Question 7.6: A transistor of width W is laid out with one gate finger and...

With a width of W/4, each gate finger now has a distributed resistance of R_G/4 and hence a lumped-model resistance of R_G/12. Since the four fingers are in parallel, the net resistance is given by R_G/48, yielding a noise spectrum of

\overline{V_{n R G}^2}=4 k T \frac{R_G}{48}                     (7.31)

(In general, if the gate is decomposed into N parallel fingers, the distributed resistance falls by a factor of N².)