Q factor

Mar 21, 2005 2 Replies

Hello All



Say Impedance Z i = jwL + Rs (Rs is in series and it is actually the internal series resistance, this means inductor is an ideal one)



So if we assume this way, then does it mean jwL comes from the ideal inductor? Not from any of the Rs at all?



If we want to find Q of the inductor we will use Q= wL/Rs where SL(or jwL) is not involved totally in the Q equation.



Am I right ? Kindly enlighthen Thank you


Jason


If your actual inductor acts exactly like a perfect inductor in series with a resistor yes. Otherwise no. Many times in RF work your actual inductor will either act like it has both series and parallel loss, or (probably closer to reality) like it's transformer-coupled to a lossy circuit. This is why if you plot the Q of an inductor against frequency it'll come to some broad peak then slip down again.

Tim Wescott Wescott Design Services http://www.wescottdesign.com

The RF sereis resistance goes up with frequency due to the skin effect so this alone can cause the Q to level off and decline at higher frequencies giving the broad peak.

Mark

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