he filter capacitor is used in the power supply rectifier circuit to filter out the AC component. Smoother DC output.
    Decoupling capacitors are used in the amplifier circuit where no AC is required to eliminate self-excitation and make the amplifier work stably.
    The bypass capacitor is used when there is a resistance connection and is connected to both ends of the resistance to enable AC signals to pass smoothly.

1. Understanding of the energy storage role of decoupling capacitors
1.1) Decoupling capacitors are mainly used to remove high-frequency interference such as RF signals, and the entry of interference is through electromagnetic radiation.
    In fact, the capacitor near the chip also has the role of energy storage, which is the second.
    You can think of the total power supply as Miyun reservoir, every household in our building needs water supply, at this time, the water is not directly from the reservoir, that distance is too far, and when the water comes, we have been thirsty.
    The actual water comes from the water tower on top of the building, which acts as a buffer.
    If the microscopic point of view, when the high-frequency device is working, its current is discontinuous, and the frequency is very high, and the device VCC has a distance to the total power supply, even if the distance is not long, in the case of a high frequency, the impedance Z=i*wL+R, the inductance of the line will be very large, which will lead to the device in the need of current, can not be supplied in time.
    Decoupling capacitors can make up for this deficiency.
    his is one of the reasons why many circuit boards place small capacitors at the VCC pins of high-frequency devices (the vcc pins are usually paralleled by a de-coupling capacitor so that the AC component is grounded from this capacitor).
1.2) The high-frequency switching noise generated by the active device during switching will propagate along the power line.

    The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the transmission of switching noise on the board and guide the noise to the ground.

2. Difference between bypass capacitor and decoupling capacitor
    Decoupling: The removal of RF energy from high-frequency devices into the distribution network during device switching. Decoupling capacitors can also provide a localized DC voltage source for the device, which is particularly useful in reducing cross-plate inrush current.
    Bypass: Transfer unwanted common-mode RF energy from a component or cable. This is mainly by generating AC bypass to eliminate unintentional energy into the sensitive part, in addition to providing baseband filtering (bandwidth-limited).
    We can often see that the decoupling capacitor is connected between the power supply and the ground, which has three functions: one is as the energy storage capacitor of the integrated circuit; The second is to filter out the high-frequency noise generated by the device and cut off the path of its propagation through the power supply circuit; The third is to prevent the noise carried by the power supply from interfering with the circuit.
    In electronic circuits, decoupling capacitors and bypass capacitors play an anti-interference role, the position of the capacitor is different, the name is not the same. For the same circuit, the bypass capacitor is the high-frequency noise in the input signal as the filter object, the high-frequency clutter carried by the front stage is filtered out, and the decoupling capacitor is also known as the decoupling capacitor, the interference of the output signal as the filter object.