How to improve the Q factor of the inductor?

We all know that the inductor has a loss due to the resistance r_s in series with it.

Hence it can be easily seen that the Quality Factor should be

Q= ω_oL/ r_s

If 'r_s' is very small then no problem and the Q value will be high. If Q value is low then according to Sedra and Smith book it can be increased by coupling through an autotransformer. I can find that the inductance value as well as the resistance value decreases through autotransformer but I don't know how it improves the Q factor. Could you please help me?

Thanks in advance.

I don't know about any auto-transformer. I know there is an active circuit called a "Q multiplier". Basically an active circuit is used in a feedback system (possibly using an auto-transformer) to reduce the effect of the series resistance.


Google "Q multiplier" and tell us what you find!

dave

Q factor is also depended on
-Series equivalent resistance
-Substrate Eddy currents
-Coupling effects of peripheral metallic components..(self mutual couplings between the spirs are included)

There are few things that affect the Q of an inductor.
- Q of an inductor depends directly on the inductance.
- Q depends by the conductor thickness to spacing ratio.
- Q increases with an increase in the inductor outside diameter.
- Q depends by frequency (skin effect)

The other thing that improves the Q of an inductor is to keep the internal stray capacity down by using a basket weave technique of winding it. I used to test inductors with Qs ~470 that were made like this.
Frank