1.

Two identical NMOS transistors M1 and M2 are connected as shown below. The circuit is used as an amplifier with the input connected between G and S terminals and the output taken between D and S terminals. Vbias and VD are so adjusted that both transistors are in saturation. The transconductance of this combination is defined asΒ \({{\rm{g}}_{\rm{m}}} = \frac{{\partial {{\rm{i}}_{\rm{D}}}}}{{\partial {{\rm{V}}_{{\rm{GS}}}}_\;}}\) while the output resistance is \({{\rm{r}}_{\rm{o}}} = \frac{{\partial {{\rm{V}}_{{\rm{GS}}}}_\;}}{{\partial {{\rm{i}}_{\rm{D}}}}}{\rm{\;}}\), where iD is the current flowing into the drain of M2. Let gm1, gm2 be the transconductances and r01, r02 be the output resistances of transistors M1 and M2, respectively.Which of the following statements about estimates for gm and r0Β is correct?

A. π‘”π‘š β‰ˆ π‘”π‘š1Β π‘”π‘š2Β π‘Ÿ02 and π‘Ÿ0 β‰ˆ π‘Ÿ01 + π‘Ÿ02
B. π‘”π‘š β‰ˆ π‘”π‘š1Β + π‘”π‘š2 and π‘Ÿ0Β β‰ˆ π‘Ÿ01 + π‘Ÿ02
C. π‘”π‘š β‰ˆ π‘”π‘š1 and π‘Ÿ0Β β‰ˆ π‘Ÿ01. π‘”π‘š2. π‘Ÿ02
D. π‘”π‘š β‰ˆ π‘”π‘š1Β and π‘Ÿ0Β β‰ˆ π‘Ÿ02
AnswerΒ» D. π‘”π‘š β‰ˆ π‘”π‘š1Β and π‘Ÿ0Β β‰ˆ π‘Ÿ02


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