I am working on a design with cascode CS amplifier with resistors in the feedback. What are the advantages and disadvantages of such topology? How the resistors in the feedback affects noise figure? It will be great there's a book or paper that I can reference to.
How is this done? We simply scale up the Rnoise and the 2 gain-set resistors of OA#2, by Gain^2 of the prior stage. Thus RG1=66ohm, RF1=594ohm; RG2=6Kohm, Rf2=56Kohm. (not exactly 100:1 scaleup, between stages, I know)
The final low-pass is needed to ensure the final opamp does not contribute more noise than the first opamp. That final opamp has nothing filtering its noise contributions, whereas the first opamp is "filtered" by the finite frequency response of 2nd stage.