DisplayPort / DVI signal splitting

[velis]

Not sure if this is the forum to ask this, but it seems the most appropriate, so here I go:
I came up with this idea that if I ever want a high DPI monitor, I'd have to build it myself.

The most feasible method seems to be to take some of those mobile (AMOLED) 800x480 displays and glue them together to get the final resolution.
So stacking 8 x 3 = 24 of these displays in portrait mode would yield me a nice 3840x2400 resolution. Though this would only yield an 18" monitor using 3.7" displays. Maybe even more should be stacked together to yield a nice 24" monitor?

There are two problems with this idea:
1. Displayport can hardly drive such a resolution at a satisfactory refresh rate. I suppose this could be mitigated using multiple connections, like 2xDP or 2x DVI-D. Using ATI EyeFinity or NV equivalent this problem is solvable.

2. I can't seem to find an IC that would take a DP/DVI signal and split it to multiple displays as suggested above. All the chips I found took an input and were able to drive ONE single panel from that.
Does such a chip even exist? If not, how would one go about doing this using other components?

 

[William Gaatjes]

I suggest a good place to start is to find out how ATI and Nvidia do it.
That is drive multiple displays.

However, in the video business i have seen systems that allow multiple displays stacked together as is seen in television shows or assembled multiple screens for live shows.
Wikipedia will not help you. The writer only knows about pc's, ati and nvidia.

Video walls come to mind...


http://www.9xmedia.com/new/products/xtops.php

^_^

 

[Modelworks]

There are several chips that exist to split a single display into multiple ones. The normal way this works is that a video signal say 4096 x 2048 is fed to the controller. Digital video is a series of bits for each frame. With the proper firmware on the controller you can select which bits each controller should 'listen' to and which to 'ignore' . It is a lot easier to do this now than it was with analog signals. Analog required precise timing or you would get a half frame on one display and then the next second that half frame problem would be somewhere else.

One such chip that can do it



http://focus.ti.com/docs/prod/folders/print/tms320dm365.html

 

[velis]

I can't see how this chip can do the signal splitting. No matter how hard I looked, this particular chip doesn't have a digital video input (only a SD analog one) and it also only has 3 analog outputs.
If analog would be my thing, than this chip would be interesting, as it is, it is not. It's also pretty sophisticated - a complete SoC with an ARM core and media processing capabilities which is great, but largely unneeded for this particular purpose.

I went searching a bit more and found no chip that's capable of cropping a DP signal and possibly even output it directly to a panel. I found a signal duplicator though (takes one DP and creates 2 identical ones from it). But no Soc with DP input.

This one http://www.st.com/stonline/products/literature/bd/15729.pdf would do the job if it supported a higher resolution
This one http://www.st.com/stonline/products/literature/bd/15144/gm68020h.pdf may be more interesting, but it too can't handle too much resolution, and also has no cropper...

Seems like IC manufacturers haven't come up with a similar idea yet.

 

[DominionSeraph]

So stacking 8 x 3 = 24 of these displays in portrait mode would yield me

... 24 boxes.

The displays are not going to butt together seamlessly.

 

[Modelworks]

I can't see how this chip can do the signal splitting. No matter how hard I looked, this particular chip doesn't have a digital video input (only a SD analog one) and it also only has 3 analog outputs.

A chip that takes in a dvi connection and outputs it as 8 images does not exist because really there is no need for it because solutions already exist.

DVI are TMDS signals. Serial bits that have to be decoded so a DSP can process them .
http://en.wikipedia.org/wiki/Transition_Minimized_Differential_Signaling

Convert the signal to parallel bits:
http://focus.ti.com/docs/prod/folders/print/tfp401a.html

Process the signal with the DSP above

Convert the bits back into a serial TMDS signal for the display
http://focus.ti.com/docs/prod/folders/print/tfp410.html

The thing you need is a DSP with lots of IO ports, doesn't need to be video specific. You would need one tfp410 for each display.

 

[velis]

Modelworks,
I guess I'm too bad in technical to understand what you're trying to tell me. Please bear with me a while longer.

While I understand the first chip will convert a 1600x1200 DVI signal into parallel and the second chip will convert back for use with a panel, I still fail to see how either of these chips would be able to simultaneously split the signal into, say, 2x 800x1200 or 4x 800x600 streams.

This is of course assuming 1600x1200 would be the right resolution to start from. I was hoping for a chip that could do more. The second chip I proposed supports 2560 x 1600, but outputs to LVTTL (and still does no cropping)

So where in this picture does the cropping fit in?

 

[Raghu]

You could use a FPGA to have the custom logic that splits input 1600x1200 DVI signals into 4 800x600 signals. Its quite easy and a really small/cheap FPGA will work fine. However, FPGA frequencies top out at ~300MHz depending on the complexity of the logic. Input resolutions more than 2560x1600 (60Hz) might become really difficult to work with.

 

[Modelworks]

Modelworks,
While I understand the first chip will convert a 1600x1200 DVI signal into parallel and the second chip will convert back for use with a panel, I still fail to see how either of these chips would be able to simultaneously split the signal into, say, 2x 800x1200 or 4x 800x600 streams.

Those chips do not change the signal content. They convert it from serial to parallel bits so that a DSP chip can process the signal. Once it becomes parallel bits you would feed it into the data lines of the DSP . Inside that DSP is where you would convert the 1 frame into 2 or more separate parts. After you converted the signal you would need 1 chip per monitor that converts it back to a signal the panel can understand. That is why you need a DSP with enough data lines that you can connect to the tfp410 chips for each monitor. If you exceed the amount of data lines for monitors then you have to use a second DSP chip and coordinate data between the first DSP chip.

The problem is that when you start dealing with resolutions like 1080p it is hard to find a chip that can do more than 2 monitors, more monitors faster the chip and more bandwidth it needs. The cost to put lots of monitor support into one chip outweighs the benefit , so engineers use a 2 monitor solution and just multiply that times the monitors needed.


Even the FPGA solutions are costly as the very best ones can only do 3 displays at a cost of $4k for one development board.
Lower cost devices exist that take an input stream like mpeg2 and output to 12 monitors because they do not have to decode the input signal but can send the stream to decoders directly.


If you look for the retail 1 input to 8 monitor output at 1080p boxes they cost about $3-6K

 

[velis]

Process the signal with the DSP above

So this line should actually read: Process the above signal with a DSP?

Could you suggest a DSP that would be fit for the job? I have searched a lot but it seems I don't know the correct keywords that would allow me to find such a DSP.

 

[cirthix]

I made a board to do something like this for a vp2290b, but ended up running into some singlal integrity problems that made noise in the image.

I used two slilicon image dual-link dvi receivers (7181 iirc) and four transmitters (silicon image sil164) along with an ecp2-20 256pin fpga.

if you're serious about this, email me: cirthix atgmailcom.