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in the following webinar from youtube, a recommendation is presented about the kelvin connection at the 41st minute of the video. but I couldn't get it. (second language)

https://www.youtube.com/watch?v=gq-0ZpcGm8E

why those vias are placed? where is the other end of those vias connected? and what do those added circles around the vias do? (you may say the answers are in figures but I don't know what is the "internal plane"? why is this placed "by default"? how do those circles ensure the accuracy of measurement? are they conductive?)

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The circles represent the fact that the vias do not connect to the ground plane, despite the fact that they belong to the ground net.

The vias in this case are just necessary because the Kelvin trace is routed in an internal layer. If it was on the top layer, you would not need them.

The Kelvin connection is used to measure the potential across the current sense resistor. That potential is very small (sometimes just a few tens of mV), so you want to ensure that almost no current flows through the trace. This is because the trace has some resistance too, and any stray current through it could easily develop another few mV of potential (Ohm's law), which would cause a significant measurement error.

For that reason the Kelvin connection is routed from inside the resistor footprint to avoid the high current parts of the resistor pads.

For the same reason, when one side of the resistor is grounded you want to ensure that the Kelvin trace remains a "dead end" so that no stray current can flow through it, and so that it remains unaffected by any potential difference that can develop across the ground plane. So, even though it's technically GND, you want to keep it separate from the GND plane.

Another way to do this is to use a special 4-terminal sense resistor footprint, which lets you use a different net name for the Kelvin sense ground. Then the vias will naturally not connect to the ground plane.

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