ECE 3040 Microelectronic Circuits Quiz 2 - Thévenin Equivalents and Diode Characteristics, Quizzes of Electrical and Electronics Engineering

Download ECE 3040 Microelectronic Circuits Quiz 2 - Thévenin Equivalents and Diode Characteristics and more Quizzes Electrical and Electronics Engineering in PDF only on Docsity! ECE 3040 Microelectronic Circuits Quiz 2 May 26, 2004 Professor Leach Name Instructions. Print your name in the space above. The quiz is closed-book and closed-notes. Honor Code Statement: I have neither given nor received help on this quiz. Initials 1. It is given that V1 = 30V, R1 = 1.5kΩ, R2 = 3kΩ, and R3 = 1kΩ. (An alternate version of the problem had V1 = 15V, R1 = 3kΩ, R2 = 1.5 kΩ, and R3 = 1kΩ. (a) Solve for the Thévenin voltage VS and Thévenin resistance RS seen by the diode. VS = V1 R1 R1 +R2 = 10V RS = R1kR2 +R3 = 2kΩ (b) Draw the load line for the diode on the characteristics given and estimate the diode voltage and current at the Q point. 2. (a) A diode is biased at a constant current. If the temperature changes in constant increments ∆T , describe the mathematical variation of the diode voltage. Answer: It changes by an additive amount, i.e. you add or subtract something each time the temperature increases by ∆T . (b) If the temperature of a diode changes in constant increments ∆T , describe the mathematical variation of the saturation current of the diode. Answer: It changes by a multiplicitave factor, i.e. you multiply by something each time the temperature increases by ∆T . (c) Represent the total voltage across a diode by vD = VD+vd and the total current through the diode by iD = ID+ id, where VD and ID are the Q-point values and vd and id are small-signal changes about the Q point. In deriving the small-signal model of the diode, what is the basic mathematical step that is used to relate id to vd? Answer: You solve for the slope or derivative of the iD versus vD curve at the Q point and set this equal to the ratio id/vd. Although not part of the answer, this slope is the reciprical of the small-signal resistance rd. 1