AD9854

Hi!

Can you comment if I can characterize VPHS performance evaluation of AD8302 using AD9854 EVAL kit.

Sincere regards,

Dr.Babankumar

  • 0
    •  Analog Employees 
    on May 12, 2014 10:57 PM

    Hi,

    I am not an expert of AD8302. Looking at some of the thread about AD8302, I came upon this thread:

    http://ez.analog.com/message/19708#19708

    It was noted there that the 2 input power levels should be as close to each other.

    As I have understood your question, the input of your AD8302 will be taken from AD9854.

    The output of AD9854 is close to each other because the current output depends only on one variable, the RSET. Just make sure that you terminate I and Q with the same load impedance.

    The AD9854 is a quadrature digital up converter. The output I (IOUT1 and IOUT1B) and Q (IOUT2 and IOUT2B) are sine and cosine outputs so the outputs are 90 degrees out of phase.

    To check if the output of AD9854 is compatible with the input of AD8302, we have to check:

    1. input voltage range (IVR) of AD8302 for INPA and INPB :

            AC-Coupled (0 dBV = 1 V rms)              –73 min  –13 max   dBV

            @ 50 Ω                                                   –60 min      0 max   dBm

    2. frequency input of AD8302

         >0 to 2.7GHz

    3. output voltage of AD9854

          @50 ohm load, and 20mA IOUT, Vout= 1V (should not be exceeded because of compliance range)

    4. output frequency of AD9854

         DC to 150MHz

    The AD9854 eval board has the following output:

    • 10mA current output for both I and Q
    • 120-MHz LPF
    • 50 ohm load so output voltage is 0.5V. Converting it to PdBm, the output power would be -23dBm. This is within AD8302's IVR.

    To conclude, you can use AD9854 eval board to provide input to your AD8302 INPA and INPB.

    -Sittie

  • Dear Sittie,

    Let me first congratulate you for drafting such a beautiful response for me.

    Well, still matter remains, as you are  hitting incomplete exactly to where and what it should have been.

    Before, adding my inputs, I would wonder and request if you can bring Joel (the one who responds to my ad8302 queries, an expert on that) on this discussion platform / thread. Because what I'm asking him relates ad8302 and then it includes some portion of ad9854 too, which is your area. That's when my problem starts because like you said "you are not an expert on ad8302". He too saying something same that he is not an expert and rather requested someone to come on-board from "ad9854, DDS" community for that matter.

    Can we get away with this impediment you think??

    For me it would be a best situation conversing with both experts under one thread, as all would be reading every on-going details. That would result in pouring-in exact and much more enriched / helpful experience in terms of its contents.

    Coming back to technical aspect:

    I was asking you about VPHS characterization of ad8302 using ad9854 because to do that, we need to bring I/ps of ad8302 in quadrature. That is the first requirement. This brings VPHS output of ad8302 to nominal that is 900mV. From there, rest all differences of phase variations are measured between two I/ps of ad8302.

    Rest, I fully agree as regards I/p limitations of ad8302 what you cited in your last post. And your detailed explanation on that considering ad9854 o/ps to clearly notice differences and feel cautious about, are worth for deciding upon use of any attenuators, if need be.

    I simply feel curious to know if I can see VPHS o/p changing in steps according to I/p change applied from ad9854. This is what i.e.STEPWISE variation in magnitude at the VMAG o/p of ad8302 was observed by me using two function generators to characterize magnitude performance of ad8302. These two function generators allowed me changing I/p magnitude supply to the two I/p channels of ad8302 to observe corresponding variation in the VMAG  o/p of the ad8302.

    To determine "MAGNITUDE' and "PHASE' variations of the two i/p RF signals is what this IC ad8302 does, right?  That's something I'm trying to validate and understand to proceed further on actual application development.

    My application would require to use 100KHz-100MHz operating freq band for the I/p signals.

    Can you comment as above.

    Regards,

    Dr.Babankumar

  • 0
    •  Analog Employees 
    on May 15, 2014 1:49 AM

    Hello Dr. Babankumar,

    If you change the phase of the input signals on the AD8302, it will change VPHS. 

    I thought the ad9854's outputs we in quadrature, always.  So if you insert a load between the two parts that changes the phase, then the AD8302 should be able to measure it.  Keep in mind if the phase change of the load is anywhere in the 90 degree area, your total phase will be back to 0 or 180 degrees, and VPHS will be in error.

    Regards,

    Joel

  • Dear Sittie and Joel,

    Thanks to both for bringing yourself on common platform.

    Sittie in her last post confirmed safe use of ad9854 for applying i/p signals to ad8302. She did inform her point with detailed explanation supported with actual calculations considering ad9854 EVAL board's component as well as absolute limitations, and ad8302's i/p limits.  I appreciate these details.

    Joel said: as soon as phase on the i/p channels of ad8302 varies, it is measured successfully as long as such i/p channel phase variations are kept within +/- 15 To +/- 165 deg range. Beyond this range, phase linearity error would surface as per TPC 26.

    Can you both now comment on my intention to check VPHS o/p on ad8302 for a systematic, STEPWISE phase variation applied from ad9854. Do you think, ad9854 can supply STEPWISE phase variations to i/p channels of ad8302 such that ideal ramp (+ve/-ve slope) characteristics can be plotted using VPHS o/p values for every associated i/p phase changes applied. What probably I mean is, ad9854 would apply say INPB(fixed) using its IOUT1, and vary phase on INPA using IOUT2. Can these two o/ps (IOUT1 & IOUT2) of ad9854 be varied independently to bring systematic phase variations to ad8302 for checking complete VPHS characteristics. Can ad9854's o/p be controlled independently for phase, one fixed and other variable, to check VPHS characteristic of ad8302???

    Sincere regards,

    Dr.Babankumar

  • 0
    •  Analog Employees 
    on May 15, 2014 11:56 PM

    zHi Dr. Babankumar,

    It sounds like you can put whatever data you need into the control DAC (and thus make is a stepwise phase variation referenced to the I DAC):

    CONTROL DAC
    The 12-bit Q DAC can be reconfigured to perform as a control
    or auxiliary DAC. The control DAC output can provide dc
    control levels to external circuitry, generate ac signals, or enable
    duty cycle control of the on-board comparator. When the SRC
    Q DAC bit in the control register (Parallel Address 1F hex) is
    set high, the Q DAC inputs are switched from internal 12-bit
    Q data source (default setting) to external 12-bit, twos complement
    data supplied by the user. Data is channeled through the serial
    or parallel interface to the 12-bit Q DAC register (Address 26 hex
    and Address 27 hex) at a maximum data rate of 100 MHz. This
    DAC is clocked at the system clock, 300 MSPS (maximum), and
    has the same maximum output current capability as that of the I
    DAC. The single R
    SET
    resistor on the AD9854 sets the full-scale
    output current for both DACs. When not needed, the control
    DAC can be separately powered down to conserve power by
    setting the Q DAC power-down bit high (Address 1D hex).
    Control DAC outputs are designated as IOUT2 and
    IOUT2
    ,
    Pin 52 and Pin 51, respectively.
    That excerpt is on page 30 of the AD9854 datasheet. 
    Hope this helps,
    Joel