# Homework Help: NEXT and FEXT Crosstalk

1. Jun 12, 2015

### MrBondx

1. The problem statement, all variables and given/known data
For a lossless line:
The characteristic impedance is given by Zo=sqrt(L/C)

and the velocity of propagation by Vp =1/(sqrt(L*C))

where L and C are, respectively, the line's inductance and capacitance per metre length.

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

a) Use the following equations:

VNE = KNE[Vs(t) - Vs(t - 2td)]
KNE = (Vp / 4)[(CM * Zo) + (LM / Zo)]

VFE = KFE * l * (d / dt)[Vs(t - td)], where l is the length of the line.
KFE = 1/2[(CM * Zo) - (LM / Zo)]

to 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.

[Note that the Vs voltage at the input to the aggressor conductor is
Vs = Vin[Rin / (Rin + Zo)] .]

CM and LM are, respectively, the mutual capacitance and inductance per metre length.

[ mentor note: no success adding image inline; so readers must click this thumbnail to see larger image ]

b) Sketch the NEXT and FEXT waveforms.

2. Relevant equations

VNE = KNE[Vs(t) - Vs(t - 2td)]
KNE = (Vp / 4)[(CM * Zo) + (LM / Zo)]

VFE = KFE * l * (d / dt)[Vs(t - td)]
KFE = (1 / 2)[(CM * Zo) - (LM / Zo)]

3. The attempt at a solution

Calculate for Zo and Vp

Zo = 70.71

Vp =176776695.3

Then plug in numbers to find KNE

KNE = 3124970032 ( number looks massive not sure if it's right)

Getting stuck on finding VNE

Not sure if t = rise time. Is Vin = 2? How do I find td?

[ mentor note: excessive bold text corrected ]

Last edited by a moderator: Jun 13, 2015
2. Jun 18, 2015