inductor coil using Transmission line

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Mona Fouad

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Dear all,

How can I implement a series inductor coil using a coupled strip line?
I attached picture that shows what i do? is it correct?

Thanks in advance,**broken link removed**
 

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  • CPS.png
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Why you want to use a coupled strip line? Why not microstrip or cpw? What is your frequency and substrate?
 

johnjoe said:
Why you want to use a coupled strip line? Why not microstrip or cpw? What is your frequency and substrate?
Click to expand...

Because in my design I want to transfer all data in differential mode, My frequency band is 60GHz , substrate is TSMC 65nm.
 

I believe there's no priciple difference if you model the structure as differential coplanar strips or coupled striplines. In any case, it can be described as a differential and a common mode transmission line impedance. The parameters defining the common mode impedance, e.g. substrate height are yet missing in your schematic. The common mode impedance will show as a parasitic capacitance to ground.

The 110 nH value shown in the schematic is completely out of range for 60 GHz. The maximum reactance can be achieved by a λ/4 stub and is numerical equal to the transmission line impedance, e.g. 0.25 nH @ 60 GHz for a 100 ohm line.
 
Mona Fouad said:
How can I implement a series inductor coil using a coupled strip line?
Click to expand...

With "strip line", you mean transmission line? Or do you really mean stripline, which is enclosed between two grounds above and below?
https://en.wikipedia.org/wiki/Stripline

On-chip transmission lines are usually implemented as microstrip lines, with a conductor above a single ground plane.
https://en.wikipedia.org/wiki/Microstrip

A segment of narrow line behaves like a series inductor (with series resistance, and parasitic capacitance to ground). If you make the line wider, the inductance goes down and the parasitic shunt capacitance goes up.

If you implement a series inductor for differential circuit as two narrow lines, then coupling between the two lines will reduce the effective series inductance, and also the Q factor. So ideally, you don't want/need the lines to couple.
 


yes, I meant microstrip lines.

I simulated a coupled microstrip with short circuit from one side and other side with two ports on HFSS , and I export S parameters file from HFSS and use it in cadence. I simulated this extracted file on cadence using "nport" , and excited it with differential and common mode . I measure differential i/p impedance and common i/p impedance for (250um,length)
Zdiff=2+53.3j , Zcommon= 0.52+41.2j

So, which one of these impedance's have the major effect when use it as a series inductor? or which mode will propagate?
 

Mona Fouad said:
I simulated a coupled microstrip with short circuit from one side and other side with two ports on HFSS
Click to expand...

How is this related to your goal of creating series inductance for symmetric (differential) lines? You will then need series inductance in both conductors.
 

volker@muehlhaus said:
How is this related to your goal of creating series inductance for symmetric (differential) lines? You will then need series inductance in both conductors.
Click to expand...

How can I do so? I simulated it as two ports and calculated Z11=Z22=5.8+j156, where Z11 and Z22 are the i/p impedances of one terminal when the other one is open circuited. Is that mean it's an inductor and can be used in series?

FvM said:
Both impedances are inductive. Have you shorted the microstrip lines to ground?
Click to expand...

yes, I do, Is that not correct?
 

yes, I do, Is that not correct?
Click to expand...
In post #1 you have the transmission line stubs shorted against each other but not to ground. That's a difference.

But as volker@muehlhaus I have also difficulties to understand how you want to "transfer all data in differential mode". The schematic in post #1 shows a singled ended configuration.
 


This schematic is not my design, it is an example that explain how I will connect my transmission line in my main differential LNA circuit.
 

FvM said:
Why don't sketch a corrected schematic, also with updated inductance values?
Click to expand...

I attached here a figure with my design, I need to replace each coil (That I selected by red circle) with a coupled microstrip Transmission line.
 

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  • My Schematic.png
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