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Original question:

DS90UB953A-Q1: Buffer errors trying to stream 3840x1080 @ 30 fps

DS90UB953A-Q1: Understanding FPD Link III speeds

Luis Villaran
Prodigy 80 points
Part Number: DS90UB953A-Q1


I have two questions related to FPD Link II speeds:

1) I'm trying to understand the frame rate limits listed in the datasheets of a DS90UB953-to-DS90UB954 link.

As an example, we have an image that is 3840x1080 i.e. 4MP.  If it's 10-bit then the bandwidth needed to go 60FPS would be 3840x1080x10x60 =~ 2.5GBps.  The FPD Link III is a 4Gbps link, so does that mean that it should support going 60fps with this image?  The data sheet lists the max frame rate at 30 FPS for 4MP and I'm trying to understand why?

2) My second question: in the case of a dual deserializer, like the 954, what happens when we add a second sensor? Does the effective bandwidth halve? For example, let's say the frame rate limit for a FPD link is 30fps @ 4MP, then does adding a second sensor mean that each link can now only support 15fps @ 4MP or can each link do 30fps @ 4MP.

Thanks,

luis

  • +1
    TI__Guru** 109170 points

    Hello Luis,

    1) Your calculation is correct but you need to add the Blanking (approx. 15-30%) of the Image sensor. So it would be: 3840x1080x10x60x1.25= 3.11Gbps. This is the pure CSI throuput coming out of the image sensor into the SER. For calculating the linerate over the FPD-Link you should add approx. 25% overhead. 

    The numbers in the datasheet, i.e. 30Fps for 4MP is just an example.

    2) No, each DES input can support up to 4.16Gbps linerate.

    Nevertheless, you will not be able to transfer the above mentioned data over both links, because the DES has some CSI-2 overhead at the output, which makes the max supported input datarate over both links = 5.91Gbps.

    Which means if you want to have the above resolution, you need either to reduce the blanking on the Image sensor, or reduce the frame rate from 60Fps to ~58fps