According to the working principle of decoupling capacitor, both decoupling capacitor and bypass capacitor play an anti-interference role in electronic circuits, and their names are different according to different positions of capacitors. For the same circuit, the bypass capacitor takes the high-frequency noise in the input signal as the filtering object to filter the high-frequency clutter carried by the previous stage, while the decoupling capacitor, also called decoupling capacitor, takes the interference of the output signal as the filtering object. Decoupling capacitor is used to amplify the center of the circuit that does not need AC, eliminate self-excitation and make the amplifier work stably. The decoupling capacitor plays the role of battery, which can meet the current change of driving circuit and prevent mutual coupling interference.
Decoupling and bypassing can be regarded as filters. Decoupling capacitor is equivalent to battery, which prevents voltage drop caused by sudden change of current, and is equivalent to filter. The detailed capacity value can be calculated according to the current, the desired texture wave and the action time. Decoupling capacity is usually large, which is completely ineffective for higher frequency noise. Bypass capacity is aimed at high frequency, that is, the frequency impedance characteristic of application capacity.
As far as the circuit is concerned, there is always a driving power supply and a driven load. If the load capacity is relatively large, the driving circuit should charge and discharge the capacity to complete the signal jump. When the rising edge is relatively steep, the current is relatively large, so the driving current will absorb a large amount of power supply current. Inductance and resistance in the circuit (especially inductance rebound of chip pin) This current is actually noise under normal circumstances, which affects the normal operation of the previous stage. This is coupling.
Decoupling capacitance is the capacitance of the power supply end installed on the component in the circuit. The capacitor can provide a more stable power supply, at the same time, it can also reduce the noise of the combination of the component and the power supply terminal, and indirectly reduce the influence of other components on the noise of the component. Capacitance is usually regarded as RLC series model. When resonance occurs at a certain frequency, the impedance of the capacitor is equal to ESR. If you look at the frequency impedance graph of capacitance, you will find that it is usually a V-shaped curve. The detailed curve is related to the dielectric of capacitor, so you should consider the dielectric of capacitor when choosing bypass capacitor. Compared with insurance, one method is to have multiple capacitors.
