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Frequently Asked Question

What is the effect of REF CLK jitter on the DDS?

REF CLK jitter will directly affect the DDS. The DDS output is sampled by the REF CLK, and therefore the REF CLK jitter determines the quality of the output signal. It directly affects the jitter characteristics of the DDS output.

If the REF CLK multiplier (PLL) is utilized, then the PLL (because its loop bandwidth acts as a bandpass filter) helps to filter out frequency components of the REF CLK that are outside of the loop bandwidth of the PLL. However, using the REF CLK multiplier will increase the effective noise on the REF CLK within the loop bandwidth of the PLL (typically a few hundred kHz). The increase of noise within the loop bandwidth will follow the formula of dB = 20log x, where x is the REF CLK multiplication value.