HDMI 1.4a signal in a less than ideal environment

I have a product that puts out HDMI 1.4a with a 32 bit color depth.  I have to go through some less than ideal connections that will exhibit impedance bumps, and then are subjected to a noisy EMI environment.  To accomplish this I was thinking of utilizing something like the ADV7622 but one that only has 1 input and 1 output, and operates in -40 to +85C.  I was thinking maybe something to boost the signal of the 1.4a, 32 bit color depth resolution, or just retransmit it right as it leaves my system, and see if that will mitigate the effects of the impedance bumps, and operate in the extended temp range.  Does anyone have a way to do this, or a better idea?

  • 0
    •  Analog Employees 
    on Oct 12, 2012 4:42 PM


    First HDMI1.4 specs 24, 30, 36 or 48 bit color.  A minor detail that doesn't effect this discussion.

    First problem is our video transceivers generally have a operating range of 0 - 70C.  There are a few receivers that handle the -40C to 85 C

    The second problem is that any transmitter is designed to drive into the specified HDMI load.  If it's a strange load that you are not guaranteed the end of the cable will have a good eye pattern. 

    You might look at the AD8195 which is a HDMI buffer with equalization control that has the temperature range your looking for.

  • Thanks for your help and insight.  I am fairly new to this realm, and so I apologize for not understanding the full range of specifications.  If I understand you correctly, you are saying that the device will have no problem with the 1.4a 32 bit color depth even though the datasheet only calls out the 1.3a 12 bit color depth (guessing this is maybe an encapsulation or something similar to that)?

    Also, I have come across the AD8195 in the past, and thought that it would be a good fit.  However, when I looked at the datasheet it talks about 1.3a, and only able to go to 2.25 Gbps.  The reason this discrepancy concerned me was that the change notes say that it was changed to be 2.25 Gbps instead of 3 Gbps.  My system outputs the full 2.6 Gbps, so I am worried as whether the device will suffice.  Can you offer any input here?

  • 0
    •  Analog Employees 
    on Oct 13, 2012 1:15 AM

    OK, a real quick overview of HDMI:

    Video is defined in resolutions such as 1080p60 which mean the video stream contains 60 frames per second with each frame consisting of 1920 x 1080 active pixels plus blanking intervals giving us a pixel clock of 148.5MHz.  The pixels are color coded in RGB 444 or YCbCr 444 / 422.  Nominally one pixel is defined with 8 bits per color plane or for RGB 444 it's 24 bits total.  Or we can define one pixel in the YCbCr color space and it would still be 24 bits.  The HDMI cable is comprised of 4 twisted pairs.  Pair 0 has the pixel clock (TMDS clock) on it or 148MHz.  Pairs 1,2 & 3 carry the color plane bits in a 8b10 encoding so they have 10 x 148.5Mhz = 1.485 GHz.

    Now comes the fun part.  If we want to run deep color or 10 bits per color plane, the HDMI encoders bumps pair 0 (TMDS clock) to 148.5 * 125% = 185.625Mhz and the color bits are interleaved and transmitted at 10 * 185.625Mhz = 1.85625 GHz.  For 12 bits per color plane we end up with 148.5 * 150% = 222.75Mhz and pairs 1,2,3 are transmitting at 2.2275GHz.  This is what we reference as 2.25G.  16 bit per color plane give us 297Mhz and 2.97GHz respectively.

    This is no 32 bit color definition, just 24(3x8), 30(3x10), 36(3x12) or 48(3x16)

    Now back to your questions.  The data rate depends on the resolution you plan to transmit.  If you're only doing 720p60 then everything drops in half.  So is 2.6GHz your true data rate and if so what is your resolution?

  • Thanks for the explanation, it helped me get some more information out of the designers of the board.  The information that I have been able to dig up is that it will support up to 1920x1200 with Intel clear video technology HD (basically a bunch of HD and 3d stuff).    You probably know a ton more about that than me.  I also found out that the interface supports link-speeds of 2.7 Gbps on 1,2,or 4 data lanes.  Does that provide enough information as to whether the AD8195 will work?

  • 0
    •  Analog Employees 
    on Oct 15, 2012 7:57 PM

    It sounds like you are using display port and not HDMI.  These are two different physical transport methods.  I need to ask someone else what's the best buffer for display port.