FAQ: Why isn't the SFDR of my DDS with 14 bit DAC better than the SFDR of one with a 10 bit DAC?

Document created by JLKeip on Mar 12, 2010Last modified by AndyR on Jan 31, 2012
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Q.

Why isn't the SFDR of my DDS with 14 bit DAC better than the SFDR of one with a 10 bit DAC?

 

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A.

Let's start by talking about wideband SFDR.  The highest spurs you see in the wideband spectrum are harmonic spurs.  The size of harmonic spurs is at least to a first order, not dependent upon the resolution of your DAC.  The size of these spurs is primarily a function of the linearity of the digital to analog converter that is used.  The place where you will see the difference of having more resolution in your DAC is when you look narrowband, and look at some of your other spurious components.  Fundamentally, the primary glaring difference you see as you increase your DAC resolution is that the noise floor gets lower.

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