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ADS54J20EVM: common mode voltage and sampling frequency range with 10MHz reference

Majid Boloorian
Prodigy 220 points
Part Number: ADS54J20EVM

Hello

what is the ADC common mode voltage set to on this EVM in the default ac coupled configuration or do I need to supply this? I will have an input signal that swings from 0-1.9V, I take it that this is the limit, are the input transformers 1:1?

what is the range of ADC sampling rates that I can set on this EVM, I would like to test at 100MSPS, 200MSPS, 500MSPS, 1GSPS. Is this possible with supplying a 10MHz external reference to the onboard clocking solution. I would like to synchronize other boards hence the use of the external 10MHz reference.

Thanks

  • 0
    TI__Genius 12780 points
    Hi Majid,

    We are taking a closer look into your question, and will be back with you soon.

    Best Regards,

    Dan
  • 0
    TI__Guru* 91947 points

    Majid,

    With the EVM setup for AC coupling, the inputs are referenced to the internal common mode, which is 2.0V nominal. The input transformers are 1:1. If you plan on using AC coupling, you do not have to provide a common mode voltage.

    By default, the EVM uses a 122.88MHz VCXO, which allows the LMK to provide the following ADC sample rates:

    122.88MHz, 245.76MHz, 491.52MHz, and 983.04MHz. These configuration files are all available from the GUI. If you were to change this VCXO to a 100MHz part, you would then be able to generate the frequencies you mentioned above.  Providing an external 10MHz reference clock will only allow you to synchronize the VCXO, which would allow you to synchronize multiple boards.

    If you can provide an external 1GHz clock, you could run the LMK in clock distribution mode and generate all of the desired frequencies by dividing down this clock. 

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 220 points
    Jim - Thanks. We might be able to get away with the current VCXO as those rates are close enough.