GATE EC 2020 Set 1 — Question 51
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Analog Circuits → Op-Amp Circuits → Active Filters (Sallen-Key)
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Question
The components in the circuit given below are ideal. If and , the cut-off frequency of the circuit in Hz is
Correct answer
(D) 79.58
Solution
The inverting input of the ideal op-amp is a virtual ground, and the node joining the input resistor , the capacitor and the resistor is exactly that inverting-input node.
1.Because this node sits at , the and branches have zero voltage across them and carry no current. They do not affect the transfer function.
2.The input current is , and all of it flows through the feedback network .
3.So
This is a first-order low-pass response with DC gain magnitude 1.4.The frequency is
The other values (14.92, 34.46 and 59.68 Hz) come from wrongly including the grounded and branches.Answer: (D) 79.58Continue learning with Success Tracker
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