I have inherited a termination scheme for an AD9910 application which I suspect is non ideal. Given that the DAC internal to the DDS has open drain outputs and the data sheet says they require 50 ohms to analog ground.
The current termination is a 100 ohm resistor attached between the two current outputs with no ground path other then a balun transformer whose inputs are also attached to the current outputs (i.e. the resistor in parallel with the balun inputs). From what I can tell this results in a DC short between the two outputs and is an AC differential load of 50 ohms. Can anyone comment on whether this is appropriate? I suspect the better way to do this would be to have a 50 ohm series resistor between the DDS output and each leg of the balun.