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CDCV304-EP: CDCV304 EP OUTPUT POWER

REKHA K
Prodigy 20 points
Part Number: CDCV304-EP
Other Parts Discussed in Thread: CDCV304

Hi, I am planning to use CDCV304 ep. Can I use this to drive a 50 ohm load? How much power(in dBm) will be available at each of its output? Thank you Rekha

  • 0
    TI__Genius 14540 points

    Hi Rekha,

    The device is PCI-X compliant so it can drive 50-ohms.  The conventional way to spec digital outputs is to guarantee VOH and VOL for a given current load. Therefore, it is very difficult to extrapolate power values from the datasheet as the impedance of the load is unknown using this test convention.  However, if you look at the IBIS model you can see the rise and fall time characteristics are given for the device when driving 50 ohms.  Assuming your output clock is 50% duty cycle, the rms value of your output signal, and therefore, power,  can be calculated shown below:

    Using the typical values:

    Vrms = ((2.5^2 + 0.7^2)/2)^0.5 = 1.83Volts

    P =Vrms^2/R =  (1.83^2)/50 = 0.0674 Watts = -41.7 dBm on 50ohms


    What are you trying to do with this device?  We don't often get questions about power delivered to 50 ohms from a clock buffer.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    TI__Genius 14540 points
    Hi,

    If this answers your question, please click the "This resolved my question" button so we can close the thread and add this to our database of searchable archived responses.

    Thanks
    Christian
  • 0 in reply to Christian Yots
    Prodigy 20 points

    Hi Christian,

    Thanks a lot for such a timely and detailed reply. I really appreciate your efforts to answer my question and it clarifies my doubt. 

    I am sorry for the late reply but i was slightly confused that, In your answer it is written that 'P =Vrms^2/R =  (1.83^2)/50 = 0.0674 Watts = -41.7 dBm on 50ohms'. But i think 0.0674 watts is 18.26 dbm. But how did you get -41.7dBm on 50 ohms? I didnt understand it. 

    I am actually trying to connect this device out to the reference input of a frequency synthesizer. I just want to make sure that it can meet the input specifications. 

    Regards,

    Rekha

  • 0 in reply to REKHA K
    TI__Genius 14540 points
    Hi Rekha,

    You are correct. I have no idea how I arrived at -41.7dBm. Sorry about that. Answer is +18.26dBm.

    Thanks
    Christian
  • 0 in reply to Christian Yots
    TI__Genius 14540 points
    Hi again,

    If this answers your question, please click the "This resolved my question" button so we can close the thread and add this to our database of searchable archived responses.

    Thanks
    Christian