Chapter 7
Q. 7.6
A transistor of width W is laid out with one gate finger and exhibits a total gate resistance of R_G [Fig. 7.23(a)]. Now, we reconfigure the device into four equal gate fingers [Fig. 7.23(b)]. Determine the total gate resistance thermal noise spectrum of the new structure.

Step-by-Step
Verified Solution
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.)