = 3.0 x 10 25 donor / m 3 Junction cross sectional area A J = 100 μm 2 = 1.0 x 10 -10 m 2 a) Sketch a cross sectional view of the junction at zero bias, showing the depletion region and overall charge density (similar to the plots we did in class). b) Find the built-in voltage V bi . (SPICE parameter VJ) c) Find the extent of the depletion region x p into the P side and x n into the N side at zero bias. Verify that the depletion region extends mostly into the lightly doped side. d) Find the small-signal junction capacitance per unit area for the zero bias condition (SPICE parameter CJ) e) For a step junction, the SPICE parameter for the junction capacitance exponent is MJ=0.5. Using the small signal junction capacitance equation C j ( total ) = A J CJ 1 + V R VJ " # \$ % MJ find the total junction capacitance at zero bias and at a reverse bias of V R = 5V.

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2) [Integrated circuit design] You are helping a colleague troubleshoot an integrated circuit design. The part of the design in question is the signal path in a low distortion audio integrated circuit, shown below. The diode represents the PN junction associated with a MOSFET further along in the signal path. Your colleague expresses the view that, since the PN junction is always reverse biased, there will be no current flowing in the resistor, no voltage drop across the resistor, and therefore V
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4902C2009hw1 - EE4902 C2009 HW Set 1 Due in class Friday...

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