HDMI or DVI-D (Dual Link) to LVDS Conversion for 10-bit LCD Panels

Hello Steve, thanks for your detailed question.

I looked up the two monitor models you mentioned, the Sony and Ikegami.  They both appear to have a DVI-D single-link input port.  So if your Lumagen outputs an HDMI signal, that could be directly connected to the DVI ports on those monitors.  As you may be aware, the 3 TMDS data pairs and the 1 clock of HDMI is identical to DVI-D single-link.  So a mechanical adapter can make them connect.

TI does have a solution for converting HDMI/DVI to LVDS, and even dual-LVDS.  But please let me know if you really need LVDS.

Thanks,
RE

Thanks for your response Ross.

The monitors I mentioned are seriously over-specified (and over-priced!) for my application.  I mentioned them since they may be using true 10-bit, 32 inch, 1920 x 1080 native resolution panels whereas it would appear that there are no such panels currently used in the consumer domain - they are all 8-bit, or pseudo-10-bit achieved by dithering, I'm told.

My intention is to purchase an LCD panel - perhaps of the same type as used in one of the aforementioned monitors - and drive it directly from the Lumagen.  If you check the datasheets for these types of panel they require the 24- or 30-bit digital video data describing each pixel to be delivered to the panel's built-in driver board as LVDS - at a refresh rate of 50Hz that's a data throughput of up to 3.1Gb/s.

The panel data sheets say, for example, "...has been designed to apply the 10-bit 4-port LVDS interface" or "...has been designed  to apply the 8-bit 2-port LVDS interface"

The Lumagen outputs video of 10-bit word size (or greater) via its HDMI output, so I need a means of converting this to LVDS suitable for my chosen panel.  In concept, an easy job - but maybe more difficult in practice?

Steve,

I agree that the monitors you mentioned likely support 24-bit pixel inputs, just based on the fact that they use DVI-D inputs.  DVI single-link is inherently 24-bit.

It sounds like what you need is a TMDS receiver, and a dual-link LVDS transmitter solution.  This is very doable.  If you go the 24-bit color route, the TFP403 is a suitable DVI receiver, and it can output on 48-bits, splitting odd/even pixels.  TI's dual-LVDS solution involves a 1:2 clock fanout buffer and two SN75LVDS83B device.  The primary concern here is skew between the two devices, and it's important for the panel receiver to have skew tolerance.  This has been successfully implemented with an OMAP platform driving a 1920x1200 panel.

I'm much less familiar with 30-bit color systems.  HDMI receivers that support this are likely available, but I'm not sure about LVDS transmitters, and what standard 30-bit panels use (including the number of LVDS channels and the bit ordering).

I hope that's helpful!
RE

Thanks for this, Ross.

I've realised that for 10-bit fidelity I'll need to use HDMI in YCrCb 4:2:2 format as I gather RGB 4:4:4 format is limited to 8-bits for backwards-compatibility with DVI-D.

I have now obtained the 32" panel I'll be using and have spent some time studying its specifications (all 38 pages!)  The spec was finalised in Feb 2010 - so I guess the panel must be used in some current or recent products.  It's a "10-bit(D)" panel - the "D" may stand for "dithered" but I'm not so sure, now that I have understood how the panel's memory receives digital video data...

...which is four pixels at a time, via 4 channels of LVDS, each 5 bits-and-a-clock wide - this reduces the clock from 297MHz to a more manageable 74.25MHz. The clocks drive PLLs producing 7 sampling points per clock cycle coinciding with the 7 data bits sent on each of the 5 lines during each clock cycle - so 35 bits are available to be written to the panel's memory for each pixel - 30 of these are used for 10-bit RGB data.

I'm not sure whether the above description of the interconnect does or does not exclude the use of dithering.

The LCD timing controller has pins for JEIDA/VESA select and 8-bit/10-bit(D) select. JEIDA and VESA appear to be data-mapping options for the LVDS interface.

The panel is specified for 95 to 122Hz refresh rate (not sure what would happen if I try to drive it at 50Hz).

So, summarising, the job now is to unpack the 10-bit 4:2:2 YCrCb data from the HDMI interface, matrix it to form 10-bit 4:4:4 RGB data, apply some lineartity correction for gamma, double the frame rate to 100Hz (I gather this may mean inserting black frames), and then send the data on 4 channels of LVDS clcoked at 74.25MHz to the panel.

Piece of cake.

It sounds like you're making progress!

I suppose you have a 120Hz 1080p panel.  If you tried running at 50Hz (while its spec is 95-122Hz), you'd have a 31MHz clock that's likely too slow for its PLL range.

Best regards,
RE

Thanks Ross.  At 50Hz I make it that the clock would be 37.125MHz but yes, of course you're right, those PLLs (all four of them) would be well out-of-lock.

I could try and get hold of the 50/60Hz version of the timing controller board and fit this to the panel (100Hz refresh isn't essential - it's just that availability of panels is limited) but the spec for the panel says "The performance of the electro-optical characteristics may be influenced by variance of the vertical refresh rate and the horizontal frequency."  Here's a picture of the 100/120Hz timing controller board the panel came with:

(Prio)

Hi guys,

I noted you are deeply into the details of an area I'm related to:

Are you aware of any way of how to make or buy an LCD controller board that produces a double LVDS output, and takes a DVI or Displayport as input?

The simpler the better. Preferably one that works for different input resolutions.

Thanks!
Mikael

Hi Mikael

I amassed quite a lot of information during my research into building a full-HD picture monitor based around the 32" LG Display panel I acquired - there's a picture of it under test on my Flickr page:  http://www.flickr.com/photos/38818955@N07/

I gave up on this project because it would have required far more work than I thought.  There are copyright protection issues associated with decoding an HDMI signal; my panel was a 100Hz panel so I would have had to convert from 50Hz input frame-rate...  I soon realised that the likes of LG basically use a "TV-on-a-chip" solution where all the inputs (HDMI, DVI, analogue) are fed direct to a big chip which does everything, often directly driving the LCD panel without an intermediate T-con board.

Tell me a bit more about what you're trying to achieve and I might have some leads for you.

Incidentally, we finally bought an LG TV which uses basically the same panel as the one I bought, so I have a spare.

Cheers 

Mikael, TI has a 2-chip solution to convert HDMI/DVI to LVDS.  It complies with single-link DVI (24bpp) and supports any resolution from 640x480 to 1920x1200:  http://www.ti.com/lit/an/slla325/slla325.pdf

Best regards,
RE

Hi, thank you for your response.

Is any chip with dual LVDS output about to be released anytime soon (as to support resolutions > 2000px x 1000px)? (as to make a LCD controller with this capability and DVI/Displayport/VGA input)

Thanks

We have a new device, the SN65DSI85, that bridges dual MIPI DSI to dual LVDS, and supports and output clock of up to 154MHz (2ch), which is higher than VESA's 2560x1600 frequency of 268.5MHz.

Best regards,
RE

Hi Ross - great! Yours is the first mentioning of the SN65DSI85 that I find on the Internet. Where can I read more about it, and where can it be bought or a sample be gotten?

What would you recommend for turning Displayport or DVI-D into MIPI DSI in the first place?

Are you aware of any efforts to make anything like a LCD display controller board by any manufacturers of such?

Thanks

hey i am nisha

i am doing a project where i am trying to interface lcd pannels of differtent resolutions and interfaces using a single board.i am using an omap board but my bord does not have dvi input.its has only lvds interface for lcd so is there any converter which i acan use to convert lvds to dvi so that i can connect dvi supporting monitors.please help

Hello nisha, please clarify: do you need to convert DVI video into LVDS?

Thanks,
RE

Hi all,

I realize this thread started before the Ti acquisition of NSC was complete, so there weren't many dual LVDS options in the TI portfolio. However, Ti is able to offer a wider selection of LVDS output devices now that the acquisition has closed.

The DS90C387 is capable of supporting single pixel LVCMOS inputs to single pixel LVDS (SISO), single pixel pixel LVCMOS inputs to dual pixel LVDS (SIDO) and dual pixel LVCMOS inputs to dual pixel LVDS (DIDO).

The soon to be released DS90C187 is a lower power version of the DS90C387 and operates off of a single 1.8V supply. This device is also capable of supporting SISO, SIDO and DIDO configurations.

These devices are ideal solutions for dual LVDS output systems because the dual LVDS serialization/conversion can be done in a single device and also without the need for a clock buffer.

If you have any questions about either device, please let me know.

Mike Wolfe

DPS APPS / SVA

hi

i am having an lvds ouput signal from the board which i want to convert to dvi signal in

Nisha,

Is your LVDS 2-channel or 1-channel?  In other words, does it have 3-4 data lanes, or 6-8?

If it's 2-channel, it won't be easy to convert it to DVI, since our DVI transmitter (the TFP410) has a 24-bit data input, and 2-channel LVDS receivers often output 48-bit data.

If it's 1-channel, it should be straightforward to convert it to DVI, but your pixel clock frequency range will be limited, which limits your possible resolutions.  Most 1-channel receivers have a max frequency of 85MHz, which gets you up to 1366x768.

Can your graphics source output RGB instead of LVDS?  If so, it would probably be easier to use the RGB output with the TFP410, for a fully capable DVI transmitter.

Best regards,
RE

Hi Mikael,

We have a device planned that  may meet your requirements- please contact me at  jay.canteenwala<at>TI<dotcom>

 and we can continue the discussion

hi

the board which i am using has a single channel lvds output.it doesnt have rgb output.

regards

nisha

Hi Nisha,

If your LVDS is 8 or 6 bit color the conversion to DVI  can be done with a two chip solution. If your LVDS is 10-bit color the two chip solution will still work, but you will lose some color depth in the process and end up with 8-bit color.

The two chip solution will deserialize the LVDS to RGB data, which is then fed to a TMDS transmitter.

Any of the chips mentioned below would be paired with a TFP410 TMDS transmitter. Depending on the resolution of the displays and the corresponding pixel clock speed you want to use you can use the following parts to deserialize the incoming LVDS data:

For 6-bit color (RGB-666):

- DS90CR218A, clock range of 12-85 MHz, latches out data on rising clock edge only

- DS90CF366, clock range of 20 - 85 MHz, latches out data on the falling clock edge only

For 8-bit color (RGB-888):

-DS90CR288A, clock range of 20-85 MHz, latches out data on the rising clock edge only

-DS90CF386, clock range of 20-85 MHz, latches out data on the falling clock edge only

If you need a higher clock speed, then the following parts could also be considered:

- DS90CR486, clock range of 66 - 133 MHz, latches out data on the rising clock edge only

- DS90CR484A, clock range of 33 - 112 MHz, latches out data on the rising clock edge only

- DS90CF388, clock range of 40 - 112 MHz, latches out data on the falling clock edge only

The devices with the high clock speed support dual pixel interfaces. If necessary you can tie off any unused inputs. The draw back to these higher speed parts is the added board space due to the unused channels.

Mike Wolfe

DPS APPS / SVA

hi mike

thank you for your reply i wanted to know if there are any evaluation boards or converter boards which perform lvds to dvi conversion.i also saw an ic chip chrontel(ch7036 ) which converts lvds to       dvi as well as hdmi  are any evaluation boards presnt for this chip which i can use for conversion purpose

Nisha, do you know the max clock frequency of your LVDS source?

We can provide 2 EVMs (one for LVDS RX, one for TMDS TX) that you can connect together.

Thanks,
RE

hi thge board which i am using has TI-OMAP 3530 Cortex-A8 having a frequency of 600 Mhz

Thanks but I was actually asking about the max pixel clock frequency of the LVDS output.  It's probably somewhere between 25-100MHz.  Or if you don't have that info, maybe you can tell me the max resolution supported by the LVDS output.

Thanks,
RE

hi

max resolution supported by my board is 1280X 800

Ok; that commonly uses a 71MHz pixel clock.  1 last question: do you have 3 or 4 LVDS data lanes (18-bit or 24-bit color)?

With this info, hopefully we can get you the most suitable EVMs.

Thanks,
RE

hi

 the board has 4 lvds channels and it has 24 bit colour input

Nisha, please send me an email at reisenbeis <at> ti <dotcom>, and we'll arrange to send you EVMs that do LVDS to DVI conversion at 1280x800.

Thanks,
RE

hi rosse 

sorry for the late reply, my email id is nisharamanak@gmail.com

regards

nisha

This is exactly what I was looking for.  Thanks for making my research that much easier!