How to increase the BW of the spiral inductor?

[tony_lth]

I am designing a spiral inductor, but its -10dB bandwidth is too narrow, how to make it wider?
Many thanks.

 

[N.Narayanan]

Hi,
Reduce the length of the indctor or try to reduce the inductance.

 

[BigBoss]

I think you talk about Q factor because there isn't such "Bandwidth" definition for an inductor in the literature.
Reduce Q factor by connecting a resistor in parallel or increase series resistance of the coil by using narrower strip width or decrease overall diameter.

 

[jiripolivka]

Depends on the real purpose. For instance, conical coils are best as chokes up to ~50 GHz

 

[Bob60]

I am designing a spiral inductor, but its -10dB bandwidth is too narrow, how to make it wider?
Many thanks.

Decrease Q factor and by the way play with sqrt L/C.

 

[vfone]

You have to reduce the Q factor of the inductor:
- Inductor Q-factor is proportional with inductance.
- Width-to-spacing ratio and the outside diameter affect the Q of the spiral inductor.
- The Q-factor decreases with a decrease in the outside diameter.
- The Q of an inductor can be decreased by using a thin copper metal.
- Rectangular inductors have lower Q than circular inductors.

 

[tony_lth]

Thank you very much for so many ideas.

 

[tony_lth]

If I want to shifter the center freq to lower, what should I do?

 

[jiripolivka]

If I want to shifter the center freq to lower, what should I do?

Add several turns and make the coil tighter. More turns makes inductance larger, tighter turns increase the capacitance. Both shift the resonance frequency down.

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At frequencies lower than ~500 MHz you can try to insert a ferrite core but it often increases the loss (wider BW)

 

[PA4TIM]

If I understand it right you do not want to increase the bandwidth (an inductor does have a bandwidth in theory, but because of paracitics it has a selfresonance frequency and you can shift that by building it in certain ways) A LC combination has a bandwidth. This you can increase by adding resistance but this is also adding loss.

If I understand it right You need to increase the selfinductance. This can be done by increasing the number of turns or a larger diameter or core material etc. Download Analog SEEKrets from L Green, it is a free Download and you find allmost everything you want to know. Including completer formulas for coils and not only the simplified Wheekler. To get a better view on the different forms of resonant and the math behind it AC Theory from D Knight is a good and also free download.

What frequency are you talking about en what sort of coil ?

A ferite core can also increase the Q because you use less turns and can get less distributed capacitance. But core material can add loss and you can get things like saturation. I made a 500 kHz HAM transmitter and my m,atching network with core material added to much loss. Air gave the best result but in a 10 MHz transmitter I had better results by adding a core.

 

[tony_lth]

Actually I used two layers, so it has bandwidth. Thanks.

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In CST, does it has any way to automatically setup spiral indcutor? I think so, but I don't know how to do.
I have to input every corner's axis position in CST now, and it's really bored.

 

[Bob60]

Actually I used two layers, so it has bandwidth. Thanks.

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In CST, does it has any way to automatically setup spiral indcutor? I think so, but I don't know how to do.

Yes it`s possible.