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What is the input impedance of the following circuit, if channel length modulation is present?(a) gm || 1/ro(b) gm * ro(c) gm || 2/ro(d) gmI got this question in an interview for internship.Origin of the question is MOSFET Amplifier with CG Configuration in chapter FET Amplifiers of Analog Circuits

Answer»

Right answer is (a) gm || 1/ro

To explain: The input impedance can be found by performing a small SIGNAL ANALYSIS at the input NODE i.e. source of the MOSFET. Due to channel length modulation, the effect of ro would make the input impedance gm || 1/ro.



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