I've just published a paper about a rail-to-rail bulk-driven operational amplifier using the open source Sky130 PDK. Unfortunately, I didn't have time to make its layout. A gate driven version, although not rail-to-rail, could be a very interesting design for a future project. Most amplifiers I see here are two-stage Miller amplifiers which could be replaced with a class AB with indirect frequency compensation and achieve better results. https://www.researchgate.net/publication/371162159_Rail-to-rail_inputoutput_bulk_driven[…]_operational_amplifier_with_improved_composite_transistors