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Design >> Mixed-Signal Design >> pll chargepump o/p noise profile
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Message started by yvkrishna on Jan 7^th, 2014, 1:58am

Title: pll chargepump o/p noise profile
Post by yvkrishna on Jan 7^th, 2014, 1:58am

Hi,

When I run pss+pnoise using spectre on the chargepump circuit I see an o/p noise profile which has flicker and thermal noise floor, which is expected as shown in the fig here.

However I was expecting the noise profile to have flicker noise(peaks) at every Fref (as its convolution in freq domain since its multiplication of noise waveform with square wave of small duty cycle)

Even if I put 20 harmonics/sidebands in spectre pss,pnoise settings I hardly see any such aliased components in the plot.

Also going by the exact math shown in the paper, the peak of the image at Fref has to scaled by sinc function response which is actually ~1 (and not <<1)

"Enhanced Phase Noise Modeling of Fractional-N Frequency Synthesizers
Himanshu Arora, Student Member, IEEE, Nikolaus Klemmer, Senior Member, IEEE, James C. Morizio, Member, IEEE, and Patrick D. Wolf"

Just wondering why the o/p pnoise plot doesnt contain those images at multiples of fref.

Thanks,
yvkrishna

Title: Re: pll chargepump o/p noise profile
Post by yvkrishna on Feb 13^th, 2014, 1:22am

Got it. I just need to simulate enough number of samples around multiples of Fref.

Thats why those images are not visible earlier.