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Unformatted text preview: Tufts University, ECE Dept.
Mar 03, 2008 BE 12: Homework # 6, Spring 2008 Due: Mar 10, 2008 1. A two-port model of an unilateral ampliﬁer is shown in Figure—1. Assume Zi = 1/69, Z, =
1M 9 and Gm = 1mA/ V. Let Rs and RL represent the source resistance of the input
source and load resistance, respectively. (a) Find the gain 120/1)S assuming ideal source and unloaded output (ie. R5 = 0 and
RL = 00) (b) Find the gain vo/vs for R3 = 1/69 and RL = 1M9. Figure—A '_ * __, _. _ _ _’ 3. A Wien—Bridge oscillator is shown in Figure-3. Find:
(a) The Loop gain (L(s), L(jw)). (b) The condition for oscillation ie.(i) the frequency at which the phase of the Loop is
zero and (ii) the required ratio R2 / R1. EB 12: Homework # 6 Page 2 of 2 4. Draw the small—signal model for the circuits shown in Figure-4(a) and 4(b). Using
Mason’s Gain Formula, ﬁnd the following transfer functions: (a) Voltage gain (yo/vi).
(b) Input Impedance (m- /z,) (0) Output Impedance (vo/io). (Write all your expressions in terms of the given variables and assume standard small~
signal variables for the NPNs (ie. rmﬁmo). Also assume Cl and 02 to short for the
frequency of interest. ) Figure- A} ‘ ...
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- Spring '08