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Frequently Asked Question

What are the considerations of SFDR performance vs. the REFCLK Multiplier function in a DDS system?

The use of reference clock multiplication has an impact on SFDR (spurious-free dynamic range). As an example, let's consider the spectral plots of two devices, with the same output frequency, one device has the 6x clock multiplier function engaged, and the other is directly clocked. The plots of close-in SFDR (± 1 MHz) will show an SFDR of –68 dBc for the clock multiplied output and –78 dBc for the direct clocked device. Also, a slightly elevated noise floor will occur on the multiplied device.