Consider you have 100ppm crystal oscillator, 80ps jitter driving a DCM that is configured to output x1.5 the input frequency. What will happen to the jitter? Will it increase or decrease? And by what factor?
In addition, its histogram is gaussian in shape (from the CLKFX) output.
Some folks have been really suprised that the jitter histogram is gaussian in shape, but does not have the same RMS to peak to peak ratio that is commonly assumed from a PLL (14 to 1), and yet it is still random....(power spectral density has no peaks).
One can think of the output of the DCM as being multiple input clock jitter histograms (which are usually very gaussian from crystal oscillators), offset by a tap or two (at random + and -). Thus the peak to peak vs RMS is closer to 4:1 or 6:1.
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