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8th August 2019, 09:12 #1
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When simulating center tapped inductor in ADS
Hello, I'm drawing and testing centertapped inductor with ADS simulator. Centertap will be connected to VDD.
After drawing inductor,
I assigned term 1&2 to two ends of inductor and term3 to center tap to simulate sparameter simulation.
Setting of term impedances are defaults ( 50ohm ).
But I think I have to set impedance of term3 to 0 ohm because it will be connected to the VDD.
Do I have to set impedance of term 3 as a default? or some other value?
Thank you

8th August 2019, 11:38 #2
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Re: When simulating center tapped inductor in ADS
Leave the port impedances set to 50 Ohm. The circuit simulator later takes care of the calculating the voltages and currents for the external impedances connected to the model. Sparameters don't work for 0 Ohm reference impedance.
When you evaluate results for your inductor in differential configuration, the center tap is at 0V due to symmetry anyway.
https://muehlhaus.com/support/adsap...uctoremports

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8th August 2019, 13:34 #3
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Re: When simulating center tapped inductor in ADS
Thank you for your reply
May I ask one more question?
I've learned that Q of centertapped is higher than not tapped one and I wanna exploit this feature.
Also, in my idea, inductor of inductance of L1 is divided by factor of 2 when we use centertap.
However, my centertapped inductor shows higher inductance and lower SRF.
So, I'm confused and I'm not convinced with my simulation.
If you have any idea about this phenomenon, please let me know. Thank you.
Below figure is my simulation setting and Sparameter plot of it

8th August 2019, 13:46 #4
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Re: When simulating center tapped inductor in ADS
Yes.
See schematics in https://designersguide.org/forum/Ya...m=1205240723#9

8th August 2019, 14:21 #5
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Re: When simulating center tapped inductor in ADS
There is no port 3 in your linked post. Which is fine.
   Updated   
I am working on these inductor simulations for many years, and never heard that. The center tap is a virtual ground when used with symmetric excitation. I think you might refer to differential vs. common mode Q factor.
I'm not sure what you compare, the full inductor (port 1 to port 2) vs. half of the inductor (port 1 to port 3)? Have a look at my appnote linked above. The important thing is to use the correct excitation  if you drive the inductor single ended from port 1 only, it behaves differently from the differential excitation. Also, that single ended excitation is not the typical use case. You should investigate differential operation.Last edited by volker@muehlhaus; 8th August 2019 at 14:37.

8th August 2019, 14:34 #6
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Re: When simulating center tapped inductor in ADS
Surely see schematics.
https://designersguide.org/forum/At.../Diff_Ind2.jpg
Port3 is connected to center tap.

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8th August 2019, 14:38 #7
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8th August 2019, 14:54 #8
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Re: When simulating center tapped inductor in ADS
See https://designersguide.org/forum/Ya...m=1205240723#9
R0=50
Sdiff = (s11s12s21+s22)/2.0
Zdiff = 2*R0*(1+Sdiff)/(1Sdiff)
freq = xval(s11)
Ldiff = imag(Zdiff)/(2*pi*freq)
Qdiff = imag(Zdiff)/real(Zdiff)
Z1 = 1/y11
L1 = imag(Z1)/(2*pi*freq)
Q1 = imag(Z1)/real(Z1)
https://designersguide.org/forum/Ya...m=1205240723#8
Qdiff > Q1
Consider Ldiff not L1.
Ldiff= 2*(Ldiff/2)
It is valid for differential mode excitation.
For evaluation of L1 and Q1, port3 must not be connected.Last edited by pancho_hideboo; 8th August 2019 at 15:01.

8th August 2019, 15:08 #9
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8th August 2019, 18:11 #10
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Re: When simulating center tapped inductor in ADS
I couldn't see the proof of Qdiff>Qse ??

8th August 2019, 18:23 #11
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Re: When simulating center tapped inductor in ADS
Last edited by volker@muehlhaus; 8th August 2019 at 18:33.

8th August 2019, 19:06 #12

8th August 2019, 19:08 #13
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Re: When simulating center tapped inductor in ADS
If we consider the equivalent circuit of an inductor and when we make short circuit P2, corresponding distributed components are becoming short circuit.
So, the difference which coming from SE and DIFF measurements might be result of this error. I'm saying that is an error because it does not sound very healthy to me.
In my opinon , DIFF measurement looks like more healthy..

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8th August 2019, 19:42 #14
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Re: When simulating center tapped inductor in ADS
What post and P2 do you refer to? In my post #11 the center tap is at Port 3 and that's floating in this comparison.
The difference between single ended Q and differential Q is also seen for the 2port case, not related to center tap. You are correct that it can be understood by looking at the shunt path in the equivalent circuit.
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