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please help to enlighten me on some passive filter question

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Newbie level 3
Dec 16, 2005
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can any one recommend me some reference book or enlighten me on wht effect or purpose does the gnd plane have in a multilayer filter design...

in addition is there any books or website have any information on the equivalent circuit of a square resonator and how does it work ??? or radiate???/

Re: please help to enlighten me on some passive filter quest

hi, what is the structure of your multilayer? on which layer is the filter, what kinf of filter?
Respect the equivalent circuit of the resonator, if you don't have any idea of how it behaves, I think you can use an Em simulator and extract the spice model, nearly all simulators have this feature..


Re: please help to enlighten me on some passive filter quest

Not sure exactly what you mean, but yeah, ground planes make a huge difference. For one thing, you need uniform distribution of ground currents, otherwise you end up with parasitic inductances that throw your bandwidth and center frequency off. A good example is a lumped filter where a resonating L-C pair are used. The LC pair had better be mounted right next to each other, beacuse the circulating current will be high and if they have to send that current thru a long and winding ground plane pattern, then you will have unpredictable consequences.

Also, since stray capacitance can load down any filter, even distributed ones, how close the ground plane is makes a difference. Sometimes, if you have an odd ground plane geometry, like a close bottom ground plane but a far top ground plane, you can excite some odd dispersion effects.

Thats interesting, Is there any books that expains this one? Im sorry but it is easier to understand if there were images so its easy to visualize the effect of proper ground planes on the circuit. Thanks

Re: please help to enlighten me on some passive filter quest

the package is actually a filter realise using a ltcc package which have 3 layer. the first is a dielectric layer, the 2nd is the feed lines and the filter resonator layer and the 3rd is the gnd plane.

Each layer is 0.1mm thick. and for the 2nd layer substrate, the feed line and the resonator is actually space 0.1mm apart from each other therefore the feed line is on top of the square shape resonator resulting the feed line will have an overlap on the resonator to provide a higher Q response.

the resonator use for the filter is a square shape resontor that have the dimension of half wavelength.

i will like to knoe if there is any books that will explain how the ground plane of a multilayer system on package actually affect the response of the filter response. cos when i vary the gnd plane dimemsion, the insertion loss of the filter did vary alot.

hope that there is someone out there that could advice me on this issue ,....

thanks alot

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