Below is my speculation:
I posted earlier that the patent literature suggests that adjusting initialization (both floating and rising blacks) prevents the need to raise scan (address) voltage or width.
There is a voltage drop issue at high APL due to impedence and there is also a change in materials (MgO) with increased usage time. Both these issues cause the pixels to misfire because the voltage required for discharge is raised relative to the applied scan (address) voltage
. This is due to a lack of priming electrons.
So we can then break it down into the following cases:
- If nothing is adjusted the pixels will misfire at high APL (due to voltage drop) and also misfire after the panel ages (due to MgO sputtering).
- If scan(address) voltage is adjusted to compensate then no misfiring will happen but power consumption will change (higher power for higher voltages).
- If scan(address) pulse width is adjusted to compensate then no misfiring will happen but too much time is consumed (less time to emit light as scan pulse width is lengthened). Efficiency is reduced.
- If initialization voltage is adjusted to compensate then no misfiring will happen but black level will change (higher black for higher voltages). Power is not increased.
On top of that, a smaller pixel will exaggerate the stability problem as the voltage required for discharge goes up as the pixel becomes smaller. Panasonic moved to 1080p in 2007 as you mentioned and floating blacks became prominent (coincidence?).
Also, the luminance decreases with smaller pixels and to compensate more Xenon gas is used which has the drawback of requiring more voltage to discharge which again decreases stability. Part of NeoPDP is higher Xenon Gas Pressures (2009 as you mention) and again floating blacks became prominent (coincidence?).
Originally Posted by Panasonic patent app#20090303222 In recent years, however, there is an expectation of further improvement in image display quality of plasma display devices along with their increasing definition and screen size. One of the approaches to improve image display quality is to increase the luminance. The luminance can be effectively increased by increasing the xenon partial pressure. This, however, requires a higher voltage for an address operation and makes the operation unstable
................., in order to achieve a stable address operation, it is necessary to increase the address pulse voltage
Now here is the kicker. AFAIK, all of the issues with stability could have been solved by incresing the initialization pulse number or voltage high enough (increasing the black level). This would keep the discharge start voltage low even at high APL, increased usage time, and smaller pixels, and higher Xenon Gas content.
But Panasonic wanted to maintain highest contrast at low APL and at time zero so they chose to dynamically adjust the initiallization instead (dynamic black level - with time and APL)
Hence rising blacks and floating blacks.
But the question still remains. Even before power was important (pre - 2007 I guess). Why did Panasonic choose to mess with initialization rather than just adjust scan voltages??? Unless power has always been a concern? Even so I don't recall Panasonic designs being Power savers over the competition pre 2009?