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Design >> RF Design >> good quality off-chip inductor problem?
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Message started by liletian on Nov 2^nd, 2009, 8:15pm

Title: good quality off-chip inductor problem?
Post by liletian on Nov 2^nd, 2009, 8:15pm

Hi Guys
It is well known you can make some off-chip good quality inductor. Does anyone have idea how well the off-chip can be?
for example, can a off-chip inductor 1uH with a quality factor of 500? If they do, can you tell me where I can find the data sheet for those inductor.
Also, besides the cost, what prevent the off-chip inductor usuage?
Thank you

Title: Re: good quality off-chip inductor problem?
Post by pancho_hideboo on Nov 3^rd, 2009, 2:44am

You have to specify operation frequency.
And can you permit any cost truely, for example, do you accept super conductivity ?

Title: Re: good quality off-chip inductor problem?
Post by liletian on Nov 3^rd, 2009, 7:19am

the frequency is 1GHz, and I do not think I can accept super conductivity. But it will be nice to comment on superconductitity.
thanks

Title: Re: good quality off-chip inductor problem?
Post by loose-electron on Nov 3^rd, 2009, 8:45am

It's called a component specification - why don't you start here:

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_homepage_link=hp_ProductIndex&lang=en&site=US&keywords=

Title: Re: good quality off-chip inductor problem?
Post by RFICDUDE on Nov 6^th, 2009, 6:40am

A good questions is ...
"Why do you need 1uH at 1GHz?"

Inductors are just coils of wire used to concentrate the magnetic field produced by current flowing through the wire. A practical problem is that there is some amount of capacitance between the coil wires. This capacitance is somewhat proportional to the inductance, so the bigger the inductance the lower the self resonant frequency of the inductor.

I doubt that you can find a 1uH inductor that works at 1GHz, because it would take as little as 250fF of interwinding capacitance to cause the inductor to resonant.

If you are using this as a RF choke then you simply need to understand what the circuit impedance is an make the choke impedance suitably higher not to disturb the circuit and calculate the appropriate value of inductance.

Have fun.