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help in AFE5808 clocking

chandu dusa
Intellectual 870 points

Other Parts Discussed in Thread: CDCE949, AFE5808, AFE5808A

Hi,

   I'm designing a 8 channels rx ultrasound board. currently I am trying to give clock inputs by cdce949 with PLL1(3 outputs to CLKP_16x, CLKP_ADC, CLKP_1x ).And What are the connections for negative clock inputs?. Also how much the clock frequency(in Mhz) required for three afe clock inputs?. Please suggest me If any better way of giving clock inputs and correct me. What diiference between CLKP_  ,CLKM_  . Please suggest connections for CLKP_16x,
CLKM_16x  , CLKP_1x  ,CLKM_1x , CLKP_ADC  ,CLKM_ADC.


Thank you.


regards,
chandu.
  • 0
    TI__Intellectual 2635 points

    Dear Chandu,

    the AFE5808 can accept both differential and single ended clocks both in CW and TGC mode and as per datasheet it doesn't seem to make any difference in terms of performances. With that being said, assuming you do want to use the CDCE949 chip and hence a single ended LVCMOS clock, you need to ground the pins CLKM_1x, CLKM_16x, CLKM_ADC. The other option might be to use a differential clock and the best way to do that is to use a single-ended input to differential output transformer like the ADT4-1WT.

    The reason why you have a CLKP_ and a CLKM_ pin is just because the chip can be driven by a differential clock as well. So like in every differential signal you need a positive, CLKP_ , and negative, CLKM_, input whose difference  is the differential signal you actually apply to the chip.

    With regards to the clock frequency required for each input clock, keeping in mind that the CW clock and the ADC one are not correlated and assuming that you want to use the CDCE949 and that it does the job, a possible set of frequencies might be:

    CLKP_ADC = 40MHz
    CLKP_1x = 2.5MHz
    CLKP_16x = 40MHz
     
    Anyway, whatever the set of frequencies is the only concern is making sure that the CLKP_16x is 16 times the CLKP_1x.
     
    Please have a look at the AFE5808A EVM user's guide schematic section for much more information:
     
     
    Hope it helps.
     
    Regards,
     
    Fabio
    Applications Engineer
    TI Healthtech/Imaging