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Original question:

DS90UB953-Q1: DS90UB953 CLOCK MODE QUESTION

DS90UB953-Q1: clock mode configuration

Dongbao Zhou
Expert 4170 points
Part Number: DS90UB953-Q1

Hello,

Could you let me know why providing REFCLK to sensor then forward CLK to 953 is not recommended? Is it because the jitter of sensor CLK is not good enough?

Can we use independent REFCLK  (from two crystal oscillators) to sensor and 953? It works according to my customer's test, is there any risks for such kind of application? I think the only disadvantage is adding cost and pcb size.

Thanks

Dongbao

  • 0
    TI__Expert 3390 points
    Hi Dongbao,

    REFCLK can't be provided to a sensor, CLK_OUT can be provided to a sensor. As shown in Figure 9 of the DS90UB953-Q1 datasheet, In Sync mode, REFCLK goes into the Deserializer and then is sent to the 953 via the Back channel, the 953 then uses it to generate the Forward channel and optionally can provide a CLK_OUT to a sensor. This is typically recommended since you are using a single clock source to drive the receiver and all of the sensors and the system is locked to a common clock in the same clock domain.

    Yes, if you are in non-sync mode, you can provide a clock to a sensor and another to the 953 CLKIN Pin and that will work. In sync mode, as described above, you can provide a REFCLK to the 954 and then a seperate clk to a sensor, the 953 will work based on the refclk from the 954 or compatible Des.

    Regards,
    Mandeep Singh
  • 0 in reply to Mandeep S
    TI__Expert 4170 points

    Hi Mandeep,

    Thanks for your reply.

    Please check the original question for my first question, application diagram as below, although the picture is captured from 933 d/s, i think it works for 953 and 954, it's just not recommended because of the pclk jitter. 953 and 954 works in unsynchronized mode for this configuration.

    Dongbao

  • 0 in reply to Dongbao Zhou
    TI__Expert 3390 points

    Yes, this is not recommended for 953-954 as mentioned in the original post. In non-sync mode, you have two options. You can use two independent osc/crystals to provide a clock into the CLKIN pin of the 953 and the other crystal directly into the imager. The other option, as mentioned in the original post is to provide a clock into the CLKIN pin and use the CLK_OUT of the 953 to provide a clock to your imager. The second option will save you space and cost of another osc/crystal. In either case, please refer to the max allowable input jitter (0.05UI*) for the CLKIN pin in the DS90UB953-Q1 Datasheet ROC section of the Electrical Tables.

    Mandeep