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AFE7686: Leakage on TXC and TXD at 2949.12 MHz

Buu Duong
Prodigy 10 points
Part Number: AFE7686
Other Parts Discussed in Thread: AFE7688

I am using the AFE7688 which has sampling clock at 2949.12 MHz. However, I have seen the spur coming out from TX output of the AFE7688 at 2949.12 MHz. The spur comes out strongest in TXD (pins P20/R20) and TXC (pins V20/W20). Spur in TXB (pins F20/G20) and TXA (pins B20/C20) are much lower (about 7-10dB). Can you please help us to identify the problem and find solution for that?

Our goal is to eliminate the spur or at least to reduce its power in TXC/TXD to be the same as inTXA/TXB.

Thanks.

BD

  • 0
    TI__Guru* 79364 points

    Hi,

    The TXDAC is operating at either 6GSPS or 9GSPS. The DAC should not be running at 2949.12MSPS. 

    I suspect there is a clock leakage from the CLKOUTp/m pins to the TXC/TXD. Could you please terminate the CLKOUTp/m pins to see if this improves the leakage of the CLKOUT spur of 2949.12MSPS? Thank you

  • 0 in reply to Kang Hsia
    TI__Guru* 79364 points

    Hi Buu,

    Just checking in on this. You may also tri-state the CLKOUT output by doing the following commands:

    0x11 0x10 //open PLLDIGP0 page

    0x24 0x04 //tri-state clkout

    0x11 0x00// close PLLDIGP0 page