Question about Razavi Example Fig. 3.23

[020170]

From "Design of Analog CMOS Integrated Circuits" by Razavi, I have a question about circuit analysis.

How do I transform from Fig. 3.23 (b) to Fig 3.23 (c) for circuit analysis?

I don't understand how M1's dependent source is changed to 1/(gm+gmb) resistor, especially one node is tied to ground.

Thanks.

 

[LvW]

I think, in Fig. 3.20 and Fig. 3.22 it is clearly shown how the effective equivalent resistance at the source node can be found (in case the drain-source resitance ro is considered separately).
In addition, you should realize that these figures do not show amplifying properties but how the device reacts upon changes at the drain node.