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a resonation in transmission line is when the capacitate part cancels the inductive part. Why in the case bellow at resonance our S-param drops?
Thanks.
The via stub resonance happens at multiple 10 GHz, I guess that's not your operation frequency? There will be nevertheless noticeable impedance at mismatch at low GHz frequencies, but it's not due to resonance. Consider wavelength in FR4 about half of the value in air, thus 1.5 mm stub (lambda 1/4) resonance is at 25 GHz. Discontinuities due to via stubs can be reduced by via back-drilling.
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Power supply impedance is a quite different topic, I won't mix it with transmission line impedance problems. Presumed you have massive ground and power planes, the question is about how to do the escape routing and where to place bypass capacitors.
Hello,i am viewing things with impedance and voltage dropr perspective.
Suppose we have a power delivery network of a driver which has resonanse at f0.
resonanse is when our impedance reaches its minimal point. so how it will ruin the input signal to the buffer. higher voltage will be delivered to the driver so the reciever will get higher voltage value at certain frequency.
But how exactly resonanse can cause impedance increase thus dropping the VDD supply to the driver?(equation will be good)
Thanks.
The open ended stub (open ended part of the via) behaves like a capacitor. When length reaches lambda/4, it gives a short circuit (infinite capacitance).
hello Valker,I mean as shown bellow We have PDN transmission line and transmition lines between buffers.
Is there a way in PDN transmission line so it will be in resonanse and its impedance will increase?
i cant see the formulas for that.
Thanks.
Sorry, I don't understand your question. To cancel the effect of open ended stub, stub length must be 1/2 wavelength. That is really long, so you better avoid the stub (blind via).
my question is not about stubs but about transmission lines in general .
so we take a transmition line between two ports (50 ohms)
is there a way that the impedance of the transmition line will increase in resonance?
because as i see it by the formula bellow the resonance will always decrease the impedance.
I am afraid your understanding of transmission line is wrong.
If your transmission line impedance Zline=sqrt(L/C) is equal to the source/load impedance, the line will just create a delay - and that response is broad band.
The popular RLGC model is just an simplified representation of the distributed effects in the line.
For the matched line case with Zline=Zsource=Zload there is no resonance. Resonance is seen only when the line is not matched to source/load impedance.
Hello Wolker,my question is in what type of unmatched transmission line the impedance will reach high peak at resonanse,and i what type of transmission line the impedance will reach low peak at resonanse?
Thanks.
"High peak" and "low peak" of what? S11 linear? S11 dB? S21 db?
If the line is not matched, you will get maximum reflection when line length is 90° + n*180°
And you will get no reflection where line length is n*180° because then Zin=Zload no matter what the Zline value is (one full circle in Smith chart).
For a better understanding look at Smith chart basics.
Hello Volker,yes you are correct about the formula of input impedance.
In signal integrity there is resonance fenome and it ruins the signal.
i am trying to understand how exactly resonance ruins data?
Thanks.
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