Help with NEXT and FEXT volatage magnitudes

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SUMMARY

The discussion focuses on calculating the magnitude of Near-End Crosstalk (NEXT) and Far-End Crosstalk (FEXT) voltages in a transmission line formed by two identical parallel tracks on a printed circuit board. The line length is 50 mm with a characteristic impedance (Zo) of 70 Ω, and the source voltage (Vin) is a 2 V step with a rise time of 100 ps. Key calculations include determining Vs, Kne, and Kfe, with values of 0.995 V, 0.08, and 3.99515E9 respectively. The participants also clarify the definitions of NEXT and FEXT and seek assistance in understanding the timing variables t and td in relation to the equations provided.

PREREQUISITES
  • Understanding of transmission line theory
  • Familiarity with crosstalk concepts (NEXT and FEXT)
  • Knowledge of differential signaling in PCB design
  • Proficiency in using mathematical equations for electrical engineering
NEXT STEPS
  • Research the impact of rise time on crosstalk in transmission lines
  • Study the derivation and application of NEXT and FEXT equations
  • Explore simulation tools for analyzing crosstalk in PCB designs
  • Learn about differential signaling techniques and their benefits
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Electrical engineers, PCB designers, and students studying transmission line theory and crosstalk effects in high-speed digital circuits.

Callum Plunkett
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Homework Statement


A transmission line is formed by two identical parallel tracks in a printed circuit board. The line has a length of 50 mm and all line terminations are of 70 Ω. The line can be assumed to be lossless.

calculate the magnitude of the NEXT and FEXT voltages generated in the victim conductor when the source voltage, Vin, in the aggressor conductor is a voltage step of 2 V with a rise time of 100 ps.

Homework Equations


Vs = Vin x Rin/(Rin+Zo)
Kne =Vp/4 (CmZo + Lm/Zo)
Vne = Kne (Vs(t) - Vs(t-2td)
Kfe = 1/2(CmZo - Lm/Zo)
Vfe = Kfe x length (d/dt)[Vs(t-td)]

The Attempt at a Solution


Zo = root L/C = 70.7Ohms
Vp = 1/root LC = 17677695
Vs = Vin x Rin/(Rin+Zo) = 0.995v
Kne =Vp/4 (CmZo + Lm/Zo) = 0.08

I start to struggle with the next part (assuming the previous are correct) in regard to t and 2td. I'm sure from my notes t=vp but I'm unable to find the page any more and so I'm unable to verify this.

Vne = Kne (Vs(t) - Vs(t-2td) = 0.08

Again I'm struggling to find d and dt in regard to Far end

Kfe = 1/2(CmZo - Lm/Zo) = 3.99515E9

Vfe = Kfe x length (d/dt)[Vs(t-td)]

Any help would be much appreciated.
 
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How many transmission lines do you have?
One line made from two parallel tracks, fed with a differential signal, or;
Two lines over a ground plane that work as a backward wave coupler?
All voltages are differential. What is/are the reference voltage(s).
FEXT = Far end cross talk, from what to what, relative to what?
NEXT = Near end cross talk, from what to what, relative to what?
 
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upload_2018-6-7_21-47-33.png


The above picture accompanied the original question this is all the information I've been given.
 

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You sir are a gentleman and a scholar, thank you very much!
 
is t the rise time? 100ps?

I am thinking not, because later in the notes it expresses td to be half the rise time.

If so what is t? for both the NEXT and FEXT equations??

thanks
Craig
 
is it this:

t = length √LV
td = Tr / 2