genie_q wrote on May 14th, 2012, 8:25am:Hello,
Could you please tell me why Q or BW for ring VCO is not important? Razavi has a paper predict the Q of ring VCO.
I'm confusing this. I designed a differential 3-stage ring VCO, running at 100MHz. I got -110dB phase noise at 1M offset. How to link this number to the Q of ring VCO? Equation of Q=Wo/deltaW, is not usefull anymore.
loose-electron wrote on Apr 21st, 2012, 1:15pm:A ring oscillator really does not have a BW or Q so to speak.
A min max range of operable frequencies, yes, but thats about it.
Ali Hajimiri did a paper on this a while back, search IEEE JSSC
I wish this one was as simple as an LC tank oscillator and its Q.
Can you approximate it using linear means? Yes, but its really not that meaningful after you have done a few of these in the real world.
If you sweep an LC tank, it exhibits a Q and a frequency response profile that will fir into an S plane model.
A ring oscillator tends to be more flat in the pass band an the max freq and min freq do not exhibit symmetric profiles.
Trying to apply a linear system model to something that is inherently not linear does not work that well.