The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Modeling >> Passive Devices >> Curve fitting of center-tapped inductor https://designers-guide.org/forum/YaBB.pl?num=1205764700 Message started by neoflash on Mar 17th, 2008, 7:38am

 Title: Curve fitting of center-tapped inductor Post by neoflash on Mar 17th, 2008, 7:38am Hi, folks:I come up with a strange thing when doing curve fitting for a differential center-tapped inductor.The original version of the inductor is a two-terminal differential inductor. I did curve fitting to find the equivalent circuit model. And the fitting seems good.The next step I added a center-tap and got a 3-port s-parameter from field solver. The problem is when I'm doing the curve fitting again. the mutual inductance in the circuit model was forced to zero by the fitting tool. The fitting seems OK but not as good as two-port one. The inductance and Q is ok but the s-parameter related with the third port are not well fitted.Any one ever experience same thing before? Any suggestions?Regards,Neoflashattached is the equivalent circuit model for curve fitting. Parameters are found by fitting tool.

 Title: Re: Curve fitting of center-tapped inductor Post by neoflash on Mar 18th, 2008, 5:52am The most strange thing is that the mutual coupling between inductors are forced to be zero by fitting tool, I can't understand.

 Title: Re: Curve fitting of center-tapped inductor Post by pancho_hideboo on Mar 18th, 2008, 9:53pm How is port-3 treated in your fitting tool ?Isn't Port-3 treated as ground ?

Title: Re: Curve fitting of center-tapped inductor
Post by neoflash on Mar 19th, 2008, 5:41am

neoflash wrote on Mar 18th, 2008, 5:52am:
 The most strange thing is that the mutual coupling between inductors are forced to be zero by fitting tool, I can't understand.

No. It is not treated as ground. Since this port will connect to a current source in circuit design. Top-biasing of current will be used.

 Title: Re: Curve fitting of center-tapped inductor Post by pancho_hideboo on Mar 19th, 2008, 6:58am If port 1 and port2 are drived with symmetrical odd mode,  where only differential(odd) mode is characterized,port 3 is virtual ground.And even if you are not driving port 1 and port2 with symmetrical odd mode, manupulation of S-parameter for differential characterization results in port 3 as virtual ground. Or you are doing full 9 parameters S parameter fitting without invoking odd and even mode concept ?

Title: Re: Curve fitting of center-tapped inductor
Post by neoflash on Mar 19th, 2008, 7:04am

pancho_hideboo wrote on Mar 19th, 2008, 6:58am:
 If port 1 and port2 are drived with symmetrical odd mode,  where only differential(odd) mode is characterized,port 3 is virtual ground.Or you are doing full 9 parameters S parameter fitting without invoking odd and even mode concept ?

I'm treating the 3-port network as a full 9 parameters network.

 Title: Re: Curve fitting of center-tapped inductor Post by email_gz on Mar 27th, 2008, 9:43pm Physically,differential inductor is just a special 3 port transform (T coil) and this sharing port have no ac current pass through. so when you connect this port  to a current source , so Iac*S*(-M)=0,then just can be seen as two inductor L+M,L+M series conneted.