Why do decoupling capacitors need to be close to the power pins of powered devices?

Generally, power integrity is an overall concept, and the word "integrity" conveys the following meanings:

(1) Comprehensiveness and comprehensive consideration: Integrity means taking into account all aspects of the system, including power supply design, power lines, power delivery, power management, etc. It requires sufficient attention throughout the system to ensure that the power supply is functioning properly in all critical parts.

(2) Robustness: Integrity also covers the system’s ability to adapt to external disturbances and changes. A system with good power integrity is able to maintain the stability of its functionality under the influence of adverse factors such as voltage fluctuations, current changes, and electromagnetic interference.

(3) Overall stability of the system: This term emphasizes the stability of the power system as a whole. This includes reliability in terms of power supply and ensuring that the entire system maintains its performance levels under normal and abnormal conditions.

(4) Maintenance of functions: Integrity also involves ensuring that the various functions of the system can be maintained under various conditions. This includes electronic equipment, computer systems, or other equipment that relies on power. Power integrity is directly related to the reliability and stability of these equipment.

Power integrity is to confirm whether the voltage and current at the source and destination of the power supply meet the requirements. Power integrity is very important in today's electronic products, involving the chip level, chip packaging level, circuit board level and system level.

Whether the power integrity results meet the requirements is comprehensively determined by three parts, namely the power supply module, the transmission path and the power consumer. When we design the power circuit, the requirements for the power supply are low noise, low ripple, and accurate and stable output voltage, so as to reduce the introduction of interference as much as possible.

Ensuring power integrity ultimately ensures the noise margin of power-consuming chips [51] [xz2]. The process of calculating the margin for power supply noise is as follows.

(1) The chip specification will give a standard value, usually 5%; the DC output error of the voltage stabilizing chip must be taken into consideration, which is generally ±2.5%, so the peak amplitude of the power supply noise does not exceed ±2.5%.

(2) If the working voltage range of the chip is 3.13~3.47V and the output voltage of the voltage stabilizing chip is 3.3V, install