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Design >> RF Design >> Loaded quality factor of voltage control oscillator
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Message started by transign on Nov 27^th, 2020, 10:53pm

Title: Loaded quality factor of voltage control oscillator
Post by transign on Nov 27^th, 2020, 10:53pm

Hello,

How can I calculate in virtuoso the loaded quality factor of the VCO's main tank? Is there a specific test bench that I could use? Should I add only the parasitics of active devices?

Thanks a lot!

Title: Re: Loaded quality factor of voltage control oscillator
Post by Horror Vacui on Mar 27^th, 2021, 5:30am

It requires the presence of the active devices -- like cross-coupled pair, or the amp in Colplitts - in its working condition. Therefore the circuit has to oscillate during the measurement¹, which makes things complicated. I can think of multiple ways how to approach this problem, but probably the simplest is to run a PSS & PAC analysis.

Add a PAC current source in parallel with your tank. Sweep the injection frequency and measure the voltage across the tank
a) amplitude (Q= one-sided relative 3dB bandwidth)
b) phase change (Q=d(phi)/d(omega) omega_0/2)

¹ Yes, I am using the phrase measurement even though the desired information is obtained by simulation and not with an instrument.