CPLD Jitter

Mike wrote:
> I think we can take things one step further. Mini Circuits thoughtfully
> provides us with the typical phase noise of their VCO (-86dBc @1kHz offset),
> and the VCO gain (1-4MHz/V, which we will take to be 2.5MHz/V).
>
[snip]
>
> The point of all this is that your noise is probably not coming from your
> crystal reference oscillator. I think it's more likely that it's coming from
> your VCO, and (if my assumptions about Kd*R are roughly correct) is
> approximately what you'd expect to see.
>
> -- Mike --

Mike, thank you.  I just had one of those "Doh! Why didn't I think of
that?" moments.  I think you may have solved the mystery.  The loop
bandwidth is only slightly wider than 1 KHz, so of course there is very
little attenuation of VCO noise at that frequency!  I've just checked
the predicted response of my loop for noise injected by the VCO, using
my SCILAB model, and it agrees to within a few dB with the
measurements.  I'd like it to be closer though .....