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HDMI or DVI-D (Dual Link) to LVDS Conversion for 10-bit LCD Panels
I've just registered and this is my first post - a little about me at the end.
I am hoping to prototype a quite basic picture monitor for high-end applications. A picture monitor differs from a TV in that it has no provision for audio and does not include a tuner; it differs from a computer monitor in that it is designed to accept a video format rather than a PC format signal. In CRT technology, picture monitors were designed to add nothing to, or take anything away from, the signals fed to them and used bespoke high resolution CRTs - often with the original delta gun arrangement - and (in Europe) the correct "EBU" phosphors for accurate colorimetry.
My LCD picture monitor would be used with a Lumagen Radiance XE 10-bit video processor which would act as a switcher, take care of deinterlacing of interlaced inputs, upscale standard definition inputs, manage colour and gamma - and always output 1920 x 1080 progressive at 50Hz on HDMI.
I am still to choose my LCD panel - I am looking for: 32 inch : 1920 x 1080 : 50Hz : 10-bit : S-IPS or AS-IPS. I still have some research to do regarding refresh rate and number of bits. To preserve picture quality I want to avoid frame-rate conversion and work at 50Hz throughout, but the video processor can convert to 60Hz if I have to work 60Hz. I'm not sure if true 10-bit (total: 30 bits) panels are available - it seems many 10-bit panels are actually dithered 8-bit (total: 24 bits) panels. There are two products - a Sony LMD3250MD 32" medical grade monitor and an Ikegami HLM-3250W 32" broadcast grade monitor - which claim to use 10-bit panels which I am investigating.
So, in principle, this is a straightforward task and, once I've chosen my LCD panel, all I need is a means of converting the HDMI signal from the Lumagen Radiance XE video processor to the (multi-port) LVDS signals required by the panel. I'm not sure yet whether the converter will need a control interface but think this is likely as with ICS's NT15H LCD Controller Board and multi-button NK05A OSD Control Board - see http://www.icsco.kr/what_we_serve/sub_02.asp
So, to summarise I need:
Can't be that difficult... can it?
About me: I'm a semi-retired, degree-qualified electronics engineer - I graduated from Imperial College, London in 1979 and then joined BBC TV where I worked as an engineer in their London television studios on the full range of broadcast equipment and have some 30 years' experience designing, building, repairing and modifying professional and consumer electronics. In 1987 I moved to Channel 4 TV, London where I worked until 2006, at the end as manager of the team of engineers which kept the transmission operations running.
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 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?
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.
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:
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.
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.
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
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)
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.
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?
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?
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.
DPS APPS / SVA
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