1 Introduction
As the size of the system decreases, the operating frequency increases, and the complexity of its functions rises, requiring multiple embedded functional modules to operate simultaneously. For the entire system to function properly, each individual module must possess excellent EMC (Electromagnetic Compatibility) and low EMI (Electromagnetic Interference). This demands that the system not only has robust performance to shield external interference but also avoids generating severe EMI when interacting with other systems. Additionally, switching power supplies are becoming more prevalent in high-speed digital system designs, often necessitating multiple power supplies within a single system. Not only is the power system vulnerable to interference, but the noise generated by the power supply can create significant EMC issues for the entire system. Consequently, in high-speed PCB (Printed Circuit Board) design, how to effectively filter out power supply noise becomes crucial for ensuring good power integrity. This paper examines the filtering characteristics of capacitors, the impact of parasitic inductance and capacitance on filter performance, and the current loop phenomena in PCBs. Furthermore, it provides recommendations for selecting bypass capacitors. This article also explores the mechanisms behind power supply noise and ground bounce noise, analyzing and comparing various methods of placing bypass capacitors on PCBs.
2 Capacitor Insertion Loss Characteristics, Frequency Response Characteristics, and Capacitance Filtering Characteristics
2.1 Insertion Loss Characteristics of Ideal Capacitor
The ability of an EMI (Electromagnetic Interference) power filter to reject interference noise is typically measured using the Insertion Loss characteristic. Insertion loss is defined as the ratio of the noise power P1 transmitted from the noise source to the load and the noise power P2 transmitted by the noise source to the load when no filter is connected, expressed in decibels (dB). Figure 1 illustrates the insertion loss characteristics of an ideal capacitor. It is evident that the slope of the insertion loss curve corresponding to a 1μF capacitor approaches 20dB per decade.
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Power systems play a critical role in maintaining the stability and reliability of electronic devices, especially in modern applications where high-frequency operations and complex functionalities are common. The increasing use of switching power supplies has brought about new challenges in terms of power integrity and electromagnetic compatibility. Ensuring that these systems operate efficiently without introducing excessive noise or interference requires a deep understanding of the underlying principles of power filtering and noise suppression. By carefully selecting appropriate components such as capacitors and optimizing their placement on the PCB, engineers can significantly enhance the overall performance of their designs. Future research should focus on developing advanced materials and techniques to further improve the efficiency and reliability of power systems in high-speed environments.
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