Noise Design & EMC

Everyone has felt static, but why does it kill semiconductors, and what does the discharge current look like? The machine model as an equivalent circuit, why R ≈ 0 turns the discharge into a damped oscillation, and how to choose and place TVS, varistor and GDT protection.

An aluminium case does not shield anything on its own. A floating shield becomes the mid-point of a capacitive divider and passes noise straight through. Electrostatic, magnetic and electromagnetic shielding, reflection and absorption, and why the length of an aperture matters more than its area.

Why are the wires in a LAN cable twisted? Balanced wiring receives external interference as common mode, which makes it removable. This article explains how the twist cancels the induced EMF, and when balanced wiring is worth the extra conductors.

Common-mode vs normal mode — what's the difference, and why is common mode easy to remove? Learn the definitions (EN = EA−EB, EC = (EA+EB)/2), how a common-mode choke and differential receiver reject it, explained with filter circuits.

Why does a PCB radiate noise? The hidden loop formed by a signal trace and its GND return sets the radiation. Learn why radiation ∝ loop area × current × frequency², and how a ground plane minimizes the loop.

Single-point ground or a ground plane? Both are correct — but which you use depends on frequency. Learn how common impedance and stray capacitance decide it, compared in uSimmics, plus mixed analog/digital board tips.

Why must a decoupling capacitor sit close to the IC? Learn how wiring inductance (L_wire) and the capacitor's ESL kill high-frequency performance, verified with uSimmics waveforms, plus two-stage placement and layout tips.

GND is supposed to be 0V — so why does noise appear? Learn how wiring inductance and V = L×di/dt cause ground bounce, verified with uSimmics simulations, plus three fixes: decoupling caps, a solid ground plane, and reducing di/dt.