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TMDS341A: Clock Rates

Mark Philip Felipe
Genius 9775 points
Part Number: TMDS341A

Hi Team,

We would like to seek your assistance for clarification.

The HDMI 1.3a, it shows clock rates around 100MHz to 300MHz, On the white paper it states that there are 10 bits per packet. We would like to clarify the real frequency of the signal.

https://www.ti.com/lit/an/slla263/slla263.pdf

Thank you very much.

- Mark 

  • 0
    TI__Guru**** 160416 points

    Mark

    Video information is transmitted as a series of 24-bit pixels and 10 bits per pixel clock period are transmitted.

    Pixel clock = Htotal * Vtotal * refresh rate 

    TMDS clock = Pixel clock * Bits/Pixel / 24

    For example, if we have a 1080p30 video with 24 bits/pixel.

    Htotal = Hactive + Hblanking = 1920 + 280 = 2200

    Vtotal = Vactive + Vblanking = 1080 + 45 = 1125

    Refresh rate = 30

    So pixel clock = 2200 * 1125 * 30 = 74.25MHz

    TMDS clock = 74.25 * 24/24 = 74.25MHz

    If the bits/pixel is 30, then the pixel clock frequency does not change, but TMDS clock = 74.25 * 30/24 = 92.81MHz.

    Thanks

    David