I am sorry, Stefan
My question is as shown below.
For example, when I calculate the POLE and ZERO of the common-gate amp as shown below. What is the resistor of note X to ground? in its small signal as shown below, Rs and 1/gm//1/gmb is in series, but both of them do not connect to ground, but in Razavi is book, the resistor of it to ground is RS//[1/(gm+gmb)], why? and also the question to note Y.
And should we short the output and input to ground when calculate?
common gate amp
![](http://images.elektroda.net/25_1208656575.jpg)
small signal model
![](http://images.elektroda.net/35_1208656658.jpg)
Thank you.
Best regards.