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DAC12DL3200: Calculation of Full Scale Output power

Aaron Van Rossum
Prodigy 10 points
Part Number: DAC12DL3200


Tool/software:

Hello, 

I am trying to figure out my cascaded analysis for an RF powerchain and wanted to know what my expected output should be.

If we set course current and fine current to its max digital value, we should have a differential current Iffswitch to be 20.5mA based on the equation give by page 58 in the datasheet.

Given that Rterm is 106ohms, then the output power for a single sign wave should be Irms^2*Rterm = (20.5mA)^2*106 = 44.5mW. Converting this to dBm gives around 16dBm full scale.

After taking in account the Normalized Magnitude response, my output power is still about 15 dB less than expected. I know I am outputting FS current, so am I calculating the output power wrong?

  • 0
    TI__Mastermind 41940 points

    Hi Aaron,

    See page 14 of the datasheet, the output power is only 1.4dBm.

    Therefore, the output is ~1Vpp DIFF or 500mVpp SE.

    So it seems as if you are getting the right output power.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 10 points

    Hi Rob, 

    Thanks for you quick response. 

    Does this output power include the dbFS frequency response? I am looking to to figure out what the theoretical output power ignoring the frequency response given in the first page. 

    That frequency value on page 14 is not in my bandwidth region, so I'm trying to extrapolate to the FS to calculate the output power given my mode and output frequency. 

    Thanks,

    Aaron 

  • 0 in reply to Aaron Van Rossum
    TI__Mastermind 41940 points

    Hi Aaron,

    Does this output power include the dbFS frequency response? RR: No, this is measured at the output pins with only the appropriate load, but no output network. I am looking to to figure out what the theoretical output power ignoring the frequency response given in the first page. RR: that is given in the datasheet on page 58, 7.3.2.1 DAC Output Structure

    That frequency value on page 14 is not in my bandwidth region, RR: is the frequency value more or less than your BW region? so I'm trying to extrapolate to the FS to calculate the output power given my mode and output frequency.  RR: that is given in the datasheet on page 58, 7.3.2.1 DAC Output Structure

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 10 points

    Hi Rob, 

    I'm still having trouble understanding the output power expected from the DAC. My design uses 2:1 impedance ratio balun which is the same as the 100 ohm load as described in footnote (5) on page 15.  I am at FS current as described in in page 58 and am operating with a normalized frequency of 1.2 in 2xRF mode which is -6dB from fullscale. 

    This is what I calculate the output power to be with a 2:1 balun:

    Pout = (Irms^2)(Rterm || Rload) = 47mW -> 16.8 dBm, so I should measure 16.8dBm 0-6dB = 10.8dBm.

    I want to clarify my baseline for power, because I am only measuring -40 dBm and need to figure out what is going wrong.

    Thank you for your assistance on this,

    Aaron

  • 0 in reply to Aaron Van Rossum
    TI__Mastermind 41940 points

    Hi Aaron,

    Please share your schematic and I will look this over. What is the output frequency used for your measurement? -40dBm seems way too small.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 10 points

    Hi Rob,

    Thank you for taking your time for this. Is there anyway we can chat off of a public forum for schematic screenshots? 

    Thank you,

    Aaron

  • 0 in reply to Aaron Van Rossum
    TI__Mastermind 41940 points

    Hi Aaron,

    Yes, I will close this post and send you an email.

    Please be on the lookout for it.

    Regards,

    Rob