Hi All,
I read Razavi book and got stuck at the below figure
I do not know how Figure3.23(b) be simplified to Figure3.23(c).
Thing that bother me is that why 1/(gm+gmb) connected to ground (vss) while ro is connected to delta V.
For existing configuration, I think 1/(gm+gmb) // ro so, the other ends of both resistors 1/(gm+gmb) and ro
have to be connected to the same potential.
Thank you very much for your explanation.
Regards,
Tomph
Hi In2Dusk,
Thanks for the reply. I still did not get why 1/gm+gmb connected to VSS and ro connected to delta V in the figure 3.23(c) ( previous post).
In the book "Design of Analog Of CMOS Integrated Circuits", page 65, Prof. Razavi mentioned he derived the figure 3.23(c) from the below
However, according to this figure , when looking from the source of transistor M1, 1/gm+gmb and ro are connected to the same potentials.
Please help me on this .
The mosfet you have there has its substrate(bulk) connected to ground (as shown in the picture in your 2nd post)
and not to the source as is usual, so 1/(gm+gmb) is resistance of the subsrate.
Pages 15-18 of this document shows equations and small signal model of mosfet with its substrate not connected to its source:
**broken link removed**