how do LCD driver ICs work??

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jlafarga
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how do LCD driver ICs work??

Post by jlafarga » 17 Jul 2014, 20:54

first let me explain what I mean by the driver IC (I'm not 100% sure about the exact name of things ok?), as far as I know in most LCD displays we have the display controller (which I think is what that cirtix dude engineered to run his panel @ 240hz) whose job is to recieve the signal from the graphics card and do something to it in order to feed it to the driver IC's, in most displays theres just one controller and MANY driver IC's, the controller sends a signal to the driver IC's which in turn are the ones in charge of actually driving the pixels. These driver ICs are the ones that look like long thin stripes around the panel, they dont even look like integrated circuits (at least the type of IC we are all used to). Now those are the ones I mean. So, anyone knows how do they work?? the reason I wanna know is because I think they are the ones that ultimately limit the refresh rate of a display(whether its LCD or OLED, though OLED probably uses a "special" kind of driver, this is because it takes more energy to drive an OLED pixel than to drive an LCD pixel, I think...). Meaning they probably top at 240hz thats why cirtix couldnt get the thing to run any faster. Check out this video of the eevblog on youtube of an LCD TV teardown https://www.youtube.com/watch?v=kdtyxt9OLlU in it you can see at about half the video where dave zooms in on these driver ics, they are made by a company called novatek, here's their webpage and their display driver IC's http://www.novatek.com.tw/products/DisplayDriverIC.asp if you read the specs they all say: " Support up to 240Hz frame rate", now I dont know if these things can also be overclocked in order to squeeze more frames per second out of them, I have no idea whether overclocking just overclocks the controller or BOTH the controller AND driver IC's (if someone could confirm this). So in conclusion I'd say if anyone had any interest in going beyond 240hz it would require NEW driver ICs that can support it, also I haven't looked for other driver ICs from other companies but theres no reason to think they would go beyond 240hz. So finally I'd love to hear your thoughts on how these chips work, I have a few ideas myself but would like to hear yours, my guess is internally they are some kind of serial in parallel out shift registers though I havent worked out the part of how they manage to feed each pixel a different voltage (depending on the color depth, for instance 24 bit colors would require 8 bits for red, 8 bits for blue and 8 bits for green, so each pin should be able to output between 8 different voltages), maybe this is done with some kind of DAC and a MUX, dunno know, but what I do know is that probably theres no PWM involved here, in most microcontroller projects where they are using PWM to drive an LED matrix, those matrices (unless you built the matrix from scratch) are PASSIVE MATRICES thats why they can use PWM to drive each led at a different "intensity". So anyway people, I leave this open for any ideas.

Saludos!
JLafarga

Q83Ia7ta
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Re: how do LCD driver ICs work??

Post by Q83Ia7ta » 17 Jul 2014, 21:52

Simple scheme:
LCD panel <- T-CON(Timing controller) <- Main Board <- Power Supply
Also:
LED driver <- Main Board.

AFAIK there are a lot of limiting factors.

For more information look inside some photos at here: http://display-corner.epfl.ch/ for example bottom of the page: http://display-corner.epfl.ch/index.php/BenQ_XL2411Z

http://home.sogang.ac.kr/sites/aiprc/su ... ce_V10.pdf

http://forums.blurbusters.com/viewtopic.php?f=8&t=1070

The Sky’s the Limit
Or why Asus says we may actually see higher-than-144Hz panels
http://www.maximumpc.com/refresh_rate_2013?page=0,1

jlafarga
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Re: how do LCD driver ICs work??

Post by jlafarga » 17 Jul 2014, 22:31

hi Q83Ia7ta, theres no info about LCD driver chips in any of your links.

Saludos!

Q83Ia7ta
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Re: how do LCD driver ICs work??

Post by Q83Ia7ta » 18 Jul 2014, 00:19

jlafarga wrote:hi Q83Ia7ta, theres no info about LCD driver chips in any of your links.
Saludos!
I hope from reading this links you will understand there are too many limiting factors like T-CON, LCDs main board, and others. Of course ICs on LCD monitors are different and limits not only by ICs. Vendors can easily make their firmwares to accept only certain timings and resolutions. And they do it mainly to prevent users damaging hardware by overclocking. Or just to sell new 168/192/240Hz monitor model in furure :)

jlafarga
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Re: how do LCD driver ICs work??

Post by jlafarga » 18 Jul 2014, 00:51

I know there are other limiting factors, Im just asking about one of them which is the driver IC, I just think they are interesting because nobody talks about them, now, if you made every other "limiting factor" run faster you wouldn't get higher framerates unless you also get these chips to run faster. (i.e. if you wanted to go beyond 240hz, I think this is the reason why cirtix could not go beyond it).

Saludos!

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Re: how do LCD driver ICs work??

Post by Chief Blur Buster » 18 Jul 2014, 07:36

Running drivers faster does not necessarily improve motion. It can. But there can be cases where GTG becomes longer than a refesh cycle, and motion just do not improve. But colors continue to degrade because of less time pulsing each pixel.

Do not forget about strobe backlights, either. See:
http://www.blurbusters.com/faq/creating ... backlight/
About how strobe backlights work. It also has high speed videos of an LCD being refreshed, showing the momentum limitation (GTG) of liquid crystals and how it affects strobing.

GTG (pixel transitions) is actually momentum of molecules moving from old position to new position, liquid crystals rotating into a new position. Momentum continues even after the LCD driver pulses the pixels, so GTG does not speed up if you refresh pixels more briefly (more pixels per second refreshing, higher refesh rate)
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jlafarga
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Re: how do LCD driver ICs work??

Post by jlafarga » 20 Jul 2014, 22:01

you guys love talking about gtg, so, lets talk about it then, yes I agree gtg is partially due to the liquid crystal properties BUT pixel capacitance definitely plays a role, now what percentage of gtg is due to pixel capacitance I dont know, btw before I go any further does anyone know exactly how this capacitor is "placed" in the circuit?? what I mean by that is the following: on a modern LCD display each pixel (or subpixel rather) is turned on by a tiny transistor and a capacitor, based on this image Image
you can see that the transistors gate is wired the column, its source is wired to the row and the drain goes to the pixel, now afaik the pixel itself is part of the capacitor, but exactly how?? it is said that the actual liquid crystal acts as the insulator between the two conducting plates of this capacitor, so, if one plate goes to the transistor drain and the other plate goes to ground, then how does the pixel gets turned on?? a capacitor is not supposed to let thru any current, so how does the liquid crystal manages to change??? or is it the actual electric field generated by the voltage between the plates that makes the pixel change?? can anyone please explain how this works?

Saludos!
Last edited by jlafarga on 20 Jul 2014, 22:25, edited 2 times in total.

jlafarga
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Joined: 06 May 2014, 23:56

Re: how do LCD driver ICs work??

Post by jlafarga » 20 Jul 2014, 22:22

is it like this??
Image
and yes thats a pink post it and no Im not a girl.

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Re: how do LCD driver ICs work??

Post by Chief Blur Buster » 09 Aug 2014, 19:10

Yes, pixel capacitance plays a role, I consider it all part of the GtG equation. Both the capacitance and the liquid crystal properties, affect how fast a pixel can change. And there can be manufacturing inconsistencies from edge to edge, and temperature can vary from edge to edge (liquid crystals respond more slowly when cold). That can be the cause of non-uniformity along the surface too. And, generally, the higher the refresh rate, the lower the contrast ratio often becomes, and the worse the uniformity becomes.
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