Quote:I don't understand why he used cascoded tail current source with one transistor controlled by biasing network and another by cmfb.
Just to make the TCS cascoded to improve Rout. Here, the current is controlled by the lower CMFB guided NMOS only, NOT the biasing ckt.
Quote:Any particular advantage of this topology compared to normal cmfb tail current source (two parallel transistor)?
Just the advantage of Higher rout & closer to ideal current source. Other than that, it has a disadvantage of 100% cmfb control instead of only a part as is the case with parallel bias + cmfb control NMOSes.