Calculating Crosstalk: Electrical Currents, dB & Ideas

[patrickewen]

I am currently looking into crosstalk. I have never really heard of this and I wondered if anyone could help me.

If I have two wires wrapped together which have an electrical current running through them, hows to best way to find out the crosstalk? From what i have been reading, the leakage from one wire to another can be capacitive or inductive and am i right in saying its measured in dB?

Any theorectical or practical ideas would be great! :)

 

[berkeman]

There are several kinds of crosstalk, including near-end crosstalk (NEXT), far-end crosstalk (both of those are for adjacent twisted pair cables), and straight capacitive crosstalk.

NEXT: http://www.flukenetworks.com/fnet/en-us/supportAndDownloads/KB/Datacom+Cabling/dsp-4000+series/Near+End+Crosstalk+(NEXT)+-+DSP+4x00+CableAnalyzer.htm

The NEXT and far-end crosstalk come about mainly due to inductive coupling between the twisted pairs. In order to minimize this effect, multi-pair cables use a different "lay length" for each twisted pair -- that is, the twist rate is slightly different for each twisted pair. This keeps the loops from lining up next to each other for the whole cable run, and generally gives pretty good B-field coupling cancellation.

Straight capacitive coupling between PCB traces or adjacent wires in a ribbon cable, etc., is just a straightforward capacitive divider effect, with the source impedance and load impedance taken into account. When you have two PCB traces running together over a ground plane, then the capacitive coupling increases with the capacitance between them (like when they are moved closer to each other in the layout), and decreases with increasing capacitance to the ground plane (like if you use a 4-layer PCB with its internal ground plane layer, versus a 2-layer PCB with the ground plane on the opposite side).

 

[ravenprp]

Crosstalk is a phenomenon that occurs when there is unwanted interference between two electrical signals. In your case, the two wires wrapped together with electrical currents running through them can create crosstalk. This can be a common issue in electronic circuits and can cause distortion or loss of signal integrity.

To calculate crosstalk, you will need to measure the amount of signal leakage from one wire to another. This can be done by measuring the signal strength at the receiving end of the affected wire and comparing it to the signal strength at the sending end. The difference between the two measurements is the amount of crosstalk.

Crosstalk can be measured in decibels (dB), which is a unit of measurement for signal strength. The higher the dB value, the stronger the signal. In the case of crosstalk, a higher dB value indicates a greater amount of interference.

To reduce crosstalk, there are several approaches you can take. One is to physically separate the wires to minimize the interaction between them. Another is to use shielding or twisted pair wires, which can help reduce the effects of crosstalk. Additionally, careful circuit design and layout can also help minimize crosstalk.

Overall, the best way to find out the crosstalk in your circuit is to measure it using specialized equipment such as an oscilloscope or spectrum analyzer. However, understanding the principles behind crosstalk and using good design practices can also go a long way in reducing its impact. I hope this helps and good luck with your research!