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What do you think about that simulation?

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gnammy

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Dear All,

I am using a software of keysight which call ADS and I am simulating a balun with impedence matching. This is the circuit: (It shows in image ).

It is a balun which links a differential mode to single ended and after there is a impedance matching.In one side there is normal impedance 50 Ohm instead at the other side there is the impedance of antenna which is not adapted

Now, I wanna obtain the S-Parameters, that is S_(11) and S_(12) similar to datasheet of antenna. (See datasheet antenna the graph where stay a lot of curves in different colours).

S_(21)-------->1.5 GHz corresponds -25 dB

I did two simulation.
One -is when at left side is linked two resistance of 50 Ohm
S_(21) ------>1.5 GHz corresponds -21 dB
Two-is when at left side is linked one resistance of 50 Ohm
S_(21) ------>1.5 GHz corresponds -18 dB
Now i think that the first way approaching to datasheet graph but it s not exactly.

What do you think about that? Is it correct my simulation?
 

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  • balun.png
    balun.png
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  • datasheet.png
    datasheet.png
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  • SIMULATION ONE-circuit.png
    SIMULATION ONE-circuit.png
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  • SIMULATION ONE-graph.png
    SIMULATION ONE-graph.png
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  • SIMULATION TWO-circuit.png
    SIMULATION TWO-circuit.png
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  • SIMULATION TWO-graph.png
    SIMULATION TWO-graph.png
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LC baluns like the shown circuit are designed for small band only, e.g. 915 MHz or 2.45 GHz. Also the antenna impedance is surely valid for a specific operation frequency only. It makes no sense to perform wide band S parameter simulations of the circuit. You are mentioning CC13xx family, if you refer to the multiband devices they have separate transceiver ports for sub-GHz and 2.45 GHz.

Firstly, you need to specify the operation frequency.
Secondly, the antenna impedance in the simulation circuit is far from 50 ohms and need a specifically designed matching network. What you presently have looks more like a 50 ohms matched harmonic filter.
 

-Balun is not symmetrical and unusual ( i don't know how it works and what the Phase Relationships are maintained )
-Single Ended simulation set-up is wrong because if you divide the circuit by , you have also to divide the Port Impedance by so each port should have 25 Ohm internal impedance.
-Insertion Loss from 50 Ohm to Antenna is too much even with ideal components,There might be some design errors ( Balun, Filter or both )
-Ripple is to high due to design errors remarked above..

Balun component values are NOT consistent for any frequency.

The values must maintain these equations.

L=X/(2*PI*F0) AND C=1/(2*PI*F0*X)

Here X=SQRT ( RIN*ROUT)
 
Last edited:

-Balun is not symmetrical and unusual ( i don't know how it works and what the Phase Relationships are maintained )
The LC balun has been apparently copied from a TI application note. It works in real circuit, but people have often problems to reproduce the behavior in a simulation, several previous Edaboard threads about the topic. The design method is e.g. sketched in AN068. One problem of the simulation attempts is a wrongly assumed of PA impedance. It's neither real nor floating. My personal experience with a 915 MHz reference design is that the component values should be adjusted for symmetrical output swing and best suppression of even harmonics.

-Single Ended simulation set-up is wrong because if you divide the circuit by , you have also to divide the Port Impedance by so each port should have 25 Ohm internal impedance.
The biggest mistake is to assume a floating PA impedance, the real PA can be better described by two out-of-phase single ended outputs.

-Insertion Loss from 50 Ohm to Antenna is too much even with ideal components,There might be some design errors ( Balun, Filter or both )
It's mainly caused by the unmatched antenna (10-j100) without respective matching network. Can be corrected by recalculating the double pi network, of course for a single frequency only.
 

Attachments

  • AN068 - Design Steps and Results for Changing PCB Layer Thickness.pdf
    792.5 KB · Views: 56

Thanks for your fast answer. To analize the balun diferrretial mode can I converte the differential mode in single ended mode?
How can I do?
thanks in advance

- - - Updated - - -

Well thanks @Fvm for your attachments. I found Rdiff= 44 Ohm while Ldiff=j*15 Ohm. Now I put on the left side 50 Ohm and after in series 22Ohm (Rdiff/2) and Ldiff/(1.375nH). After I took the top branches of the balun without the inductance between two branches. After I put the impedance matching closed in to not adapted impedance antenna(Z= 9.8927-j*87.811).
Is it correct? what do you think?
 

The textual description isn't clear to me. You also didn't clarify about the operation frequency, 915 MHz is just a guess of mine.
 

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