# q13 - If the resistor increases in value, it should be...

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ECE 3050 Analog Electronics Quiz 13 April 15, 2009 Professor Leach Name Instructions. No calculators are allowed on this quiz. Print your name in the space above. Honor Code: I have neither given nor received help on this quiz. Initials 1o f2 . The f gure shows a Wien Bridge oscillator that puts out a sine wave signal with no input signal. (a) In words, how would you go about solving for the frequency at which this circuit would oscillate? Answer: Break the loop between V o and C 2 , solve for the frequency at which the phase of the loop-gain transfer function is zero degrees, choose R 3 and R F so that the loop gain is unity. (b) One of the resistors in the circuit is to be varied electronically to maintain a constant amplitude sine wave at the op-amp output. If the value of the resistor increases as the amplitude of the output sine wave increases, which resistor would you vary? Explain your choice. If v O ( t
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Unformatted text preview: If the resistor increases in value, it should be where R 3 is in the circuit. 2 of 2. The block diagram of an oscillator which uses an inverting ampli f er with a gain K is shown. The feedback network has the transfer function H ( s ) = 1 (1 + s/ ) 3 (a) Solve for the frequency at which the phase of the loop-gain transfer function KH ( s ) is (or any multiple of 360 ). Answer: The phase of H ( j ) must be 180 . This occurs when tan 1 = 60 = = tan (60 ) = 3 (b) If the circuit is to oscillate at the frequency found in part (a), what must be the value of K ? At the oscillation frequency, K | H ( j/ ) | = K 1 + j 3 3 = 1 or K = 1 + j 3 3 = 8 . 1...
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## This note was uploaded on 05/26/2011 for the course ECE 3050 taught by Professor Hollis during the Summer '08 term at Georgia Institute of Technology.

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