Question 6.23: Repeat the above example for a common-gate stage containing ...
Repeat the above example for a common-gate stage containing a gate resistance of R_G and a source resistance of R_S.
We draw the small-signal circuit as shown in Fig. 6.54. For the computation of zero-value time constants, the main input is set to zero. Thus, the resulting equivalent circuits are identical for C_S and C_G stages, yielding the same time constants and hence the same bandwidth. After all, the circuits in Figs. 6.53(a) and 6.54 are topologically identical and contain the same poles.
Does this result contradict our earlier assertion that the C_G stage is free from the Miller effect? No, it does not. In a C_G stage, we strive to avoid R_G, whereas in a C_S stage, R_G represents the preceding circuit’s output resistance and is inevitable.
