GATE EC 2015 Set 1 — Question 51
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Analog Circuits → Feedback & Oscillators → Barkhausen Criterion
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Question
The circuit shown in the figure has an ideal opamp. The oscillation frequency and the condition to sustain the oscillations, respectively, are
Correct answer
(D) (1)/(2CR) and R₁ = 4R₂
Solution
The feedback network consists of a series branch and a parallel branch .
The feedback factor is:For oscillations, the phase of must be zero. Substituting :Phase is zero when .
At this frequency, .
The gain of the non-inverting amplifier is .
By Barkhausen criterion, .
The feedback factor is:For oscillations, the phase of must be zero. Substituting :Phase is zero when .
At this frequency, .
The gain of the non-inverting amplifier is .
By Barkhausen criterion, .
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