What is Quality Factor in RF Inductors?

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Raghav Kapur - everything RF

Jul 6, 2018

The Q factor is a dimensionless parameter that tells us how close a real inductor is to an ideal inductor. Every real world inductor has some unwanted resistance associated with it. This unwanted resistance can be due to several factors - Standard DC resistance, Skin effect, radiated energy and core losses etc. If we realize the equivalent circuit of an inductor, it consists of an inductor with a series resistance (See Image below).

The Q factor is the ratio of the inductive reactance to the series resistance of the inductor at a given frequency. Higher the Q factor the closer its performance compared to an ideal inductor.

The Q indicates energy loss relative to the amount of energy stored within the system. When current flows through an inductor, the inductor opposes the flow of current with some resistance. Lower the resistance, higher the quality or Q-factor of the inductor and the better its performance.

One important point to note is that the higher the Q, the narrower the 3 dB bandwidth of the Inductor. So in certain cases, one may choose to tradeoff a lower Q for a wider bandwidth.

Click here to use the Inductor Q Factor Calculator.