Paul
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Hi,
this topology has been published in A compact power-efficient 3 V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries Hogervorst, R.; Tero, J.P.; Eschauzier, R.G.H.; Huijsing, J.H.; Solid-State Circuits, IEEE Journal of Volume 29, Issue 12, Dec. 1994 Page(s):1505 - 1513
This topology provides class-AB operation of the output stage at a power-supply independent (and first-order process independent) quiescent current. Indeed, the use of a simple inverter in an integrated op-amp is usually prohibitive due to the large power consumption variations with process, temperature and supply.
As the amplifier output voltage is not affected actively, the amplifier gain is not modified. However, I am not exactly sure how M5 (added for symmetry?) in the other FC branch affects the amplifier behavior.
Hope this helps
Paul
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