Lecture 22: Lookup table based systematic design of analog circuits (gm/Id based design)

In this lecture, the technique of sizing transistors using pre-computed lookup tables saving width-independent parameters like gm/Id, Id/W, fT, gm/W, gm/gds, etc., is discussed in detail. An example common-source amplifier design is demonstrated following this technique in LTSpice.

[@Mr_Truth.]

thanks

[@marmosetman]

gm is proportional to the square root of width while Id is proportional to width. How is gm/id independent of width. If I follow your reasoning it should also be independent of length?

[@vinayk531]

yes. gm/Id is independent of technology node

[@aswincvenu3958]

Please tell me how does the vds affect gm/id plots?
Will I get the same gm/id plot if I use a vds of 0.9 and 1.8 volts?
In a practical circuit different transistors have different vds valus right?

[@sscdiitk]

As mentioned in the lecture, to be exact, the characterization has to be done for different values of Vds and Vbs. The corresponding set of data has to be used while sizing.