AD9176 DAC Output Network


We are looking are switching to the AD9176 from the AD9172. One thing I noticed is the AD9172 recommends a DC coupling output network to the Balun with RF Chokes close to the balun. On the AD9176, page 69 of the datasheet, it talks about being able to do this still but the recommended diagram shows the rf chokes and AC Coupling caps. I was curious why the AC Caps were added for the AD9176. If possible, I would like to keep the board as it was for the AD9172 but if it is highly recommended to add the AC caps, I will move forward and make that change.

  • +1
    •  Analog Employees 
    on Aug 28, 2019 4:23 PM

    The purpose of RF chokes are to set the DAC output common mode(VCM). And AD9172 prefers to have VCM as close to 0v(GND) as possible. The DC current for each leg is about FSC/2. i.e. if FSC is 20mA, the DC current of each leg is about 10mA.

    Adding ADC caps is to have DC current to go through RF chockes instead of Balun center tap(notes that not all the Baluns have the center tap).

    if Balun has center tap and tolerate FSC/2 with some margin, the RF chockes can be removed and DC coupling between DAC and Balun. 

    In short, no changes are needed for AD9176 if your current network for AD9172.