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ADRF6701 Query

I am using AD9854 (I & Q output DDS) with ADRF6701(I & Q input Quadrature Modulator with Integrated VCO) to generate SSBSC output (hopping between 935-960 MHz)

The PCB is in design stage at the moment and expected to complete sometime soon within 10 days.

However, I have one query on ADRF6701. Please go through the attached pdf (extracted from ADRF6701 datasheet). I dont seem to understand from the datasheet the 0 & 90 phase shift of VCO, whose frequency would be 850 MHz (Fixed) , be applied to which Mixer-Upper or Lower (mixing with QP, QN or IP, IN)?

I intend to mix this 850 MHz from VCO (0 & 90 phase shift) with 85-110 MHz from DDS (AD9854-I & Q signals) to generate SSBSC with Lower Sideband Supressed.

I will appreciate if help is arrived soon

ADRF67011.pdf
  • Hi, Sudhanshu,

        In the ADRF6701 block diagram, the "div/2 0/90" block is consisted of a pair of dividers that divide opposite phases of the input (2xLO) frequency by two, SIMULTANEOUSLY, to generate two outputs with phase difference of 90 deg.  (The 180 deg. difference between the two input phases are halved, to produce 90 deg. in difference at the outputs).  Whether upper or lower sideband is generated depends on the phase relations of the I & Q signals, so you may have to invert one of them (or switch I with Q) to generate the desired sideband.

        Hope this helped.

    Benjamin

  • Hello Benjamin,

    Yeah, I already knew that. But you did not specify what input from DDS be applied to this ADRF6701 to generate upper sideband.

    In other words, Do I need to connect IOUT of DDS to IP & QOUT to QP to generate upper sideband or is it other way round?

    Quick reply would be appreciated.

    Sudhanshu

  • Hi, Sudhanshu,

       Sorry -- I didn't realize that was the main question.  I can never remember which way is up, so I always have to try it on the bench to be sure.  I know we should have this down and well documented with waveforms by now, but life doesn't allow us to complete everything we want.  Do you have access to the evaluation boards to try this out?

    Benjamin

  • Dear Benjamin,

    Yeah you got me finally. I am afraid that I don't have the evaluation board (any of upconverter's EVM) to try this out and my PCB design should be completed within a week or so after that PCB would go to fabrication. Before that I want to be sure which way is UP.

    So, I request you to do this for me and update the documentation. It will be highly appreciated not even by me, but by other users too who want to use ADRF670x without using the Evaluation Board.

    Sudhanshu

  • Sudhanshu,

    There is a good tutorial on the math behind quadrature modulation in the AD9777 high speed DAC datasheet. The most important thing to remember is that the RF output of an IQMod is the real part output of a complex mixing operation where the complex input (I +j*Q) is multiplied by the complex mixer signal e^(j*2*pi*f). When going through this math, it is sometimes easy to get plus signs and minus signs mixed up. If, after going through the math the signal still ends up on the wrong side of the LO there is a fallback. If this happens you can simply multiply either the I or the Q signal by (-1) in the digital domain and the image will swap from positive to negative frequency. If you need more detailed information on the math, please let me know, I can write up a few slides,

    Steve 

  • Dear Steve,

    Yeah you are right, but I simply can't do away with multiplying either the I or Q signals by (-1) as I am feeding the base band input to the quadrature modulator from the DDS AD9854, rather than to simply swap from negative to positive frequency and vice-versa on PCB.

    Yeah, you can always take time out to experiment  AD9854 with ADRF6701 and write-up a few slides about the math behind it, so users like me become more aware of it like where to feed in the I & Q inputs in Quadrature Modulator to get the desired sidebands. PCB redesign is an expensive affair, and mine is getting completed within a week or so after it goes into fabrication. So consider my request on top-priority. I have to complete this project in less than a month and I am already stressed.

    I already sent the same query to Analog Devices, Bangalore Office, India numerous times. But I am not getting a satisfactory response from their side making me feel like Analog Device's claim about their support is best in its field.

  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin