For any science geeks here, I’ve accumulated around 30 patents and patent applications describing high efficiency and high contrast (the two are related) plasma display technology. Rather than post them, as they are so difficult to read, I’ll give you a simple summary of what I read. First I’ll write some background and then a couple sentences describing the actual invention. Hopefully the background makes the invention more clear
Note: There is no proof these patents relate to actual products in the market but they are relatively recent.High Contrast
: As you may know the reason plasma cells emit light when they are off is because just like fluorescent bulbs, they need to be primed to be able to turn on quickly
. This priming involves discharging the cell to get free charges into the cell gap. The priming discharge generates some UV light which in turn excites the phosphor and emits some unwanted light. And this occurs in all pixels many times per frame whether they are active or not to make sure the cell is ready to be activated quickly. The longer a cell is off without priming the harder and longer it takes to start it again (just like a fluorescent bulb).
A few years ago, Panasonic developed a ramp priming pulse that caused very little unwanted light to be emitted (dark discharge). But there is still room for improvement. Also, since plasma displays are somewhat passive matrix (no TFT switch) they must use dielectric material in the cell that accumulates wall charges. The wall charges allow the cells to be selected
individually for activation. To create this wall charge they need to once again ionize the gas in the cell (more unwanted discharge). In fact in every stage of addressing the pixel, except the sustain stage (where the actual picture is generated) unwanted light is emitted. So reducing or eliminating stages that produce unwanted light during dark periods would lower the black level and increase contrast.Invention
: For Pioneer, thanks to a super efficient high gamma coating (secondary electron source) on the bottom of the cell they have made it possible to keep the cell primed with very little discharge and light emission. In fact it is so efficient that they only need to prime the cell once at the very beginning of each frame, as well as only one erase period at the very end of each frame. This eliminates unwanted discharge from constantly priming the cell as well as constantly resetting and erasing the cell for each pulse in the PWM scheme.
I will post several patent summaries on high efficiency (10 lumen tech) technology later.