Pixel behaviour in sample and hold, in unchanging image.

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blargg
Posts: 66
Joined: 20 Sep 2014, 03:59

Re: Pixel behaviour in sample and hold, in unchanging image

Post by blargg » 16 Dec 2014, 01:30

My obvious google search found something describing TN operation that makes sense. My understanding of that page: Normally the crystals form a twist, which twists the polarization of the light. When a field is applied, the crystals align end-to-end between the two electrodes, eliminating the polarization twist. The crystals aren't polarized so when the field reverses polarity, they have no need to flip around; they can just stay where they were. The polarity change introduces a momentary drop in the field as the voltage passes through zero, so the crystals would jiggle a bit and thus be able to get a little closer to their most stable state with the field present.

spacediver
Posts: 505
Joined: 18 Dec 2013, 23:51

Re: Pixel behaviour in sample and hold, in unchanging image

Post by spacediver » 16 Dec 2014, 03:21

I wonder if the same end would be achieved if, instead of reversing polarization, there was just a quick depolarization and repolarization. Presumably that would also cause that jiggle. And I'm assuming the jiggle serves two purposes:

1) prevents the molecules from "sticking" in particular twist orientation (i'm assuming if they're allowed to remain stationary for too long, they will be less "elastic")

2) pushes the pixels closer to target state.

blargg
Posts: 66
Joined: 20 Sep 2014, 03:59

Re: Pixel behaviour in sample and hold, in unchanging image

Post by blargg » 16 Dec 2014, 12:17

The alternating polarity is to avoid migration of the ionic substances to one electrode and damage as a result (electroplating).

spacediver
Posts: 505
Joined: 18 Dec 2013, 23:51

Re: Pixel behaviour in sample and hold, in unchanging image

Post by spacediver » 16 Dec 2014, 13:53

ah, thanks blargg, that makes more sense now.

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Chief Blur Buster
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Re: Pixel behaviour in sample and hold, in unchanging image

Post by Chief Blur Buster » 20 Dec 2014, 15:17

blargg wrote:The alternating polarity is to avoid migration of the ionic substances to one electrode and damage as a result (electroplating).
That's likely the cause of some permanent burn-in I've seen at some LCDs (especially ones with flawed overdrive & displaying static screens like older information boards). The kind that's not easily eraseable.

This doesn't happen much, and many LCDs are immune to permanent burn-in unless you run an inversion-defeating pattern sequence for long periods (e.g. flicker patterns that stays perfectly in phase for days on end)
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