DAC AD9115 with ADRF6720-27

I have implemented the DC blocking capacitor as shown on a previous post to create the level shift at 2.7V.

https://ez.analog.com/rf/f/q-a/72214/adrf6720-27-rfoutput-problem/168465#168465

I am seeing some ringing on the Vector Signal Analyzer on the burst power output.  Attached are the pictures of the VSA output and the IQ waveforms into the modulator.

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  • I realized that I probed the output of the DAC (AD9115) and did not show the output of the lvl shifted waveform.  The waveform does not look good going into the ADRF6720-27.  

    I have ordered the ADRF6720 so that I don't have to have the level shift circuit.  Looking at the datasheet for the ADRF6720 it shows a sample interface in Figure 45.  It says to set the DAC to 10mA midscale current.  I am using the pin mode configuration for the AD9115.  Should I set the FSadj current value to full scale 20mA or 10mA?  Is this level shift circuit with the DC blocking capacitor causing this ringing on the output that I am seeing?  

  • +1
    •  Analog Employees 
    on Jul 25, 2019 5:58 PM over 1 year ago in reply to aclee1

    Hello, 

    It looks baseband inputs to ADRF6720-27 are the modulated signal. I suggest to check it with a CW single-tone (few MHz) and check four inputs at phase/amplitude.

    what is CH3 on your screen shot?    Is it enable signal to transmit signal?

    Is ADRF6720-27 and level shifter all time on and just control baseband inputs on/off? I am not sure if we can see any abnormal operation (like ringing in 200us range) on spectrum analyzer but can you try to check output spectrum with spectrum analyzer? 

    I don't think DC blocking capacitor causes this ringing. Let's see how it looks like with a CW tone.

    For ADRF6720 with AD9115 DAC,

    Set full scale 20mA on AD9115 and 10mA midscale with set 500mV with 50 ohm termination on DAC.  

    Thanks

    Tony

  • CH3 is the ENBL on the IQ modulator.

    I switched the IQ modulator to the ADRF6720 and everything seems to be working well.  Thanks for the support.

  • +1
    •  Analog Employees 
    on Aug 8, 2019 9:44 PM over 1 year ago in reply to aclee1

    It is good to hear ADRF6720 works.

    FYI, If you consider ADRF6720-27, it can interface to AD9152/54 directly without a level shifter.

    Thanks

    Tony

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