Tag
decoupling
3 articles.
- Your 2.2 µF is 0.68 µF: DC bias and the capacitance you did not buy
Ceramics lose capacitance under DC voltage. Würth measured a 25 V X7R part losing 69 % of its value at its rated voltage, and the datasheet never mentions it.
- The via is the decoupling: 40 dB from layout alone
Würth built one board with the same ferrite and the same two 100 nF capacitors in every channel, and changed only the layout. The worst channel is 40 dB down.
- Why 100 nF, and the frequency where it stops being a capacitor
The value is inherited, not derived. What decides if a decoupling capacitor works is its inductance, and above a few tens of megahertz 100 nF is an inductor.