AD9739_R2-EBZ  DAC Output stage termination

Document created by analog-archivist Employee on Feb 23, 2016
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My application requires a wideband, single-ended, 50 Ohm output (20MHz -
2.5GHz). I was thinking to use the output stage as implemented on the
evaluation board (AD9739_R2-EBZ EVALUATION BOARD).
However, I noticed that the characteristic impedance of the implemented balun
(TC1-33-75G2+) is 75 Ohm.

 

You are right!  The AD9739’s output has an impedance of 75ohms and in the
Evalboard, this is in parallel with 90ohms on both the negative and positive
analog outputs and this implies an output impedance into the transformer of
about 50ohms.

The Product Expert for this device has confirmed that they looked at this balun
over the 1st, 2nd, and 3rd Nyquist zones and it gave the best performance of
the baluns in the group they tested. So, they chose this one for the Evalboard.

Therefore, the Evalboard setup with the TC1-33-75G2+ will suffice for your
50ohm single-ended output.

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