AD9777: Full-Scale Output Current limit

Hi

I am wondering if it is possible to get more than 20mA fullscale output current from the AD9777, without degrading performance.

I see all of the plots in the datasheet are for 20mA.

I am hoping to use this device (or similar) on an ATE board, to interface with a new IQ modulator. The modulator is specified for 20mA, but having the capability to go up to 25mA would be ideal.

This board will then be used in Production Test.

I need the capability to source either a 10MHz sine wave or 10MHz/11MHz dual tone.

The digital on my ATE is limited to 50 MSPS at present, but with a licence add on I can get 100MSPS. Plus my ATE digital generates CMOS/TTL levels. I would require an CMOS->LVDS converter for any of the LVDS DACS. (Not a major issue)

Based on this limitation and having the ability to go greater than 20mA, is there a significant degradation in IMD when sourcing the dual tone mentioned.

The target Output IP3 of the Modulator is ~30dBm

I have looked at other devices, but I want to keep the pcb design as simple as possible and I'd like a DAC, I can get up and running relatively easily.

If you have and comments or other DACS in mind please let me know.

If you need more details, please let me know.

Thanks

Kind Regards,

        Paul.

  • 0
    •  Analog Employees 
    on Jun 27, 2012 10:22 PM

    The AD9777 has max output current of 21 ma. We have newer parts AD9779 and AD9125 which both support output currents up to 31ma and also show IMD performance curves  at 10ma,20ma and 30ms so you can see the perforamance change with output current. The AD9125 is our newest part with CMOS data interface. If offers the most features smallest package and should be able to support the performance you are looking for.

                                       Best Regards

                                       Tom

  • 0
    •  Analog Employees 
    on Jun 28, 2012 2:30 PM

    Hi Tom

    Many thanks for your quick reply.

    The AD9125 looks impressive and it has the CMOS inputs and an NCO. I had looked at the AD9779 and it looks good, except for the LVDS inputs.

    From looking at the plots, the data is for a FData of 125MSPS. Can I assume I can go all the way down to 50MSPS, for my application.

    The modulator I am testing also has some filters in it. The max being 500MHz cutoff. I was thinking of two methods to test this.

    1: Use the NCO to generate a carrier tone with no modulation, but not sure if 500MHz is capable, given  there is a 1000MHz spec on the AD9125.

    2: Use a harmonic of the DAC clock to test the filter, i.e. setup the AD9125 so that its second harmonic is at 500MHz, then enable/disable the filter in the modulator.

    I would be very interested in obtaining an Eval board. This way I can hook it up to the tester an get my code operational before I design my test board.

    Is ordering it on the ADI website the best way of getting this?

    AD9125-M5375-EBZ

    Thanks again.

    Kind Regards,

               Paul.

  • 0
    •  Analog Employees 
    on Jun 29, 2012 11:53 PM

    From looking at the plots, the data is for a FData of 125MSPS. Can I assume I can go all the way down to 50MSPS, for my application.

    Yes we can support down to 50MSPS Data rate

    The modulator I am testing also has some filters in it. The max being 500MHz cutoff. I was thinking of two methods to test this.

    1: Use the NCO to generate a carrier tone with no modulation, but not sure if 500MHz is capable, given  there is a 1000MHz spec on the AD9125.

    No you cannot do this with the NCO it only covers +/- Fdata/2. But there are filter modes shown in table 21 with 8x interpolatio that will shift a tone at DC to 4Fdata which is 500MHz when data rate is 125MSPS.

    2: Use a harmonic of the DAC clock to test the filter, i.e. setup the AD9125 so that its second harmonic is at 500MHz, then enable/disable the filter in the modulator.

    This is similar to coarse modulation which uses images but table 21 ninth row down on 8x interpolation is what will do this.

                   Best Regards

                   Tom

  • 0
    •  Analog Employees 
    on Jul 2, 2012 12:38 PM

    Hi Tom

    Thanks very much.

    Kind  Regards,

               Paul.

  • 0
    •  Analog Employees 
    on Jul 19, 2012 5:02 PM

    Hi Tom

    Got another quick question for you. I just got an AD9125 eval board and I want to hook it up to the Tester.

    For the DACCLK_P & DACCLK_N inputs. This is supplied from an AD9516-1BCPZ. To avoid having to write code to get this working, I was planning on making the following edit to the board and supply it with an RF source from the tester. see attached.

    Is this a valid edit?

    Many thanks

    Kind Regards,

                    Paul.