[SI-LIST] Re: Spiral Inductor


If you use a low number of turns, the aspect
ratio of the spiral will also affect Fres.
If you squash a square spiral so it is wider
than it is high (I/Os are farther apart) the
resonant freq moves up. If you make it taller
than it is wide, resonant freq moves down.

When designing printed filters I used to use
1 and 3/4 turn spirals. Was good compromise
for achievable inductance and maximizing the
resonant freq. Can be crudely modeled as a
coupled pair with a single line conection from
input to output. An accurate model has to include
all the non-adjacent couplings across the inductor.

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Dan

Dan Swanson             EMAIL:  d.swanson@xxxxxxxx
Forem USA                       PHONE:          978-834-4085
37 South Hunt Road      FAX:    978-388-7077
Amesbury, MA  01913

> -----Original Message-----
> From: atifshamim khan [mailto:atifshamimkhan@xxxxxxxxx]
> Sent: Tuesday, April 15, 2003 7:12 PM
> To: varvij@xxxxxxxxx; dgun@xxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Spiral Inductor
> 
> 
> Hi I can provide you with some tips for inductor design at 
> this frequency ..may be they will help1.single loop inductors 
> can provide large L and Q..The design formula are given in 
> "microwave solid state circuit design" by "Bahl and 
> Bhartia".2.the resonant frequency of the inductor is given by 
>   Fres = 1/( 2* pi * sqrt(L * C/2 )) So you have to have a 
> low capacitance to increase your resonant frequency.3.To 
> estimate the inductors unloaded Q ,series resistance must be 
> added to the equivalent model...(ref again Bahl and 
> Bhartia)4.Spiral inductors provide the largest inductance but 
> then there is the interwinding capacitance .You can use the 
> the spiral inductors with entire air bridges in it (less 
> interwinding capacitance) I.D.Robertson discusses these 
> models.5.For a given outer diameter Q(circular spiral ) >Q 
> (square spiral),so use spiral inductors6.Multiturn inductors 
> have higher Q but lower Fres due to interwinding capacitance 
> , so use lesser number of turns. Hope this is of so
>  me help to you.ThanksAtif
> 
> 
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