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DS90UB924-Q1: Relationship between PCLK (MHz), DSI rate (Gbps), FPD line rate (Gbps), and video data (resolution, colour depth, frame rate)

Laurence Parkins
Prodigy 10 points
Part Number: DS90UB924-Q1
Other Parts Discussed in Thread: DS90UB941AS-Q1

Hi,

We have been trying to quantify the limitations on video data rate imposed by the SerDes interface.

Our basic setup is a DS90UB941AS-Q1 paired with a DS90UB924-Q1.

The DS90UB924-Q1 datasheet suggests it can only support 720p video (section 1).

But my calculations (based on similar calculations in this forum) show it can support up to 1080p:

1920 x 1080 x 30 (fps) x ~1.2 (blanking) = 88MHz.

This is within the 95MHz pixel clock specification of DS90UB924-Q1 (section 1).

Have I understood this correctly?

Related question: Where does colour depth (e.g. 24 bit per pixel) become involved? I would have guessed this would be part of the same calculation, but the result then becomes 2.1Gbps. Is this now representative of the FPD line rate? If so, again it appears to be within the datasheet specification of 2.976 Gbps (section 7.3.1). Have I understood this correctly?

Are there any misunderstandings here, and are there any more stringent limitations placed by the SerDes set (e.g. MIPI DSI rate at the serialiser)?

Kind regards

Laurence

  • +1
    TI__Genius 13250 points

    Hi Laurence,

    Laurence Parkins said:

    The DS90UB924-Q1 datasheet suggests it can only support 720p video (section 1).

    But my calculations (based on similar calculations in this forum) show it can support up to 1080p:

    1920 x 1080 x 30 (fps) x ~1.2 (blanking) = 88MHz.

    The DS90UB924 can support a PCLK between 5MHz and 96MHz when LFMODE=0. As long as this is met and the FPD-Link data rate is met the 924 will be able to handle it. For your example 1080p at 30Hz, I calculated 75.2MHz by adding 10% blanking to each Vertical and horizontal active parameters.

    • PCLK = 2112 x 1188 x 30Hz = 75.2MHz
    Laurence Parkins said:
    1920 x 1080 x 30 (fps) x ~1.2 (blanking) = 88MHz.

    I did the calculation for the equation provided and got the result 74.6MHz. This should still be fine.

    Laurence Parkins said:
    Related question: Where does colour depth (e.g. 24 bit per pixel) become involved? I would have guessed this would be part of the same calculation, but the result then becomes 2.1Gbps. Is this now representative of the FPD line rate? If so, again it appears to be within the datasheet specification of 2.976 Gbps (section 7.3.1). Have I understood this correctly?

    You are correct, the color depth is used to calculate the FPD-Link data rate needed between the 941 and the 924:

    • Data Rate = PCLK x bpp

    Best Regards,

    Gil Abarca

  • 0 in reply to Gil Abarca Ramos
    Prodigy 10 points

    Apologies for my poor maths. And many thanks for your support, this has answered my question.

    Kind regards

    Laurence