Indeed the "noise shaping of the loop" could mean the the loop filter shape, but this terminology can also be used to refer to other things in the PLL (depending on the circumstances/architecture of the PLL....)

Anyway in your case its the loop BW is about 10MHz (roughly the width of the plateau at 2). The hump at 2 and roll-off between 2 and 3 is due to the net loop filter response. Levelling-off at 3 could be due to wideband noise of PLL signal (e.g. due to buffers etc.), but also analyser noise floor.

hope this helps... for more information on PLL loop dynamics, Dean Banerjee from National semiconductor writes good application notes. Google him!

cheers

aw

Quote:
Wrong.

Judging PLL XF from PLL Phase noise plot could be tricky.
The peaking that you see in phase noise plot in region 2 could be from either osc. phase noise dominating due to low BW, or i/p jitter peaking due to peaking in XF or BOTH.

Hence, to obtain loop response params, simulate loop characterstics for PLL XF separately, instead of judging them from PLL phase noise plot.

--
Mayank.

you cannot easily obtain PLL Xfunction from the spectrum analyzer. What you can do is compare your measurement with sims and vary the sim parameters to make it match measuremnts. This will at least give you an idea of what could be off in your sims.