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[TRF3702EVM] please, help me. I need your help.

Taeyeop Kwon
Prodigy 150 points
Other Parts Discussed in Thread: DAC5686

Hello everybody

I'm Taeyeop from Seoul, Korea. I'm sorry to be poor at English.

I have been used TRF3702EVM(I/Q modulator) for WCDMA applications. In datasheet of TRF3702, the best performance of ACLR is 71 dBc using single-carrier WCDMA at -14 dBm channel power. The measurement set-up for this is combination of DAC5686(16 bit resolution) and TRF3702.

By the way, I use 14-bit AWG(Aribtrary waveform generator). Differences are below.

Datasheet : 16-bit DAC, differential input of TRF3702, measurement @ 2.14 GHz, Optimization of measurement circuit.

My case : 14-bit DAC, single-ended input of TRF3702, measurement  @ 1.85 GHz, Using TRF3702EVM(Evaluaton board) through 0.5m cables(Both I and Q) from AWG.

These are main 4 items of difference between datasheet and my set-up. Any other set-ups are almost same and I replace proper balun for 1.85 GHz applications. I also replace some resistors with proper value. As a result, ACLR measurement value of my case is 57 dBc by Spectrum Analyzer(LG Innotek SA 930).

The problem is that I cannot retain sufficient ACLR value like datasheet, 71 dBc. If there are no any other difference from datasheet, what can I do for better linearity?

Is it possible for degradation of chip performance cause difference of set-up mentioned above?? If possible, then which part is suspicious ?

This is very important part of my research. Any kind of advises will be helpful for me.
I thank you in advance for your concern.

 

  • 0
    TI__Intellectual 1650 points

    Hello Taeyeop,

     

    ACLR setups can be tough to setup as the issue could be related to the instruments, the device or some setting.  It may help this discussion if you can forward a screen shot of your ACLR signal that may help me understand what you are seeing.

     

    TRF3702 conditions:

    Do you have a 3.7V common mode input?

    Can you confirm your channel output power is at -14dBm for single carrier WCDM signal?

     

    Spectrum Analyzer:

    I’m not familiar with the SA-930.  I tried to look up the datasheet on line, but did not have any luck finding one.  In my experience the spectrum analyzer selection and settings are the biggest piece to the puzzle of making good SA measurement. 

    -          Have you ever measured  71dBc type ACLR numbers on this SA before?

    -          Recommended spectrum analyzer adjustements

    • Optimizing the reference and attenuation levels so that you are not seeing the non-linearities of the spectrum analyzers
    • Some spectrum analyzers have pre-amps that add some non-linearity, so I would try it with the pre-amp off
    • Averaging, I would recommend turning the averaging function on  (maybe up to 32 or 64 averages) and see if that helps
    • If your spectrum analyzer has noise correction, that can improve your ACLR also.
    • VBW/RBW – minimize the size of these so that the artifacts from the channel edges are not bleeding over to the next channel (and affecting your ACLR measurement).

     

    AWG:

    Have you ran the AWG input into your SA to see if your system ACLR is better than 71dBc?

    Some AWGs maybe not be capable of that level of performance.  I’m not sure what model you have?

     

    Hope this helps some

    Chris

  • 0 in reply to Chris Pearson
    Prodigy 150 points

    Hi Chris

     

    Thank you for your reply. I really thank you.

    * TRF3702
     I use exact 3.7 V for common mode input. In my set-up, output power of TRF3702EVM is about -13 dBm when ACLR is the best. I think 1 dBm difference is acceptable.

     

    * Spectrum Analyzer
    SA-930 is product of LG-Innotek. I think the model is used widely in South Korea. It's not familiar model.
    I agree with your opnion. I have never seen ACLR measurement using this model. This is my first experience.
    I would better measure ACLR using another spectrum analyzer, Agilent.
    I'll check every item you mentiond above about SA.

    *AWG
    The model is M2i.6034 of SPECTRUM. I think it is one of the best performance AWG among PCI interface.
    http://spectrum-instrumentation.com/de/products/da-arbitrary-waveform-generators-pci-pci-x-125-mss

    I'll check set-up mainly specturm analyzer. It is more possible than other variable.
    Thank you very much again Chris.
    Have a nice day.