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.

Parents
  • 0
    •  Analog Employees 
    on Jul 30, 2012 8:26 PM

    Hi Tom

    Many thanks for this.

    After a lot of wire mods, I got the AD9125 eval board working with the tester. I am able to read and write to the device and get a signal on the DAC outputs using the NCO. I tried the Parallel port, but this was unsucessfull and I have a few questions for you. Sorry but this device is new to me and I really aprechiate all your help.

    1:

    I got a 3MHz test tone on the DAC output, but I noticed the 2nd harmonic was ~-64dBc. Is this expected? I though it might be a lot lower.

    2:

    I performing the following writes to get the NCO to operate. I got this code from the AD9122 production program

    Name                              Addr         

    Comm:                             0x00                                   Perform a Software Reset

    HB1 Control                     0x1C                                  write all 0's

    HB2 Control                     0x1D                                  write all 0's

    HB3 Control                     0x1E                                  write all 0's

    Datapath Control            0x1B             0xC6 :  Select sideband = 1

                                                                                   Bypass Sync = 1                  

                                                                                   Bypass Premod = 1

                                                                                   Bypass NCO = 0

    FTW1                                  0x30                         Word corresponding to 3Mhz                                                  

    FTW2                                  0x31

    FTW3                                  0x32

    FTW4                                  0x33

    NCO FTW Update            0x36                         Write 0

    NCO FTW Update            0x36                         Write 1: Then Read back and confirm FTW Ack: OK

    To get the Parallel input working all I changed was "bypass NCO = 1"

    Data Format                      0x03                          Write all O's   (2's complement format)

    Datapath Control            0x1B             0xE6 :  Select sideband = 1

                                                                                   Bypass Sync = 1                  

                                                                                   Bypass Premod = 1

                                                                                   Bypass NCO = 1

    Is this correct, or are there any other writes I need to perform?

    I am seeing nothing on the DAC outputs except the clock rate at which I clock the Parallel port, ~45MHz.

    Perhaps I have something wired wrong or a mistake in the software that is used to clock the Parallel input. But I said I would ask you first, before I spend more time on it

    Actually does any example code exist?

    3:

    I have placed the AD9125 on my schematic and just want to ask you a few questions on the configuration I have placed some of the pins. I have copied most of the eval board.

    A: REFCLKP, REFCLKN

          Since I am not using the internal PLL and I won't need the sync option either, I ac coupled these pins to ground

    B: I am powering up the device with two 1A regulators, ADP1706, 3.3v & 1.8v

         I have connected AVDD33 to IOVDD & CVDD18 to DVDD18. I think this should be ok...right?

    C: I am using the balun + circuit from the apps board as the interface to the DACCLK P/N pins

    Thanks again

    Kind Regards,

                          Paul. 

Reply
  • 0
    •  Analog Employees 
    on Jul 30, 2012 8:26 PM

    Hi Tom

    Many thanks for this.

    After a lot of wire mods, I got the AD9125 eval board working with the tester. I am able to read and write to the device and get a signal on the DAC outputs using the NCO. I tried the Parallel port, but this was unsucessfull and I have a few questions for you. Sorry but this device is new to me and I really aprechiate all your help.

    1:

    I got a 3MHz test tone on the DAC output, but I noticed the 2nd harmonic was ~-64dBc. Is this expected? I though it might be a lot lower.

    2:

    I performing the following writes to get the NCO to operate. I got this code from the AD9122 production program

    Name                              Addr         

    Comm:                             0x00                                   Perform a Software Reset

    HB1 Control                     0x1C                                  write all 0's

    HB2 Control                     0x1D                                  write all 0's

    HB3 Control                     0x1E                                  write all 0's

    Datapath Control            0x1B             0xC6 :  Select sideband = 1

                                                                                   Bypass Sync = 1                  

                                                                                   Bypass Premod = 1

                                                                                   Bypass NCO = 0

    FTW1                                  0x30                         Word corresponding to 3Mhz                                                  

    FTW2                                  0x31

    FTW3                                  0x32

    FTW4                                  0x33

    NCO FTW Update            0x36                         Write 0

    NCO FTW Update            0x36                         Write 1: Then Read back and confirm FTW Ack: OK

    To get the Parallel input working all I changed was "bypass NCO = 1"

    Data Format                      0x03                          Write all O's   (2's complement format)

    Datapath Control            0x1B             0xE6 :  Select sideband = 1

                                                                                   Bypass Sync = 1                  

                                                                                   Bypass Premod = 1

                                                                                   Bypass NCO = 1

    Is this correct, or are there any other writes I need to perform?

    I am seeing nothing on the DAC outputs except the clock rate at which I clock the Parallel port, ~45MHz.

    Perhaps I have something wired wrong or a mistake in the software that is used to clock the Parallel input. But I said I would ask you first, before I spend more time on it

    Actually does any example code exist?

    3:

    I have placed the AD9125 on my schematic and just want to ask you a few questions on the configuration I have placed some of the pins. I have copied most of the eval board.

    A: REFCLKP, REFCLKN

          Since I am not using the internal PLL and I won't need the sync option either, I ac coupled these pins to ground

    B: I am powering up the device with two 1A regulators, ADP1706, 3.3v & 1.8v

         I have connected AVDD33 to IOVDD & CVDD18 to DVDD18. I think this should be ok...right?

    C: I am using the balun + circuit from the apps board as the interface to the DACCLK P/N pins

    Thanks again

    Kind Regards,

                          Paul. 

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