Understanding The Energy Storage Function Of Decoupling Capacitors

Decoupling capacitors are mainly used to remove high-frequency interference such as RF signals, and the way interference enters is through electromagnetic radiation.

In fact, the capacitors near the chip also have the function of energy storage, which is secondary. You can think of the main power supply as Miyun Reservoir. Every household in our building needs water supply. At this time, the water does not come directly from the reservoir, which is too far away. When the water comes, we are already thirsty. The actual water comes from the water tower on top of the building, which actually serves as a buffer. If viewed from a microscopic perspective, the current of high-frequency devices is discontinuous and the frequency is high, and there is a distance between the VCC of the device and the main power supply. Even if the distance is not long, at high frequencies, the impedance Z=i * wL+R will have a significant impact on the inductance of the circuit, which will cause the device to be unable to be supplied in a timely manner when current is needed. Decoupling capacitors can compensate for this deficiency. This is also one of the reasons why many circuit boards place small capacitors at the VCC pins of high-frequency devices (usually a decoupling capacitor is connected in parallel on the VCC pins, so that the AC component is grounded from this capacitor).

The high-frequency switching noise generated by active devices during switching will propagate along the power line. The main function of decoupling capacitors is to provide a local DC power supply to active devices, in order to reduce the propagation of switch noise on the board and guide noise to ground.