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Output power of TRF374017

jeetendra hyanki
Prodigy 190 points
Other Parts Discussed in Thread: TRF370417, DAC5672, DAC908, TRF3705

Hi,

I have designed my custom board for direct upconversion.

I am generating analog IQ (.416 Peak to peak)signal using AD5672 DAC and feeding to TRF374017 with LO 4800MHz( -11dBm)

output is coming but LO leakage is visible in the modulated output and power is also very low -35dBm.

Point 1 : I want output power 0dBm.What should i do.?

Point 2: There is a term that common mode voltage should be 1.7V before TRF374017. How to do it?

Point3: How to interface DAC5672 with TRF370417 with 1.7V common mode voltage.

Point4: Which material should I use for PCB?

Regards

J S Hyanki

  • Prodigy 190 points
    TRF374017 is TRF370417. It is typographic mistake.
    Regards
    J S Hyanki
  • Prodigy 40 points

    Hi,

    I did something really similar just Yesterday. I used a TRF3705 as IQModulator and two DAC908 for BB generation (1 for I and 1 for Q). I was quite satisfied of the result even if also I discovered a "leakage" of the LO. You may see in the picture that there is my pulsed signal (Radar Application) at a frequency of LO + IF (0 dBm) and the original LO frequency about 30dB under the signal.

    I really do not remember what isolation the datasheet of the modulator reported, but I am sure that there will always be some LO at the output.

    Now, to answer your questions:

    • The datasheet of the TRF370417 reports in all the example a LO power of 4dBm single ended. Your LO is -11dBm and it is probably to weak.
    • The common voltage can be achieved with simple resistors and it is important to keep it in the range specified in the datasheet, but keep in mnd that you will lose some peak to peak voltage (and so output power in the resistors). Have a look if there are different IQModulators with different common voltage ranges (the one I used, TRF3705 accepts from 0 to 0.5 V)
    • I think I already answered your third point
    • At these frequency I continue to use FR408 from osh park (4 layers at 10$ per square inch), but I know I am mean.

    Hope I helped you

  • in reply to fabrizio de rosa
    Prodigy 40 points
    I forgot... I will try to reduce my LO leakage throw DC calibration (the 0 of the DACs is not exactly 0V of ifference between + and -), I think I can gain some dB.
  • in reply to fabrizio de rosa
    TI__Mastermind 18095 points

    Check out this app note: http://www.ti.com/lit/pdf/slaa399.  It describes how to interface current source DACs to a 1.7V common mode voltage of the modulator.  Alternatively, you can switch to the TRF3705 which operates with a 0.25 or 0.5V common mode that does not require a translation network..

    --RJH

  • in reply to RJ Hopper
    Prodigy 190 points
    Hi RJH,
    Thanks for giving me a app note. Now i am looking that how to kill LO leakage and achieve 0dBm modulated power.
    for that if you have app note please forward.

    Regards
    J S Hyanki