Grounding: Reference vs Return Path

Rectifier charging pulses, relay coils, a power amp’s output return. Log scale 1 mA–10 A.

Vertical position of the noisy return path on the plane — how far the dirty end sits from the quiet end.

How much sharper the edges are than a sine of the same amplitude: 1× sine, ~10× rectifier pulses, ~1000× a logic edge or relay-coil collapse. Multiplies dI/dt, so it drives the inductive term only.

Log 1 Hz–100 MHz. Above $f_c\!\approx\!100$ kHz return current hugs the trace; below it, the current spreads out over the plane.

Sheet resistance $R_\square=\rho/t$. Copper $\rho=1.72\times10^{-8}\,\Omega{\cdot}$m; 1 oz $=34.8\,\mu$m.

Trace-to-plane spacing. At HF the return spreads to about $\pm 3h$ — thin dielectric = tight return.

Distance between the two points the victim calls “ground” — e.g. the jack sleeve and the op-amp’s own ground pin. This is the copper it shares.

Log 10 µV–10 V. Moving-magnet cartridge $\approx$ 5 mV; line level $\approx$ 1 V.

Bogatin’s fix: carry the source’s own reference alongside the signal instead of picking it off the plane.

The single copper tie between the two zones. Everything DC must funnel through it.

Forces the return current to detour to the bridge — huge loop area, huge inductive crosstalk.

Header pins plus ribbon cable. Mutual inductance scales linearly with length.