loose-electron wrote on Apr 17th, 2008, 3:16pm:Input rail to rail design is typically down with a PMOS differential pair and an NMOS differential pair structure -
Each has its own current source, and each has its own "current mirror diode" active load.
The second gain stage of each device mirrors out as a current, and then the signals from the two structures are summed together, and used to drive the output driver.
The concept is roughly illustrated in the attached picture. Although this implementation uses diode connected loads, but the general idea is shown.
Hi loose-electron,
thanks for your post , this looks very different i have not seen this structure anywhere in the textbooks, so no idea on how to design to get constant gm over entire input common-mode range
i have doubt regarding this can you explain the need of feeding the o/p (n1,n2) o/p of PMOS stage to NMOS stage loads @ p3,n4 through transistors P8 and n4 ?
do let me know regarding this rail-rail design which is the best book? (i have refered many of them listed in above) but none of them gives design strategy as the one Allen holberg gives
thanks
kiran