# Why is ground meaningless in high speed circuits whereas more important is the path of return current?

I know everything about this topic but I don't know why ground is meaningless in high speed circuits. So basically in high speed circuits these are the factors we need to consider-:

Decoupling caps

Coupling/Crosstalk

Bandwidth

Ground bounce

Impedance matching

Timing

I know about routing signal traces, we should keep check of these things-:

1. Distribution of signal and return

2. Coupling

3. Common impedance

4. Trace impedance matching

5. Trace density

6. Transmission line concerns(Basically stuffs of high speed design)

Also I know that in low speed, return current goes the path of least resitance whereas in high speed circuits, return current returns to path of loweset inductance.

Similarly, I know there should not be slot in ground plane(Although I don't know why, maybe because it increases loop area). But I am not able to conclude why ground is meaningless in high speed circuits and why return current path is more important?

• Pretty much everything you will need to know about high-speed circuits is in the book by Ralph Morrison, "Fast Circuit Boards: Energy Management" 1st Edition 2017. Commented Oct 27, 2021 at 9:45
• Why is ground meaningless in high speed circuits - it's not so, unless you have improperly cited something, this question will likely be closed. Commented Oct 27, 2021 at 10:18
• They say ground is meaningless but only return current path matters in high speed circuit. That is the question we were given in our university exam. Commented Oct 27, 2021 at 12:34
• @gidser It is meaningless only in the sense that GND is often thought of as a sinkhole for current with 0V potential and no voltage drop at all. This is true in simplified circuit theory but very misleading as soon as real-life circuits (and their layouts) are considered. I too highly recommend Ralph Morrison's book. It will give you a completely different spin on things. My two other recommendations would be Right the First Time Vol1&Vol2 by Lee Ritchey, and Signal and Power Integrity - Simplified by Eric Bogatin. Commented Oct 27, 2021 at 13:15