[SOLVED] Cadence S-parameter analysis

kenambo · Mar 22, 2017

Hi All,

I set up a circuit to check sp analysis in cadence. I m having 2 ports with one port has 50 ohm and another port has 100ohm. I connected these two ports together.While I am doing SP analysis, I got the following results.

S11 = S22--> 333.33m

S12=S21 --> 942.809m

How S12 is calculated in the above case. I couldn't find any formula reference for the above values.

Can anyone tell me how spectre determines these values?

Thanks.

pancho_hideboo · Mar 22, 2017

Show us your DUT.

kenambo · Mar 22, 2017

Here is my test bench. It is two ports connected together.

https://obrazki.elektroda.pl/2421423900_1490187435.jpg

pancho_hideboo · Mar 22, 2017

Too easy, kindergarten level.

>> r01=50;
>> r02=100;

>> s11=(r02-r01)/(r02+r01)
s11 = 0.3333

>> s22=(r01-r02)/(r01+r02)
s22 = -0.3333

>> Pa1=1/(4*r01);
>> Pa2=1/(4*r02);

>> Pload2=(r02/(r01+r02))^2/r02;
>> Pload1=(r01/(r01+r02))^2/r01;

>> s21=sqrt(Pload2/Pa1)
s21 = 0.9428

>> s12=sqrt(Pload1/Pa2)
s12 = 0.9428

See https://www.designers-guide.org/Forum/YaBB.pl?num=1266168115/1#1

kenambo · Mar 23, 2017

Hi

Thanks for the answer. I got it. But when I insert a transmission line between these two ports the s-parameter looks different. Is there any derivations or equation for s-parameter with transmission line included?
My setup is two 50 ohm ports are connected using TLINE of 100 ohms characteristic impedence with 25cm length. It will include the length of the transmission line right?

Thanks.

volker@muehlhaus · Mar 23, 2017

I can provide an equation for input impedance of a lossless line with arbitrary load impedance:

You can calculate S11 from this. And for a lossless line, we have |S11|² + |S21|² = 1 so you can calculate magnitude of S21 also.

For cascading, look at ABCD parameters and how they are converted to/from S-parameters.

kenambo · Mar 23, 2017

volker@muehlhaus said:
I can provide an equation for input impedance of a lossless line with arbitrary load impedance:

View attachment 137251

Hi

Thanks for the hint. Is this from any book? If so can you please tell the book's name?

And I am interested to see the cadence analysis of a transmission line.

Thanks

pancho_hideboo · Mar 23, 2017

kenambo said:
Is this from any book?

You can see such very basic equation in any basic text on linear circuit theory.

kenambo said:
If so can you please tell the book's name?

I recommend following standard text book, if you don't have any text book.
https://www.amazon.com/Microwave-En...d=1348984645&sr=1-3&keywords=microwave+mixers

kenambo said:
And I am interested to see the cadence analysis of a transmission line.

You will face many fatal bug of Cadence Spectre.
I don't recommend to believe Cadence Spectre reagarding RF.

kenambo · Mar 24, 2017

Thank you guys.

I will study the basics..

- - - Updated - - -

pancho_hideboo said:
Too easy, kindergarten level.

>> r01=50;
>> r02=100;

>> s11=(r02-r01)/(r02+r01)
s11 = 0.3333

>> s22=(r01-r02)/(r01+r02)
s22 = -0.3333

>> Pa1=1/(4*r01);
>> Pa2=1/(4*r02);

>> Pload2=(r02/(r01+r02))^2/r02;
>> Pload1=(r01/(r01+r02))^2/r01;

>> s21=sqrt(Pload2/Pa1)
s21 = 0.9428

>> s12=sqrt(Pload1/Pa2)
s12 = 0.9428

See https://www.designers-guide.org/Forum/YaBB.pl?num=1266168115/1#1

Hey pancho,

I need one more help. How can I convert the above values into a smith chart? Do you have any idea? I have done it using sp anlysis in cadence. I saw some theory formulae too. But I couldn't relate my values to them. So any clue will help.

i have found it for s11. s11=0.333 which is our reflection coefficient. So smith chart is a impedence thing. so it converts to 2+j0 . [ z1 = 1+s11/1-s11]. right? and I am seeing the same result on smith chart.

But for s21 which is 0.942 it converts to 33.97+j0 in smith chart. Do you know any formula or calculation for this?

thanks

pancho_hideboo · Mar 24, 2017

kenambo said:
How can I convert the above values into a smith chart?
Do you have any idea?
I have done it using sp anlysis in cadence.
I saw some theory formulae too.
But I couldn't relate my values to them.
So any clue will help.

I can not understand what you want to mean at all.

Describe correctly.

kenambo said:
i have found it for s11.
s11=0.333 which is our reflection coefficient.
So smith chart is a impedence thing.

I can not understand what you want to mean at all.

Describe correctly.

kenambo said:
so it converts to 2+j0.
[z1 = 1+s11/1-s11].
right?

Wrong.
Zin/r01 = (1+s11)/(1-s11), r01=50

kenambo said:
But for s21 which is 0.942 it converts to 33.97+j0 in smith chart.

I can not understand what you want to mean at all.
Can you understand s21 surely ?
You can not s21 on smith chart.
s21 is plotted on Polar Chart.

kenambo said:
Do you know any formula or calculation for this?

I can not understand what you want to mean at all.

Simply, you can not understand Smith Chart at all.
See https://www.designers-guide.org/Forum/YaBB.pl?num=1455889675/1#1

kenambo · Mar 27, 2017

pancho_hideboo said:
I can not understand what you want to mean at all.

Describe correctly.

I can not understand what you want to mean at all.

Describe correctly.

Wrong.
Zin/r01 = (1+s11)/(1-s11), r01=50

I can not understand what you want to mean at all.
Can you understand s21 surely ?
You can not s21 on smith chart.
s21 is plotted on Polar Chart.

I can not understand what you want to mean at all.

Simply, you can not understand Smith Chart at all.
See https://www.designers-guide.org/Forum/YaBB.pl?num=1455889675/1#1

Hi,

yeah your description for z01 is right. I forgot to say it is normalized for 50Ohm.

Yeah S21 is not impedence thing. But in cadence SP analysis I saw a point located for s21 in smith chart. So that I was confused. Ok, so s21 has to be plotted on polar chart.

What I want to tell is, How to convert S-parameters into a smith chart? Is it clear now? If it is not possible, why in cadence SP analysis we have smith chart representation.?

I got some understanding about smith chart. How the circles are drawn so that I am confused with SP-analysis smith chart.

Thanks.

pancho_hideboo · Mar 27, 2017

kenambo said:
I forgot to say it is normalized for 50Ohm.

Not only that.
There is no parenthesis in your expression.

kenambo said:
But in cadence SP analysis I saw a point located for s21 in smith chart.

I can not understand what you want to mean at all.
Describe correctly.

kenambo said:
How to convert S-parameters into a smith chart?

I can not understand what you want to mean at all.
Describe correctly.
Smith Chart is a plane of S(reflection coefficient).
So there is no need to convert S-parameters into a smith chart at all.

kenambo said:
why in cadence SP analysis we have smith chart representation.?

I can not understand what you want to mean at all.
Describe correctly.

kenambo said:
I got some understanding about smith chart.

You can not understand even very basic at all.
Surely study https://www.designers-guide.org/Forum/YaBB.pl?num=1455889675/1#1

kenambo said:
How the circles are drawn so that I am confused with SP-analysis smith chart.

I can not understand what you want to mean at all.
Describe correctly.

Surely study S-Parameters.

kenambo · Mar 27, 2017

I will study it by myself. Thanks

[SOLVED] Cadence S-parameter analysis

kenambo

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