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What is the total output impedance at node x?(a) R1 || ro1 || 2 * ro2 || ro2 || 2*ro4… || ron(b) R1 || 2 * ( ro1 || ro2 … || ron)(c) R1 || ro1 || ro2 … || ron(d) R1 + (ro1 || ro2 … || ron)This question was posed to me in quiz.My question is based upon MOSFET Amplifier with CG Configuration topic in portion FET Amplifiers of Analog Circuits |
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Answer» RIGHT answer is (c) R1 || ro1 || ro2 … || ron The best EXPLANATION: We note that all the MOSFET’s are in parallel. The output impedance of the i^th MOSFET is given by ROI. Hence, the total impedance at node X is simply R1 || ro1 || ro2…|| ron. Note that R1 is parallel to each MOSFET. This is because, while dining the output impedance, we SET Vin and Vcc to zero. Note that R1 is connected from node X to ground, all the MOSFET’s are connected form node x to ground. |
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