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What is the value of resultant gm if two non identical FETs are connected in parallel?(a) (µ1 rd1 + µ2 rd2)/ (rd1+rd2)(b) (µ1 rd2 + µ2 rd1)/ (rd1+rd2)(c) 0(d) µ1 rd1+ µ2 rd2I got this question during an interview.The doubt is from The JFET Volt-Ampere Characteristics in division Field-Effect Transistors of Electronic Devices & Circuits

Answer»

The correct answer is (b) (µ1 rd2 + µ2 rd1)/ (rd1+rd2)

The best explanation: we know that µ=GM RD

But gm’=gm1+gm2

And rd’=rd1 ×rd2/rd1+ rd2

From the above TWO equations, gm’=(µ1 rd2 + µ2 rd1)/ (rd1+rd2).



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