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Video Latency of FPD-Link III

Dan Miller14
Prodigy 20 points

Hello,

I am looking into using FPD-Link III to serialize/de-serialize an LVDS video link. Specifically interested in "ds90ub947" and "ds90ub948" as a component pair. Assume a 720P video signal at 60Hz with 24-Bit color depth over one lane.

What I need to know is how much video latency will be introduced in the video path by these 2 chips. I saw a field that states 294T and 147T in each datasheet respectively for latency in nanoseconds. T is defined by 1/OLDI Frequency. OLDI is stated to be between 25MHz and 96MHz dependent on frame rate and resolution. In the case of this equation, I am selecting 25MHz to drive the highest latency, knowing that I will be closer to 96MHz from the use case above. If I am running the equation correctly, this comes to the following...

294 * ( 1 / 25,000,000 ) + 147 * ( 1 / 25,000,000 ) = 17.64 femtoseconds.

Is this fully encompassing of the induced latency from video frame in to video frame out? I am not concerned about the SPI, I2C, GPIO latency.

  • 0
    TI__Genius 13475 points
    Hello Dan
    My apologies for the datasheet being somewhat confusing. If you are running a 25MHz PCLK, then the period is 40ns per PCLK period - T is the bit period on the serial link, which is the PCLK period, if you are working with one of the OLDI parts such as the DS90UB947, the bit period is 1/35th of the PCLK period, so the T in this case is ~1.1ns, Latency for the '947 is typically 294 bit cells, or about 330ns. The deserializer is about half this, so a good estimate of the worst case latency would be ~500ns. There will be a few more ns added for the propagation delay through the cable, which will depend upon the length of the cable used, but that should be small.
  • 0 in reply to Mark Sauerwald88474
    Prodigy 20 points
    Mark,

    That helps me out very much. Thanks for the detailed answer.

    -Dan