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analog_cha Junior Member Offline Posts: 16 India	quality factor Jan 27^th, 2009, 5:06am Could any body tell me how to measure the loaded Q factor of an LC VCO using spectre?? Thanks.
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pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: quality factor Reply #1 - Jan 28^th, 2009, 6:02am analog_cha wrote on Jan 27^th, 2009, 5:06am: Could any body tell me how to measure the loaded Q factor of an LC VCO using spectre?? What is your question ? Just usage of specific EDA vendor's simulator, Cadence Spectre ? Definition of loaded Q of LC VCO ?
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analog_cha

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Re: quality factor
Reply #2 - Jan 30^th, 2009, 5:07am

Say,i am using an inductor of tsmc18rf in the LCVCO design. I choose some value for the inductance while instantiating it. But after doing dc simulation and seeing the operating point of the inductor, the inductance value is different. Is it because of loading??
And also i would like to know the quality factor of the inductor after being kept in the LCVCO.

Thanks.

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pancho_hideboo

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Re: quality factor
Reply #3 - Jan 30^th, 2009, 5:57am

Your question is not "RF Measurement".
You don't seem to understand a definition of loaded Q of LC VCO.

analog_cha wrote on Jan 30^th, 2009, 5:07am:

Say,i am using an inductor of tsmc18rf in the LCVCO design. I choose some value for the inductance while instantiating it.

Did you confirm inductance value by AC or SP analysis ?
I think you just believe inductance value in setting parameter of inductor component provided in tsmc18rf PDK without confirming its value by AC(SP) analysis.
http://www.designers-guide.org/Forum/YaBB.pl?num=1205240723/9#9

analog_cha wrote on Jan 30^th, 2009, 5:07am:

But after doing dc simulation and seeing the operating point of the inductor, the inductance value is different. Is it because of loading??

I don't think so.

Generally inductor model is composed of multiple L, R and C.
http://www.designers-guide.org/Forum/YaBB.pl?num=1205764700
What value is showed as the operating point of the inductor in tsmc18rf PDK ?
And what value is used as parameter of inductance of PDK ?

You have to consider these issues.
Do you think such inductance value by DC analysis is meaningful for VCO design ?

analog_cha wrote on Jan 30^th, 2009, 5:07am:

And also i would like to know the quality factor of the inductor after being kept in the LCVCO.

Loaded Q of oscillator is calculated from phase noise plot.
QL=f0/(2*fa), where f0 is oscillation frequency and fa is coner frequency of -6dB/oct and floor noise.
See page.4 of the following.
http://www.zen118213.zen.co.uk/Systems_And_Devices_Files/PhaseNoise.pdf

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« Last Edit: Jan 30^th, 2009, 8:48pm by pancho_hideboo »

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pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: quality factor Reply #4 - Feb 9^th, 2009, 4:48am See figure-10 and figure-11 in the following. Easy method is used to evaluate loaded Q of resonator. http://www.zen118213.zen.co.uk/RFIC_Circuits_Files/LC_Oscillator.pdf
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