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mid - Dalhousie University Department of Electrical and...

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1 Dalhousie University, Department of Electrical and computer Engineering ECED3201: Introduction to Electronics Fall 2007- Midterm Exam Dr. Kamal El-Sankary Guidelines Only double-sided one letter size formula sheet is allowed . Show all your work and reasoning on the exam in order to receive full or partial credit. • Exam Time: 150 minutes Problem 1 - [3 points]: Consider V DD =2.5, v (t)=0.01sin t (V), and R=2k in the circuit shown in Fig. 1 Assume that the diode has a 0.7V drop across when the ac signal v(t) is reduced to 0. R V DD v ( t ) v D ( t ) i D ( t ) + - + - + - Fig.1 a. [0.75 pt] Find the dc current, I D , in the diode. b. [0.75 pt] Find the small-signal resistance (ac resistance) of the diode (consider n=2). Assume the diode is at room temperature (V T 25mV). c. [1.5 pt] Write mathematical expressions for the total instantaneous current i D (t) and total instantaneous voltage v D (t). Problem 2 - [5 points]: Consider the circuit shown in Fig.2. R 1 = 10k V 1 = 2V v I + - + - V 2 = 4V R 2 = 10k + + _ _ v O D 1 D 2 Fig.2
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