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Measurements >> Phase Noise and Jitter Measurements >> Phase noise of differential oscilator
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Message started by shortckt on Apr 6^th, 2006, 5:24pm

Title: Phase noise of differential oscilator
Post by shortckt on Apr 6^th, 2006, 5:24pm

Hello,

While setting up PSS and PNOISE analysis of diffferential oscillator, should the refrence node be selected as ground or complementary node? I get difference in phase noise results if I select complementary signals, not ground. To make my question more clear:

Oscillator node: /Vout+
Reference node: /gnd! OR /Vout-

Also, how can I calculate the phase difference between signals using calculator in spectre? Right now I can calculate by running transient simulation and converting the time shift observed by visual inspection into phase shift, but it is not very accurate.

Thanks.

Title: Re: Phase noise of differential oscilator
Post by ACWWong on Apr 7^th, 2006, 8:52am

the reference node should be Vout-, as you will use the VCO signal as a differential signal.

with regards to the phase, you can see the how "differential" the differential ouptus are from the pss run. using the main form you can plot the phase of Vout+, and the phase of Vout- against harmonics of the VCO frequency. You can use the "add to outputs" button to get thexact calculator expression, and value it at the VCO frequency.

an example for a 1MHz frequency is:

value(phaseDegUnwrapped(v("/Voutp" ?result "pss_fd")),1M)-value(phaseDegUnwrapped(v("/Voutn" ?result "pss_fd")),1M)

hope this helps

Title: Re: Phase noise of differential oscilator
Post by shortckt on Apr 7^th, 2006, 10:04am

Hi,

Awesome. It works perfectly :)

Thanks alot.