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Request the schematic review with AD9251-80 and ADA4937-1


My customer wnats to get your advice about their schematic with AD9251-80 and ADA4937-1.

They used AD9251-65 and ADA4937-1 in their system, but now they will change the sampling frequency of their system.

So they need your help.

The sampling frequency that they want to use is 76MHz and IF is between 47.5MHz and 95MHz.

And their target application is LTE ICS repeater.

Would you confirm their schematic with AD9251-80 and ADA4937-1 ASAP?



  • Hi Se-woong,

    I am looking more at the ADC portion of the schematic. I think it looks pretty good, with the following comments/questions.

    • The CLK+/- pins are internally biased, so they should be AC coupled to the clock source. I do not see AC coupling capacitors in the schematic, for the clock.
    • The VCM pin on the AD9251 is connected directly to R328, R306, R317 and R308. This is OK. One additional thing I would consider is adding pads for additional series resistors after the fanout to channel A and channel B. These could be populated with 0Ohms initially. The intention is to give the flexibility to add some resistance for isolation between channels, if desired.

    • What are the differences between this schematic and the one that was used before for the AD9251-65?
    • What is the supply voltage for the ADA4937?
    • What is the amplitude of the analog input to the ADA4937?

    Thank you.


  • Hi, Doug

    Thank you for your kind help.

    Actually they want to use the same schematic as the one that was used before for the AD9251-65.

    So they want to get your confirmation for using same schematic even though the sampling rate of AD9512 is increased from 65MSPS to 80 MSPS.



    PS. Their ICS repeaters already deployed to commertial LTE networks in Korea several years ago.

  • Hi Se-woong,

    If their original system worked fine, and the only change in the new system is the ADC sample rate, and the analog input frequency is the same between the old system and new system, then we can be confident that the analog input path (including the ADA4937) is still OK.

    Is the input frequency the same in the new system as the old?