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Frequently Asked Question

Why is output termination so critical to the overall performance of a DDS system?

Regardless of what output termination scheme is chosen, experience has shown that optimum spurious and harmonic suppression is achieved when both Iout and /Iout outputs are terminated equally (assuming a differential current output). Failure to do so may not be noticed at lower frequencies, but at higher output frequencies, where every dB of SFDR (spurious-free dynamic range) counts, this practice will give a cleaner output spectrum, lower spurs, and higher SFDR. This practice is especially applicable to situations where only one of the outputs is utilized. The use of a transformer driven by the differential output is a good idea for converting the differential output into a single-ended output.