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If g is the transconductance, r is the resistance due to channel length modulation and if M2 has channel length modulation but M1 and M3 doesn’t, what is the total resistance at the source of M2?(a) (1/ g || R) || (1/g || r)(b) (1/ g) || (1/g || r)(c) R || (1/g || r)(d) (1/ g || R) || 1/gThis question was addressed to me in semester exam.My doubt is from MOSFET Amplifier with CD Configuration topic in portion FET Amplifiers of Analog Circuits |
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Answer» CORRECT option is (a) (1/ g || R) || (1/g || r) To explain: The source of M2 is connected to the source of M1. Since channel length modulation isn’t present in M1, the source of M1 offers a RESISTANCE of 1/g. Again, we FIND the source of M2 offers a resistance of (1/g || r) due to channel length modulation. Therefore, we conclude that the total impedance at the source of M2 is (1/ g || R) || (1/g || r). |
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