Different value decoupling capacitors?

Thread Starter


Joined Jul 7, 2017
I've seen cases when for example a 0.1uF capacitor has been placed in parallel with a 10uF capacitor. Would this be equivalent of having a 10.1uF capacitor all alone since capacitance add up in parallel? Does the addition of capacitance in parallel somehow not apply in this senario?


Joined Mar 2, 2015
A good part of the reason for placing a small ceramic capacitor in parallel with a larger electrolytic capacitor is that the two types have very different behavior over frequency.

The electrolytic capacitor does a good job of decoupling at frequencies below a megahertz or so, but becomes a series resonant circuit (due to its internal effective series inductance) at some frequency above that, and thereafter acts as an inductor instead of a capacitor, at frequencies above that point.

The ceramic capacitor, due to its construction and physically small size, has its self-resonant point at a much higher frequency than the electrolytic and therefore can perform better in decoupling at high frequency. Putting the two types of capacitor in parallel thus allows the decoupling to cover a broader spectrum.

The fact that 10 μF + 0.1 μF = 10.1 μF is of no importance.