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ADC12J4000EVM Input Power

Chris8529
Prodigy 70 points
Other Parts Discussed in Thread: ADC12J4000EVM, ADC12J4000

Hello, I am testing the ADC12J4000EVM eval board and need to compute the absolute power in dBm into the ADC.  I have a measurement of power at the input to the board @ the RF input SMA connector.  I assume there is some insertion loss and a matching network on the front end that attenuates the input before RF is provided to the ADC.  Can anyone help translate power into the board to power into the ADC?

  • 0
    TI__Genius 13335 points

    Hello Chris,

    It is unclear whether you mean absolute maximum input power that the device can handle without destruction or full scale input power in absolute terms like dBm.

    1) The maximum input to the ADC is defined on page 8 of the ADC12J4000 datasheet, which is listed for 3 different conditions in dBm.

    2) The full scale input range can be found by looking at VID in the electrical spec table on page 12 which is listed in mVpp and must be converted to dBm. The default full scale range is 725mVpp into 100Ω, which translates to -1.82dBm. The full scale range can be adjusted from 500mVpp to 950mVpp through the GAIN_FS register setting (registers 0x022 and 0x023). These can also be converted to dBm the same way. 

    On the EVM there is only a 1:2Ω balun (B0430J50100AHF) which does not require a matching circuit. To get the required dBm value, you must simply account for the balun insertion loss which varies over frequency.

    So for example, at 725mVpp full scale setting assuming you want to have an input signal of -0.5dBFS @ 900MHz seen by the ADC you could calculate the following:

    (FSRdBm) + (Desired_dBFS) - (Balun_insertion) = Required Power at SMA Input

    (-1.82dBm) + (-0.5dBm) - (-1.2dBm) =  -1.12dBm

    Keep in mind if you are using cabling or a filter prior to the EVM, then you need to account for those losses too. You can typically calibrate these out by measuring on a spectrum analyzer and compensating for the drop.

  • 0 in reply to Luke LaPointe
    Prodigy 70 points

    Luke, thanks for the reply.  Very helpful.  Your second response answered my question; we're trying to compute full scale input power in dBm by accounting for the eval board insertion loss.  And yes, we have calibrated our setup and have a measurement of absolute power into the SMA connector in dBm.


    I'm very impressed with TI's responsiveness on the E2E forums.  Keep up the good work!