W05 ex3 soln - EECS 314 Winter 2005 Exam 3 Solutions The...

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EECS 314 // Winter 2005 // Exam 3 // Solutions Alexander Ganago Page 1 of 25 April 6 – 19, 2005 The Key A B C D E 6 2 1 3 8 7 4 10 5 9 11 13 13 17 16 12 18 20 19 15 14 See the comment along with solution of problem 13
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EECS 314 // Winter 2005 // Exam 3 // Solutions Alexander Ganago Page 2 of 25 April 6 – 19, 2005 Section One: 2-point questions 1 This BJT circuit is used as a logic gate. If the input and output voltages in this circuit are interpreted using positive logic, then voltages + 5 V correspond to binary “1” and voltages 0 V correspond to binary “0” Assume that positive logic is used and determine the type of this logic gate: A. AND B. OR C. NAND D. NOR E. None of the above. = = = = Each BJT acts as an open circuit if the voltage applied to its base is 0 V Each BJT acts as a short circuit if the voltage applied to its base is 5 V The two BJTs are connected in series thus, in order for the current to flow from the 5 V terminal to the ground, both should act as short circuit. It means that the current flows to the ground only if both A and B are 5 V If any of A and B is 0 V then the current does not flow to the ground. If the current flows to the ground, then the output voltage is 0 V If the current does not flow to the ground, then the output voltage is 5 V In terms of positive logic, the truth table is: A B Output 0 0 1 1 0 1 0 1 1 1 1 0 This is a NAND gate. Answer: C.
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EECS 314 // Winter 2005 // Exam 3 // Solutions Alexander Ganago Page 3 of 25 April 6 – 19, 2005 2 (Contributed by Philip Choi) This circuit is given the following input: Which output plot is most appropriate? A. B. CORRECT C. D. E. None of the above Answer: The circuit is an integrator, so B is the only appropriate graph.
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EECS 314 // Winter 2005 // Exam 3 // Solutions Alexander Ganago Page 4 of 25 April 6 – 19, 2005 3 (Contributed by Philip Choi) The circuit is given 5Vsin " t ( ) input. The diode has a turn-on voltage of V DO = 0.7V . The output V out has period " . For what percentage of " is V out non-zero? A. 36.5% B. 39.5% C. 42.5% D. 45.5% CORRECT E. 48.5% Answer: V out is non-zero when 5Vsin t ( ) > 0.7V . This is 2 " 2 # sin # 1 0.7 5 $ % & ( ) $ % & ( ) 2 " * 0.455
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EECS 314 // Winter 2005 // Exam 3 // Solutions Alexander Ganago Page 5 of 25 April 6 – 19, 2005 4 Consider the Schmitt trigger circuit shown on the diagram. The Op Amp saturates at –12 V and at +12 V. The input voltage varies from -12 V to +12 at the rate of 2 V per second, as shown on the sketch below. Which of the following waveforms correctly represents the output voltage? (On each sketch, the dashed line shows the input voltage): = = = Solution From the analytic solution given in HW 09 problem 2 assignment, the output voltage initially equals +12 V and stays at +12 V until the input exceeds +10 V (at 11sec). At the moment when the input voltage equals +10 V (at 11sec), the output immediately jumps to –12 V and stays at –12 V until the input decreases below –8 V (at 22 sec). This corresponds to waveform B shown below.
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