# Help with NEXT and FEXT volatage magnitudes

• Callum Plunkett
In summary: LIn summary,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.The rise time is 100 ps.
Callum Plunkett

## 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.

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?

berkeman

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

#### Attachments

9.3 KB · Views: 498
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

## 1. What is NEXT and FEXT voltage magnitude?

NEXT (Near-End Crosstalk) and FEXT (Far-End Crosstalk) are two types of crosstalk that occur in data communication. They refer to the interference between two adjacent cables, where NEXT is the interference at the receiving end and FEXT is the interference at the transmitting end.

## 2. How are NEXT and FEXT voltage magnitudes measured?

NEXT and FEXT voltage magnitudes are measured using instruments called network analyzers. These instruments send a signal through the cable and measure the amount of interference at both ends. The difference between the two measurements gives the NEXT and FEXT voltage magnitudes.

## 3. What factors affect NEXT and FEXT voltage magnitudes?

The main factors that affect NEXT and FEXT voltage magnitudes are the distance between the cables, the quality of the cables, and the number of twists per inch in the cables. Other factors such as electromagnetic interference and improper termination of the cables can also contribute to higher NEXT and FEXT voltage magnitudes.

## 4. How can NEXT and FEXT voltage magnitudes be reduced?

To reduce NEXT and FEXT voltage magnitudes, proper cable installation and routing is crucial. Keeping cables at a distance from each other and using high-quality cables with more twists per inch can help decrease crosstalk. Additionally, using shielding and proper termination techniques can also help reduce NEXT and FEXT voltage magnitudes.

## 5. Why is it important to minimize NEXT and FEXT voltage magnitudes?

NEXT and FEXT voltage magnitudes can cause data transmission errors and affect the overall performance of a network. High crosstalk can lead to slow data transfer rates, increased packet loss, and degraded signal quality. Minimizing NEXT and FEXT voltage magnitudes is essential to maintain a reliable and efficient data communication system.