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lumped filter design on ADS - RF Cafe Forums

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balajisu

Post subject: lumped filter design on ADS Posted: Mon Jul 17, 2006 4:24 pm

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

Hi group,

Designed a lumped element filter using the Filter design guide in ADS. I would like to replace the ideal components with the vendor library components. What are the important parameters/issues that I need to take care of while selecting the replacement components. Any suggestions will be really appreciated.

regards

Balaji

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IR

Post subject: Posted: Wed Jul 19, 2006 11:11 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello,

The most important parameter that you should consider is the Q. For inductors it is more critical since their Q is smaller and when they are connected in parallel with capacitors their lower Q prevails (Exactly the same as connecting 2 resistors in parallel). There are models available for inductors and capacitors which include Q data for capacitors (Murata) and inductors (You can find good models in Coilcraft website).

_________________

Best regards,

- IR

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languer

Post subject: Posted: Wed Jul 19, 2006 4:36 pm

Captain

Joined: Sun May 14, 2006 8:53 pm

Posts: 17

Location: Earth

After Q, as IR metioned, I would also add resonant frequency. This one will normally affect more the bigger component values and will de-tune your circuit. Resonant frequency will tell you when a capacitor stops behaving as a capacitor and looks more like and inductor (or the opposite in the case of inductors).

As a rule-of-thumb, Q will make the filter more lossy and SRF (series resonant frequency - note there is also parallel resonant frequency) will limit the usable frequency range of the components.

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IR

Post subject: Posted: Thu Jul 20, 2006 1:29 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Languer is right, as long as the ADS allows you to enter the SRF as a parameter. I don't remember if this is possible.

_________________

Best regards,

- IR

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balajisu

Post subject: Posted: Tue Jul 25, 2006 11:27 am

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

thanks for your valuable comments. Can I consider SRF to be the self resonant frequency of inductor or capacitor or Is this term different from series resonant (or parallel resonance)

I have made the response look more like what I intended to do except for the loss part. I guess I need to get better Q inductors and try retuning the circuit for required performance.

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IR

Post subject: Posted: Tue Jul 25, 2006 11:52 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

The inductor model includes SRF which is a parallel resonance frequency - this is the capacitance of the inductor winds. The capacitor model includes SRF which is serial. So if you have the information per the device you are using just add it for the ADS simulation. As you mentioned, Q will affect the insertion loss of the filter.

More information:

Inductor Model:

http://www.intusoft.com/articles/inductor.pdf

Capacitor model:

http://www.ecircuitcenter.com/Circuits/ ... model1.htm

Good luck!

_________________

Best regards,

- IR

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balajisu

Post subject: Posted: Wed Jul 26, 2006 8:54 am

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

Hi

Thanks for the links.

If i'm using Vendor models(coilcraft, vishay or AVX) in ADS do I still need to add the SRF component to get the right results.

Balaji

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IR

Post subject: Posted: Wed Jul 26, 2006 9:16 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello,

You are welcome!

If the models contain the SRF value, and the ADS allows you to enter this value then you should use it.

Good luck!

_________________

Best regards,

- IR

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balajisu

Post subject: Posted: Wed Jul 26, 2006 11:53 am

Captain

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 24

Location: Germantown,MD

Hi

I do have a datasheet that provides SRF value for the models but looks like ADS doesn't let me add the SRF value to the component. I guess I just need to assume that the model uses the SRF value. Is there anyway around this?

Thanks for your time

Balaji

Top

IR

Post subject: Posted: Wed Jul 26, 2006 3:46 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

The ADS will use the parasitic capacitance value to calculate the SRF for an inductor and the parasitic inductance for capacitor to calculate the same. These calculations are formulas built in the model.

_________________

Best regards,

- IR

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