Overclocking

[Peter A]

Very exciting project.  Panelook.com lists the M280DGJ-L30 as a 4k 60Hz panel, and your system drives it at 4k @ 120Hz.  In your youtube video titled "ZisWorks X39 display demonstration", you mention overclocking.  Are you driving the panel at twice the manufacturer's specified frequency?  Or was the glass made for 120Hz, and the limitation was the 60Hz TCON provided by the panel manufacturer?  Thank you.

[ZisWorks]

Innolux does not offer the glass separately and the 60Hz rating is for the full system including the innolux tcon, which being an 8L vx1 model, is an obvious limiter.

As far as I know, there is no rating on the glass itself.

Datasheets for the row/column drivers are all closed, so no hints there.

Is it running beyond specification?  Can't tell for sure either way, so the answer is maybe.

[Maksim Polyakov]

Hi your projects is awesome. I am working on my own student project for driving small lcd 320x240 directly by controlling source/gate drivers with fpga.Currently I am gathering information on existing drivers and how control an data signals are formed. 

Display that I have can do 60 hz but I wan't to also try some faster modes to get some measurements of pixels response to higher clocks and also investigate overdriving, etc.

I have read your description of how you reached such a high refresh rate. But still one thing is not clear to me. You have written that in high hz modes you are controlling gate driver in a way that it is enabling two or more lines at once. As I understood you are pushing 2'b11 into STV or even 4b'1111 to activate multiple lines at once?
But the clock CPV is still limited by some value, 276 000 hz in your case. So even when activating 4 lines at once you have to do 4 clk edges to move to next 4 lines. So you are still limited by gate driver max clk and total vertical frame time is the same.

I don't understand how do you do it. Can you please explain? Or are you using some other driving method. Thanks.

[ZisWorks]

CKV limit is significant, but some tricks to make it less important. 

In the compatible innolux panels, main limit is datarate into the column drivers, but the CKV limit isn't that far behind.

If you notice, 2160*120, 1080*240, 720/360, 540*480 all are from roughly the same linerate.  Shifting multiple bits into STV is part of the solution.

[Maksim Polyakov]

Yes I see that those modes are related by integer coefficient. As I understood column drivers are just fast enough to deliver 60 hz. But there is two sets of them one for left and one for right side of display. So driving them simultaneously you can get 120 hz. 

But for vertical driver I can't imagine right setup. Can you please share an example with numbers and data pushed to main lines if its not secret info?

[ZisWorks]

Column drivers are just barely fast enough for 4k120.  This was known from work with a previous panel (M270HHF) which used the same column drivers and was capable of 1080p240Hz, and is the main reason why the board was designed for m280dgj in the first place.

I don't really want to get into the details of how things were made to work at full speed, sorry.

[Maksim Polyakov]

I understand. Maybe you can suggest me some books or articles to read to understand more on how modern lcd panels work?

[ZisWorks]

Find some old/leaked datasheets and stufy those. Minilvds spec from TI is interesting too.