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An amplifier is designed using fixed bias configuration, what is its input impedance (source Resistor is un bypassed)?(a) RD+rd(b) RG(c) RD || rd(d) 0This question was addressed to me by my school teacher while I was bunking the class.This intriguing question comes from The Common Source Amplifier topic in division Field-Effect Transistors of Electronic Devices & Circuits

Answer» CORRECT answer is (b) RG

Easy explanation: From the AC small signal model, the input IMPEDANCE of FET is open CIRCUIT.

Gate resistance RGis in parallel with open circuit resulting in Zin=∞||RG=RG.


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