Magnachip applications US20080283885 and US20080283886 talk about saving a reset transistor in 4T pixel by substituting it by a diode built vertically above the substrate. 20080283886 pixel also uses JFET as a source follower transistor to reduce the noise, while 20080283885 pixel has a set diode, in addition to the reset one. The reset and set diodes are formed between the diffusion and poly, amorphous silicon, local epi-layer or metal (Schottky version). Probably, JFET was thrown in 20080283886 to improve its chances to be granted, as when each idea separately would be rejected (there is a good chance they would), it still might pass as a combination.
The set diode in 20080283885 application improves the reset operation of the reset diode by biasing both at slightly different voltage, so that a small forward current flows through the diodes, keeping floating diffusion at mid potential.
Sony application US20080284250 talks about 3-level power supply for powering transfer get of 4T pixel. 3 levels are used to reduce image lag and noise, but it creates a number of start-up problems in mobile device, where the highest voltage might be not available initially. Sony proposes a solution for this specific problem.
Sharp application US20080284891 describes about yet another circuit eliminating "black sun" effect. For those who is still suffering from it, it's worth reading.
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